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Radical Monocationic Guanidino-Functionalized Aromatic Compounds (GFAs) as Bridging Ligands in Dinuclear Metal Acetate Complexes: Synthesis, Electronic Structure, and Magnetic Coupling Benjamin Eberle, Marko Damjanović, Markus Enders,* Simone Leingang, Jessica Pfisterer, Christoph Kram ̈ er, Olaf Hübner, Elisabeth Kaifer, and Hans-Jörg Himmel* Ruprecht-Karls-Universität Heidelberg, Anorganisch-Chemisches Institut, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: In this work, the oxidation of several new dinuclear metal (M) acetate complexes of the redox-active guanidinofunctionalized aromatic compound (GFA) 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1) was studied. The complexes [1{M(OAc)2}2] (M = Ni or Pd) were oxidized to the radical monocationic complexes [1{M(OAc)2}2]+ •. From CV (cyclic voltammetry) measurements, the Gibbs free enthalpy for disproportionation of [1{M(OAc)2}2]+ • into [1{M(OAc)2}2] and [1{M(OAc)2}2]2+ could be estimated to be roughly +20 kJ mol−1 in CH2Cl2 solution. A characteristic feature of the [1{M(OAc)2}2]+ • complexes is the presence of intense metal−ligand charge-transfer bands in the electronic absorption spectra. The complex [1{Ni(OAc)2}2]+ • combines three paramagnetic centers with four metal-centered unpaired electrons and a ligand centered π-radical and exhibits a sextet electronic ground state. Spin distribution of the Ni complexes was evaluated by paramagnetic 1H and 13C NMR and was correlated with calculations. The strong ferromagnetic metal−ligand magnetic coupling was studied in the solid state by magnetometric (SQUID) measurements and by quantum chemical (DFT) calculations. The temperature dependence of the paramagnetic NMR shift was used for the evaluation of the magnetic coupling between the Ni centers and the π-radical in solution.

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fluorescence (e.g., for Zn) or quenches fluorescence (for paramagnetic metals, and also for CuI).25 Guanidines are attractive ligands and guanidine-metal complexes served as catalysts in many reactions.31−34 Especially copper-guanidine complexes were thoroughly studied.35−39 Also, GFAs were shown to be versatile redox-active ligands.40 Recently, we showed that the radical monocationic complex [1{Cu(OAc)2}2]+ • could be synthesized either by oxidation of the neutral complex [1{Cu(OAc)2}2] or by a comproportionation reaction from the neutral complex [1{Cu(OAc)2}2] and the dicationic complex [1{Cu(OAc)2}2]2+ (see Scheme 1b).41 The radical monocationic complex [1{Cu(OAc)2}2]+ • distinguishes itself by strong acetate−GFA ligand−ligand chargetransfer (LLCT) bands, and the acetate groups seem to play a significant role in stabilizing the radical cationic GFA ligand. In this work, we use this “acetate effect” for the synthesis of the first dinuclear nickel and palladium complexes with a bridging radical monocationic GFA ligand, and analyze in detail their electronic structure.

INTRODUCTION

Metal complexes with radical ligands were intensively studied.1−6 They are interesting, with respect to the role they play in enzymatic reactions (e.g., galactose oxidase7,8), for catalytic reactions,9−17 and for the design of new molecular magnetic materials (“metal-radical approach”).3 Examples of studied radical ligands include benzosemiquinones,18 oiminobenzosemiquinones,19 phenoxyls,1,20 dithiolene,2 thiazyls,6 verdazyls,21 and 1,2,4-benzotriazinyls.22 We recently developed guanidino-functionalized aromatic compounds (GFAs) as a new class of strong organic electron donors and redox-active ligands. Scheme 1a shows three compounds as representative examples: 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1), 23 1,4,5,8-tetrakis(tetramethylguanidino)naphthalene (2),24 and 2,3,7,8-tetrakis(tetramethylguanidino)phenazine (3).25 The molecules show interesting properties as reducing agents. We recently reported their use in photochemical reductive C−C coupling reactions,26 as redox switches for hydrogen-bonded aggregates,27 for the stabilization of polyhalides,28 as component in semiconducting organic donor−acceptor materials,29 and as strong bases for the deprotonation of C−H acidic compounds such as CH3CN or acetylenes.30 Furthermore, GFA 3 is a strongly fluorescent dye, and metal coordination either enhances the quantum yield for © XXXX American Chemical Society

Received: November 12, 2015

A

DOI: 10.1021/acs.inorgchem.5b02614 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Scheme 1. (a) The Three GFA Compounds (1,2,4,5-tetrakis(tetramethylguanidino)benzene (1), (1,4,5,8tetrakis(tetramethylguanidino)naphthalene (2), and (2,3,7,8-tetrakis(tetramethylguanidino)phenazine) (3); (b) Diagram Showing That the Free Monocation 1+ • Is Not Stable in Solutiona

A mixture of 12+ and 1 contains No 1+ •. By contrast, the radical monocation could be stabilized by complexation with Cu(OAc)2. Reaction between [1{Cu(OAc)2}2] and [1{Cu(OAc)2}2]2+ cleanly gives [1{Cu(OAc)2}2]+ •. a

Scheme 2. Synthesis of the Dinuclear Acetate Complexes That Are Relevant for This Article

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RESULTS AND DISCUSSION Synthesis and Characterization. We synthesized a series of dinuclear acetate complexes, namely, the six compounds [1{Co(OAc)2}2], [1{Ni(OAc)2}2], [1{Pd(OAc)2}2], [1{Cu(OAc)2 }2], [1{Zn(OAc)2} 2], and [1{Pb(OAc)2 }2 ] (see Scheme 2). Of these, [1{Cu(OAc)2}2] has already been studied comprehensively41 and motivated the survey in this work. In addition, the neutral complex [1{Co(OAc)2}2] was already synthesized previously,42 but its redox properties were not yet studied. All neutral complexes could be synthesized by reaction between 1 and M(OAc)2 in EtOH (for M = Co, Ni, Zn, or Pb) or CH3CN (for M = Pd, Cu) solutions at room temperature (see Scheme 2). Recrystallization from CH2Cl2, or (in the case of M = Pb) from CH3CN gave crystals suitable for an X-ray diffraction (XRD) analysis. The structures of [1{Co(OAc) 2}2]42 and [1{Cu(OAc)2}2]41 were already

reported. Figures 1−4 display the structures of the four new acetate complexes in the solid state. It can be seen that the coordination modes and geometries vary. As expected, [1{Pd(OAc)2}2] exhibits a planar coordination geometry, in which only one of the O atoms of each acetate binds to Pd. In the case of [1{Ni(OAc)2}2], both oxygen atoms of each acetate are bound to the metal. In all other cases, both μ1 and μ2 coordinated acetate groups are present. In the case of [1{Pb(OAc)2}2], an excess of Pb(OAc)2 must be avoided, since it leads to the formation of one-dimensional (1D) and two-dimensional (2D) coordination polymers of the formula [1{Pb4(OAc)8}] (see Figures S1a and S1b in the Supporting Information). In the 1D polymer, four of the AcO− units were terminally bound, with both O atoms bound to the same Pb atom. The other four AcO− units bridge two Pb atoms, with a μ1:μ2-coordination mode. In case of the 2D polymer, two AcO− B


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Inorganic Chemistry

Figure 3. Structure of the complex [1{Zn(OAc)2}2]. Hydrogen atoms are omitted for the sake of clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected structural parameters are given as follows: Zn1−O1, 2.0962(17) Å; Zn1−O2, 2.351(2) Å; Zn1−O3, 1.9473(15) Å; Zn1···O4, 3.322(2) Å; Zn2−O5, 2.0100(15) Å; Zn2− O6, 2.575(3) Å; Zn2−O7, 1.9554(14) Å; Zn2···O8, 2.920(3) Å; Zn1− N1, 2.0614(17) Å; Zn1−N4, 2.0636(15) Å; Zn2−N7, 2.0640(17) Å; Zn2−N10, 2.0332(15) Å; N1−C7, 1.320(2) Å; N4−C12, 1.325(2) Å; N7−C17, 1.322(2) Å; and N10−C22, 1.324(2) Å; N1−Zn1−N4, 81.86(6)° and N7−Zn2−N10, 82.33(6)°.

Figure 1. Structure of the complex [1{Ni(OAc)2}2]. Hydrogen atoms are omitted for the sake of clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected structural parameters are given as follows: Ni−O1, 2.1070(18) Å; Ni−O2, 2.1429(14) Å; Ni−N1, 2.0467(16) Å; N1−C1, 1.405(2) Å; N1−C3, 1.326(2) Å; C1−C1′, 1.408(4) Å; and C1−C2, 1.398(2) Å; O1−Ni−O2 62.07(7)°; and N1−Ni−N1′ 81.70(9)°.

Figure 2. Structure of the complex [1{Pd(OAc)2}2]. Hydrogen atoms are omitted for the sake of clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected structural parameters are given as follows: Pd−O1, 2.0175(16) Å; Pd···O2, 3.159(3) Å; Pd−O3, 2.0497(16) Å; Pd···O4, 3.130(2) Å; Pd−N1, 2.0173(18) Å; Pd−N4, 2.0104(17) Å; N1−C1, 1.414(3) Å; N1−C4, 1.337(3) Å; N2−C4, 1.348(3) Å; N3−C4, 1.342(3) Å; N4−C2, 1.419(2) Å; N4−C9, 1.345(3) Å; N5−C9, 1.341(3) Å; and N6−C9, 1.358(3) Å; N1−Pd− N4, 81.19(7)° and O1−Pd−O3, 83.99(6)°.

Figure 4. Structure of the complex [1{Pb(OAc)2}2]. Hydrogen atoms are omitted for the sake of clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected structural parameters are given as follows: Pb−O1, 2.342(2) Å; Pb−O2, 2.814(2) Å; Pb−O3, 2.438(2) Å; Pb−O4, 2.943(2) Å; Pb−N1, 2.565(3) Å; Pb−N4, 2.436(3) Å; N1−C1, 1.417(3) Å; N1−C4, 1.320(4) Å; N2−C4, 1.353(4) Å; N3− C4, 1.372(4) Å; N4−C2, 1.417(3) Å; N4−C9, 1.343(4) Å; N5−C9, 1.353(4) Å; N6−C9, 1.360(4) Å; C1−C2, 1.404(4) Å; C1−C3, 1.398(4) Å; and C2−C3′, 1.404(4) Å; O1−Pb−O3, 76.70(9)° and N1−Pb−N4, 67.54(8)°.

groups are bound to three Pb atoms with μ1:μ2:μ1-coordination modes, whereas the other six AcO− units are, with both O atoms, terminally bound to one Pb atom. Some selected bond distances for the dinuclear complexes are compared in Table 1. The mean NC bond distance varies between 1.323 and 1.344 Å and, thus, are elongated, relative to the uncoordinated GFA 1 (1.289 Å).23 This elongation could be rationalized by the interplay between σ- and π-contributions to the metal−guanidine bonding.43 The M−N bond distances are relatively similar for all complexes (1.986−2.057 Å), with the exception of the lead complex, which has a significantly larger M−N bond distance of 2.501 Å and, consequently, a relatively small N−M−N bite angle of 67.5°. Next, we studied the redox chemistry of all complexes with cyclic voltammetry (CV) measurements. As expected, the oxidation potentials of the complexes are larger than that of the free ligand. The complexes could be grouped into two categories. Figure 5a compares the CV curves of the three complexes [1{Cu(OAc)2}2], [1{Ni(OAc)2}2], and [1{Pd-

Table 1. Comparison of Some Structural Parameters of the Acetate Complexes Bond Length (Å) [1{Co(OAc)2}2] [1{Ni(OAc)2}2] [1{Pd(OAc)2}2] [1{Cu(OAc)2}2] [1{Zn(OAc)2}2] [1{Pb(OAc)2}2]

NC

M−N

bond angle, N−M−N (deg)

1.332 1.326 1.341 1.344 1.323 1.332

2.057 2.047 2.014 1.986 2.056 2.501

82.0 81.7 81.2 83.6 82.1 67.5

(OAc)2}2] that belong to the first category and show reversible one-electron redox events. Their redox potentials (measured C


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Inorganic Chemistry

For [1{Ni(OAc)2}2] and [1{Cu(OAc)2}2], one obtains a value of ΔE ≈ 0.20 V. Disproportionation of the radical monocationic complex is endergonic and ΔG could roughly be estimated to be +19 kJ mol−1 for both complexes. The equilibrium constant (Kdiss) under standard conditions amounts to ∼4.67 × 10−4. In the case of [1{Pd(OAc)2}2], a slightly higher value of ΔE = 0.23 V results, yielding ΔG = +22 kJ mol−1 and Kdiss = 1.39 × 10−4. The complexes [1{Co(OAc)2}2], [1{Zn(OAc)2}2], and [1{Pb(OAc)2}2] belong to the second category. Their CV curves do not show reversible separated one-electron oxidation waves (see the CV curves reproduced in Figure 5b). The CV curve of [1{Co(OAc)2}2] exhibits two broad oxidation waves at −0.42 and −0.13 V vs Fc/Fc+, and a sharper reduction wave at −0.77 V. For [1{Pb(OAc)2}2], two oxidation waves appeared at −0.37 and 0.08 V vs Fc/Fc+, but only one clear reduction wave at −0.75 V. In the case of [1{Zn(OAc)2}2], only one oxidation wave appeared at −0.22 V vs Fc/Fc+, which had a tail toward higher potentials. In the direction of reduction, a wave appeared at −0.61 V. Obviously, the next step was to oxidize the complexes [1{Ni(OAc)2}2] and [1{Pd(OAc)2}2] via chemical means. Reaction between [1{Ni(OAc)2}2] and the silver salts (Ag(PF6) or Ag(SbF6)) resulted in one-electron oxidation to give the salts [1{Ni(OAc)2}2](PF6) and [1{Ni(OAc)2}2](SbF6), respectively (see Scheme 3a). In the case of both compounds, dark-green crystals were grown from CH2Cl2 solutions. Figure 6, as well as Figure S7 in the Supporting Information, illustrate their structures. Table 3 compares some structural parameters of the neutral complex [1{Ni(OAc)2}2] with those found in the radical monocation [1{Ni(OAc)2}2]+ •. The structural changes upon oxidation are quite small, the largest change being the decrease of the Cring−N bond from 1.405 Å before oxidation to 1.367 Å after oxidation, and the increase of the C−Cmax distance within the C6 ring from 1.408 Å to 1.451/1.457 Å. These changes are consistent with the Lewis structures sketched in Scheme 3a. In the UV-vis spectra recorded in CH3CN solutions, an intense and broad band appears at 635 nm for [1{Ni(OAc)2}2]+ • (see Figure 7). Oxidation of [1{Ni(OAc)2}2] with I2 led to two-electron oxidation and the formation of a brown-colored salt: [1{Ni(OAc)2}2]2+(I3−)2. No crystals could be drawn from this compound. In the UV-vis spectrum, the large charge transfer transition observed for the radical monocationic complex is absent (see Figure 7). Hence, this absorption is characteristic for complexes of the radical monocationic ligand. In the case of [1{Pd(OAc)2}2], one electron oxidation could be achieved by reaction with Fc(PF6) in CH3CN solution (see Scheme 3b). The product salt [1{Pd(OAc)2}2]+•(PF6)− was isolated as a dark-green solid. In the UV-vis spectra recorded in CH3CN solutions, an intense and broad band appeared at 708 nm for [1{Pd(OAc)2}2]+• (see Figure 8a). Hence, the band

Figure 5. Comparison between the CV curves of the dinuclear acetate complexes [1{M(OAc)2}2] studied in this work (measurements in CH2Cl2 solution, Bu4NPF6 as supporting electrolyte, SCE electrode, potentials given relative to Fc/Fc+): (a) M = Ni, Pd, Cu and (b) M = Co, Zn, Pb.

versus the redox couple ferrocene/ferrocenium) are listed in Table 2, and increase in the order 1 < [1{Ni(OAc)2}2] < [1{Pd(OAc) 2 } 2] < [1{Cu(OAc) 2 } 2 ]. The NC bond distances in the ligand unit (see Table 1) follow the same trend, indicating increasing metal−ligand bond strength. The differences ΔE between first and second E1/2 values could be used to estimate the Gibbs free-energy change ΔG for disproportionation of the radical monocation and the disproportionation constant Kdiss, using the simple formula ΔG 0 = F ·ΔE 0 and

(1)

⎛ F ⎞ Kdiss = exp⎜ − ΔE 0⎟ ⎝ RT ⎠

(2)

Table 2. Redox Potentials (in V, Relative to the Fc/Fc+ Redox Couple) in CH2Cl2 Solution Redox Potentials (V) compound

E1(ox)

E1(red)

(E1)1/2

E2(ox)

E2(red)

(E2)1/2

1 [1{Ni(OAc)2}2] [1{Pd(OAc)2}2] [1{Cu(OAc)2}2]

−0.62 −0.45 −0.36 −0.33

−0.77 −0.59 −0.49 −0.44

−0.70 −0.52 −0.43 −0.39

−0.62 −0.26 −0.14 −0.14

−0.77 −0.40 −0.25 −0.24

−0.70 −0.33 −0.20 −0.19

D


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Inorganic Chemistry

Scheme 3. (a) One-Electron Oxidation of the Complex [1{Ni(OAc)2}2] with the Silver Salts Ag(PF6) and Ag(SbF6) and TwoElectron Oxidation with Elemental Iodine; (b) One-Electron Oxidation of the Complex [1{Pd(OAc)2}2] with the Ferrocenium Salt Fc(PF6)

ligand 1+ •. At 35 K, the spectrum shows some sign of fine structure, while the g-value does not change significantly (see the Supporting Information). For the Pd complex, no clear NMR signature was obtained. These results again demonstrate that the electronic situations that cause slow relaxation in EPR generally lead to fast relaxation in nuclear magnetic resonance (NMR) and vice versa. The electronic structure of complex [1{Ni(OAc)2}2]+• was further studied by magnetometric (SQUID) measurements. Figure 9 displays the χ−1 and χT vs T plots, and in addition to a fit of the magnetization curves with the help of the JulX program.44 The metal−ligand and metal−metal coupling constants (JNi−π and JNi−Ni, respectively), the g-factors for Ni and the GFA ligand (gNi and gL, respectively), and three zerofield splitting parameters (D1, D2, and D3) were used as fit parameters (no TIP or paramagnetic impurity was included). We obtained the following values: JNi−Ni = +0.3 cm−1, JNi−π = +186 cm−1, gNi = 2.27, gL = 2.00, D1 = D3 = 3.28 cm−1, D2 = 1.32 cm−1, E/D1 = 0.43, and E/D2 = 1.01. The relatively large ferromagnetic metal−ligand magnetic coupling constant JNi−π (cf. JNi−R coupling constants in other nickel complexes with radical ligands of 60 cm−1 for tetraoxolene,45 60−100 cm−1 for iminonitroxide,46,47 and 100−150 cm−1 for verdazyl ligands48,49) leads to a sextet electronic ground state (6A) of the complex (five unpaired electrons). A doublet ((2)A) term should then be observed, followed finally by a quartet ((4)A) term. For comparison, SQUID measurements were also carried out for the neutral complex [1{Ni(OAc)2}2]. JNi−Ni, gNi, and the two zero-field splitting parameters D1 and D2 were used as fit parameters. Also, a small paramagnetic impurity of 0.4% and a TIP of 64 × 10−6 emu were included. Figure S5 in the

Figure 6. Structure of the complex [1{Ni(OAc)2}2](PF6). Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected structural parameters are given as follows: Ni−O1, 2.1283(15) Å; Ni−O2, 2.0815(15) Å; Ni−N1, 2.0517(14) Å; Ni−N1′, 2.0516(14) Å; N1−C1, 1.367(2) Å; N1−C3, 1.359(2) Å; N2−C3, 1.325(2) Å; N3−C3, 1.352(3) Å; C1−C1′, 1.451(3) Å; C1− C2, 1.3936(19) Å; O1−Ni−O2, 62.72(7)° and N1−Ni−N1′, 79.95(7)°.

maximum shifted from [1{Cu(OAc)2}2]+ • (576 nm) to [1{Ni(OAc)2}2]+ • (635 nm) to [1{Pd(OAc)2}2]+ • (708 nm). The monocation [1{Ni(OAc)2}2]+ • is completely electron paramagnetic resonance (EPR) silent (even at 35 K). On the other hand, it can be studied in detail by NMR spectroscopy (see below). The EPR spectrum measured at room temperature for [1{Pd(OAc)2}2]+ •(PF6)− shows a signal with a g-factor of 2.003 (see Figure S11 in the Supporting Information), which is consistent with the presence of a radical monocationic GFA E


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Inorganic Chemistry Table 3. Comparison between Selected Bond Distancesa in the Neutral and Radical Monocationic Nickel Complexes Bond Distances (Å) Ni−N Ni−O C−Cmax C−Cmin CN Cring−N a

[1{Ni(OAc)2}2]

[1{Ni(OAc)2}2]+ •(PF6)−

[1{Ni(OAc)2}2]+ •(SbF6)−

2.047 2.125 1.408 1.398 1.326 1.405

2.052 2.105 1.451 1.394 1.359 1.367

2.049 2.108 1.457 1.399 1.361 1.362

Average values.

Figure 7. Comparison between the UV-vis spectra of [1{Ni(OAc)2}2], [1{Ni(OAc)2}2](PF6), and [1{Ni(OAc)2}2](I3)2 dissolved in CH3CN.

Supporting Information shows the χ−1 and χT vs T plots and the fit of the magnetization curves. The resulting value of +1 cm−1 for the metal−metal coupling constants JNi−Ni shows no significant coupling between the two Ni centers, which is consistent with the findings for the monocationic complex [1{Ni(OAc)2}2]+ • and also with the results from previously studied nickel complexes with neutral GFA ligands.42 The fit also returned a value of gNi = 2.14, zero-field splitting parameters of D1 = D2 = 10.15 cm−1, and E/D1 = E/D2 = 0.15. The experimental data were compared with the results of quantum chemical calculations. Five electronic states of [1{Ni(OAc)2}2]+ • were calculated with three functionals (TPSSh, B3LYP, and BHLYP) that differ in the amount of exact Hartree−Fock exchange. To limit the theoretical effort, we used the SV(P) basis set in these calculations. In all cases, the calculations predict a sextet electronic ground state (ferromagnetic coupling). Table 4 summarizes the relative energies of some states (see Figure 10) of [1{Ni(OAc)2}2]+ •. Using time-dependent DFT, we calculated the electronic transitions for the sextet state of [1{Ni(OAc)2}2]+ •. The calculations are compared with the experimental electronic absorption spectrum in Figure 8b. It can be seen that the general level of agreement is pleasing. The calculations predict a strong transition at 663 nm, which is consistent with the band at 635 nm found in the experiments. The transition could be

Figure 8. (a) Comparison between the UV-vis spectra recorded for [1{Ni(OAc)2}2](PF6), [1{Pd(OAc)2}2](PF6), and [1{Cu(OAc)2}2](PF6) dissolved in CH3CN. (b) Theoretical UV-vis spectrum from TD-DFT calculations (B3LYP/SV(P)) for [1{Ni(OAc)2}2]+ • (only transitions above 300 nm are considered) and visualization of the molecular orbitals that contribute most in the electronic transition. Calculated isodensity surfaces of the orbitals that make the major contribution (91%) to the electronic transition at 663 nm are also shown.

described as a metal−ligand charge transfer. The contributions from orbitals at the acetate groups is smaller than for [1{Cu(OAc)2}2]+•. Similar observations could be made for the time-dependent DFT calculations for the doublet ground state of [1{Pd(OAc)2}2]+ •. Figure S12 in the Supporting Information shows the experimental electronic absorption spectra, in comparison to the TD-DFT calculation as well as the contributing orbitals of the transition at 773 nm (respectively at 708 nm in the experimental spectrum). This transition could again be described as a metal−ligand charge transfer. Here, the contributions from orbitals at the acetate F


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Inorganic Chemistry

Figure 9. (a) Plot of χ−1 and χT vs T from magnetometric (SQUID) measurements of [1{Ni(OAc)2}2](PF6). (b) Fit of the magnetization curves with the JulX program package.

Table 4. Relative Energies of the States of [1{Ni(OAc)2}2]+ • and Estimated Coupling Constants JNi−π and JNi−Ni for Calculations with the def2-SV(P) Basis Set and Several Functionals def2-SV(P) TPSSh electronic state (2) A-1 (4) A-1 (4) A (2) A 6 A coupling constants JNi−π JNi−Ni

0.701 0.673 0.057 0.027 0.00

eV eV eV eV

+115 cm−1 −2 cm−1

B3LYP 0.680 0.660 0.039 0.019 0.00

eV eV eV eV

+80 cm−1 −1 cm−1

BHLYP 0.900 0.886 0.029 0.014 0.00

eV eV eV eV

Figure 10. Quantum chemical calculations (spin density, relative energies of the terms).

+59 cm−1 −0.4 cm−1

but one must be aware of the fundamental problems of current density functional theory (DFT) in describing exchange coupled systems.52 In our case, the calculated JNi−π values are significantly smaller than the value derived from the magnetometric measurements. This deviation might be caused by the inaccuracy of the applied calculational methods. A superposition of the computed molecular structure (B3LYP/SV(P)) and the experimental geometry (X-ray) of [1{Ni(OAc)2}2]+ • by the Kabsch algorithm53,54 was performed (see Figure S6 in the Supporting Information). The root-mean-square deviation (RMSD = 0.299 Å, superposition R2 = 99.6%) shows that the molecular structure of the complex is reproduced very well by the quantum-chemical computation.

groups also are significantly smaller than for [1{Cu(OAc)2}2]+ •. Table 4 also includes the calculated coupling constants JNi−π and JNi−Ni (for details of their calculation, see the Supporting Information). The calculations predict JNi−Ni to be small and JNi−π to be much larger, which is consistent with the SQUID results. However, the values vary significantly with the chosen functional (for JNi−π, a value of +115 cm−1 was obtained with the TPSSH functional and a value of +59 cm−1 was obtained with the BHLYP functional). In particular, they are dependent on the amount of exact Hartree-Fock exchange, which is a wellknown fact.50,51 Thus, the choice of a certain amount of exact exchange can lead to good agreement with the observed values, G


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Inorganic Chemistry

The 1H NMR spectra of [1{Ni(OAc)2}2] and of [1{Ni(OAc)2}2]+ •, recorded at 295.0 K, are shown in Figure 12. The

Therefore, to have a broader fundamental to compare the experiments with theory, we also studied the magnetic coupling in solution. Indeed, the presence of two paramagnetic metal centers (in [1{Ni(OAc)2}2]) and of an additional π-radical (in [1{Ni(OAc)2}2]+ •) constitutes a seldom opportunity for a solution analysis of magnetic coupling by paramagnetic NMR (pNMR). Variable-temperature 1H NMR measurements were used for obtaining exchange coupling constants in solution, thus complementing broken-symmetry DFT calculations on the individual molecule and SQUID measurements on the solid material. A detailed introduction to pNMR and to its application for the experimental determination of magnetic exchange has been published55 and is summarized in the Supporting Information. The assigned 13C NMR spectra of [1{Ni(OAc)2}2] and of [1{Ni(OAc)2}2]+ •(PF6)− are given in the Supporting Information. In a recent study, Borgogno et al. showed that B3LYP* is the functional of choice for calculating paramagnetic NMR spectra of FeII/III complexes, in combination with a triple-ζ basis set.56 For this reason, we used the same functional to compute the Fermi-contact shifts of [1{Ni(OAc)2}2]. Figure 11 shows that the calculation by

Figure 12. 1H NMR spectra of the paramagnetic complexes, recorded at 295.0 K: (a) [1{Ni(OAc)2}2] and (b) [1{Ni(OAc)2}2]+ •. The spectra were recorded at a field strength of 14.09 T. Signal assignments and deuterated solvents are given in the figure.

assignment of 1H NMR spectra of [1{Ni(OAc)2}2] and of [1{Ni(OAc)2}2]+ • is straightforward, based on signal intensities and relative magnitudes of the chemical shifts. From 1H measurements at variable temperatures, it is apparent that the rotation barrier of the guanidine fragments in 1 is significantly lowered upon oxidation, which is consistent with structural data in Table 3. The case-specific equations for the extraction of exchange coupling constants were derived from theory (Supporting Information) and are given here (eq 3 for [1{Ni(OAc)2}2] and eq 4 for [1{Ni(OAc)2}2]+ •):

Figure 11. Plot of δcalc vs δexpt at 275.0 K. The calculated shift was obtained via the addition of an orbital shift and a calculated Fermicontact shift.

( ) + 15 exp(− ) ( ) + 5 exp(− ) E3 kBT

E

δFC,T

DFT methods with the chosen functional (B3LYP*/TZVP) reproduces the experimental NMR shifts well. Consequently, the Fermi-contact term is the major contribution to the paramagnetic shift. The pseudo-contact contribution in the neutral complex [1{Ni(OAc)2}2] is small, despite the fact that this class of complexes contains a non-neglectable zero-field splitting (see also SQUID measurements).57 In the cationic complex [1{Ni(OAc)2}2]+ •, a ligand-centered pseudo-contact shift originating from the π-radical could contribute to the shift of the Cring−H unit. Therefore, we calculated this contribution by a method of Kuprov et al., which goes beyond a point dipole approximation of pseudo-contact shift.58 Using the software library Spinach,59 and the hyperfine coupling tensors and susceptibility tensors from a single-point DFT calculation, it was possible to calculate the ligand pseudo-contact shift of the 1 H nucleus in the Cring−H group of [1{Ni(OAc)2}2]+ •. However, the calculated values for the π-radical pseudo-contact shift are in the range between +0.1 ppm to +1.5 ppm only and have therefore not been considered in our fitting procedure for magnetic coupling.

2 ⎛ g β ⎞ 3 exp − kBT e e ⎜ ⎟ = 10 × ANMR ⎜ ⎟ ⎝ 3γHkBT ⎠ 1 + 3 exp −

6

E3 kBT

E2 kBT

(3) ⎛ gβ ⎞ e δ FC,T = 106 × ANMR ⎜⎜ e ⎟⎟ ⎝ 3γHkBT ⎠

( ) + 15 exp(− ) + 52.5 exp(− ) 2 exp(− ) + 4 exp(− ) + 6 exp(− ) E

×

1.5 exp − k T1 B

E1 kBT

E3 kBT

E2 kBT

E2 kBT

E3 kBT

(4)

where δFC,T is the experimental, temperature-dependent Fermicontact shift, 106 the conversion factor (to ppm), ANMR the hyperfine coupling constants of the observed proton resonance (in Hz), ge the mean electron Zeeman factor, βe the Bohr magneton, γH the proton gyromagnetic ratio, T the absolute temperature, and kB the Boltzmann constant. The E terms are the energies of the total spin states and their exact relationship to JNi−π and JNi−Ni is given in the Supporting Information. For [1{Ni(OAc)2}2], E2 and E3 are the energies of the states with total spin multiplicities of 3 and 5, respectively. For H


Article

Inorganic Chemistry [1{Ni(OAc)2}2]+ •, E1, E2, and E3 describe the states with multiplicities 2, 4, and 6, respectively. The 1H NMR data of [1{Ni(OAc)2}2] agrees well with a model where the JNi−Ni coupling is zero (see the Supporting Information), which is also confirmed by the SQUID measurements of the neutral complex [1{Ni(OAc)2}2]. From the 1H NMR data of [1{Ni(OAc)2}2]+ • (see the fit curves in Figure 13), a JNi−π constant for metal−ligand coupling was

(i.e., vibronic coupling). It was previously observed by Hilbig et al. that all phenomena which make the hyperfine coupling and J dependent on the temperature influence the precision and scatter of J values obtained by pNMR.55f Thus, the mentioned factors may contribute to a nonideal behavior of the temperature dependence of the paramagnetic shift and, thus, to the quality of fitting the experimental data with the theoretical model. For these reasons, the uncertainty of the exchange coupling constant between the metals and the ligand radical, as obtained by NMR, is estimated to be in the order of ±20 cm−1 in our case. Nevertheless, in the case of a complex system such as [1{Ni(OAc)2}2]+ •, pNMR is a powerful tool for a semiquantitative, near-ambient-temperature solution study of magnetic coupling. Furthermore, from a sample containing the mixture of the complexes [1{Ni(OAc)2}2] and [1{Pd(OAc)2}2]+ •(PF6)−, the electron exchange rate between the complexes was estimated to be of the order of 108 M−1 s−1 by NMR (Supporting Information), which is a typical value for an organic M+/M0type self-electron transfer process. In the cationic complex, the positive charge is delocalized over a large π-system, which leads to lesser geometry changes upon the oxidation of the complex, and, accordingly, to a fast electron transfer process.60

■

CONCLUSIONS Herein, we report the first dinuclear nickel and palladium complexes with a bridging radical monocationic tetrakisguanidine ligand. Several dinuclear metal acetate complexes with bridging neutral GFA ligands were synthesized and, on the basis of CV measurements, the nickel and palladium complexes were selected for chemical oxidation experiments. The complex [1{Ni(OAc)2}2] was oxidized with AgX (X = PF6 or SbF6) to the radical monocationic complex [1{Ni(OAc)2}2]+ •, and with I2 to the dicationic complex [1{Ni(OAc)2}2]2+. The analogue Pd complex, [1{Pd(OAc)2}2], was oxidized with Fc(PF6) to the radical monocationic complex [1{Pd(OAc)2}2]+ •. Both [1{Ni(OAc)2}2]+ • and [1{Pd(OAc)2}2]+•(PF6)− are distinguished by large charge-transfer transitions in the UV-vis spectra at ca. 635 nm for [1{Ni(OAc)2}2]+ • and ca. 708 nm for [1{Pd(OAc)2}2]+ •. The [1{Ni(OAc)2}2]+ • monocation exhibits a sextet electronic ground state. The magnetic exchange in the monocation was studied in the solid material with SQUID, in solution with pNMR, and by quantum chemical calculations on the individual molecule. A strong ferromagnetic metal−ligand coupling was found (JNi−π = +186 cm−1) in the solid state by SQUID measurements. In solution, a comprehensive NMR analysis combined with DFT calculations allowed an unambiguous assignment of 1H and 13C NMR signals. The origin of the hyperfine shift is strongly dominated by Fermicontact interactions, which is the basis for the determination of magnetic coupling data. Fitting the temperature dependence of the chemical shift to a model containing the energies of the contributing spin states leads to an estimated coupling constant JNi−π of +80 cm−1, which shows that the sextet spin state is the ground state in solution, in accordance with the results obtained in the solid at low temperatures.

Figure 13. Plot of δFC for [1{Ni(OAc)2}2]+• versus temperature (T). Experimental data points are shown in red color. Data obtained by fitting experimental data with eq 4 is presented as black dashed lines. The fitting procedure was done with a simplex algorithm in such a manner that the sum of the square of the differences between experimental and calculated δFC values was minimized. For each of the fitted 1H signals, JNi−π and ANMR were fitted, whereas JNi−Ni was set to zero. For the methyl groups of 1, only the 1H NMR data recorded at 260.0 K and above was used in the fitting (at this temperature, the methyl groups give only one signal).

found to be of the order of +80 cm−1, in fair agreement with the calculated value. Hence, the sextet electronic state (6A) is confirmed as the ground state, followed by the doublet ((2)A), and then by the quartet ((4)A) electronic state (Supporting Information). The results of the fits are summarized in Table 5. The agreement between experimentally obtained 1H hyperfine shifts and those obtained by eqs 3 and 4 is satisfactory, considering the presence of zero field splitting, of dynamic processes (rotation of guanidine and dimethylamino fragments) and of low-energy vibrational modes in the studied complexes Table 5. JNi−π and ANMR Values Obtained from Fitting 1H NMR Data of [1{Ni(OAc)2}2]+· Recorded at Various Temperaturesa group

JNi−π (cm−1)

ANMR (MHz)

A′NMR (MHz)

ADFT (MHz)

Cring−H acetate CH3 GFA CH3

77.10 77.30 81.79

0.4288 0.2040 0.1803

0.4274 0.2035 0.1813

0.48263 0.3594 0.2792

Javg (cm−1)

78.73

■

Averaged A (ANMR ′ ) values obtained by fitting the data with the averaged JNi−π (Javg). Theoretical values of A due to the ligand radical and due to a single metal center are given (ADFT, obtained from a single point DFT calculation of [1{Ni(OAc)2}2]+ • at the B3LYP*/ TZVP level; see the Supporting Information for more details). a

EXPERIMENTAL DETAILS

All reactions were carried out under an inert atmosphere using standard Schlenk techniques. Solvents were dried with an MBraun Solvent Purification System, degassed by three freeze−pump−thaw cycles and stored over molecular sieves prior to their use. Deuterated solvents (MeCN-d3, toluene-d8, and DMF-d7, all purchased from I


Article

Inorganic Chemistry

and dried in vacuo (95 mg, 97 μmol, 86%). Upon recrystallization from CH2Cl2, dark red crystals of [1{Pd(OAc)2}2] were obtained. Elemental analysis (%) for C34H62N12O8Pd2 (979.772): calcd. C 41.68, H 6.38, N 17.16; found C 40.71, H 6.48, N 16.55. 1H NMR (600.13 MHz, CD2Cl2): δ = 4.95 (s, 2H, CHarom), 2.95 (s, 24H, CH3), 2.71 (s, 24H, CH3), 1.79 (s, 12H, CH3COO) ppm. 13C NMR (150.90 MHz, CD2Cl2): δ = 177.22 (s, CH3COO), 165.69 (s, Cguanidine), 139.62 (s, Cring−N), 103.09 (s, CHarom), 40.63 (s, CH3), 39.97 (s, CH3), 23.15 (s, CH3COO) ppm. 1H NMR (600.13 MHz, MeCN-d3): δ = 5.01 (s, 2H, CHarom), 2.88 (s, 24H, CH3), 2.71 (s, 24H, CH3), 1.75 (s, 12H, CH3COO) ppm. 13C NMR (150.90 MHz, MeCN-d3): δ = 176.87 (s, CH3COO), 166.24 (s, Cguanidine), 140.04 (s, Cring−N), 103.66 (s, CHarom), 40.91 (s, CH3), 40.11 (s, CH3), 23.50 (s, CH3COO) ppm. IR (CsI): ṽ = 3448 (m), 3005 (w), 2929 (w), 2794 (w), 1616 (m), 1575 (vs), 1517 (s), 1491 (s), 1466 (m), 1420 (m), 1395 (vs), 1327 (m), 1295 (m), 1252 (m), 1231 (m), 1187 (m), 1159 (m), 1106 (w), 1062 (w), 1033 (m), 975 (w), 918 (w), 894 (m), 842 (w), 817 (w), 707 (w), 684 (m), 644 (w), 622 (w), 503 (w) cm−1. UV-vis (CH3CN, c = 2.03 × 10−5 mol L−1): λmax (ε in L mol−1 cm−1) = 225.5 (5.82 × 104), 319 (1.69 × 104), 397 (1.31 × 104), 524 (2.81 × 103) nm. MS (FAB+): m/z (%) = 327.2 (20), 343.2 (42), 386.5 (43), 391.1 (73), 427.3 (27), 460.1 (41), 486.3 ([C24H44N11]+, 53), 530.4 ([1]+, 52), 547.2 (10), 613.1 (11), 635.3 ([1(Pd)−H]+, 35), 695.2 ([1{Pd(OAc)}] + , 15), 801.1 ([1{Pd 2 (OAc)}] + , 16), 921.1 ([1{Pd2(OAc)3}]+, 8), 1030.1 ([1{Pd3(OAc)3}]+, 5). CV (CH2Cl2, SCE potential relative to Fc/Fc+, conducting electrolyte Bu4NPF6, 100 mV s−1): Eox = −0.36, −0.14 V; Ered = −0.49, −0.25 V; E1/2 = −0.43, −0.20 V. Crystal data for ([1{Pd(OAc) 2 } 2 ]·2CH 2 Cl 2 ): C36H66Cl4N12O8Pd2, Mr = 1149.61 g mol−1, 0.25 mm × 0.20 mm × 0.15 mm, monoclinic, space group P21/n, lattice constants a = 12.776(3) Å, b = 11.170(2) Å, c = 19.674(4) Å, β = 101.37(3)°, V = 2752.5(10) Å3, Z = 2, dcalc = 1.387 Mg m−3, Mo Kα radiation (graphitemonochromated, λ = 0.71073 Å), T = 100 K, θrange 2.11°−30.11°. Number of reflections measured: 29 302; number of independent reflections: 8058; Rint = 0.0389. Final R indices [I > 2σ(I)]: R1 = 0.0369, wR2 = 0.0955. [1{Zn(OAc)2}2]. A solution of 60.0 mg of 1 (113 μmol, 1 equiv) and 41.5 mg of zinc(II) acetate (226 μmol, 2 equiv) in 12 mL of EtOH was stirred for 1 h at room temperature. After removal of the solvent, the beige-colored precipitate was washed with toluene and Et2O and dried in vacuo (95 mg, 106 μmol, 94%). Upon recrystallization from CH2Cl2, light yellow crystals of [1{Zn(OAc)2}2] were obtained. Elemental analysis (%) for C34H62N12O8Zn2 (897.69): calcd. C 45.49, H 6.96, N 18.72; found C 45.74, H 7.05, N 19.02. 1H NMR (600.13 MHz, CD2Cl2): δ = 5.58 (s, 2H, CHarom), 2.82 (s, 48H, CH3), 1.83 (s, 12H, CH3COO) ppm. 13C NMR (150.90 MHz, CD2Cl2): δ = 176.89 (s, CH3COO), 164.12 (s, Cguanidine), 135.01 (s, Cring−N), 109.45 (s, CHarom), 40.42 (s, CH3), 39.35 (s, CH3), 23.31 (s, CH3COO) ppm. 1 H NMR (600.13 MHz, MeCN-d3): δ = 5.67 (s, 2H, CHarom), 2.81 (s, 48H, CH3), 1.75 (s, 12H, CH3COO) ppm. 13C NMR (150.90 MHz, MeCN−d3): δ = 176.75 (s, CH3COO), 164.65 (s, Cguanidine), 135.73 (s, Cring−N), 110.55 (s, CHarom), 40.58 (s, CH3), 39.55 (s, CH3), 23.38 (s, CH3COO) ppm. IR (CsI): ṽ = 3452 (m), 3002 (w), 2940 (m), 2896 (m), 2801 (w), 1636 (s), 1619 (s), 1537 (vs), 1489 (vs), 1472 (s), 1422 (vs), 1393 (vs), 1368 (s), 1331 (m), 1318 (s), 1282 (m), 1237 (m), 1182 (s), 1157 (vs), 1104 (w), 1064 (m), 1030 (vs), 961 (w), 926 (w), 914 (w), 895 (m), 861 (m), 815 (m), 804 (m), 730 (m), 715 (w), 675 (w), 639 (w), 615 (w), 581 (w), 532 (w), 502 (w), 439 (w), 428 (w) cm−1. UV-vis (CH3CN, c = 2.14 × 10−5 mol L−1): λmax (ε in L mol−1 cm−1) = 214 (3.89 × 104), 286 (2.37 × 104), 328.5 (2.41 × 104), 366 (1.66 × 104) nm. MS (ESI+, CH2Cl2): m/z (%) = 327.28 ([1{Zn(OAc)}+H]2+, 11.0), 389.53 (36.6), 653.51 ([1{Zn(OAc)}] + , 100), 835.03 ([1{Zn 2 (OAc) 3 }] + , 64.1), 1368.93 ([(1)2{Zn2(OAc)3}]+, ≤5), 1550.76 ([(1)2{Zn3(OAc)5}]+, ≤5), 1732.69 ([(1)2Zn4(OAc)7]+, 22.1). CV (CH2Cl2, SCE electrode, potentials relative to Fc/Fc+, supporting electrolyte Bu4NPF6, 100 mV s−1): Eox = −0.22 V; Ered = 0.61 V; E1/2 = −0.42 V. Crystal data for [1{Zn(OAc)2}2]: C34H62N12O8Zn2, Mr = 897.70 g mol−1, 0.35 mm × 0.30 mm × 0.20 mm, monoclinic, space group P21/c, lattice constants a = 18.759(4) Å, b = 10.796(2) Å, c = 25.634(9) Å, β = 123.93(2)°, V

Sigma−Aldrich) were dried with conventional methods (over CaH2) and degassed before use with the freeze−pump−thaw technique. The following chemicals were purchased and used as delivered: Co(OAc)2 (Sigma−Aldrich, 99.995%), Ni(OAc)2·3H2O (ABCR, 98%), Pd(OAc)2 (Sigma−Aldrich, ≥99.9%), Cu(OAc)2 (Sigma−Aldrich, 98%), Zn(OAc) 2 (Sigma−Aldrich, 99.99%), Pb(OAc)2 ·3H 2 O (Sigma−Aldrich, ≥99.99%), Ag(PF6) (ABCR, 99%), Ag(SbF6) (ABCR, 98%), and Fc(PF6) (Sigma−Aldrich, 97%). Compounds [1{Co(OAc)2}2]42 and [1{Cu(OAc)2}2]41 were prepared as described previously. Elemental analyses were carried out at the Microanalytical Laboratory of the University of Heidelberg. NMR spectra were recorded on a Bruker Model Avance II 400 system (BBFO probe) and a Bruker Model Avance III 600 spectrometer (QNP Cryoprobe, inner coil tuned to 13C, cold preamplifier). Prior to variable temperature measurements, temperature calibration was done using the method of Berger et al.61 Solvent resonances were taken as references for all 1H and 13C NMR spectra.62 Samples for NMR measurements were prepared and stored in an inert gas atmosphere. For IR spectroscopy, CsI disks of the compounds were measured with an FTIR spectrometer (Biorad, Model Merlin Excalibur FT 3000). UV-vis spectra were recorded with a Cary 5000 spectrophotometer. Mass spectrometric data were obtained with the aid of a Bruker ApexQe hybrid 9.4 FT-ICT (ESI) or MAT 8400 device and a JEOL JMS-700 (FAB) device. EPR spectra (X-band) were recorded with a Bruker ESP 300 E spectrometer. A Quantum Design MPMS-XL-5 (5T) machine was used for SQUID magnetometric measurements. For the CV measurements an EG&G Princeton 273 apparatus with an SCE as reference electrode was used. The curves were recorded at room temperature at a scan rate of 100 mV s−1. CH2Cl2 was used as solvent for the individual compounds (c = 10−3 mol L−1), whereas Bu4NPF6 (electrochemical grade (≥99.0%), Fluka) was employed as supporting electrolyte (c = 0.1 mol L−1), if not stated otherwise. [1{Ni(OAc)2}2]. A solution of 100.0 mg of 1 (188 μmol, 1 equiv) and 93.8 mg of nickel(II) acetate tetrahydrate (377 μmol, 2 equiv) in 12 mL of ethanol (EtOH) was stirred for 1 h at room temperature. After removal of the solvent, the green−yellow precipitate was washed with n-hexane and Et2O and dried in vacuo (162 mg, 183 μmol, 97%). Upon recrystallization from CH2Cl2, yellow−green crystals of [1{Ni(OAc) 2 } 2 ] were obtained. Elemental analysis (%) for C34H62N12Ni2O8 (884.32): calcd. C 46.18, H 7.07, N 19.01, found C 46.54, H 7.13, N 18.76. 1H NMR (600.13 MHz, 295.0 K, toluened8): δ = 47.13 (s, 12H, CH3COO), 25.59 (s, 2H, CHarom), 24.27 (s, 12H, CH3), 22.53 (s, 12H, CH3), 18.97 (s, 12H, CH3), 12.30 (s, 12H, CH3) ppm. 1H NMR (600.13 MHz, 295.0 K, CD2Cl2): δ = 46.54 (s), 25.81 (s), 22.94 (s), 19.98 (s), 12.31 (s) ppm. 1H NMR (600.13 MHz, 295.0 K, MeCN-d3): δ = 46.02 (s), 25.82 (s), 22.50 (s), 19.63 (s), 12.11 (s) ppm. IR (CsI): ṽ = 3448 (m), 3006 (w), 2932 (w), 2898 (w), 2799 (w), 1560 (vs), 1522 (vs), 1492 (m), 1458 (s), 1420 (m), 1398 (vs), 1316 (m), 1283 (m), 1233 (m), 1188 (m), 1155 (m), 1108 (w), 1065 (w), 1028 (m), 939 (w), 919 (w), 898 (w), 866 (w), 806 (w), 739 (w), 708 (w), 673 (m), 622 (w), 503 (w), 475 (w) cm−1. UV-vis (CH3CN, c = 2.06 × 10−5 mol L−1): λmax (ε in L mol−1 cm−1) = 226.5 (4.42 × 104), 301.5 (2.07 × 104), 373 (2.25 × 104) nm. MS (ESI+, CH2Cl2): m/z (%) = 324.33 ([1{Ni(OAc)}+H]2+, 21.6), 382.32 (100), 530.33 ([1]+, 9.5), 647.20 ([1{Ni(OAc)}]+, 64.2), 822.91 ([1{Ni2(OAc)3}]+, 70.9), 1707.95 ([12{Ni4(OAc)7}]+, 8.0). CV (CH2Cl2, SCE potentials vs Fc/Fc+, supporting electrolyte Bu4NPF6, 100 mV s−1): Eox = −0.45, −0.27 V; Ered = −0.59, −0.42 V; E1/2 = −0.52, −0.35 V. Crystal data for [1{Ni(OAc)2}2]: C34H62N12Ni2O8, Mr = 884.38 g mol−1, 0.60 mm × 0.40 mm × 0.45 mm, orthorhombic, space group Ccca, lattice constants a = 15.666(3) Å, b = 26.291(5) Å, c = 12.257(3) Å, V = 5048.3(18) Å3, Z = 4, dcalc = 1.164 Mg m−3, Mo Kα radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K, θrange = 3.03°−30.08°. Number of reflections measured: 7053; number of independent reflections: 3702, Rint = 0.0231, final R indices [I > 2σ(I)]: R1 = 0.0496, wR2 = 0.1551. [1{Pd(OAc)2}2]. A solution of 60.0 mg of 1 (113 μmol, 1 equiv) and 50.8 mg of palladium(II) acetate (226 μmol, 2 equiv) in 16 mL of CH3CN was stirred for 1 h at room temperature. After removal of the solvent, the dark red precipitate was washed with toluene and Et2O J


Article

Inorganic Chemistry = 4307.5(9) Å3, Z = 4, dcalc = 1.384 Mg m−3, Mo Kα radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K, θrange = 2.19°− 30.04°. Number of reflections measured: 46 500, number of independent reflections: 12 595, Rint = 0.0388, final R indices [I > 2σ(I)]: R1 = 0.0375, wR2 = 0.0909. [1{Pb(OAc)2}2]. A solution of 60.0 mg of 1 (113 μmol, 1 equiv) and 85.8 mg of lead(II) acetate trihydrate (226 μmol, 2 equiv) in 12 mL of EtOH was stirred for 2 h at room temperature. After removal of the solvent, the yellow precipitate was washed with n-hexane and Et2O and dried in vacuo (122 mg, 103 μmol, 91%). Upon recrystallization from CH3CN, yellow crystals of [1{Pb(OAc)2}2] were obtained. Elemental analysis (%) for C34H62N12O8Pb2 (1181.33): calcd. C 34.57, H 5.29, N 14.23; found C 34.56, H 5.31, N 14.20. 1H NMR (600.13 MHz, CD2Cl2): δ = 2.80 (s, 48H, CH3), 1.74 (s, 12H, CH3COO) ppm. 13C NMR (150.90 MHz, CD2Cl2): δ = 178.87 (s, CH3COO), 39.90 (s, CH3), 26.57 (s, CH3COO) ppm. 1H NMR (600.13 MHz, MeCN-d3): δ = 5.44 (s, 2H, CHarom), 2.76 (s, 48H, CH3), 1.67 (s, 12H, CH3COO) ppm. 13C NMR (150.90 MHz, MeCN-d3): δ = 178.89 (s, CH3COO), 114.35 (s, CHarom), 40.03 (s, CH3), 26.63 (s, CH3COO) ppm. IR (CsI): ṽ = 3409 (m), 2994 (w), 2934 (w), 2886 (w), 2865 (w), 2799 (w), 1542 (vs), 1490 (s), 1470 (m), 1411 (vs), 1398 (vs), 1339 (m), 1285 (m), 1255 (m), 1234 (m), 1185 (m), 1155 (m), 1108 (w), 1063 (w), 1029 (m), 966 (w), 924 (w), 895 (m), 866 (m), 807 (m), 785 (m), 713 (m), 658 (m), 622 (m), 577 (m), 503 (w), 423 (w) cm−1. UV-vis (CH3CN, c = 3.52 × 10−5 mol L−1): λmax (ε, L mol−1 cm−1) = 241 (7.68 × 104), 326 (2.74 × 104) nm. MS (FAB+): m/z (%) = 391.2 (23), 460.1 (12), 486.3 ([C24H44N11]+, 22), 531.7 ([1+H]+, 67), 797.3 ([1{Pb(OAc)}]+, 32), 904.3 (7). CV (CH2Cl2, SCE potential relative to Fc/Fc+, supporting electrolyte Bu4NPF6, 100 mV s−1): Eox = −0.37; +0.08 V; Ered = −0.75 V; E1/2 = −0.56 V. Crystal data for ([1{Pb(OAc)2}2]·4CH3CN): C42H74N16O8Pb2, Mr = 1345.55 g mol−1, 0.40 mm × 0.25 mm × 0.25 mm, triclinic, space group P1̅, lattice constants a = 11.121(2) Å, b = 11.600(2) Å, c = 12.199(2) Å, α = 81.31(3)°, β = 63.37(3)°, γ = 73.33(3)°, V = 1347.2(4) Å3, Z = 1, dcalc = 1.659 Mg m−3, Mo Kα radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K, θrange = 2.11°−30.13°. Number of reflections measured: 22 728, number of independent reflections: 7908, Rint = 0.0387. Final R indices [I > 2σ(I)]: R1 = 0.0283, wR2 = 0.0679. [1{Ni(OAc)2}2](PF6). A solution of 40.0 mg of [1{Ni(OAc)2}2] (45 μmol, 1 equiv) and 11.4 mg of Ag(PF6) (45 μmol, 1 equiv) in 12 mL of CH3CN was stirred for 3 h at room temperature. The gray precipitate of elemental silver was separated from the dark green solution by filtration. After removal of the solvent, the dark green precipitate was washed with toluene and Et2O and dried in vacuo (38 mg, 37 μmol, 81%). Upon recrystallization from CH2Cl2, dark green crystals of [1{Ni(OAc)2}2](PF6) were obtained. Elemental analysis (%) for C34H62F6N12Ni2O8P (1029.28): calcd. C 39.67, H 6.07, N 16.33; found C 40.50, H 6.01, N 16.39. 1H NMR (600.13 MHz, 295.0 K, MeCN-d3): δ = 115.31 (s, 2H, Cring−H), 54.85 (s, 12H, CH3COO), 50.52 (s, 24H, CH3) ppm. The signal intensity for the CH3 groups of the GFA ligand is lower than expected. These groups undergo chemical exchange at room temperature, which invokes both the contact and dipolar relaxation mechanisms, thus reducing signal intensity.63 IR (CsI): ṽ = 3449 (w), 3021 (w), 2945 (w), 2872 (w), 2816 (w), 1590 (m), 1543 (m), 1513 (m), 1458 (m), 1421 (m), 1398 (s), 1318 (m), 1301 (m), 1267 (m), 1229 (w), 1164 (m), 1066 (w), 1032 (m), 941 (w), 907 (w), 843 (vs), 810 (w), 739 (w), 709 (w), 675 (w), 626 (w), 585 (w), 557 (m), 518 (w), 481 (w), 423 (w) cm−1. UV-vis (CH3CN, c = 6.32 × 10−5 mol L−1): λmax (ε, L mol−1 cm−1) = 234 (3.52 × 104), 306 (2.05 × 104), 448 (2.35 × 104), 635 (1.23 × 104) nm. MS (ESI+, CH3CN): m/z (%) = 255.75 (24.5), 265.51 ([1]2+, 27.5), 323.75 ([1{Ni(OAc)}]2+, 24.6), 382.44 (59.5), 411.73 (55.4), 530.39 ([1]+, 78.8), 647.25 ([1{Ni(OAc)}]+, 18.8), 706.15 ([1{Ni(OAc)2}]+, 61.3), 868.89 ([1{Ni(OAc)2}2]−CH3]+, 19.5), 882.01 ([1{Ni(OAc)2}2]+), 100). Crystal data for [1{Ni(OAc)2}2](PF6): C34H62F6N12Ni2O8P, Mr = 1029.35 g mol−1, 0.40 mm × 0.40 mm × 0.15 mm, tetragonal, space group P4̅b2, lattice constants a = 17.321(2) Å, b = 17.321(2) Å, c = 7.8540(16) Å, V = 2356.3(7) Å3, Z = 2, dcalc = 1.451 Mg m−3, Mo Kα radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K, θrange = 2.35°−30.06°. Number of

reflections measured: 40 247, number of independent reflections: 3446, Rint = 0.0671, final R indices [I > 2σ(I)]: R1 = 0.0338, wR2 = 0.0787. [1{Ni(OAc)2}2](SbF6). A solution of 40.0 mg of [1{Ni(OAc)2}2] (45 μmol, 1 equiv) and 15.5 mg of Ag(SbF6) (45 μmol, 1 equiv) in 12 mL of CH3CN was stirred for 3 h at room temperature. The gray precipitate of elemental silver was separated from the dark green solution by filtration. After removal of the solvent, the dark green precipitate was washed with toluene and Et2O and dried in vacuo (48 mg, 43 μmol, 95%). Upon recrystallization from CH2Cl2, dark green crystals of [1{Ni(OAc)2}2](SbF6) were obtained. Elemental analysis (%) for C34H62F6N12Ni2O8Sb (1120.07): calcd. C 36.46, H 5.58, N 15.01, found C 37.08, H 5.58, N 15.35. IR (CsI): ṽ = 3463 (w), 3019 (w), 2944 (w), 2870 (w), 2815 (w), 2796 (w), 1617 (m), 1590 (m), 1546 (m), 1513 (m), 1483 (m), 1457 (s), 1420 (m), 1398 (vs), 1318 (m), 1301 (m), 1266 (m), 1228 (m), 1164 (m), 1065 (w), 1032 (m), 941 (w), 907 (w), 892 (w), 831 (w), 810 (m), 739 (w), 677 (m), 659 (s), 625 (w), 585 (w), 555 (w), 519 (w), 504 (w) cm−1. UV-vis (CH3CN, c = 6.86 × 10−5 mol L−1): λmax (ε, L mol−1 cm−1) = 234 (3.80 × 104), 306 (2.25 × 104), 448 (2.48 × 104), 635 (1.31 × 104) nm. MS (ESI+, CH3CN): m/z (%) = 255.28 (22.9), 323.78 ([1{Ni(OAc)}]2+, 27.9), 382.31 (45.41), 411.57 (54.4), 530.40 ([1]+, 84.7), 647.27 ([1{Ni(OAc)}]+, 15.7), 706.15 ([1{Ni(OAc)2}]+, 65.3), 881.97 ([1{Ni(OAc)2}2]+, 100). Crystal data for [1{Ni(OAc)2}2](SbF6): C34H62F6N12Ni2O8Sb, Mr = 1120.13 g mol−1, 0.35 mm × 0.30 mm × 0.20 mm, tetragonal, space group P4̅b2, lattice constants a = 17.411(2) Å, b = 17.411(2) Å, c = 7.9700(16) Å, V = 2416.0(7) Å3, Z = 2, dcalc = 1.540 Mg m−3, Mo Kα radiation (graphitemonochromated, λ = 0.71073 Å), T = 100 K, θrange = 2.34°−33.19°. Number of reflections measured: 57 429, number of independent reflections: 4626, Rint = 0.0467, final R indices [I > 2σ(I)]: R1 = 0.0540, wR2 = 0.1152. [1{Ni(OAc)2}2](I3)2. A solution of 40.0 mg [1{Ni(OAc)2}2] (45 μmol, 3 equiv) and 11.4 mg I2 (45 μmol, 3 equiv) in 12 mL of CH3CN was stirred for 2 h at room temperature. After removal of the solvent, the brown precipitate was washed with n-hexane and Et2O and dried in vacuo (71 mg, 43 μmol, 96%). Elemental analysis (%) for C34H62I6N12Ni2O8 (1645.75): calcd. C 24.81, H 3.80, N 10.21; found C 24.36, H 3.70, N 10.16. IR (CsI): ṽ = 3448 (w), 3019 (w), 2964 (w), 2934 (w), 2807 (w), 1617 (vs), 1560 (m), 1529 (s), 1494 (s), 1457 (s), 1400 (vs), 1306 (vs), 1225 (m), 1170 (m), 1139 (w), 1106 (w), 1063 (m), 1028 (m), 942 (w), 897 (w), 798 (w), 745 (w), 685 (m), 622 (w), 586 (w), 506 (w), 420 (w) cm−1. UV-vis (CH3CN, c = 2.83 × 10−5 mol L−1): λmax (ε, L mol−1 cm−1) = 213 (1.54 × 104), 291 (2.18 × 104), 363 (1.10 × 104), 430 (6.58 × 103) nm. [1{Pd(OAc)2}2](PF6). A solution of 50.0 mg of [1{Pd(OAc)2}2] (51 μmol, 1 equiv) and 16.9 mg of Fc(PF6) (51 μmol, 1 equiv) in 10 mL CH3CN was stirred for 1.5 h at room temperature. After removal of the solvent, the dark green precipitate was washed with toluene and THF and dried in vacuo (46 mg, 41 μmol, 80%). Elemental analysis (%) for C34H62F6N12O8PPd2 (1124.748): calcd. C 36.31, H 5.56, N 14.94; found C 35.44, H 5.12, N 14.82. IR (CsI): ṽ = 3449 (w), 3021 (w), 2945 (w), 2872 (w), 2816 (w), 1590 (m), 1543 (m), 1513 (m), 1458 (m), 1421 (m), 1398 (s), 1318 (m), 1301 (m), 1267 (m), 1229 (w), 1164 (m), 1066 (w), 1032 (m), 941 (w), 907 (w), 843 (vs), 810 (w), 739 (w), 709 (w), 675 (w), 626 (w), 585 (w), 557 (m), 518 (w), 481 (w), 423 (w) cm−1. UV-vis (CH3CN, c = 1.88 × 10−5 mol L−1): λmax (ε, L mol−1 cm−1) = 222.5 (7.50 × 104), 401 (1.22 × 104), 449.5 (9.59 × 103), 638.5 (5.95 × 103), 707.5 (7.88 × 103) nm. X-ray Crystallographic Study. Suitable crystals were taken directly out of the mother liquor, immersed in perfluorinated polyether oil, and fixed on top of a cryo loop. Measurements were made with a Nonius-Kappa CCD diffractometer with a low-temperature unit, using graphite-monochromated Mo Kα radiation. The temperature was set to 100 K. The data collected were processed using the standard Nonius software.64 All calculations were performed using the SHELXT-PLUS software package. Structures were solved by direct methods with the SHELXS-97 program and refined with the SHELXL97 program.65,66 Graphical handling of the structural data during solution and refinement was performed with XPMA.67 Atomic K


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Inorganic Chemistry coordinates and anisotropic thermal parameters of non-hydrogen atoms were refined by full-matrix least-squares calculations. CCDC No. 1434191 {[1{Ni(OAc)2}2](SbF6)}, CCDC No. 1434192 {[1{Ni(OAc)2}2](PF6)}, CCDC No. 1434193 ([1{Pd(OAc)2}2]·2CH2Cl2), CCDC No. 1434194 ([1{Pb(OAc)2}2]·4CH3CN), CCDC No. 1434195 (1/n[1{Pb(OAc) 2 } 4 ] n _1D·1.2CH 2 Cl 2 ), CCDC No. 1434196 ([1{Ni(OAc)2}2]), CCDC No. 1434197 ([1{Zn(OAc)2}2]), CCDC No. 1434198 (1/n[1{Pb(OAc)2}4]n_2D), and CCDC No. 1434199 ([1(PdI2)2]I2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre (www.ccdc.cam.ac.uk/ data_request/cif). Details of the Quantum Chemical Calculations. The DFT calculations were carried out with the TURBOMOLE68 program package, using the BH-LYP,69,70 B3LYP,69,71 and TPSSh functionals72 and the def2-SV(P) basis set.73 Compound [1{Ni(OAc)2}2]+ • has different states that lay close in energy, because of the spin coupling of the different unpaired electrons. To obtain estimates of the spin coupling constants JNi−π (and JNi−Ni), of the three coupled spin sites, calculations of the high-spin state (6A) and broken symmetry states ((2)A and (4)A) were carried out. The coupling constants J (H = −2JijSiSj) were then obtained according to the work of Fliegl et al.74 TD-DFT calculations68c were performed to obtain the electronic excitation spectrum. Within these calculations, the excitation energies for 50 states were determined. To calculate the 13C Fermi-contact shifts, single-point DFT calculations were performed with Gaussian 09 (for details, please refer to the Supporting Information).75

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Research and Arts and the Universities of the State of BadenWürttemberg, Germany, within the framework program bwHPC-C5. The authors also thank David Schrempp for the EPR measurements and analysis.

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(1) Lyons, C. T.; Stack, T. D. P. Coord. Chem. Rev. 2013, 257, 528− 540. (2) Sproules, S.; Wieghardt, K. Coord. Chem. Rev. 2011, 255, 837− 860. (3) Demir, S.; Jeon, I.-R.; Long, J. R.; Harris, T. D. Coord. Chem. Rev. 2015, 289−290, 149−176. (4) Kaim, W.; Schwederski, B. Coord. Chem. Rev. 2010, 254, 1580− 1588. (5) Kaim, W. Dalton Trans. 2003, 761−768. (6) Preuss, K. E. Coord. Chem. Rev. 2015, 289−290, 49−61. (7) Whittaker, J. W. Chem. Rev. 2003, 103, 2347−2364. (8) Rogers, M. S.; Dooley, D. M. Curr. Opin. Chem. Biol. 2003, 7, 189−196. (9) Chirik, P. J.; Wieghardt, K. Science 2010, 327, 794−795. (10) Broere, D. L. J.; de Bruin, B.; Reek, J. N. H.; Lutz, M.; Dechert, S.; van der Vlugt, J. I. J. Am. Chem. Soc. 2014, 136, 11574−11577. (11) (a) Kaim, W. Inorg. Chem. 2011, 50, 9752−9765. (b) Kaim, W. Coord. Chem. Rev. 2011, 255, 2503−2513. (12) Zhu, D.; Thapa, I.; Korobkov, I.; Gambarotta, S.; Budzelaar, P. H. M. Inorg. Chem. 2011, 50, 9879−9887. (13) Pierpont, C. G. Inorg. Chem. 2011, 50, 9766−9772. (14) Schauer, P. A.; Low, P. J. Eur. J. Inorg. Chem. 2012, 2012, 390− 411. (15) Lyaskovskyy, V.; de Bruin, B. ACS Catal. 2012, 2, 270−279. (16) Olivos Suarez, A. I.; Lyaskovskyy, V.; Reek, J. N. H.; van der Vlugt, J. I.; de Bruin, B. Angew. Chem. 2013, 125, 12740−12760; Angew. Chem., Int. Ed. 2013, 52, 12510−12529. (17) Broere, D. L. J.; Plessius, R.; van der Vlugt, J. I. Chem. Soc. Rev. 2015, 44, 6886−6915. (18) (a) Pierpont, C. G.; Buchanan, R. M. Coord. Chem. Rev. 1981, 38, 45−87. (b) Pierpont, C. G. Coord. Chem. Rev. 2001, 216−217, 99− 125. (c) Ohtsu, H.; Tanaka, K. Chem.Eur. J. 2005, 11, 3420−3426. (d) Alley, K. G.; Poneti, G.; Robinson, P. S. D.; Nafady, A.; Moubaraki, B.; Aitken, J. B.; Drew, S. C.; Ritchie, C.; Abrahams, B. F.; Hocking, R. K.; Murray, K. S.; Bond, A. M.; Harris, H. H.; Sorace, L.; Boskovic, C. J. Am. Chem. Soc. 2013, 135, 8304−8323. (19) (a) Chaudhuri, P.; Verani, C. N.; Bill, E.; Bothe, E.; Weyhermüller, T.; Wieghardt, K. J. Am. Chem. Soc. 2001, 123, 2213−2223. (b) Mukherjee, C.; Weyhermüller, T.; Bothe, E.; Chaudhuri, P. Inorg. Chem. 2008, 47, 2740−2746. (20) Chaudhuri, P.; Hess, M.; Müller, J.; Hildenbrand, K.; Bill, E.; Weyhermüller, T.; Wieghardt, K. J. Am. Chem. Soc. 1999, 121, 9599− 9610. (21) (a) McKinnon, S. D. J.; Patrick, B. O.; Lever, A. B. P.; Hicks, R. G. Chem. Commun. 2010, 46, 773−775. (b) McKinnon, S. D. J.; Patrick, B. O.; Lever, A. B. P.; Hicks, R. G. J. Am. Chem. Soc. 2011, 133, 13587−13603. (c) Sanz, C. A.; Ferguson, M. J.; McDonald, R.; Patrick, B. O.; Hicks, R. G. Chem. Commun. 2014, 50, 11676−11678. (22) Morgan, I. S.; Mansikkamäki, A.; Zissimou, G. A.; Koutentis, P. A.; Rouzières, M.; Clérac, R.; Tuononen, H. M. Chem.Eur. J. 2015, 21, 15843−15853. (23) (a) Peters, A.; Kaifer, E.; Himmel, H.-J. Eur. J. Org. Chem. 2008, 2008, 5907−5914. (b) Peters, A.; Trumm, C.; Reinmuth, M.; Emeljanenko, D.; Kaifer, E.; Himmel, H.-J. Eur. J. Inorg. Chem. 2009, 2009, 3791−3800. (24) Vitske, V.; König, C.; Kaifer, E.; Hübner, O.; Himmel, H.-J. Eur. J. Inorg. Chem. 2010, 2010, 115−126. (25) Bindewald, E.; Lorenz, R.; Hübner, O.; Brox, D.; Herten, D.-P.; Kaifer, E.; Himmel, H.-J. Dalton Trans. 2015, 44, 3467−3485. (26) Stang, S.; Kaifer, E.; Himmel, H.-J. Chem.Eur. J. 2014, 20, 5288−5297.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02614. Molecular structure of the “one-dimensional” and “twodimensional” coordination polymers with the formula [1{Pb4(OAc)8}]. IR spectrum, UV-vis spectrum, and cyclic voltammogram of [1{Zn(OAc)2}2]. SQUID data for [1{Ni(OAc)2}2]. Superposition of the calculated and the experimentally obtained structures of [1{Ni(OAc)2}2]+ •. Molecular structure, IR spectrum, and UV-vis spectrum of [1{Ni(OAc)2}2](SbF6). Comparison of the IR spectra (CsI) recorded for [1{Ni(OAc)2}2], [1{Ni(OAc)2}2]+ • and [1{Ni(OAc)2}2]2+. IR and EPR spectra of [1{Pd(OAc)2}2](PF6). Theoretical UV-vis spectrum from TD-DFT (B3LYP/SV(P)) calculations for [1{Pd(OAc)2}2]+ •. Analysis of [1{Ni(OAc)2}2] and [1{Ni(OAc)2}2](PF6) by paramagnetic NMR (pNMR) spectroscopy. Details of the calculation of magnetic coupling constants with DFT methods. (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Deutsche Forschungsgemeinschaft (DFG) for continuous financial support. A Ph.D. scholarship from the Beilstein-Institut zur Förderung der Chemischen Wissenschaften is greatly appreciated (M.D.). The authors are grateful for the computational resources provided by the bwForCluster JUSTUS, funded by the Ministry of Science, L


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Inorganic Chemistry (27) Wild, U.; Neuhäuser, C.; Wiesner, S.; Kaifer, E.; Wadepohl, H.; Himmel, H.-J. Chem.Eur. J. 2014, 20, 5914−5925. (28) Vitske, V.; Herrmann, H.; Enders, M.; Kaifer, E.; Himmel, H.-J. Chem.Eur. J. 2012, 18, 14108−14116. (29) Herrmann, H.; Ziesak, A.; Wild, U.; Leingang, S.; Schrempp, D.; Wagner, N.; Beck, J.; Kaifer, E.; Wadepohl, H.; Himmel, H.-J. ChemPhysChem 2014, 15, 351−365. (30) (a) Emeljanenko, D.; Peters, A.; Vitske, V.; Kaifer, E.; Himmel, H.-J. Eur. J. Inorg. Chem. 2010, 2010, 4783−4789. (b) Emeljanenko, D.; Kaifer, E.; Himmel, H.-J. Eur. J. Inorg. Chem. 2011, 2011, 2975− 2983. (31) (a) Edelmann, F. T. Adv. Organomet. Chem. 2008, 57, 183−352. (b) Edelmann, F. T. Coord. Chem. Rev. 1994, 137, 403−481. (c) Barker, J.; Kilner, M. Coord. Chem. Rev. 1994, 133, 219−300. (d) Bailey, P. J.; Pace, S. Coord. Chem. Rev. 2001, 214, 91−141. (e) Herres-Pawlis, S. Nachr. Chem. 2009, 57, 20−23. (f) Coles, M. P. Dalton Trans. 2006, 985−1001. (g) Coles, M. P. Chem. Commun. 2009, 3659−3676. (h) Himmel, H.-J. Hydrogenation and Dehydrogenation of Dinuclear Boron- and Gallium Hydrides: Quantum Chemical Calculations and Experiments. In Modeling of Molecular Properties; Comba, P., Ed.; Wiley−VCH: Weinheim, Germany, 2011. (i) Jones, C. Coord. Chem. Rev. 2010, 254, 1273−1289. (j) Edelmann, F. T. Adv. Organomet. Chem. 2013, 61, 55−374. (32) Day, B. M.; Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B. Chem. Commun. 2011, 47, 4995−4997. (33) Schwamm, R. J.; Day, B. M.; Mansfield, N. E.; Knowelden, W.; Hitchcock, P. B.; Coles, M. P. Dalton Trans. 2014, 43, 14302−14314. (34) Maronna, A.; Hübner, O.; Enders, M.; Kaifer, E.; Himmel, H.-J. Chem.Eur. J. 2013, 19, 8958−8977. (35) (a) Schatz, M.; Raab, V.; Foxon, S. P.; Brehm, G.; Schneider, S.; Reiher, M.; Holthausen, M. C.; Sundermeyer, J.; Schindler, S. Angew. Chem. 2004, 116, 4460−4464; Angew. Chem., Int. Ed. 2004, 43, 4360− 4363. (b) Würtele, C.; Gaoutchenova, E.; Harms, K.; Holthausen, M. C.; Sundermeyer, J.; Schindler, S. Angew. Chem. 2006, 118, 3951− 3954; Angew. Chem., Int. Ed. 2006, 45, 3867−3869. (c) Lanci, M. P.; Smirnov, V. V.; Cramer, C. J.; Gauchenova, E. V.; Sundermeyer, J.; Roth, J. P. J. Am. Chem. Soc. 2007, 129, 14697−14709. (d) Maiti, D.; Lee, D.-H.; Gaoutchenova, K.; Würtele, C.; Holthausen, M. C.; Narducci Sarjeant, A. A.; Sundermeyer, J.; Schindler, S.; Karlin, K. D. Angew. Chem. 2008, 120, 88−91; Angew. Chem., Int. Ed. 2008, 47, 82− 85. (e) Peterson, R. L.; Ginsbach, J. W.; Cowley, R. E.; Qayyum, M. F.; Himes, R. A.; Siegler, M. A.; Moore, C. D.; Hedman, B.; Hodgson, K. O.; Fukuzumi, S.; Solomon, E. I.; Karlin, K. D. J. Am. Chem. Soc. 2013, 135, 16454−16467. (f) Saracini, C.; Liakos, D. G.; Zapata Rivera, J. E.; Neese, F.; Meyer, G. J.; Karlin, K. D. J. Am. Chem. Soc. 2014, 136, 1260−1263. (36) (a) Hoffmann, A.; Binder, S.; Jesser, A.; Haase, R.; Flörke, U.; Gnida, M.; Salomone Stagni, M.; Meyer-Klaucke, W.; Lebsanft, B.; Grünig, L. E.; Schneider, S.; Hashemi, M.; Goos, A.; Wetzel, A.; Rübhausen, M.; Herres-Pawlis, S. Angew. Chem. 2014, 126, 305−310; Angew. Chem., Int. Ed. 2014, 53, 299−304. (b) Hoffmann, A.; Bienemann, O.; dos Santos Vieira, I.; Herres-Pawlis, S. Polymers 2014, 6, 995−1007. (c) Jesser, A.; Rohrmueller, M.; Schmidt, W. G.; HerresPawlis, S. J. Comput. Chem. 2014, 35, 1−17. (d) Bienemann, O.; Hoffmann, A.; Herres-Pawlis, S. Rev. Inorg. Chem. 2011, 31, 83−108. (37) (a) Neuba, A.; Haase, R.; Meyer-Klaucke, W.; Floerke, U.; Henkel, G. Angew. Chem. 2012, 124, 1746−1750; Angew. Chem., Int. Ed. 2012, 51, 1714−1718. (b) Neuba, A.; Floerke, U.; Meyer-Klaucke, W.; Salomone-Stagni, M.; Bill, E.; Bothe, E.; Höfer, P.; Henkel, G. Angew. Chem. 2011, 123, 4596−4600; Angew. Chem., Int. Ed. 2011, 50, 4503−4507. (38) Chiarella, G. M.; Melgarejo, D. Y.; Rozanski, A.; Hempte, P.; Perez, L. M.; Reber, C.; Fackler, J. P., Jr. Chem. Commun. 2010, 46, 136−138. (39) Oakley, S. H.; Coles, M. P.; Hitchcock, P. B. Inorg. Chem. 2004, 43, 5168−5172. (40) (a) Himmel, H.-J. Z. Anorg. Allg. Chem. 2013, 639, 1940−1952. (b) Wiesner, S.; Wagner, A.; Hübner, O.; Kaifer, E.; Himmel, H.-J. Chem.Eur. J. 2015, 21, 16494−16503.

(41) Trumm, C.; Hübner, O.; Walter, P.; Leingang, S.; Wild, U.; Kaifer, E.; Eberle, B.; Himmel, H.-J. Eur. J. Inorg. Chem. 2014, 2014, 6039−6050. (42) Roquette, P.; König, C.; Hübner, O.; Wagner, A.; Kaifer, E.; Enders, M.; Himmel, H.-J. Eur. J. Inorg. Chem. 2010, 2010, 4770− 4782. (43) Roquette, P.; Maronna, A.; Peters, A.; Kaifer, E.; Himmel, H.-J.; Hauf, Ch.; Herz, V.; Scheidt, E.-W.; Scherer, W. Chem.Eur. J. 2010, 16, 1336−1350. (44) Bill, E. JulXSimulation of Molecular Magnetic Data, v. 1.6; Max Planck Institute for Bioinorganic Chemistry: Mülheim an der Ruhr, Germany. (45) Dei, A.; Gatteschi, D.; Pardi, L. Inorg. Chim. Acta 1991, 189, 125−128. (46) Luneau, D.; Rey, P.; Laugier, J.; Belorizky, E.; Cogne, A. Inorg. Chem. 1992, 31, 3578−3584. (47) (a) Yamamoto, Y.; Suzuki, T.; Kaizaki, S. J. Chem. Soc., Dalton Trans. 2001, 1566−1572. (b) Yamamoto, Y.; Suzuki, T.; Kaizaki, S. J. Chem. Soc., Dalton Trans. 2001, 2943−2950. (48) Barclay, T. M.; Hicks, R. G.; Lemaire, M. T.; Thompson, L. K. Chem. Commun. 2000, 2141−2142. (49) Brook, D. J. R.; Richardson, C. J.; Haller, B. C.; Hundley, M.; Yee, G. T. Chem. Commun. 2010, 46, 6590−6592. (50) Illas, F.; Martin, R. L. J. Chem. Phys. 1998, 108, 2519−2527. (51) Hübner, O.; Fink, K.; Klopper, W. Phys. Chem. Chem. Phys. 2007, 9, 1911−1920. (52) Illas, F.; Moreira, I. de P. R.; Bofill, J. M.; Filatov, M. Theor. Chem. Acc. 2006, 116, 587−597. (53) (a) Kabsch, W. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, A32, 922−923. (b) Kabsch, W. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1978, A34, 827−828. (54) Coutsias, E. A.; Seok, C.; Dill, K. A. J. Comput. Chem. 2004, 25, 1849−1857. (55) (a) La Mar, G. N. NMR of Paramagnetic Molecules: Principles and Applications; Academic Press: New York and London, 1973. (b) Bertini, I.; Luchinat, C.; Parigi, G. Solution NMR of Paramagnetic Molecules: Applications to Metallobiomolecules and Models; Elsevier: Amsterdam, 2001. (c) Liimatainen, H.; Pennanen, T. O.; Vaara, J. Can. J. Chem. 2009, 87, 954−964. (d) Banci, L.; Bertini, I.; Luchinat, C. The 1 H NMR parameters of magnetically coupled dimersThe Fe2S2 proteins as an example. In Bioinorganic Chemistry, Vol. 72; Springer: Berlin−Heidelberg, Germany, 1990; pp 113−136. (e) Hilbig, H.; Hudeczek, P.; Köhler, F. H.; Xie, X.; Bergerat, P.; Kahn, O. Inorg. Chem. 1998, 37, 4246−4257. (f) Reger, D. L.; Pascui, A. E.; Pellechia, P. J.; Ozarowski, A. Inorg. Chem. 2013, 52, 12741−12748. (g) Kopf, P. W.; Kreilick, R. W. J. Am. Chem. Soc. 1969, 91, 6569−6573. (h) Damjanović, M.; Morita, T.; Katoh, K.; Yamashita, M.; Enders, M. Chem.Eur. J. 2015, 21, 14421−14432. (i) Enders, M. Assigning and Understanding NMR Shifts of Paramagnetic Metal Complexes. In Modeling of Molecular Properties; Comba, P., Ed.; Wiley−VCH: Weinheim, Germany, 2011;. (j) Roquette, P.; Maronna, A.; Reinmuth, M.; Kaifer, E.; Enders, M.; Himmel, H.-J. Inorg. Chem. 2011, 50, 1942−1955. (k) Machonkin, T. E.; Westler, W. M.; Markley, J. L. Inorg. Chem. 2005, 44, 779−797. (56) Borgogno, A.; Rastrelli, F.; Bagno, A. Dalton Trans. 2014, 43, 9486−9496. (57) Gaudette, A. I.; Jeon, I.-R.; Anderson, J. S.; Grandjean, F.; Long, G. J.; Harris, T. D. J. Am. Chem. Soc. 2015, 137, 12617−12626. (58) Charnock, G. T. P.; Kuprov, I. Phys. Chem. Chem. Phys. 2014, 16, 20184−20189. (59) Hogben, H. J.; Krzystyniak, M.; Charnock, G. T. P.; Hore, P. J.; Kuprov, I. J. Magn. Reson. 2011, 208, 179−194. (60) Eberson, L. Electron-Transfer Reactions in Organic Chemistry. In Advances in Physical Organic Chemistry, Vol. 18; Gold, V., Bethell, D., Eds.; Academic Press: London, 1982; pp 79−185. (61) Findeisen, M.; Brand, T.; Berger, S. Magn. Reson. Chem. 2007, 45, 175−178. M


Article

Inorganic Chemistry (62) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organometallics 2010, 29, 2176−2179. (63) Bertini, I.; Luchinat, C. Coord. Chem. Rev. 1996, 150, 77−110. (64) DENZO-SMN Data Processing Software; Nonius, 1998; available via the Internet at: http://www.nonius.nl. (65) (a) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution; University of Göttingen: Göttingen, Germany, 1997; available via the Internet at: http://shelx.uni-ac.gwdg.de/SHELX/index.php. (b) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; available via the Internet at: http://shelx.uni-ac.gwdg.de/ SHELX/index.php. (66) International Tables for X-ray Crystallography, Vol. 4; Kynoch Press: Birmingham, U.K., 1974. (67) Zsolnai, L.; Huttner, G. XPMA; University of Heidelberg: Heidelberg, Germany, 1994; available via the Internet at: http://www. uni-heidelberg.de/institute/fak12/AC/huttner/software/software. html. (68) (a) Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Chem. Phys. Lett. 1989, 162, 165−169. (b) Treutler, O.; Ahlrichs, R. J. Chem. Phys. 1995, 102, 346−354. (c) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys. Lett. 1996, 256, 454−464. (69) (a) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098−3100. (b) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (70) Becke, A. D. J. J. Chem. Phys. 1993, 98, 1372−1377. (71) (a) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623−11627. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (72) (a) Tao, J.; Perdew, J. P.; Staroverov, V. N.; Scuseria, G. E. Phys. Rev. Lett. 2003, 91, 146401−146404. (b) Staroverov, V. N.; Scuseria, G. E.; Tao, J.; Perdew, J. P. J. Chem. Phys. 2003, 119, 12129−12137. (73) (a) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297−3305. (b) Weigend, F. Phys. Chem. Chem. Phys. 2006, 8, 1057− 1065. (74) Fliegl, H.; Fink, K.; Klopper, W.; Anson, C. E.; Powell, A. K.; Clérac, R. Phys. Chem. Chem. Phys. 2009, 11, 3900−3909. (75) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc.: Wallingford, CT, USA, 2009.

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