Redox-Active Ferrocene as a Tuning Functionality for Magnetic

Article pubs.acs.org/Organometallics

Redox-Active Ferrocene as a Tuning Functionality for Magnetic Superexchange Interactions of Bis(oxamato) Type Complexes Mohammad A. Abdulmalic,† Azar Aliabadi,‡ Andreas Kurt Petr,§ Yulia Krupskaya,∥ Vladislav Kataev,∥,○ Bernd Büchner,⊥ Torsten Hahn,# Jens Kortus,#,◆ Nicolas Yèche,∇ Hans-Henning Klauss,∇,¶ and Tobias Rüffer*,† †

Technische Universität Chemnitz, Institut für Chemie, Strasse der Nationen 62, Chemnitz, D-09107 Germany IFW Dresden, Leibniz Institute for Solid State and Materials Research, Dresden, D-01171 Germany § Leibniz Institute for Solid State and Materials Research, Institute for Solid State Research, Helmholtzstrasse 20, Dresden, D-01069 Germany ∥ IFW Dresden, Helmholtzstrasse 20, Dresden, D-01069 Germany ⊥ IFW Dresden, P.O. Box 270116, Dresden, D-01171 Germany # Institut für Theoretische Physik, Technische Universität Bergakademie Freiberg, Freiberg, D-09596 Germany ∇ Institut für Festkörperphysik, TU Dresden, Dresden, D-01062 Germany ‡

S Supporting Information *

ABSTRACT: The reaction of 1,1′-diaminoferrocene with two equivalents of ethyloxalyl chloride in THF afforded the diethyl ester of N,N′-ferrocenylenebis(oxamic acid) (1,1′-fcbaH2Et2, 1). 1 was converted readily to its saponificated form only, namely [nBu4N]2[(1,1′-fcbaH2)] (2), when treated with 4 equiv of [nBu4N]OH followed by the subsequent addition of [Ni(H2O)6]Cl2, whereas [nBu4N]2[Cu(1,1′fcba)] (3) was obtained in ca. 70% yield by using CuCl2·2H2O. Oxidation of 3 with I2 led to the formation of [nBu4N][Cu(1,1′-fcba)] (4). A combined study of 4 by ESR and 57Fe Mössbauer spectroscopy, supported by DFT calculations, revealed the iron atom of 4 to possess the oxidation state +3. Treatment of 1 with MeNH2 resulted in the exclusive formation of the methyl ester of ferrocenylene-1(N-methyloxamide)-1′-(oxamic acid) (1,1′-fcooH3Me2, 5). Successive treatment of 5 with [Cu2(OAc)4(H2O)2] and [nBu4N]OH gave rise to the formation of [nBu4N]2[Cu(fcooMe)]·2H2O (6A·2H2O and 6B·2H2O), for which single crystals of the compositions [nBu4N]2[Cu(1,1′-fcooMe)]·1/2MeOH·1/2H2O (6A·1/2MeOH· 1 /2H2O) and [nBu4N]2[Cu(1,1′-fcooMe)]·2.25H2O (6B·2.25H2O) were grown. Single-crystal X-ray diffraction studies revealed 6A·1/2MeOH·1/2H2O and 6B·2.25H2O to contain [Cu(fcooMe)]2− fragments in the form of two different conformers, having a significant difference in their total energy, as found by DFT calculations. Treatment of 3 and 4, respectively, with [Cu(pmdta)(NO3)2] afforded the tetranuclear complexes [Cu3(1,1′-fcba)(pmdta)2](NO3)n (n = 2 (7), 3 (8)). The solid-state structures of 1−3, 7, and 8 were determined by single-crystal X-ray diffraction studies. The magnetic properties of 3, 4, 7, and 8 were studied by susceptibility measurements versus temperature. For 4 a weak antiferromagnetic coupling between the CuII and FeIII ions has been obtained with J = −2 cm−1, whereas 3 can be understood as a purely paramagnetic, CuII/FeII-containing complex only. For 7 a J parameter of −58 cm−1 has been obtained due to an antiferromagnetic interaction between its CuII ions. This magnetic exchange interaction modifies in 8 to −64 cm−1, and an additional ferromagnetic coupling of 4 cm−1 between the FeIII ion and the central CuII ion is obtained.

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Owing to its aromaticity and stability,4 ferrocene can survive relatively harsh reaction conditions. This makes a wide range of organic transformations possible and resulted in a vast variety of substituents as, for example, monosubstituted and 1,2- and 1,1′-disubstituted ferrocene derivatives.5 When ferrocene is

INTRODUCTION

After the discovery of ferrocene in the early 1950s,1 detailed studies were started to investigate its properties and reactivity.2 As a result, the well-defined electrochemical and spectroscopic behavior, chemical stability, and low toxicity of ferrocene paved the way for applications in different areas such as anion sensing, asymmetric catalysis, mediators between redox enzymes and electrodes, liquid crystalline materials, and materials with high second harmonic generation efficiencies for nonlinear optics.3 © XXXX American Chemical Society

Special Issue: Ferrocene - Beauty and Function

A

dx.doi.org/10.1021/om4005115 | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

used as starting materials for the syntheses of di-, tri-, and polynuclear transition metal complexes (types III−V, Chart 3), which are valuable materials for the study of magnetic superexchange phenomena and potential building blocks for molecular electronic devices.14,15 So far, type II−V complexes have not contained any functionality allowing redox events to occur and thus to induce changes of their magnetic properties. Here we report on the use of 1,1′-diaminoferrocene for the synthesis of 1,1′-ferrocenediylbridged type II and IV complexes and their structural and magnetic characterization.

substituted at the 1,1′-positions with Lewis-basic heteroatoms D, novel compounds are available which could coordinate a further transition metal ion close to the iron (cf. Chart 1). This coordination setup has been previously reviewed6 and is referred to in the following as type I (cf. Chart 1). Chart 1. Chemical Structure of 1,1′-HeteroatomDisubstituted Ferrocenes Acting as κ2D,D′ Chelating Ligands toward Transition-Metal Ions12

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RESULTS AND DISCUSSION Synthesis and Characterization. In this study, 1,1′diaminoferrocene has been used according to Scheme 1 for the synthesis of compounds 2−8 via compound 1. The synthesis of 1 was readily achieved by reaction of 1,1′diaminoferrocene with ethyloxalyl chloride in the presence of Et3N as an acid scavenger in THF (cf. Scheme 1).16 In order to prevent the oxidation of 1,1′-diaminoferrocene, this reaction has to be performed under strict anaerobic conditions. Compound 1 is stable in both the solid state and solution and is soluble in a range of polar organic solvents. According to a previously reported methodology,17 we intended to synthesize symmetric 1,1′-ferrocenylenebis(N-methyloxamide) (1,1′-fcboH4Me2). Therefore, 1 was treated with an excess of MeNH2 (3 equiv) in MeOH, although the use of MeOH might cause problems.18 After the addition of the first 1 equiv of MeNH2 at room temperature the formation of an orange solid was noticed. The subsequent addition of the remaining 2 equiv of MeNH2, followed by refluxing, did not result in any obvious change of the originally formed precipitate. The precipitate was thus isolated and checked to be insoluble in common organic solvents. Eventually, the precipitate was, on the basis of its elemental analysis and IR characterization, determined as 1,1′fcooH3Me2 (5) (cf. Scheme 1). In order to verify whether the synthesis of 1,1′-fcboH4Me2 is possible by using an even greater excess of MeNH2 and longer refluxing time, 1 was treated with a 10-fold excess of MeNH2 and the resulting mixture was refluxed for 6 h. Nevertheless, the material obtained here appears, according to its elemental analysis and IR characterization, identical with 5. For the synthesis of 3 a modified procedure of Stumpf et al.19 was employed. Thus, 1 was treated with 4 equiv of [nBu4N]OH in aqueous EtOH, followed by heating the reaction mixture. Then, an aqueous solution of CuCl2·2H2O was added, resulting in a color change from orange to green. Complex 3 could be isolated smoothly from the reaction mixture as a light green solid (cf. Scheme 1).

In spite of the large number of complexes of type I,7−11 there have been only a few reports dealing with the characterization of magnetic properties. Magnetically characterized complexes are shown in Chart 2. Trinuclear I-1 was oxidized by I2 to give the corresponding cationic I-1+ complex.7f This redox event is most probably reversible, although the reduction of I-1+ to give back I-1 again is not reported.7f The magnetic properties of I-1, a paramagnetic complex without magnetic superexchange interactions, and I-1+ are significantly different from each other, although details of the exchange interaction between the UIV and FeIII centers of I-1+ are difficult to access.7f However, this work already demonstrated that the ferrocenediyl group of complexes comprising type I fragments can be oxidized, thereby changing their magnetic properties. Furthermore, the magnetic properties of the paramagnetic binuclear I-2 and I-3, both comprising UIV and FeII ions, were investigated by susceptibility measurements versus temperature and revealed different magnetic moments μB of both complexes.7r To the best of our knowledge, there have been no further reports describing the magnetic properties of complexes containing type I fragments. This might be due to the usually diamagnetic nature of the ferrocenediyl group of type I fragments. However, the diamagnetic nature can be transferred to a paramagnetic one by oxidation, as shown for the couple I-1/ I-1+.7f When this process is reversible, as is known for the ferrocene’s [FeII/FeIII] redox couple,13 valuable complexes can be achieved, the magnetic properties of which are potentially switchable. Complexes having discrete magnetic properties associated with certain chemical and/or further physical properties are the focus of increasing interest.14 Mononuclear N,N′-bridged bis(oxamato) complexes (type II, Chart 3) have already been

Chart 2. Chemical Structures of I-1−I-3 as Magnetically Characterized Complexes Containing a Type I Fragment

B


Organometallics

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Chart 3. Basic Chemical Structures of Mono- (II), Di- (III), Tri- (IV), and Polynuclear (V) Bis(oxamato) Type Complexes

Scheme 1. Synthesis of Compounds 1−8

In principle, a controlled oxidation of the FeII atom of 3 could be achieved chemically by using I2 as oxidizing reagent. Thus, 3 was treated in CH2Cl2 with 1 equiv of I2, giving rise to an immediate color change from light to dark green and the precipitation of 4 as a dark green powder. Isolated 4 is soluble only in hot DMSO, where it remains soluble even at room temperature. Thus, treatment of FeIICuII-containing 3 with 1 equiv of I2 gave rise to the isolation of an apparently air-stable dark green powder, which could comprise in principle a singly oxidized, paramagnetic, and monoanionic FeIIICuII, a singly oxidized, diamagnetic, and monoanionic FeIICuIII, or a doubly oxidized, neutral, and paramagnetic FeIIICuIII-containing complex fragment. It needs to be emphasized that an oxidation of CuII to CuIII of 3 is likely, as Ruiz et al.17 reported on the chemical oxidation of [CuII(opboMe2)]2− by I2 to give [CuIII(opboMe2)]−

(opboMe2 = o-phenylenebis(N-methyloxamide), an air-stable CuIII bis(oxamidato) type complex. According to the elemental analysis data of the dark green powder, the formation of a neutral and paramagnetic complex could be ruled out. The 1H NMR spectrum of the dark green powder shows broad resonances (cf. Figure S11, Supporting Information) typically observed for paramagnetic complexes in general or oxidized 1,1′-diaminoferrocene in particular.20 As the aforementioned [CuIII(opboMe2)]− is diamagnetic, its 1H NMR spectrum displays sharp resonances. Thus, in the case that the dark green powder obtained represents a diamagnetic and monoanionic FeIICuIII-containing complex fragment, sharp 1H NMR resonances are expected, which is not the case. Consequently, the dark green powder comprises a paramagnetic and monoanionic FeIIICuII complex fragment and is referred to in the following as 4. This conclusion has been verified further C


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Figure 1. ORTEP plots (50 and 25% probability level) of the molecular structures of 1 in crystals of 1·CHCl3 (left) and of the anion in crystals of 2 (right). Intramolecular hydrogen bonds are indicated by dotted lines. Symmetry code used to generate equivalent atoms of 2: (A) −x + 1, −y + 1, −z.

Table 1. Selected Bond Lengths (Å) and Bond and Torsion Angles (deg) of 1·CHCl3 and 2 Bond Lengths C1−O1/C3−O2 C1−N1/C3−N2 C1−C2/C3−C4 C2−O3/C4−O5 C2−O6/C4−O4 N1−C5/N2−C10 Fe1−D1/Fe1−D2b

Bond Angles

1·CHCl3

2a

1.218(3)/1.214(3) 1.338(4)/1.351(4) 1.535(4)/1.540(4) 1.208(3)/1.210(3) 1.322(3)/1.318(3) 1.409(3)/1.407(4) 1.648(1)/1.649(1)

1.214(5)/− 1.337(6)/− 1.567(8)/− 1.232(6)/− 1.221(6)/− 1.393(7)/− 1.648(2)

N1−C1−O1/N2−C3−O2 N1−C1−C2/N2−C3−C4 O1−C1−C2/O2−C3−C4 O3−C2−O6/O4−C4−O5 O3−C2−C1/O5−C4−C3 O6−C2−C1/O4−C4−C3 D1−Fe1−D2b Torsion Angles

O1−C1−N1−C5/O2−C3−N2−C10 O3−C2−C1−O1/O5−C4−C3−O2 O6−C2−C1−N1/O4−C4−C3−N2

1·CHCl3

2a

126.2(3)/126.4(3) 112.4(2)/111.9(2) 121.4(2)/121.7(3) 125.8(2)/125.9(3) 124.1(2)/123.9(3) 110.1(2)/110.3(2) 178.6(2)

126.2(5)/− 112.2(4)/− 121.5(5)/− 127.0(6)/− 117.2(5)/− 115.8(4)/− 180.0

1·CHCl3

2a

−2.5(4)/−2.1(4) 0.9(3)/0.5(3) 2.1(2)/1.5(2)

−5.5(7)/− 9.4(5) 10.3(5)/−

a

Atom O6 corresponds in 2 to atom O2. bD1 and D2 denote the geometrical centroids of C5−C9 and C10−C14, respectively. For 2, D2 denotes the geometrical centroid of C5A−C9A.

by the addition of a MeCN solution of 2 equiv of [Cu(pmdta)(NO3)2] to a MeCN solution (a suspension in case of 4) of 1 equiv of 3 or 4 to give the desired complexes. Here, the side product [nBu4N]NO3 can be smoothly separated due to its solubility in THF, in which 7 and 8 are insoluble. Single-Crystal X-ray Diffraction Studies. The solid -state structures of 1 as 1,1′-fcbaH2Et2·CHCl3 (1·CHCl3), [nBu4N]2[1,1′fcbaH2] (2), 3 as [nBu4N]2[Cu(1,1′-fcba)]·3MeCN (3·3MeCN), 6A·2H2O as [nBu4N]2[Cu(1,1′-fcooMe)]·1/2MeOH·1/2H2O (6A·1/2MeOH·1/2H2O), 6B·2H2 O as [nBu4N]2[Cu(1,1′fcooMe)]·2.25H2O (6B·2.25H2O), 7 as [Cu3(1,1′-fcba)(pmdta)2(NO3)(MeCN)](NO3)·MeCN (7·2MeCN), and 8 as [Cu3(1,1′-fcba)(pmdta)2(NO3)](NO3)2·MeOH (8·MeOH), respectively, have been determined by single-crystal X-ray crystallographic studies; Table S4 (see the Supporting Information) summarizes selected crystal and structural refinement data. The molecular structures of 1·CHCl3 and of the anionic [1,1′-fcbaH2]2− fragment of 2 are shown in Figure 1, and selected bond lengths and angles are given in Table 1. The molecular structure of the [Cu(1,1′-fcba)]2− fragment of 3·3MeCN is shown in Figure 2, and selected bond lengths and angles are summarized in Table 2. In the case of 6A·1/2MeOH·1/2H2O and 6B·2.25H2O the asymmetric unit comprises two crystallographically independent [Cu(1,1′-fcooMe)]2− complex fragments. Related bond lengths of them differ of up to 1.5% and 0.6%, whereas

by comparative Mössbauer and ESR spectroscopic studies and the magnetic characterization of 3 and 4 (vide infra). The reaction conditions employed for the synthesis of CuIIcontaining 3 were accommodated for the synthesis of the related NiII complex. Surprisingly, treatment of 1 with 4 equiv of [nBu4N]OH and the in situ addition of NiCl2·6H2O gave only the saponificated form of compound 1, namely 2, and no complexation took place (cf. Scheme 1). Instead, the formation of a light green gel-like precipitate indicates the formation of Ni(OH)2, as we observed previously for a related case.21 Probably, the formation of Ni(OH)2 is due to the observation that the NiII ion is, in contrast to CuII, more weakly bonded to N,O-chelates.22−24 However, 2 could be separated from the reaction mixture as a fine yellow powder in 83% yield based on 1. The procedure employed for the synthesis of 3 was used eventually for the synthesis of 6 from 5. However, 6 could not be obtained sufficiently pure. Therefore, another, more convenient procedure was employed to prepare 6 (cf. Scheme 1). Hence, a gently heated solution of 1/2 equiv of [Cu2(OAc)4(H2O)2] in MeOH was added to a suspension of 1 equiv of 5 in MeOH at 50 °C. After appropriate workup, 6 was obtained as a hygroscopic solid in good yield (61%). We aim to mention here that 6 was synthesized twice following the just described procedure. The complexes obtained are referred to as 6A·2H2O and 6B·2H2O. The synthesis of 7 and 8 proceeds conveniently D


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Figure 2. ORTEP plots (50% probability level) of the molecular structures of 3·3MeCN (left), 6A (middle), and 6B (right) in two different perspective views. Packing solvent molecules and/or counterions are omitted for clarity. The angle sign refers to the interplanar angle of atoms adjoining black and gray filled areas.

CO bond distances (C2−O3/C4−O5 = 1.208(3)/1.210(3) Å) being significantly shorter in comparison to the alkyl C−O (C2−O6/C2−O5 = 1.322(3)/1.318(3) Å) distances. In contrast, for 2 the C−O bond lengths of the C(O)O− function are identical within standard deviations (C2−O2 = 1.221(6) Å vs C2−O3 = 1.232(6) Å). Other than an elongated C−C bond of the oxamate group of 2 (group I, N1, O1, O3, O2, C1, C2) in comparison to related bonds of the ethyl ester oxamic acid groups of 1·CHCl3 (group II, N1, O1, O3, O6, C1, C2; group III, N2, O2, O4, O5, C3, C4) with 1.567(8) Å for I vs 1.535(4)/1.540(4) Å for II/III, no further differences in related bond lengths and angles of 1·CHCl3 vs 2 are observed. The two 1,1′-disubstituted ferrocene derivatives 1·CHCl3 and 2 exhibit furthermore different conformations with respect to the orientation of their substituents to each other. For 1·CHCl3, groups II and III both display antiperiplanar conformations. The planarity is revealed by selected torsion angles given in Table 1 with values close to 0° or by the rmsd with 0.013 Å for II (hdp observed for O3: 0.017(1) Å) and 0.009 Å for III (hdp observed for O4: 0.012(1) Å).25 In the case of 2 the planarity of group I is less pronounced. Torsion angles of I reach ca. 10° (cf. Table 1), and the rmsd from planarity amounts to 0.079 Å (hdp observed for N1: 0.099(3) Å). Groups I−III are tilted slightly out of the plane of the cp rings to which they are bonded. The crystal structures of bis(oxamates) or their saponificated versions, to which 1·CHCl3 and 2 are related, have already attracted particular attention, as they may represent supramolecular synthons. Due to the possible formation of, e.g., intermolecular hydrogen bonds, such compounds are reported to form a unique meso-helical structure26 or other types of supramolecular assemblies.27 Nevertheless, such compounds

related bond angles show maximum differences up to 2% and 1.5%, respectively. The two related crystallographically independent [Cu(1,1′-fcba)]2− fragments of 6A·1/2MeOH·1/2H2O and 6B·2.25H2O, respectively, can be thus considered as approximately identical in terms of structural features. Therefore, Figure 2 displays the molecular structures of one crystallographically independent molecule only, denoted as 6A and 6B, and furthermore only structural features of these two [Cu(1,1′-fcooMe)]2− complex fragments are discussed in the following. For completeness and comparison, however, Table 2 summarizes the values of the two crystallographically independent complex fragments separated by a slash, respectively. The molecular structures of 7·2MeCN and 8· MeOH are shown in Figure 3. Selected bond lengths and angles of the [Cu(1,1′-fcba)(NO3)(MeCN)]3− fragment of 7·2MeCN and of the [Cu(1,1′-fcba)(NO3)]2− fragment of 8·MeOH are given in Table 2, while Table 3 gives the values of the [Cu(pmdta)]2+ fragments of 7·2MeCN and 8·MeOH, respectively. Solid-State Structures of 1·CHCl3 and 2. The neutral diethyl ester 1 in 1·CHCl3 possesses C1 symmetry in the solid state, whereas its saponificated dianionic derivate 2 exhibits crystallographically imposed inversion symmetry with the Fe1 atom located at the inversion center. With respect to the rotation of the cp rings to each other, for 1·CHCl3 a slightly distorted synperiplanar (cf. e.g. torsion angle N1−C5−C10− N2 = 12.1°) and for 2 an ideal antiperiplanar conformation is observed2 (cf. Figure 1). As expected, bond lengths and angles of the two C(O)OEt functions of 1·CHCl3 are significantly different from those of the related carboxylate C(O)O− function of 2 (cf. Table 1). For example, for 1·CHCl3 two different C−O bond lengths of each C(O)OEt function are observed, with the carbonyl E


Organometallics

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Table 2. Selected Bond Lengths (Å) and Bond and Torsion Angles (deg) of 3·3MeCN, 6A·1/2MeOH·1/2H2O, 6B·2.25H2O, 7· 2MeCN, and 8·MeOH 3·3MeCN

6A·1/2MeOH·1/2H2Ob

6B·2.25H2Ob

7·2MeCN

8·MeOH

a

Bond Lengths 1.968(2)/1.966(2) 1.950(2)/1.950(2) 1.934(2)/1.946(2) 1.960(2)/1.963(2)

N1−Cu1 N2−Cu1 X3−Cu1 O4−Cu1 O7−Cu1 N10−Cu1 C1−O1 C1−N1 C1−C2 C2−X3 C2−O6 C3−O2 C3−N2 C3−C4 C4−O4 C4−O5 C5−N1 C10−N2 Fe1−D1

1.941(2) 1.946(2) 1.9455(17) 1.9481(18)

1.958(2)/1.958(2) 1.944(2)/1.960(2) 1.928(2)/1.939(2) 1.972(2)/1.947(2)

1.244(3) 1.339(3) 1.541(4) 1.285(3) 1.235(3) 1.249(3) 1.331(3) 1.537(4) 1.290(3) 1.233(3) 1.418(3) 1.415(3) 1.642(1)c

1.241(3)/1.249(3) 1.340(3)/1.326(3) 1.550(3)/1.536(3) 1.320(3)/1.321(3) 1.239(3)/1.251(3) 1.235(3)/1.245(3) 1.339(3)/1.333(3) 1.544(4)/1.540(4) 1.275(3)/1.289(3) 1.227(3)/1.225(3) 1.415(3)/1.408(3) 1.419(3)/1.413(3) 1.647(1)/1.642(1)c

1.251(3)/1.250(3) 1.317(4)/1.320(4) 1.539(4)/1.548(4) 1.299(4)/1.305(4) 1.253(3)/1.255(3) 1.230(3)/1.232(3) 1.337(3)/1.333(3) 1.542(4)/1.548(4) 1.289(3)/1.288(3) 1.222(3)/1.224(3) 1.428(4)/1.425(4) 1.423(3)/1.425(3) 1.637(1)/1.634(1)c

1.978(4) 1.974(4) 1.965(3) 1.969(4) 2.58(3)/2.673(12)e 2.680(9) 1.272(6) 1.302(6) 1.515(8) 1.251(6) 1.265(6) 1.264(6) 1.281(7) 1.558(8) 1.247(7) 1.219(7) 1.407(7) 1.436(6) 1.625(2)c

Fe1−D2

1.644(1)c

1.640(1)/1.639(1)c

1.634(1)/1.635/1)c

1.629(3)c

N1−Cu1−N2 X3−Cu1−O4 N1−Cu1−X3 N2−Cu1−O4 N1−Cu1−O4 N2−Cu1−X3 N1−C1−O1 N2−C3−O2 X3−C2−O6 O4−C4−O5 D1−Fe1−D2

104.11(9) 88.57(8) 83.84(8) 83.86(8) 170.91(8) 171.00(9) 127.7(3) 127.6(2) 124.9(3) 125.0(3) 176.4

103.82(8)/103.29(8) 94.63(8)/95.30(7) 83.12(8)/82.99(8) 82.99(8)/83.34(7) 164.31(8)/163.57(7) 162.02(9)/161.88(8) 128.2(2)/126.1(2) 127.7(2)/127.4(2) 126.6(2)/127.2(2) 125.3(2)/124.5(2) 174.1/173.5c

Bond Anglesa 102.77(9)/102.49(9) 91.20(9)/92.79(10) 83.17(10)/82.81(11) 83.38(8)/82.84(9) 172.98(8)/172.19(8) 170.39(9)/170.07(10) 126.3(3)/126.5(3) 127.3(2)/127.6(2) 127.0(3)/128.6(3) 124.8(3)/126.3(3) 176.4/176.2c

101.93(17) 91.28(16) 83.86(16) 83.47(16) 174.10(17) 168.0(2) 125.8(5) 127.1(5) 126.6(5) 128.3(5) 176.4

1.965(7) 1.974(7) 1.989(5) 1.965(5) 2.361(8) 1.273(10) 1.287(10) 1.541(12) 1.254(10) 1.244(9) 1.241(9) 1.283(10) 1.547(11) 1.259(9) 1.238(9) 1.324(10) 1.537(10) 1.758(7)c 1.660(7)d 1.633(7)c 1.544(7)d 102.4(3) 89.9(2) 83.8(3) 83.5(2) 162.8(3) 173.5(2) 126.9(8) 127.9(7) 125.7(8) 126.9(7) 164.5/162.2

a

X = O in 3·3MeCN, 7·2MeCN, and 8·MeOH; X = N in 6A·1/2MeOH·1/2H2O and 6B·2.25H2O. bData for the two crystallographically independent molecules are separated by a slant. cD1 denotes the geometrical centroid of C5−C9 and D2 that of C10−C14. dD1 denotes the geometrical centroid of C5′−C9′ and D2 that of C10′−C14′. eO7′−Cu1.

were also observed to be discrete in the solid state.28 In the solid state of 1·CHCl3 and 2 the formation of 1D chains due to intermolecular hydrogen bonds is observed (cf. Figures S1 and S2 and Table S1 in the Supporting Information). Solid-State Structures of 3·3MeCN and 6A,B. Complex 3· 3MeCN possesses C1 symmetry in the solid state. The copper atom of 3·3MeCN is coordinated by two deprotonated amido nitrogen atoms and two carboxylate oxygen atoms, resulting in a η4(κ2N,κ2O) coordination of the chelating [1,1′-fcba]4− ligand (cf. Figure 2). This coordination type is usually observed for N,N′-bridged bis(oxamato) type ligands in complexes of type II (cf. Chart 3),29 although exceptions have been observed.30 With respect to the rotation of the cp rings to each other, for 3·3MeCN a slightly distorted synperiplanar conformation (cf. e.g. torsion angle N1−C5−C10−N2 = 2.8°) is observed. The CuN2O2 coordination environment of 3·3MeCN is nearly planar (cf. Figure 2). The planarity of the CuN2O2 unit formed by the atoms Cu1, N1, N2, O1, and O2 is expressed by slight deviations observed for a calculated mean plane (rmsd = 0.052 Å, hdp = 0.092(2) Å for N2) and further by the sum of the four

bond angles around the CuII ion, which is 360.6(2)°. For example, for related N,N′-o-C6H4-bridged type II complexes it is observed that three bond angles of the CuN2O2 unit are rather small, whereas the fourth one is substantially larger.18,29 That feature is due to the presence of 5−5−5 fused chelate rings around the CuII ions and is observed as well for 3·3MeCN with the bond angles N1−Cu1−O3, N2−Cu2−O4, and N1− Cu1−O3 (83.84(8)−88.57(8)°) being substantially smaller in comparison to the N1−Cu1−N2 angle at 104.11(9)°. In this respect, 3·3MeCN can be regarded as related to N,N′-o-C6H4bridged type II complexes. In contrast, in comparison to N,N′o-arylene-bridged type II complexes,18,29 the Cu−N bond lengths of 3·3MeCN (Cu1−N1/Cu1−N2 = 1.941(2)/1.946(2) Å) exceed the range (dmin = 1.887 Å, dmax = 1.931 Å; d̅ = 1.896 Å),29 whereas the Cu−O bond lengths (3·3MeCN: d(Cu1−O3)/(Cu1− O4) = 1.9455(17)/1.9481(18) Å) fit the observed range (dmin = 1.925 Å, dmax = 1.966 Å; d̅ = 1.941 Å)29 of type II complexes. Moreover, all bond lengths of the CuN2O2 unit of 3·3MeCN are identical within standard uncertainties. This is to some extent surprising, as for all reported N,N′-o-C6H4-bridged type F


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Table 3. Selected Bond Lengths (Å) and Angles (deg) and τ Parameters of the Terminal [Cu(pmdta)]2+ Fragments of 7· 2MeCN and 8·MeOHa 7·2MeCN Cu2−O1 Cu2−O6 Cu2−N3 Cu2−N4 Cu2−N5 Cu3−O2 Cu3−O5 Cu3−N6 Cu3−N7 Cu3−N8

Figure 3. ORTEP plots (25% probability level) of the molecular structures of 7·2MeCN (left) and 8·MeOH (right). All hydrogen atoms, packing solvent molecules, and counterions are omitted for clarity. Of the disordered atoms, only one atomic position is shown. The angle sign refers to the interplanar angle of calculated mean planes of atoms adjoining black and gray filled areas.

Cu2 Cu3 ⟨τ⟩ O1−Cu2−O6 O1−Cu2−N3 O1−Cu2−N4 O1−Cu2−N5 O6−Cu2−N3 O6−Cu2−N4 O6−Cu2−N5 N3−Cu2−N4 N3−Cu2−N5 N4−Cu2−N5 O2−Cu3−O5 O2−Cu3−N6 O2−Cu3−N7 O2−Cu3−N8 O5−Cu3−N6 O5−Cu3−N7 O5−Cu3−N8 N6−Cu3−N7 N6−Cu3−N8 N7−Cu3−N8

II complexes a shorter Cu−N bond in comparison to the Cu−O bond has been observed. This effect has been explained by the greater basicity of the N donor atoms.29 In case of 3· 3MeCN, due to the N,N′-fc bridge, the N donor atoms might have thus a similar basicity in comparison to the carboxylato O donor atoms. This seems unlikely, because the treatment of 1 with 4 equiv of [nBu4N]OH gave rise to the saponification but not deprotonation, as observed for 2 (cf. above). Instead, the fc unit forces the connected N atoms to a N···N distance of 3.065(3) Å in 3·3MeCN (in 1·CHCl3: 3.350(2) Å), in comparison to an average N···N distance of 2.53 Å in N,N′-o-C6H4bridged type II complexes.29 Most probably, the comparatively large N···N distance and thus steric requirements are responsible for the observation of four identical bond lengths of the CuN2O2 setup of 3·3MeCN. By treatment of 5 with 1/2 equiv of [Cu2(OAc)4(H2O)2] and 4 equiv of [nBu4N]OH powdered green materials of identical composition have been isolated, namely [nBu4N]2[Cu(1,1′fcooMe)]·2H2O (6A·2H2O and 6B·2H2O) (cf. the Experimental Section). As observed for 3·3MeCN, 6A,B also possess C1 symmetry in the solid state. A common feature of 6A,B, respectively, is the coordination of the [1,1′-fcooMe]4− ligand to the copper atom by the three deprotonated amido nitrogen atoms N1−N3 and the carboxylato oxygen atom O4, forming a η4(κ3N,κO) coordination environment (cf. Figure 2). Astonishingly, the CuN3O unit composed of the atoms Cu1, N1−N3, and O4 of 6A (rmsd = 0.245 Å, hdp = 0.289(1) Å for N3) is much less planar in comparison to the CuN3O unit of 6B (rmsd = 0.089 Å, hdp = 0.109(1) Å for N3). This is expressed additionally by the sum of the four bond angles of the CuN3O units of 6A (364.56(16)°) and 6B (360.52(18)°). Furthermore, calculated interplanar angles between the oxamato and the oxamidato functions of 6A,B differ, at 34.24(7)° and 17.4(1)°, respectively, dramatically from each other as well as from planarity (cf. Figure 2). Thus, the coordination geometry of the CuN3O unit of 6A can be described as distorted tetrahedral, whereas that of 6B can be considered as distorted square planar. Consequently, 6A,B represent two different conformers. For comparison, 3·3MeCN as well as recently described related complexes containing a [M(opooMe)]2− fragment (M = CuII, NiII, opooMe = o-phenylene(N′-methyloxamidato)(oxamato))31

Bond Lengths 1.947(4) 2.186(4) 2.013(9) 2.04(2) 1.992(7) 1.958(4) 2.186(4) 2.052(6) 2.013(5) 2.050(6) τ Parameters 0.305 0.276 0.290 Bond Angles 81.31(15) 89.9(3) 164.5(6) 94.5(2) 113.8(3) 96.1(5) 99.9(2) 105.1(7) 146.2(3) 70.8(6) 81.26(15) 92.0(2) 173.45(16) 92.1(2) 104.2(2) 105.28(17) 98.8(2) 86.5(2) 156.9(2) 86.9(2)

8·MeOH 1.966(6) 2.203(6) 2.016(14) 2.013(8) 2.072(9) 1.971(5) 2.191(5) 2.038(7) 1.986(7) 2.039(18) 0.178 0.461 0.320 81.4(2) 96.1(12) 176.1(3) 90.7(3) 90.6(18) 102.5(3) 103.3(3) 84.4(12) 165.4(16) 87.9(4) 80.7(2) 91.0(3) 177.6(3) 95.5(8) 113.8(2) 101.7(3) 96.3(12) 88.0(3) 149.9(11) 84.3(7)

a

Only one bond length or angle of disordered atoms is given and only one τ parameter is calculated.

are square planar in this respect. Further, crystallographically characterized asymmetric mononuclear (oxamidato)(oxamato) type complexes have not been reported. For related type II complexes (cf. Chart 3) the CuN2O2 coordination environments are usually planar, with one exception observed for [nBu4N]2[Cu(R-bnbo)] (R-bnbo = (R)-1,1′-binaphthalene-2,2′-bis(oxamato)), with a sum of bond angles of the CuN2O2 unit of 367.9(2)°. In case of [nBu4N]2[Cu(R-bnbo)] the tetrahedral distortion is, due to the steric flexibility of the [R-bnbo]4− ligand, not surprising and was even anticipated. In case of 6A, however, there is no obvious reason to explain the tetrahedral distortion of its CuN3O unit, especially when the molecular structures of 3·3MeCN and 6B are compared. With the aim of understanding the structural differences of the two conformers 6A,B, the crystal structures of 6A·1/2MeOH·1/2H2O and 6B·2.25H2O were investigated (cf. Figures S3 and S4 in the Supporting Information). However, they do not indicate any kind of intermolecular interaction which could give an explanation for the tetrahedral distortion of 6A. G


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structural features of 7·2MeCN and 8·MeOH fit in general to the observations already made for type IV complexes and are not required to be mentioned here (cf. Table S5 in the Supporting Information). Finally, a collective and comparative summary of calculated interplanar angles of selected groups of crystallographically characterized compounds described here is given in Table S6 (Supporting Information). ESR Investigations. Figure 4 shows ESR spectra of 3, 6A· 2H2O, and 6B·2H2O at a frequency f = 9.8 GHz (X-band) at

As expected, a comparison of related bond lengths and angles of the two conformers 6A,B reveals several differences (cf. Table 2). It should be mentioned here for the CuN3O units of 6A,B that the N donor atoms connected to the cp rings (Ncp) and the N donor atoms of the N′-methyloxamidato group (NMe) do have significantly different Cu−N bond distances. Thereby, the Cu−Ncp bond lengths (range for 6A,B: 1.943(2)−1.968(2) Å) are always elongated in comparison to the Cu−NMe lengths (range for 6A,B: 1.928(2)−1.934(2) Å). This is the opposite tendency in comparison to [nBu4N]2[Cu(opooMe)] and is attributed to the higher Ncp···Ncp distance of 6A/6B (3.071(3)/3.061(3) Å) in comparison to the Nar···Nar distance of [nBu4N]2[Cu(opooMe)] at 2.535 Å.31 The Fe1···Cu1 distances of 3·3MeCN (3.8744(5) Å), 6A (3.8345(4) Å), and 6B (3.9041(5) Å) are significantly higher in comparison to the sum of the van der Waals radii of iron and copper (2.65 Å),32 and thus any possible through-space interactions can be ruled out. All trials to grow single crystals of 4 suitable for X-ray crystallographic studies were unsuccessful. Compound 4 is soluble only in warm DMSO (ca. 60 °C) and then stays soluble even at room temperature. The poor solubility of 4, although it is a [nBu4N]+ salt, in common organic solvents indicates the possible formation of a coordination polymer of [Cu(1,1′fcba)]− fragments in the solid state. Likely, the intermolecular interactions responsible for the polymer formation could be analogous to those observed for two different dimeric [Cu(opba)]24− fragments.33 Solid-State Structures of 7·2MeCN and 8·MeOH. As shown in Figure 3, 7·2MeCN and 8·MeOH are composed of [Cu(1,1′-fcba)]n− fragments (n = 2 (7·2MeCN), 1 (8·MeOH)), each of which coordinates two [Cu(pmdta)]2+ fragments via their exo-cis O donor atoms. The central Cu1 atom of 7· 2MeCN is coordinated weakly by one NO3− anion (Cu1−O7/ O7′ = 2.58(3)/2.673(12) Å) and one MeCN molecule (Cu1− N10 = 2.680(9) Å). As 8·MeOH represents singly oxidized 7· 2MeCN, one might expect especially for the central Cu1 atom of 8·MeOH modified geometrical parameters of its coordination environment in comparison to 7·2MeCN due to a stronger electron demand of the fc+ unit. In fact, the Cu1 atom of 8· MeOH is coordinated by one NO3− ion, with the distance Cu1−O7 (2.361(8) Å) of 8·MeOH being significantly shorter in comparison to that of 7·2MeCN. The Cu−O and Cu−N bond lengths of the CuN2O2 coordination environment around the Cu1 atoms of 7·2MeCN and 8·MeOH are both significantly elongated in comparison to that in 3·3MeCN, although no difference between those values is observed when 7·2MeCN and 8·MeOH are compared with each other. The terminal CuII ions of 7·2MeCN and 8·MeOH possess all CuN3O2 coordination environments. According to the τ parameters34 of these CuN3O2 units (cf. Table 3) their coordination geometry can be regarded as closer to the ideal squarepyramidal case. The observed large difference in τ parameters of 8·MeOH (cf. Table 3) should not be overemphasized. As explained in the Experimental Section for the crystallographic characterization of 8·MeOH, there are certainly more atoms and/or fragments which should be regarded as disordered, although their disorder could not be reliably refined. The geometries of the Cu3-containing bis(oxamato) units of 7·2MeCN and 8·MeOH comprising the atoms Cu1−Cu3, N1, N2, C1−C4, O1−O6 are no longer planar, as indicated in Figure 3. Therefore, 7·2MeCN can be regarded as deviating more from planarity in comparison to 8·MeOH. Further

Figure 4. Experimental (E) and simulated (S) X-band ESR powder spectra of 3, 6A·2H2O, and 6B·2H2O ( f = 9.56 GHz, 4 K). The magnified signal at a magnetic field of 0.16 T represents a forbidden transition.

T = 4 K together with their simulations. The ESR spectra of 3, 6A·2H2O, and 6B·2H2O appear rather similar. The spectra comprise the main signal at a field of ∼0.33 T, and a weak signal at half field of ∼0.16 T. The latter signal is visible only in the measurement at the lowest temperature. Since FeII is nonmagnetic in these three compounds, the ESR signal should be associated with a CuII ion with a spin of 1/2. One therefore should observe just a single line with a g factor ∼2 corresponding to a transition |+1/2⟩ ↔ |−1/2⟩ according to the ESR selection rule ΔSz = ± 1. The occurrence of an additional half-field signal in the ESR spectra is usually associated with a forbidden transition ΔSz = ± 2, implying that the resonating spin centers have S > 1/2. This observation suggests that at low temperatures an intermolecular dimer-like magnetic coupling of CuII spins in neighboring molecules yielding a total spin S = 1 takes place which can give rise to a forbidden transition with g ≈ 4. The temperature-dependent magnetization M(T), which has been measured for 3 in a field μ0H = 1 T, supports this conclusion. The inverse magnetic susceptibility χm−1 = H/M of 3 was fitted using the Curie−Weiss model (cf. Figure S5, Supporting Information). The fit yields a Curie−Weiss temperature of 7 K, which suggests a very weak ferromagnetic coupling between CuII ions of neighboring molecules. We note that the ESR spectrum of 3 in MeCN (cf. Figure S6, Supporting Information) does not reveal a half-field signal even at the lowest temperature, which gives evidence for the intermolecular nature of the magnetic coupling. Thus, it seems likely that 3 is involved at very low temperatures (below 10 K) in a phase transition, giving rise to interacting anionic fragments of 3, although in the solid-state structure of 3·3MeCN determined at 110 K no fragments show any kind of intermolecular interaction. H


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The 63Cu hyperfine (HF) coupling constants A∥Cu and the g tensors of 3, 6A·2H2O, and 6B·2H2O have been obtained by the appropriate modeling of the ESR spectra. The respective values are summarized in Table 4.

gz = 2 + 4k gx , y =

Table 4. Cu HF Coupling Constants A∥Cu[G] and g Tensors of 3, 6A·2H2O, and 6B·2H2O compd

A∥Cu (±0.5)

g∥ (±0.001)

g⊥ (±0.001)

3 6A·2H2O 6B·2H2O

192 177 179

2.234 2.209 2.205

2.026 2.021 2.018

x (1 + x 2)1/2

⎛ −ξ ⎞⎟ 2 ⎜x = δ ⎠ (1 + x 2)1/2 ⎝

Here, k is the orbital momentum reduction factor, ξ is the effective spin−orbital coupling parameter, and δ is a measure of the strength of the low-symmetry field.38 Under axial symmetry, one calculates g⊥ = 0 and gII = 2 + 4k. A nonzero g⊥ value and g∥ < 2 + 4k can be obtained with a distortion of the axial symmetry, which also gives rise to a partial quenching of the orbital contribution. A larger deviation of the Fc+-A g factor from the free electron value ge = 2.0023 in comparison to that in Fc+-B can be attributed to a larger orbital contribution in the latter case. At the same time, however, one can conclude that Fc+-B is more distorted in comparison to Fc+-A. This makes it clear that 4 should possess two geometrically different ferrocenium moieties in the solid state, as noticed additionally by the 57Fe Mössbauer spectroscopic characterization of 4 (vide infra). Figure 6 shows the ESR spectra of 7 and 8 at 290 and 4 K. In both cases, an isotropic g factor of 2.11 is observed at room

The Cu HF coupling constants obtained for 6A·2H2O and 6B·2H2O are smaller than that of 3. Such reduction can be related to the substitution of O by the N atom in the coordination sphere of the CuII ion in 6A·2H2O and 6B·2H2O in comparison to 3; thus, one expects the spin density on the CuII ion to be redistributed toward the N donor atom, since the Cu−N bond is more pronouncedly covalent than the Cu−O bond. As the dipolar HF coupling constant Adip = 1/3(A∥ − A⊥) is proportional to the spin density on p and d orbitals,35 a redistribution of the spin density distribution from the CuII ion toward N donor atoms is expected to reduce the Cu HF coupling constant. Figure 5 shows the ESR spectrum of 4 at f = 9.56 GHz at 4 K. The spectrum is a superposition of a signal from CuII with

Figure 6. Experimental X-band ESR powder spectra: (top) 7 ( f = 9.56 GHz) at 290 K and 4 K; (bottom) 8 ( f = 9.56 GHz) at 290 and 4 K.

temperature. At 4 K, the X-band (9.56 GHz) ESR spectrum of 7 shows a structured signal and its peaks can be attributed to the three rhombic g values g1 = 2.14, g2 = 2.1, and g3 = 2.06 (see Figure 6), which is expected for a low-symmetry ligand coordination of CuII in this sample. Remarkably, with increasing temperature the g1 line shifts to a higher magnetic field, whereas the g3 line shifts to a lower magnetic field. The g2 line shifts to a lower magnetic field as well, but to a lesser extent. Therefore, the lines overlap and also broaden. Finally this broadened single ESR line shifts to slightly lower fields at high temperatures. The spin Hamiltonian appropriate to describe the exchange interactions in a linear symmetric trinuclear complex has the form

Figure 5. Experimental X-band ESR powder spectrum of 4 ( f = 9.56 GHz, 4K). Signals marked with * arise from Fc+-A, and the signal marked with + arises from Fc+-B.

g∥ = 2.22 and g⊥ = 2.06 and of additional signals which can be attributed to a ferrocenium moiety. The shape and the position of the peaks clearly demonstrate two different phases of ferrocenium, denoted Fc+-A and Fc+-B. In Figure 5, signals marked with * arise from Fc+-A with g∥ = 4.39 and g⊥ = 1.92 and the signal marked with + arises from Fc+-B with g∥ = 3.13. We were not able to distinguish the signal corresponding to g⊥ for Fc+-B due to the signal broadening most likely by the field effect, as was previously reported for [(C2Bz5)2Fe]+.36 Ferrocenium has a low spin-1/2 d5 ground state configuration with one unpaired electron. For ferrocenium with the 2 E2g[(e2g)3(alg)2] ground-state configuration,37 Prins38 has calculated the g-tensor (including spin−orbit coupling and low symmetry field) from

H = J(S1S2 + S2S3) + J ′(S1S3)

Here, the first term describes the interaction between adjacent spins with a coupling parameter J and the second term describes the interaction between nonadjacent spins with a coupling I


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parameter J′. The resulting spin states can be classified as |ST;S13⟩, with the total spin operator ST = S1 + S2 + S3 and an intermediate spin operator S13 = S1 + S3. Then the following spin states can be obtained: α = |1/2;1⟩, β = |1/2;0⟩, and γ = |3/2;1⟩; their corresponding energies are Eα = −J + 1/4J′, Eβ = −3/4J′, and Eγ = 1/2J + 1/4J′, respectively. The α and β states are doublets, and the γ state is a quartet. In complex 7 the central CuII ion is antiferromagnetically coupled to the terminal CuII ions with an exchange coupling constant J12 = J23 = −58 cm−1 (see Figure 6). Therefore, α is the ground state and β and γ are excited states, respectively. At 4 K mostly the doublet ground state α is populated. Therefore, the rhombic pattern of the ESR signal shown in Figure 6 is due to the g tensor of the α state. The experimentally observed shift of the g factors with increasing temperature can be explained by the progressive thermal population of the first excited doublet state β, whose g tensor components are apparently different from those of the ground state. Since the interconversion rate between the α and β doublets is usually faster than the time scale of the ESR measurement at 10 GHz,39,40 the gi peaks in the ESR spectrum correspond to the Boltzmann weighted thermal average of the g factors of the α and β states,39,40 which explains their temperature dependence. Finally, at high temperatures the thermal relaxation effects broaden the lines and the g tensor pattern is no longer resolved. In contrast to the ESR spectrum of 7, the ESR spectrum of 8 at 4 K consists of a single line which can incorporate the response from three CuII ions and one FeIII ion at a field of ∼0.32 T. Due to a ferromagnetic Fe−Cu coupling on the order of J24 ≈ ∼ 5.7 K (see the analysis of the magnetization data below), one expects an exchange narrowed common resonance of Cu and Fe spins at frequency ν ≈ 10 GHz (hν ≈ 0.5 K ≪ J24). The occurrence of the exchange narrowing effect implies that the resonance frequencies of CuII and FeIII and consequently the g factors do not differ substantially. As we discussed above, a strong distortion of the axial symmetry in the ferrocenium cation shifts both the g⊥ and g∥ values of FeIII toward a value of 2. Thus, we can attribute the observed isotropic g factor value 2.11 of the joint resonance line which is close to the usual g factor of CuII as an indication of a strong distortion of the axial symmetry in ferrocenium cation in 8. The orbital contribution to g is then completely quenched by the low-symmetry field. The single-crystal X-ray analysis of 8 supports this assignment (cf. e.g. Figure 3). Static Magnetic Properties. The temperature dependence of the inverse susceptibility χm−1 = H/M of 4, 7, and 8 is presented in Figures 7−9, respectively. The insets in the figures show a commonly used presentation of the susceptibility data as the product χmT vs the temperature. The black line represents a numerical model fit using the simulation software package julX on the basis of the Hamiltonian41

Figure 7. Temperature dependence of the inverse magnetic susceptibility χm−1 of 4. Inset: plot of of χmT as a function of T.


⎯→ ⎯

H = −2 ∑ Ji , j Si ·Sj⃗ i,j

Here, Ji,j values are exchange coupling constants of spins i and j. In order to simulate χm−1, the g factors measured by ESR have been used. The obtained exchange coupling constants are given in Table 5. The analysis yields the best possible fit with a weak antiferromagnetic coupling J12 = −2 cm−1 between the CuII and FeIII spins for 4 (cf. Figure 7). Note that the modeling reveals a rather large temperature-independent paramagnetic contribution (TIP)


χ = 0.002 erg/(G2 mol). The simulated χm−1(T) dependence of 7 (see Figure 8) reveals the antiferromagnetic coupling J12 = J23 = −58 cm−1 between the central and terminal CuII spins. J


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Table 5. Experimental/Theoretical (DFT) J Values of 4, 7, and 8 4 7 8

J12/cm−1

J23/cm−1

J24/cm−1

−2/−20 −58/−65 −64/−78

−58/−66 −64/−70

4/−9

The analysis for 8 yields the best possible fit (Figure 9) with an antiferromagnetic coupling J12 = J23 = −64 cm−1 between the central and terminal CuII spins and a weak ferromagnetic coupling J24 = 4 cm−1 between the central CuII and FeIII spins (Figure 10). The structural analysis of compounds 7 and 8

Figure 11. 57Fe Mössbauer spectra of 3 and 4 at room temperature (dots) and corresponding simulations (lines).

Table 6. Experimental Parameters of the 57Fe Mössbauer Characterization of 3 and 4 compound 3 4 Fc+-A Fc+-B

Figure 10. Scheme of the expected magnetic coupling between the spins in compound 8.

δ/mm s−1

QS/mm s−1

FWMH/mm s−1

intensity/%

0.32

2.33

0.23

100

0.42 0.38

0.53 0.06

0.49 0.35

75 25

ferrocenium fragments possess similar isomer shifts. The main difference in the Mössbauer signal resides in the collapse of the QS upon oxidation of ferrocene.43,44 The QS and δ values observed in 4 are well within the range of literature data for ferrocenium-based salts.42,45 It has been suggested by Dong et al.46 that the wide range of QS values is tightly linked to the distortion of the axial geometry of the ferrocenium fragments. Consequently, the major and minor subspectra of 4 can be attributed to two differently distorted ferrocenium moieties in 4, as observed by ESR spectroscopy as well (vide supra). Therefore, the major subspectrum is attributed to Fc+-A and the minor subspectrum to Fc+-B. DFT Calculations. To support the results of the ESR and 57 Fe Mössbauer spectroscopic characterization of 4, for 3 the removal of an electron was modeled by preparing a 3+ charged electronic configuration denoted as 3#+ out of the anionic fragment of 3·3MeCN denoted as 3#. The difference in electron densities of 3# and 3#+ is illustrated in Figure 12. It is obvious that the majority of the electron density is removed from the iron center and especially the oxygen atoms of the oxamato units of 3#, whereby almost no electron density is removed from the copper center. Thus, 3#+ represents the monoanionic complex fragment of 4 and consequently the calculated magnetic properties of 3#+ revealed a weak antiferromagnetic coupling between its CuII and FeIII ions of −20 cm−1. This calculated value agrees qualitatively with the experimentally determined J coupling for 4 of −2 cm−1. Furthermore, the magnetic properties of 7 and 8 were calculated (cf. Table 5). The calculated values for 7 agree qualitatively with the experimental data; however, the weak ferromagnetic coupling of 8 for J2/4 could not be confirmed by theory. The differences between experiment and theory for the oxidized structures 4 and 8 may arise from several reasons. Standard DFT in general overestimates the calculated J values due to its systematic error in the localization of the d orbitals.

reveals small differences in geometries around their central CuII ions. A smaller antiferromagnetic coupling of 7 in comparison to that of 8 could be attributed to this structural difference. To summarize this part, the ESR and magnetization results of 3, 6A·2H2O, and 6B·2H2O reveal a dimer-like magnetic interaction between CuII ions in neighboring molecules at very low temperatures. The data for 4 enable us to conclude that the Fe ion is magnetic and therefore should occur in the oxidation state +3 and that 4 could possess two geometrically different ferrocenium moieties in the solid state. The experimental results for 8 give evidence that Fe is magnetic and therefore should have a valence of +3 and the axial symmetry in ferrocenium cation is strongly distorted. The latter conclusion is confirmed by a singlecrystal X-ray analysis. Compounds 4 and 8 reveal a very weak magnetic coupling between the central CuII ion and the FeIII ion. 57 Fe Mössbauer Spectroscopy. The 57Fe Mössbauer spectra of 3 and 4 at room temperature are displayed in Figure 11. At room temperature, Mössbauer spectroscopy is mostly sensitive to the electron density at the iron nucleus site, reflected in the isomer shift (δ), and the electric field gradient at the nucleus site, reflected in the quadrupole splitting (QS). 3 exhibits a large QS value of 2.34 mm/s. On the other hand, the spectrum of 4 displays two signals, a sign of two types of iron in the sample. Table 6 summarizes the parameters of each subspectrum. A large QS value is consistent with literature data for compounds comprising ferrocene moieties.42 Moreover, the δ value and the small asymmetry of the doublet are consistent as well. The latter has its origin in the Goldanskii−Karyagin effect often observed when the symmetry around the iron is not octahedral. The lack of a signal with large QS value in the spectrum of 4 confirms that the iron center is in oxidation state +3. A change in the oxidation state of iron centers in molecules induces a change in δ, and it has been shown that ferrocene and K


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and 6B·2H2O) comprising ferrocene moieties were synthesized and characterized. The chemical oxidation of 3 gave its corresponding ferrocenium form, namely 4. That the oxidation of 3 is iron-centered has been verified by the combined and comparative ESR and 57Fe Mössbauer spectroscopic characterization of 3 and 4, accompanied by DFT calculations. Additionally, the novel tetranuclear complexes [Cu3(1,1′-fcba)(pmdta)2](NO3)n (n = 2 (7), 3 (8)) were synthesized from 3 and 4, respectively, and crystallographically characterized. The experimental results for 8 give further evidence that Fe is magnetic and therefore should occur in the oxidation state +3 and that the axial symmetry in the ferrocenium moiety is distorted. The latter conclusion is confirmed by a single-crystal X-ray analysis. Compounds 7 and 8 reveal antiferromagnetic couplings of −58 and −64 cm−1, respectively, between the central and terminal CuII spins. Moreover, compounds 4 and 8 showed very weak antiferromagnetic and ferromagnetic couplings, respectively, between the central CuII and FeIII ions. We could thus show and demonstrate for the first time that the ferrocenediyl moiety of complexes comprising type I fragments (cf. Scheme 1) can play a crucial role in fine-tuning readily resolvable magnetic superexchange interactions upon its oxidation. This may allow the fabrication of new, promising molecular-based materials with switchable magnetic properties.

Figure 12. Isosurface plot of the electron difference density ρdiff = ρ(3#) − ρ(3#+) overlaid by the molecular structure of 3# to pinpoint the position of ρdiff.

To some extent this effect is corrected by the application of hybrid functionals as in the present case.62 Furthermore, if the electron spin densities are not well localized onto the magnetic centers, the broken symmetry approach used to calculate the exchange coupling may be less accurate or even predict the wrong type of coupling.63 In the case of 4 and 8 we observed a delocalization of the spin density especially around the FeIII ions. In addition, our calculations were only done on singly charged molecules, avoiding the effects of counterions and crystal structure packing effects, which may lead to the observed differences in experimental and theoretical J values (cf. Table 5). Finally, it needs to be emphasized that the input geometry used to calculate the magnetic properties of 8 reflects disordered atoms in only one atomic position. In order to verify whether or not there is a difference in the total energies of the two different conformers 6A and 6B, allelectron DFT calculations of the individual free molecules were carried out. In the calculations the counterions were neglected and only the charged complex fragments were used. Geometry data of 6A,B from the X-ray measurements were used as inputs. The calculations indeed revealed a difference in the total energy of about 0.04 eV (0.92 kcal/mol), with 6B having the lower total energy. Upon geometry relaxation of the starting geometries, an increase of the energy difference to 0.11 eV (2.54 kcal/mol) was found. The molecular structures of geometry relaxed complex fragments 6A′,B′, respectively, are shown in Figure S7 (Supporting Information), including comments given there, whereas selected bond lengths and angles are summarized in Table S7 (Supporting Information) together with those of 6A,B for comparison. The comparatively small calculated difference of the total energies of 6A and 6B might indicate that the reason for the observation of two strikingly different conformers of [Cu(fcooMe)]2− fragments is rather due to different crystallization methods and consequently due to different crystal structures with variably hydrogen bonded solvents (cf. Figures S3 and S4, Supporting Information).

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EXPERIMENTAL SECTION

General Conditions. All reactions were carried out under an atmosphere of dry argon using standard Schlenk techniques and vacuum-line manipulations. All solvents were distilled prior to use. Solvents were purified according to standard procedures,47 and degassed water was prepared by ultrasonicating distilled water under vacuum. The NMR and IR spectra of the compounds under investigation are displayed in the respective figures in the Supporting Information. These figures contain in addition the numbering code used for assignment. Reagents. All chemicals were purchased from commercial sources and used as received without further purification. 1,1′-Diaminoferrocene was synthesized via the literature procedure reported by Abdulmalic and Rüffer.16 Instruments. NMR spectra were recorded at room temperature with a Bruker Avance III 500 Ultra Shield spectrometer (1H at 500.300 MHz and 13C{1H} at 125.813 MHz) in the Fourier transform mode. Chemical shifts are reported in δ (ppm) vs SiMe4 with the solvent as the reference signal ([D6]-DMSO: 1H NMR, δ 2.54; 13C{1H} NMR, δ 40.45). Infrared spectra were recorded in the range 400−4000 cm−1 using a Perkin-Elmer Spectrum 1000 FT-IR spectrophotometer as KBr pellets. Microanalysis was performed on a Thermo Flash AE 1112 series instrument. Synthesis of 1,1′-fcbaH2Et2 (1). A mixture of 1,1′-diaminoferrocene (0.54 g, 2.5 mmol) and Et3N (0.5 g, 5 mmol) in THF (25 mL) was added dropwise with stirring to a solution of ethyloxalyl chloride (0.68 g, 5 mmol) in THF (25 mL). The reaction mixture was stirred for 1 h, filtered and the volume reduced to ca. 10 mL. Addition of Et2O (100 mL) resulted in the formation of an orange precipitate which was collected by filtration, washed thoroughly with H2O, and dried in vacuo. Yield: 0.85 g (88%). Anal. Calcd for C18H20FeN2O6 (416.21): C, 51.94; H, 4.84; N, 6.73. Found: C, 52.03; H, 4.97; N, 6.78. IR: ν 3336 (s) (NH); 2980 (w), 2936 (w) (CH); 1689 (s) (CO). 1H NMR: δ 1.33 (t, 6H, H7,7′), 4.10 (t, 4H, H3,3′), 4.24 (q, 4H, H6,6′), 4.83 (t, 4H, H2,2′), 10.31 (s, 2H, 2NH). 13C{1H} NMR: δ 13.7 (C7,7′), 62.0 (C3,3′), 62.4 (C2,2′), 65.5 (C1,1′), 93.9 (C6,6′), 154.7 (C4,4′), 160.1 (C5,5′). Figure S8 (Supporting Information) gives the IR and 1H and 13C NMR spectra of 1. Orange rod-shaped crystals of 1 suitable for X-ray diffraction studies were obtained from an n-hexanelayered solution of 1 in CHCl3. Synthesis of [nBu4N]2[(1,1′-fcbaH2)] (2). In a trial to synthesize n [ Bu4N]2[Ni(1,1′-fcba)], [nBu4N]OH (0.77 g, 40% aqueous solution,

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CONCLUSION The first dinuclear bis(oxamato) type complexes [nBu4N]2[Cu(1,1′-fcba)] (3) and [nBu4N]2[Cu(fcooMe)]·2H2O (6A·2H2O L


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eliminate [nBu4N]OAc. The solvent was removed again to leave a brown-green sticky material, which was dissolved in CH2Cl2 (50 mL), dried over Na2SO4, and filtered. After the volume was reduced to ca. 5 mL, 6A·2H2O was precipitated by addition of Et2O (100 mL), filtered, and dried in vacuo. Yield: 0.27 g (61%). Anal. Calcd for C47H87CuFeN5O7 (953.61): C, 59.20; H, 9.20; N, 7.34. Found: C, 59.17; H, 9.29; N, 7.26. IR: ν 3366 (b) (OH); 2958 (s), 2932 (m) (CH); 1649 (m), 1586 (s) (CO). Figure S14 (Supporting Information) gives the IR spectrum of 6A·2H2O. Green prism-like crystals of 6A· 2H2O suitable for X-ray diffraction studies were grown by slow diffusion of Et2O into a MeOH solution of 6A·2H2O. 6B·2H2O. This compound was synthesized completely analogously to 6A·2H2O, with the exception that in this case 5 prepared by the second attempt was used as the starting material. Yield: 0.24 g (60%). Anal. Calcd for C47H87CuFeN5O7 (953.61): C, 59.20; H, 9.20; N, 7.34. Found: C, 59.21; H, 9.26; N, 7.31. IR: ν 3328 (b) (OH); 2958 (s), 2929 (m) (CH); 1650 (m), 1586 (s) (CO). Figure S15 (Supporting Information) gives the IR spectrum of 6B·2H2O. Well-shaped green crystals of 6B·2H2O suitable for X-ray diffraction studies were grown by slow evaporation of a concentrated MeOH solution of 6B·2H2O. Synthesis of [Cu3(1,1′-fcba)(pmdta)2](NO3)n (n = 2 (7), 3 (8)). A solution of [Cu(pmdta)(NO3)2] (0.08 g, 0.22 mmol) in MeCN (25 mL) was added dropwise to a solution of 3 or a suspension of 4 (0.11 mmol) in MeCN (25 mL) with continuous stirring. The reaction mixture was stirred for a further 1 h (in case of using 4, all suspended material was dissolved after the complete addition of [Cu(pmdta)(NO3)2] and stirring for a further 1 h). The resulting dark green solution was concentrated to ca. 5 mL, and THF (100 mL) was added to precipitate 7 or 8. The supernatant was removed, and the residual solid was dissolved in MeCN (5 mL). THF (100 mL) was added to precipitate a dark green powder, which was washed successively with THF and Et2O (2 × 50 mL) and dried in vacuo. Data for 7 are as follows. Yield: 0.10 g (91%). Anal. Calcd for C32H54Cu3FeN10O12 (1017.31): C, 37.78; H, 5.35; N, 13.77. Found: C, 37.16; H, 5.24; N, 13.59. IR: ν 2967 (w), 2926 (w), 2872 (w) (CH); 1592 (s) (CO); 1383 (s), 1320 (m) (NO). Figure S16 (Supporting Information) gives the IR spectrum of 7. Data for 8 are as follows. Yield: 0.09 g (76%). Anal. Calcd for C32H54Cu3FeN11O15 (1079.32): C, 35.61; H, 5.04; N, 14.28. Found: C, 35.47; H, 4.92; N, 14.16. IR: ν 3046 (w), 2905 (w) (CH); 1591 (s) (CO); 1363 (m), 1308 (s) (NO). Figure S17 (Supporting Information) gives the IR spectrum of 8. Dark green, needle-like crystals of 7 and 8 suitable for X-ray diffraction studies were grown by slow diffusion of Et2O into a MeCN solution of 7 and a MeOH solution of 8, respectively. X-ray Diffraction Analysis. Data were collected on an Oxford Gemini S diffractometer using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) for 3·3MeCN, 6A,B, and 7 or Cu Kα radiation (λ = 1.54184 Å) for 1·CHCl3, 2, and 8. All structures were solved by direct methods using SHELXS-91 and refined by full-matrix least-squares procedures on F2 using SHELXL-97.48 All non-hydrogen atoms were refined anisotropically. All C-bonded hydrogen atoms were geometrically placed and refined isotropically in riding modes using default SHELXTL parameters. The positions of O- and N-bonded hydrogen atoms were taken from difference Fourier maps and refined isotropically. In the case of 2, the C atoms C21−C23 of the [nBu4N]+ cation were refined disordered on two positions with occupancies of 0.71/0.29. In the case of 6A the C atoms C95 and C96, C109−C112, and C108 of [nBu4N]+ cations were refined disordered on two positions with occupancies of 0.55/0.45, 0.49/0.51, and 0.81/0.19, respectively. In the case of 7 the atoms N4, C17−C21 of one pmdta ligand and the two NO3− anions N9, O7−O9 and N11, O10−O12 were refined disordered on two positions with occupancies of 0.23/ 0.77, 0.29/0.71, and 0.50/50, respectively. In the case of 8, the carbon atoms of the (C5H4)2Fe unit (C5−C14) were refined disordered on two positions with occupancies of 0.49/0.51. Of the three NO3− ions, only that bonded to Cu1 (N9, O7−O9) could be refined with full occupancies and without disorder. The other two NO3− ions were included as follows: (a) N11, O12−O14 with an occupancy of 0.58333, (b) N13, O18−O20 with an occupancy of 0.50, and (c) N10/O1 and

1.2 mmol), 1 (0.12 g, 0.3 mmol), and [Ni(H2O)6]Cl2 (0.08 g, 0.3 mmol) were accommodated for the reaction as described analogously for 3. After procession through all individual synthetic steps, 2 was obtained as a faint yellow powder. Yield: 0.06 g (82%). Anal. Calcd for C46H82FeN4O6 (843.01): C, 65.54; H, 9.80; N, 6.65. Found: C, 64.95; H, 9.28; N, 6.47. 1H NMR: δ 0.94 (t, 24H, Ha), 1.32 (m, 16H, Hb), 1.57 (m, 16H, Hc), 3.17 (m, 16H, Hd), 3.78 (t, 4H, H3,3′), 4.55 (t, 4H, H2,2′), 9.20 (s, 2H, 2NH). 13C{1H} NMR: δ 13.4 (Ca), 19.1 (Cb), 23.0 (Cc), 57.5 (Cd), 61.4 (C3,3′), 65.1 (C2,2′), 95.5 (C1,1′), 162.4 (C4,4′), 164.7 (C5,5′). Figure S9 (Supporting Information) gives the 1H and 13C NMR spectra of 2. Yellow, needleshaped crystals of 2 suitable for X-ray diffraction studies were grown by slow diffusion of Et2O into a CH2Cl2 solution of 2. Synthesis of [nBu4N]2[Cu(1,1′-fcba)] (3). [nBu4N]OH (0.77 g, 40% aqueous solution, 1.2 mmol) was added to a suspension of 1 (0.12 g, 0.3 mmol) in 50 mL of 50% aqueous EtOH. The resulting mixture was stirred at 60 °C for 20 min. Then, CuCl2·2H2O (0.05 g, 0.3 mmol) in H2O (20 mL) was added dropwise with stirring at 25 °C. The thus obtained green reaction mixture was filtered, and the filtrate was extracted with CH2Cl2 (300 mL). The organic phase was separated, washed with H2O (2 × 20 mL), and dried over Na2SO4. The volume was reduced to ca. 10 mL, Et2O (100 mL) was added to precipitate 3, which was filtered off and dried in vacuo. Yield: 0.18 g (72%). Anal. Calcd for C46H80CuFeN4O6 (904.54): C, 61.08; H, 8.91; N, 6.19. Found: C, 60.88; H, 8.75; N, 5.94. IR: ν 2958 (s), 2929 (m), 2872 (m) (CH); 1686 (m), 1640 (s), 1600 (s) (CO). Figure S10 (Supporting Information) gives the IR spectrum of 3. Well-shaped green needle-like crystals suitable for X-ray diffraction studies were grown by slow diffusion of Et2O into a MeCN solution of 3. Oxidation of 3 to [nBu4N][Cu(1,1′-fcba)] (4). A solution of I2 (0.035 g, 0.12 mmol) in CH2Cl2 (25 mL) was added dropwise to a solution of 3 (0.11 g, 0.12 mmol) in CH2Cl2 (25 mL) at −30 °C with continuous stirring. The reaction solution darkened over the course of the addition of I2 solution. The resulting mixture was warmed to room temperature and stirred for 1 h. After standing for 30 min, 4 precipitated as a dark green solid, which was filtered off, washed with CH2Cl2 (10 mL), THF (10 mL) and Et2O (2 × 20 mL), and dried in vacuo. Yield: 0.06 g (81%). Anal. Calcd for C30H44CuFeN3O6 (661.19): C, 54.42; H, 6.70; N, 6.35. Found: C, 54.53; H, 6.20; N, 6.14. IR: ν 2961 (m), 2872 (m) (CH); 1581 (b) (CO). Figure S11 (Supporting Information) gives the IR and 1H NMR spectra of 4. All attempts to grow single crystals of 4 were unsuccessful. Synthesis of 1,1′-fcooH3Me2 (5). A MeOH solution (25 mL) of 1 (0.37 g, 0.9 mmol) was treated with MeNH2 (33% in absolute EtOH, 0.25 g, 2.7 mmol) with continuous vigorous stirring. After reflux for 1 h, the orange precipitate obtained was filtered off, washed with MeOH and Et2O, and dried in vacuo. Yield: 0.20 g (61%). Anal. Calcd for C16H17FeN3O5 (387.17): C, 49.64; H, 4.43; N, 10.85. Found: C, 49.69; H, 4.44; N, 10.20. IR: ν 3331 (m), 3259 (m) (NH); 3081 (w), 2936 (w) (CH); 1726 (w), 1698 (m), 1656 (s) (CO). Figure S12 (Supporting Information) gives the IR spectrum of 5. The synthesis of 5 was repeated as described above. In this case, however, a different amount of MeNH2 was used (MeNH2 (33% in absolute EtOH, 0.85 g, 9 mmol)) and the reaction mixture was refluxed for 6 h. The orange precipitate obtained was filtered off, washed with MeOH and Et2O, and dried in vacuo. Yield: 0.21 g (63%). Anal. Calcd for C16H17FeN3O5 (387.17): C, 49.64; H, 4.43; N, 10.85. Found: C, 49.62; H, 4.53; N, 10.27. IR: ν 3331 (m), 3259 (m) (NH); 3081 (w), 2929 (w) (CH); 1729 (w), 1698 (m), 1658 (s) (CO). Figure S13 (Supporting Information) gives the IR spectrum of 5. Note: due to the insolubility of 5, even in DMSO, NMR spectra were not recorded. Synthesis of [nBu4N]2[Cu(1,1′-fcooMe)]·2H2O (6A·2H2O, 6B· 2H2O). 6A·2H2O. Compound 5 (0.2 g, 0.5 mmol) was suspended in MeOH (50 mL). A hot solution of [Cu2(OAc)4(H2O)2] (0.09 g, 0.25 mmol) in MeOH (25 mL) was added dropwise with stirring. Then, [nBu4N]OH (1.29 g, 40% in MeOH, 2 mmol) was added with continuous stirring. The resulting mixture was stirred at 60 °C for a further 15 min, filtered and the solvent evaporated to dryness. The resulting oily material was treated with THF (25 mL) and filtered to M


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N14/O21 with the N atoms on specific positions (occupancy 0.1667) and the O atoms with occupancies of 0.50, respectively. All C atoms have comparatively large Ueq(max)/Ueq(min) ratios. Most probably, this is due to either a not fully resolvable and/or unresolved disorder. Trials to refine more fragments disordered gave, however, nonreliable results. ESR Measurements. ESR measurements on the powder of 3, 4, 6A·2H2O, 6B·2H2O, 7, and 8 were performed at selected temperatures with a Bruker EMX spectrometer operating in the X-band with a modulation frequency of 100 kHz. ESR spectra were processed using a Win-ESR software package,49 and spectral simulations were carried out with the Simfonia software package.50 Magnetic Measurements. Static magnetic susceptibility was measured on compounds 4, 7, and 8 with a 7 T VSM-SQUID magnetometer from Quantum Design at a field of 1 T in the temperature range 2−300 K. 57 Fe Mö ssbauer Measurements. The energy spectrum was produced using a 60Co in rhodium γ-ray source and a sinusoidal velocity profile at room temperature. Velocity calibration was done using a 10 μm high-purity iron foil. Data were gathered by a proportional counter. Respectively 45.3 and 62.4 mg of 3 and 4 were spread in a polyamide sample holder subsequently placed in the radiation path. Simulations were carried out using pure Lorentzian line shapes. Figure 11 is plotted as measured. DFT Calculations. Starting from the experimentally determined X-ray structures of the respective complexes, we generated molecular models of the free, isolated ions that have been used for the density functional theory (DFT) calculations, carried out by using the NRLMOL (Naval Research Laboratory Molecular Orbital Library) program,51−57 which is an all-electron implementation of DFT. For every structure the properties were calculated for the geometry as obtained from the X-ray data and for the geometry optimized models. For 6A,B, it was checked that the stationary point on the potential hypersurface was found, as no negative frequencies were present in the calculated vibration spectra. The magnetic exchange coupling was calculated by means of the broken symmetry approach as detailed previously.58 The DFT calculations of the isolated complex ion in its two spin configurations were carried out using the B3LYP59 functional and Ahlrichs triple-ζ valence basis set60 as implemented in the ORCA61 program package (revision 2.80).

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ACKNOWLEDGMENTS This work has been supported by the Deutsche Forschungsgemeinschaft through project FOR 1154 “Towards Molecular Spintronics”. M.A.A. thanks the DAAD for a scholarship.

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REFERENCES

(1) (a) Kealy, T. J.; Pauson, P. L. Nature 1951, 168, 1039−1040. (b) Miller, S. A.; Tebboth, J. A.; Tremaine, J. F. J. Chem. Soc. 1952, 632−635. (c) Wilkinson, G.; Rosenblum, M.; Whiting, M. C.; Woodward, R. B. J. Am. Chem. Soc. 1952, 74, 2125−2126. (d) Fischer, E. O.; Pfab, W. Z. Naturforsch. 1952, b, 377−379. (2) Togni, A., Hayashi, T., Eds. Ferrocenes: Homogeneous Catalysis, Organic Synthesis, Materials Science; VCH: Weinheim, Germany, 1995. (3) Stepnicka, P. Ferrocenes: Ligands, Materials and Biomolecules; Wiley: Hoboken, NJ, 2008. (4) Woodward, R. B.; Rosenblum, M.; Whiting, M. C. J. Am. Chem. Soc. 1952, 74, 3458−3459. (5) “Since the use of abbreviated symbols for ferrocene and ferrocenyl groups is somewhat confusing in the literature, here the ferrocenyl group (Fe(η5-C5H4)(η5-C5H5)) is denoted as ‘Fc’ and the ferrocene-1,1′-diyl group (Fe(η5-C5H4)2) as ‘fc’. By use of these abbreviations, ferrocene (Fe(η5-C5H5)2) can be formulated either as FcH or fcH2.” See: Stepnicka, , P. Ferrocenes: Ligands, Materials and Biomolecules; Wiley: Hoboken, NJ, 2008,. (6) Siemeling, U.; Auch, T. Chem. Soc. Rev. 2005, 34, 584−594. (7) (a) Shafir, A.; Fiedler, D.; Arnold, J. Dalton Trans. 2002, 555− 560. (b) Carver, C.; Diaconescu, P. J. Am. Chem. Soc. 2008, 130, 7558−7559. (c) Wrackmeyer, B.; Klimkina, E.; Milius, W. Eur. J. Inorg. Chem. 2008, 3340−3347. (d) Weng, Z.; Koh, L.; Hor, T. J. Organomet. Chem. 2004, 689, 18−24. (e) Gibson, V.; Gregson, C.; Halliwell, C.; Long, N.; Oxford, P.; White, A.; Williams, D. J. Organomet. Chem. 2005, 690, 6271−6283. (f) Monreal, M.; Carver, C.; Diaconescu, P. Inorg. Chem. 2007, 46, 7226−7228. (g) Shafir, A.; Power, M.; Whitener, G.; Arnold, J. Organometallics 2001, 20, 1365−1369. (h) Westmoreland, I.; Arnold, J. Acta Crystallogr., Sect. E 2006, 62, m2272−m2273. (i) Shafir, A.; Arnold, J. J. Am. Chem. Soc. 2001, 123, 9212−9213. (j) Carver, C.; Monreal, M.; Diaconescu, P. Organometallics 2008, 27, 363−370. (k) Siemeling, U.; Auch, T.; Tomm, S.; Fink, H.; Bruhn, C.; Neumann, B.; Stammler, H. Organometallics 2007, 26, 1112−1115. (l) Eppinger, J.; Nikolaides, K.; Zhang-Presse, M.; Riederer, F.; Rabe, G.; Rheingold, A. Organometallics 2008, 27, 736− 740. (m) Westmoreland, I.; Arnold, J. Acta Crystallogr., Sect. E 2006, 62, m2303−2304. (n) Monreal, M.; Carver, C.; Diaconescu, P. Inorg. Chem. 2007, 46, 7226−7228. (o) Siemeling, U.; Kuhnert, O.; Neumann, B.; Stammler, A.; Stammler, H.; Bildstein, B.; Malaun, M.; Zanello, P. Eur. J. Inorg. Chem. 2001, 913−916. (p) Shafir, A.; Arnold, J. Organometallics 2003, 22, 567−575. (q) Metallinos, C.; Tremblay, D.; Barrett, F.; Taylor, N. J. Organomet. Chem. 2006, 691, 2044−2047. (r) Monreal, M.; Diaconescu, P. Organometallics 2008, 27, 1702−1706. (8) Due to the vast amount of complexes (number of entries in the CSD database exceeds 600), we refer to the CSD database and ref 3. (9) (a) Allgeier, A. M.; Singewald, E. T.; Mirkin, C. A.; Stern, C. L. Organometallics 1994, 13, 2928−2930. (b) Allgeier, A. M.; Slone, C. S.; Mirkin, C. A.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L. J. Am. Chem. Soc. 1997, 119, 550−559. (c) Guo, S.; Hauptmann, R.; Losi, S.; Zanello, P.; Schneider, J. J. J. Organomet. Chem. 2009, 694, 1022−1026. (10) (a) Canales, S.; Crespo, O.; Fortea, A.; Gimeno, M. C.; Jones, P. G.; Laguna, A. Dalton Trans. 2002, 2250−2255. (b) Gibson, V. C.; Long, N. J.; Long, R. J.; White, A. J. P.; Williams, C. K.; Williams, D. J.; Grigiotti, E.; Zanello, P. Organometallics 2004, 23, 957−967. (c) Akabori, S.; Kumagai, T.; Shirahige, T.; Sato, S.; Kawazoe, K.; Tamura, C.; Sato, M. Organometallics 1987, 6, 526−531. (d) McCulloch, B.; Ward, D. L.; Woolins, J. D.; Brubaker Junior, C. H. Organometallics 1985, 4, 1425−1432. (e) Cowie, M.; Dickson, R. S. J. Organomet. Chem. 1987, 326, 269−280. (f) Seyferth, D.; Hames, B. W.; Rucker, T. G.; Cowie, M.; Dickson, R. S. Organometallics 1983, 2,

ASSOCIATED CONTENT

S Supporting Information *

Figures, tables, .xyz files, and CIF files giving structural and characterization data. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*T.R.: e-mail, tobias.rueff[email protected]; tel, +49 (0)371-531-31836; fax, +49 (0)371-531-21219. Author Contributions ○

Author to whom correspondence pertaining to the ESR spectroscopic and magnetic characterizations should be directed.

Author Contributions ◆

Author to whom correspondence pertaining to the DFT calculations should be directed. Author Contributions ¶

Author to whom correspondence pertaining to the 57Fe Mössbauer spectroscopic characterizations should be directed. Notes

The authors declare no competing financial interest. N


Organometallics

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(24) Huheey, J.; Keiter, E.; Keiter, R. Anorganische Chemie, 2nd ed.; de Gruyter: Berlin, 1995; p 402. (25) Here and in the following rmsd refers to the root-mean-square deviation from planarity and hdp to the atom with the highest deviation from planarity of calculated mean planes. (26) Blay, G.; Fernandez, I.; Pedro, J. R.; Ruiz-Garcia, R.; Munoz, M. C.; Cano, J.; Carrasco, R. Eur. J. Org. Chem. 2003, 1627−1630. (27) (a) Piotrkowska, B.; Milewska, M. J.; Gdaniec, M.; Polonski, T. Tetrahedron: Asymmetry 2007, 18, 1486−1494. (b) Piotrkowska, B.; Polonski, T.; Gdaniec, M. Acta Crystallogr. 2007, C63, o693−o696. (28) Rüffer, T.; Bräuer, B. Anal. Sci., X-ray Struct. Anal. Online 2007, 23, x53−x54. (29) (a) Turner, S. S.; Michaut, C.; Kahn, O.; Ouahab, L.; Lecas, A.; Amouyal, E. New J. Chem. 1995, 19, 773−775. (b) Vaz, M. G. F.; Pinheiro, L. M. M.; Stumpf, H. O.; Alcantara, A. F. C.; Golhen, S.; Ouahab, L.; Cador, O.; Mathoniere, C.; Kahn, O. Chem. Eur. J. 1999, 5, 1486−1495. (c) Cervera, B.; Sanz, J. L.; Ibanez, M. J.; Vila, G.; Lloret, F.; Julve, M.; Ruiz, R.; Ottenwaelder, X.; Aukauloo, A.; Poussereau, S.; Journaux, Y.; Munoz, M. C. J. Chem. Soc., Dalton Trans. 1998, 781−790. (d) Gao, E.-Q. Acta Crystallogr. 2004, E60, m1700− 1702. (e) Rüffer, T.; Bräuer, B.; Powell, A. K.; Hewitt, I.; Salvan, G. Inorg. Chim. Acta 2007, 360, 3475. (30) (a) Zhu, Z. C.; Mao, X. P.; Xu, Z.; Huang, X. Y. Chin. J. Struct. Chem. 2000, 19, 322. (b) Rüffer, T.; Bräuer, B.; Walfort, B. Inorg. Chem. Commun. 2006, 9, 1111−1113. (c) Rüffer, T.; Bräuer, B.; Meva, F.; Walfort, B. Dalton Trans. 2008, 5089−5098. (31) Abdulmalic, M. A.; Aliabadi, A.; Petr, A.; Krupskaya, Y.; Kataev, V.; Büchner, B.; Hahn, T.; Kortus, J.; Rüffer, T. Dalton Trans. 2012, 41, 14657−14670. (32) In the absence of the van der Waals radius of iron, its covalence radius (1.25 Å) and the van der Waals radius of copper (1.40 Å) has been taken from: Huheey, , J. E.; Keiter, , E. A.; Keiter, , R. L. Anorganische Chemie, 2nd ed.; de Gruyter: Berlin, New York, 1995,; p 335 and references cited therein. (33) Unamuno, I.; Gutierrez-Zorrilla, J. M.; Luque, A.; Roman, P.; Lezama, L.; Calvo, R.; Rojo, T. Inorg. Chem. 1998, 37, 6452−6460. (34) Addison, A. W.; Rao, T. N.; Reedijk, J.; Rijn, J. V.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356. (35) Morton, J. R.; Preston, K. F. Magn. Reson. 1978, 30, 577−582. (36) Zanello, P.; Cinquantini, A.; Mangani, S.; Opromolla, G. Organometallics 1994, 471, 171−177. (37) Ammeter, J. H. Magn. Reson. 1978, 30, 299−325. (38) Prins, R. Mol. Phys. 1970, 19, 603−620. (39) Banci, L.; Bencini, A.; Gatteschi, D. Inorg. Chem. 1983, 22, 2681−2683. (40) Van Slageren, J.; Ahmedova, A.; Gatteschi, A.; Massa, C. A.; Pardi, L. A. Inorg. Chim. Acta 2003, 351, 59−62. (41) http://www.mpibac.mpg.de/bac/index_en.php/logins/bill/ julX_en.php. (42) Wertheim, G. K.; Herber, R. H. J. Chem. Phys. 1963, 38, 2106. (43) Zahn, U.; Kienle, P.; Eicher, H. Z. Phys. 1962, 166, 220. (44) Collins, R. L. J. Chem. Phys. 1965, 42, 1072. (45) Motoyama, I.; Watanabe, M.; Sano, H. Chem. Lett. 1978, 513. (46) Dong, T.-Y.; Lee, S.-H. J. Organomet. Chem. 1995, 48, 77. (47) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.; Pergamon: New York, 1988. (48) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467. (b) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of Göttingen, Göttingen, Germany, 1997. (49) Weber, R. T.; Jiang, J. J.; Barr, D., ESR Division, Software Version 2.3; Bruker Instruments, Inc., 1998. (50) WinEPR Simfonia, Software Version 1.25, a fast, easy to use ESR spectral simulation; Bruker Analytical Instruments, 1996. (51) Briley, A.; Pederson, M.; Jackson, K.; Patton, D.; Porezag, D. C. Phys. Rev. B 1998, 58, 1786−1793. (52) Jackson, K.; Pederson, M. Phys. Rev. B 1990, 42, 3276−3281. (53) Pederson, M.; Jackson, K. Phys. Rev. B 1990, 41, 7453−7461. (54) Pederson, M.; Porezag, D.; Kortus, J.; Patton, D. Phys. Status Solidi B 2000, 217, 197−218.

472−474. (g) Long, N. J.; Martin, J.; Opromolla, G.; White, A. J. P.; Williams, D. J.; White, A. J. P.; Zanello, P. J. Chem. Soc., Dalton Trans. 1999, 1981−1986. (h) Takemoto, S.; Kuwata, S.; Nishibayashi, Y.; Hidai, M. Inorg. Chem. 1998, 37, 6428−6434. (i) Sidebotham, R. P.; Beer, P. D.; Hamor, T. A.; Jones, C. J.; McCleverty, J. A. J. Organomet. Chem. 1989, 371, C31−C34. (j) Gregson, C. K. A.; Long, N. J.; White, A. J. P.; Williams, D. J. Organometallics 2004, 23, 3674−3682. (k) Long, N. J.; Martin, J.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1997, 3083−3086. (l) Herberhold, M.; Jin, G.-X.; Rheingold, A. L.; Sheats, G. F. Z. Naturforsch. B: Chem.Sci. 1992, 47, 1091−1098. (m) Sato, M.; Anano, H. J. Organomet. Chem. 1998, 555, 167−175. (n) Gibson, V. C.; Long, N. J.; White, A. J. P.; Williams, C. K.; Williams, D. J. Organometallics 2000, 19, 4425−4428. (o) Allgeier, A. M.; Slone, C. S.; Mirkin, C. A.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L. J. Am. Chem. Soc. 1997, 119, 550−559. (p) Abel, E. W.; Long, N. J.; Orrell, K. G.; Osborne, A. G.; Sik, V.; Bates, P. A.; Hursthouse, M. B. J. Organomet. Chem. 1990, 383, 253−269. (q) Herberhold, M.; Jin, G.-X.; Milius, W. J. Organomet. Chem. 1996, 512, 111−116. (r) Akabori, S.; Sato, S.; Sato, M.; Takanohashi, Y. Bull. Chem. Soc. Jpn. 1989, 62, 1582−1586. (s) Cullen, W. R.; Talaba, A.; Rettig, S. J. Organometallics 1992, 11, 3152−3156. (t) Sato, M.; Suzuki, K.; Asano, H.; Sekino, M.; Kawata, Y.; Habata, Y.; Akabori, S. J. Organomet. Chem. 1994, 470, 263−269. (u) Takemoto, S.; Kuwata, S.; Nishibayashi, Y.; Hidai, M. Organometallics 2000, 19, 3249−3252. (v) Gibson, V. C.; Long, N. J.; White, A. J. P.; Williams, C. K.; Williams, D. J. Chem. Commun. 2000, 2359−2360. (w) Sato, M.; Asano, H.; Akabori, S. J. Organomet. Chem. 1993, 452, 105−109. (x) Herberhold, M.; Jin, G.-X.; Rheingold, A. L. Angew. Chem., Int. Ed. 1995, 34, 656−657. (y) Herberhold, M.; Jin, G.-X.; Trukenbrod, I.; Milius, W. Z. Anorg. Allg. Chem. 1996, 622, 724−728. (11) (a) Canales, S.; Crespo, O.; Fortea, A.; Gimeno, M. C.; Jones, P. G.; Laguna, A. J. Chem. Soc., Dalton Trans. 2002, 2250−2255. (b) Wallbank, A. I.; Corrigan, J. F. J. Cluster Sci. 2004, 15, 225−232. (c) Nitschke, C.; Wallbank, A. I.; Fenske, D.; Corrigan, J. F. J. Cluster Sci. 2007, 18, 131−140. (d) Brown, M. J.; Corrigan, J. F. J. Organomet. Chem. 2004, 689, 2872−2879. (e) Wallbank, A. I.; Corrigan, J. F. Chem. Commun. 2001, 377−378. (f) Abel, E. W.; Long, N. J.; Orrell, K. G.; Osborne, A. G.; Bates, P. A.; Hursthouse, M. B. J. Organomet. Chem. 1989, 367, 275−289. (g) Herberhold, M.; Schrepfermann, M.; Rheingold, A. L. J. Organomet. Chem. 1990, 394, 113−120. (h) Nitschke, C.; Fenske, D.; Corrigan, J. F. Inorg. Chem. 2006, 45, 9394−9401. (i) Herberhold, M.; Jin, G.-X.; Rheingold, A. L. Z. Anorg. Allg. Chem. 2002, 628, 1985−1990. (j) Wallbank, A. I.; Borecki, A.; Taylor, N. J.; Corrigan, J. F. Organometallics 2005, 24, 788−790. (12) We summarize the crystallographically characterized complexes only. (13) (a) Levada, C.; Bechgaard, K.; Cowan, D. O. J. Org. Chem. 1976, 16, 2700−2704. (b) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877−910. (14) Pardo, E.; Ruiz, R.; Cano, J.; Ottenwaelder, X.; Lescouezec, R.; Journaux, Y.; Lloret, F.; Julve, M. Dalton Trans. 2008, 2780−2805. (15) (a) Gatteschi, D.; Coronado, E. J. Mater. Chem. 2006, 16, 2513− 2515. (b) Kahn, O. Molecular Magnetism; VCH: Weinheim, Germany, 1993. (16) Abdulmalic, M. A.; Rüffer, T. Bull. Chem. Soc. Jpn. 2013, DOI: 10.1246/bcsj.20130031. (17) Ruiz, R.; Barland, C.; Aukauloo, A.; Mallart, E.; Journaux, Y.; Cano, J.; Muñoz, M. J. Chem. Soc., Dalton Trans. 1997, 745−751. (18) Abdulmalic, M. A.; Aliabadi, A.; Petr, A.; Kataev, V.; Rüffer, T. Dalton Trans. 2013, 42, 1798−1809. (19) Stumpf, H.; Pei, Y.; Kahn, O.; Sletten, J.; Renard, J. J. Am. Chem. Soc. 1993, 115, 6738−6745. (20) Shafir, A.; Power, M.; Whitener, G.; Arnold, J. Organometallics 2000, 19, 3978−3982. (21) Bräuer, B.; Weigend, F.; Fittipaldi, M.; Gatteschi, D.; Reijerse, E. J.; Guerri, A.; Ciattini, S.; Salvan, G.; Rüffer, T. Inorg. Chem. 2008, 47, 6633−6644. (22) Irving, H.; Williams, R. J. Chem. Soc. 1953, 3192−3210. (23) Sigel, H.; McCormick, D. Acc. Chem. Res. 1970, 3, 201. O


Organometallics

Article

(55) Porezag, D.; Pederson, M. Phys. Rev. B 1996, 54, 7830−7836. (56) Quong, A.; Pederson, M.; Feldman, J. Solid State Commun. 1993, 87, 535−539. (57) Porezag, D.; Pederson, M. Phys. Rev. A 1999, 60, 2840−2847. (58) Loose, C.; Ruiz, E.; Kersting, B.; Kortus, J. Chem. Phys. Lett. 2008, 452, 38. (59) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5653. (60) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571−2577. (61) (a) Neese, F. J. Chem. Phys. 2003, 119, 9428−9444. (b) Neese, F. Int. J. Quantum Chem. 2001, 83, 104−114. (62) Ruiz, E.; Alvarez, S.; Cano, J.; Polo, V. J. Chem. Phys. 2005, 123, 164110. (63) Bencinic, A.; Totti, F. Int. J. Quantum Chem. 2005, 101, 819− 825.

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