Antiferromagnetic Copper(II) - ACS Publications

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Alternating Ferro/Antiferromagnetic Copper(II) Chain Containing an Unprecedented Triple Formato/Hydroxido/Sulfato Bridge Carlos J. Gómez-García,*,† Emilio Escrivà,*,‡ Samia Benmansour,† Juan J. Borràs-Almenar,‡ José-Vicente Folgado,§ and Carmen Ramírez de Arellano∥ †

Instituto de Ciencia Molecular (ICMol), Universidad de Valencia, C/Catedrático José Beltrán, 2, 46980 Paterna (Valencia), Spain Departament de Química Inorgànica, Universitat de València, c/Vicent Andrés Estellés, s/n, 46100 Burjassot (València), Spain § Institut de Ciència dels Materials de la Universitat de València, (ICMUV), c/Catedrático José Beltrán, 2, 46980 Paterna (València), Spain ∥ Departament de Química Orgànica, Universitat de València, c/Vicent Andrés Estellés, s/n, 46100 Burjassot (València), Spain ‡

S Supporting Information *

ABSTRACT: The first example of a triple formato/hydroxido/sulfato (FHS) bridge for any metal is reported in compound [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1). Its structure shows the presence of alternating triple FHS bridges and 2,2′-bipyrimidine (bpym) ones. Although in the initial synthesis the sulfate anions were introduced accidentally, here we report the rational synthesis and the magnetic properties of this compound. The magnetic properties show that 1 is an alternating ferro/antiferromagnetic (F/ AF) chain compound with predominant antiferromagnetic interactions and were fit to an alternating F/AF S = 1/2 chain with g = 2.103, JAF = −139 cm−1, and JF = 116 cm−1 (α = JF/|JAF| = 0.83). The JAF value found corresponds very well to those previously reported for Cu−bpym−Cu bridges (average value of ca. −150 cm−1). The JF value is also very close to the estimated one (ca. 100 cm−1) from magneto-structural correlations in triply Cu−Cu bridged compounds with both hydroxido and carboxylato bridges in equatorial positions.

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syn−syn, syn−anti, and anti−anti μ-carboxylato-1κO:2κO′ bridging modes. These coordination modes afford CPs with a considerable variety of topologies and structural architectures.41−45 In order to prepare coordination polymers with at least two different bridging ligands as 2,2′-bipyrimidine (bpym) and a versatile carboxylate one, we have studied the reaction between Cu(II), formate and bpym. To our knowledge, only one coordination polymer including both formato and bpym bridging ligands has been described.46 We have directly used Cu(HCO2)2 and bpym as starting reagents in order to avoid the presence of other anions. However, the unexpected and serendipitous presence of traces of sulfate anions in the reaction media has led to the isolation of compound [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1), the first compound containing a triple formato/hydroxido/sulfato (FHS) bridge. This compound also presents bpym bridges alternating with the triple FHS bridges, resulting in a novel alternating copper(II) chain, that has not been previously described for any metal. Here we report the crystal structure and magnetic properties of this compound, and we show a complete magneto-structural study of all the copper(II) complexes with similar bridges

INTRODUCTION The rational design and synthesis of new coordination polymers (CPs) is one of the most active research areas in chemistry of materials in the past decade. This activity has been fuelled by the development of novel extended supramolecular architectures of widespread use in a variety of technological applications.1−13 A recurrent strategy for the construction of coordination polymers consists of assembling more than one type of organic ligand around the metal ion to yield CPs in which the properties and functionalities of the selected ligands combine with those of the metal ion.14−21 In this kind of system, special attention has been addressed to coordination architectures that include multiatomic bridging ligands (MABLs). Thus, MABLs such as oxalate22−27 azide28−34 or 2,2′-bipyrimidine (bpym)35−40 have been extensively used in magneto-structural studies because of their remarkable ability in mediating magnetic interactions between paramagnetic centers as well as the variety of dimensionalities (from both structural and magnetic points of view) and topologies that they can originate when adopting different coordination modes. Despite the variety of bpymincluding ternary systems characterized, those that include carboxylate groups are relatively uncommon. As is well-known, the versatile carboxylate groups bind to metal atoms in a great variety of bridging modes, with the most frequent being the © XXXX American Chemical Society

Received: January 16, 2016

A

DOI: 10.1021/acs.inorgchem.6b00105 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (although not identical, given the uniqueness of 1), in order to explain the alternating ferro/antiferromagnetic coupling found in this chain compound. Thus, the magnetic properties of 1 show that it is an alternating ferro/antiferromagnetic chain with a dominant antiferromagnetic coupling (JAF = −139 cm−1, JF = +116 cm−1). The magnitude of the magnetic interactions has been correlated to the crystal structure and compared to that observed in other related alternating Cu(II) chains containing 2,2′-bipyrimidine bridges.

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Table 1. Crystallographic Data for the Title Compound Prepared in a Serendipitous Way and in a Rational Way (1 and 1′, Respectively) empirical formula fw cryst color cryst size (mm3) T (K) wavelength (Å) cryst syst, Z Z space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) ρcalc (Mg/m3) μ(Mo Kα) (mm−1) θ range (deg) reflns collected indep reflns (Rint) reflns used in refinement, n L.S. params, p/restraints, r R1(F),a I > 2σ(I) wR2(F2),b all data S(F2),c all data Δρmax/min (e Å−3)

EXPERIMENTAL SECTION

Materials and Methods. Anhydrous copper(II) formate was prepared according to the method previously described.47 All the other reagents are commercially available and were used as received without further purification. Synthesis of [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1). An aqueous solution (25 mL) of copper(II) formate (76.8 mg, 0.5 mmol) was added to an aqueous solution (25 mL) of 2,2′-bipyrimidine (79.1 mg, 0.5 mmol). The resulting solution was stirred resulting in a bluegreenish solution with a final pH value of 7.15. Prismatic green single crystals of 1 suitable for X-ray analysis were grown by slow evaporation at 20.1 ± 0.1 °C after 6 days (8.43 mg, yield = 6.6%). Single crystals of compound 1 show the presence of sulfate anions that must have been present in the preparation. The sulfate anion contamination could have come from traces of tap water (tap water in our laboratory contains sulfate anion values of ca. 260 mg/L). Note that the Cu(II) formate used in the synthesis cannot contain sulfate anions since it is prepared by reacting CuO with formic acid.47 The synthesis of compound 1 could be reproduced in a rational way using Na2SO4 with the following method: aqueous solutions of copper(II) formate (76.8 mg, 0.5 mmol in 25 mL of H2O), 2,2′bipyrimidine (79.1 mg, 0.5 mmol in 25 mL of H2O), and sodium sulfate (35.52 mg, 0.25 mmol in 20 mL of H2O) were mixed with stirring, and the pH was adjusted to 7.20 with a 0.01 M NaOH solution. Slow evaporation of the final resulting green solution over 1 week at 20.3 ± 0.1 °C results in the formation of a polycrystalline green solid (83 mg, yield = 65%) with a single crystal X-ray structure isomorphic to the one found for compound 1 and with a powder X-ray difractogram identical to that simulated from the crystal structure of 1 (see below). Anal. Found: C, 20.42; H, 3.23; N, 10.31; S, 5.86%. Calcd for C9H18Cu2N4O12S: C, 20.27; H, 3.40; N, 10.50; S, 6.01%. Structural Characterization of Compounds 1 (Prepared by Serendipity) and 1′ (Rational Preparation). Crystals of both synthetic methods suitable for X-ray diffraction were measured on an Agilent Technologies SuperNova diffractometer using Mo Kα radiation and ω-scan mode. A summary of the data collection and structure refinements is provided in Table 1. Crystal structures were solved by direct methods and all non-hydrogen atoms refined anisotropically on F2 using the programs SHELXS and SHELXL2014.48 The [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2] polymeric unit shows mirror symmetry through all bridging OH−, HCO2−, and SO42− ligands. The sulfato ligand and one of the water solvating molecules are disordered over a mirror plane. The coordinated water molecule and a solvating water molecule are disordered over two positions, and their occupancies were refined. Disordered solvent molecules and sulfato ligands have been refined with appropriate similarity restraints (SAME, SADI) and with U value components restrained to be equal (RIGU); water hydrogen atoms were found in a Fourier synthesis map and refined as free with appropriate restraints (SADI, DFIX). Other hydrogen atoms were included as riding. The data from the major disordered component of one of the two determined polymorphs have been used in the Results and Discussion section for clarity. Powder X-ray Diffraction. A polycrystalline sample of 1 was slightly ground in an agate mortar and filled into 0.5 mm glass capillary that was mounted and aligned on a Empyrean PANalytical powder diffractometer, using Cu Kα radiation (λ = 1.54056 Å). Two scans were collected at room temperature in the 2θ range 2−50° and merged in a single diffractogram.

1

1′

C9H18Cu2N4O12S 533.41 green 0.34 × 0.06 × 0.06 120(2) 0.71073 monoclinic 2 P21/m 7.6724(4) 13.7490(5) 8.7100(4) 90 107.531(3) 90 876.13(7) 2.022 2.620 2.96−32.58 7681 3020 (0.0289) 3020 180/30 0.0285 0.0720 1.049 0.579/−0.594

C9H18Cu2N4O12S 533.41 green 0.32 × 0.10 × 0.05 120(2) 0.71073 monoclinic 2 P21/m 7.6789(2) 13.7771(4) 8.7080(3) 90 107.606(3) 90 878.09(5) 2.017 2.614 3.10−32.09 10692 2944 (0.0503) 2944 180/30 0.0340 0.0841 1.033 0.618/−0.808

R1(F) = ∑||Fo| − |Fc||/∑|Fo|. bwR2(F2) = [∑w(Fo2 − Fc2)2/ ∑wFo4]1/2. cS(F2) = [∑w(Fo2 − Fc2)2/(n + r − p)]1/2.

a

Physical Properties. Elemental C, H, N analyses were performed with a CE instrument EA 1110 CHNS analyzer. Magnetic measurements were performed with a Quantum Design MPMS-XL-5 SQUID magnetometer in the 2−300 K temperature range with an applied magnetic field of 0.1 T on a polycrystalline sample of 1 (with a mass of 8.43 mg). Susceptibility data were corrected for the sample holder and for the diamagnetic contribution of the salts using Pascal’s constants.49

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RESULTS AND DISCUSSION Synthesis. The serendipitous synthesis of 1 was carried out using copper(II) formate and bpym as starting materials. However, the crystal structure of compound 1 revealed the unexpected presence of sulfate anions acting as Cu−sulfato−Cu bridges. Sulfate anion could have been a contaminant coming from tap water (see the Experimental Section). The serendipitous presence of sulfate anions could be reproduced by adding Na2SO4 in the synthetic procedure to obtain the same compound (1′). Both the X-ray single crystal structure and powder X-ray diffraction pattern of the polycrystalline solid confirm the quantitative formation of 1 (Figures 1 and 2). Crystal Structures. Crystal Structure Description of [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1). Although the single crystals obtained with both methods are identical, here we describe the crystal structure of a single crystal of compound 1 obtained with the serendipitous method (1) since the quality of this crystal is slightly better than that of the measured single crystal prepared with the rational method (1′). Compound 1 crystallizes in the monoclinic P21/m space group. The Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2 polymeric unit has B


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Inorganic Chemistry

atom of the water molecule, O6, occupy the axial positions (see Figure 1 and Table 2). The tetragonality parameter, T (defined as the ratio between the in-plane and out-of-plane average Cu− X bond lengths),50 is 0.84. In the CuN2O4 coordination environment the two axial Cu1−O3 and Cu1−O6 distances are different (Δd = 0.0868(2) Å), resulting in a 4 + 1 + 1 coordination environment. Distortion from a regular octahedral geometry is observed for the CuN2O4 coordination environment, with a cis X−Cu1−X angle range 80.76(5)−97.67(6)° and a trans X−Cu1−X angle range 169.01(5)−171.24(4)° (see Table 2). The pyrimidyl rings of the bipyrimidine molecule are coplanar (mean deviation 0.0085 Å), which is in agreement with the observed values in related compounds where the bpym acts as bis(bidentate) bridging ligand.35−40 The formato ligand acts in a syn−syn coordination bridging mode. The Cu−Oformato bonds are roughly coplanar with the carboxylato bridge with a Cu1−O1−C1−O1i torsion angle of 4.2(4)°. The copper atom is 0.116(11) Å out of the O1−C1− O1i formato plane. This topology is in agreement with the syn− syn coplanar bridging mode usually found in the formato bridges.41,42The Cu−O bond distances are significantly shorter in the hydroxido bridge, Cu1−O2 = 1.9111(11) Å, than in the sulfato one, Cu1−O3 = 2.3332(13) Å. As a consequence of these different metal−oxygen bond lengths found for this bridging ligands, the Cu1−O2−Cu1i bond angle in the hydroxido bridge (103.53(8)°) is much larger than the corresponding Cu1−O3−Cu1i angle in the sulfato bridge (80.12(6)°). The μ-sulfato-1κO:2κO bridge shows the expected tetrahedral geometry, with bond lengths and angles in agreement with those reported previously for other similar μ-sulfato-1κO:2κO bridges.51,52 All four S−O bond distances are similar, being the longest the S1−O5B one, probably due to its participation in two moderate/strong hydrogen bonds (see below and Table 3). Moreover, all six O−S1−O angles are very close to the expected ones for a tetrahedral geometry, with a mean value of 109.75°.

Figure 1. Ellipsoid plot of a [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]2(bpym) moiety of compound 1 (50% probability level) showing Cu1−FHS−Cu1i (i: x, −y + 1/2, z) and Cu1−bpym−Cu1ii (ii: −x, −y, −z + 1) bridges. Cu···Cu distances: Cu1···Cu1i 3.0034(4) Å and Cu1···Cu1ii 5.4849(4) Å.

Figure 2. Experimental (red) and simulated (black) X-ray powder diffraction patterns for compound 1.

both a mirror plane passing through all formato, sulfato, and hydroxido ligands and an inversion center passing through the C(2)−C(2)ii bond (Figure 1). One and a half crystallization H2O molecules for every Cu atom are present in the crystal. The main bond distances and angles are given in Table 2. The coordination polyhedron around the copper(II) ions is a cis-CuN2O4 distorted octahedron. The equatorial plane is formed by two bpym ligand nitrogen atoms, N1 and N3, an oxygen atom of the formato ligand, O1, and the oxygen atom of the bridging hydroxido group, O2. The coordinated oxygen atom of the bridging sulfato, O3, and the coordinated oxygen

Table 3. Hydrogen Bonds in Compound 1a

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1

X−H···Y iii

O(2)−H(2)···O(4) O(6)−H(6A)···O(4)iii O(8)−H(8A)···O(4)iii O(7)−H(7A)···O(5A)iii O(7)−H(7A)···O(5B)iv O(7)−H(7B)···O(8)v O(8)−H(8B)···O(7)vi

Cu Atom Cu(1)−N(1) Cu(1)−N(3) Cu(1)−O(1) O(2)−Cu(1)−O(1) O(2)−Cu(1)−N(3) O(1)−Cu(1)−N(3) O(2)−Cu(1)−N(1) O(1)−Cu(1)−N(1) N(3)−Cu(1)−N(1) O(2)−Cu(1)−O(3) O(1)−Cu(1)−O(3) S(1)−O(3) S(1)−O(5B) O(5A)−S(1)−O(3) O(5A)−S(1)−O(4) O(3)−S(1)−O(4) C(1)−O(1)

2.0514(14) 2.0388(14) 1.9638(12) 97.54(6) 170.54(7) 89.10(5) 93.04(6) 169.01(5) 80.76(5) 83.10(6) 89.02(6) Sulfato

Cu(1)−O(2) Cu(1)−O(3) Cu(1)−O(6) N(3)−Cu(1)−O(3) N(1)−Cu(1)−O(3) O(2)−Cu(1)−O(6) O(1)−Cu(1)−O(6) N(3)−Cu(1)−O(6) N(1)−Cu(1)−O(6) O(3)−Cu(1)−O(6)

O(1)−C1−O(1)i

H···Y (Å)

X−H···Y (deg)

2.899(3) 2.878(3) 2.820(3) 2.626(3) 2.902(3) 2.790(2) 2.790(2)

2.31(4) 2.10(2) 2.04(2) 1.83(2) 2.14(2) 1.97(2) 1.97(2)

171.1(8) 159(4) 157(4) 165(3) 155(3) 172(4) 164(4)

Symmetry operator: iii, x + 1, y, z; iv, x + 1, −y + 1/2, z; v, x, y, z + 1; vi, x, y, z − 1. a

The structure of compound 1 is made of parallel infinite zigzag chains running along the b axis. These chains are built from Cu(II) ions which are linked by alternating triple formato/hydroxido/sulfato (FHS) bridges (Cu1−FHS−Cu1i; i: x, −y + 1/2, z) and bpym bridges (Cu1−bpym−Cu1ii, ii: −x, −y, −z + 1) (Figure 1). An alternating sequence of two different, short and long, Cu···Cu distances is present in the polymeric chain [Cu1···Cu1i 3.0034(4) Å and Cu1···Cu1ii 5.4849(4) Å]. An extensive framework of H-bond interactions involving all the anionic groups as well as the coordinated and non-

Ligand

1.4767(17) S(1)−O(5A) 1.501 (3) 109.29(13) O(5A)−S(1)−O(5B) 111.45(17) O(3)−S(1)−O(5B) 108.27(12) O(4)−S(1)−O(5B) Formato Ligand (i: x, −y + 1/2, z) 1.2536(16)

1.9119(11) 2.3332(13) 2.4200(16) 90.32(5) 95.23(6) 89.38(6) 87.52(7) 97.67(6) 89.62(7) 171.24(5)

X···Y (Å)

1.447(3) 110.0(2) 110.37(11) 107.39(16) 128.4(2) C


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Inorganic Chemistry

Figure 3. (a) Crystal packing view along the c axis showing the interchain H-bonds. (b) Detail of the network around the sulfato ligands. (c) View of the layer assembly along the b axis.

chain with its four nearest neighbors along the a and c directions forming the 3D crystal packing [O(7)−H···O(8)v; v: x, y, z + 1] (Figure 3c). The triple μ-formato-1κO:2κO′/μ-hydroxido-1κO:2κO/μsulfato-1κO:2κO (FHS) bridge present in compound 1 is, no doubt, the most original structural aspect of this compound. In fact, a search in the CCDC database (updated November 2015) shows no example of this kind of triple FSH bridge for any metal. If we search for copper complexes with triple Cu−Cu bridges, we can only find four examples containing a μ-formato1κO:2κO′ bridge plus two additional oxygen-based bridging ligands. In these four compounds the additional oxygen-based bridging ligands are two hydroxido,54 a hydroxido and a methoxido,55 two alkoxido,56 or a hydroxido and a μ-formato1κO:2κO.57 There is no example of Cu−Cu triple bridges with one of them a μ-sulfato-1κO:2κO bridge. Of course, if we look for Cu−Cu triple bridges with at least one hydroxido bridge and two additional one-atom oxygen-based bridges, then the number of examples increases to 19 although it is still limited since the total number of copper complexes with triple oneatom oxygen-based Cu−Cu bridges is quite reduced (only 36 examples have been reported to date). Magnetic Properties. The product of the molar magnetic susceptibility per Cu(II) ion (χm) times the temperature (χmT)

coordinated water molecules results in a three-dimensional network structure (Figure 3). This 3D assembly is primarily induced by moderate/strong hydrogen bonds (Figure 3 and Table 3). Both types of water molecules, crystallization (O7 and O8) and coordinated (O6), together with the hydroxido and sulfato ligands, are involved in moderate/strong hydrogen bonds.53 The corresponding O···O and O−H···O bond distances and O−H···O bond angles are shown in Table 3. The sulfato ligand of one chain acts as a hydrogen bond acceptor of two coordinated water molecules [O6−H···O4iii and O6i−H···O4iii; iii: x + 1, y, z] and of the hydroxido bridge [O2−H···O4iii] of a different chain (Figure 3), giving rise to layers perpendicular to the c axis. Additionally, the sulfato ligand acts as a hydrogen bond acceptor of three crystallization water molecules [O8−H···O4iii, O7−H···O5Aiii, and O7i−H··· O5Biv; iv: x + 1, −y + 1/2, z]. Thus, the sulfate anion is connected to all the water molecules and to the hydroxido ligand through a total of six H-bonds. These H-bonds form five cyclic networks: one R88(20), one R68(16), one R34(8), and two R44(10) (Figure 3b). This large number of H-bonds may be one of the reasons explaining the inclusion of the sulfato bridge and the formation of this unprecedented triple FHS bridge. All these H-bonds, together with those formed between the coordinated and crystallization water molecules, connect each D


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Inorganic Chemistry

μ-sulfato-1κO:2κO bridges (see below) show moderate/strong ferromagnetic couplings. Therefore, we can assume that 1 must behave as an alternating ferro/antiferromagnetic chain. The appropriate Hamiltonian for this model may be written as

for the title compound shows at room temperature a value of ca. 0.35 cm3 K mol−1, close to the expected value for an isolated S = 1/2 Cu(II) ion with g ≈ 2. When the sample is cooled, the χmT product shows a continuous decrease to reach a value close to zero at low temperatures (Figure 4). This behavior suggests

n /2

Ĥ = −J ∑ (S2̂ i·S2̂ i − 1 − αS2̂ i·S2̂ i + 1) i=1

where J is the exchange integral between a Cu(II) ion and one of its nearest neighbors and αJ is the exchange interaction of the same Cu(II) ion with the other nearest neighbor along the chain. A numerical expression for the generation of the magnetic susceptibility has been obtained by one of us.58 A very satisfactory fit in the whole temperature range is obtained with the following set of parameters: g = 2.103, JAF = −139 cm−1, JF = 116 cm−1 (α = JF/|JAF| = 0.83), and a monomeric paramagnetic impurity ρ = 0.6% (solid lines in Figure 4). Magneto-Structural Correlations. Table 4 shows the more relevant data for all the magnetically and structurally characterized copper(II) alternating 1-D chains containing bpym bridges. As can be seen in Table 4, the JAF value obtained in the title compound (−139 cm−1) is similar to those reported for the same bpym bridge in other chain compounds (in the −90 to −213 cm−1 range, with an average value of ca. −150 cm−1). Despite the relatively large Cu···Cu separation (ca. 5.4− 5.9 Å), these moderate/strong AF interactions are observed in those systems where both N atoms of the bpym ligand occupy equatorial positions35−40 (eq−eq cases in Table 4) and are attributed to the good overlap between the magnetic orbitals (built up essentially from the dx2−y2 Cu(II) orbitals) and the delocalized orbitals of the bpym bridges.40 Several attempts have been performed to analyze the more relevant structural features in order to explore the existence of magneto-structural correlations in [Cu(bpym)Cu] systems, but

Figure 4. Thermal variation of the χmT product per Cu(II) ion for compound 1. Inset shows the thermal variation of χm. Solid lines are the best fit to the alternating ferro/antiferromagnetic chain model (see text).

the presence of predominant antiferromagnetic interactions in the title compound. The broad maximum observed at ca. 120 K in the thermal variation of χm (inset in Figure 4) confirms the presence of predominant antiferromagnetic interactions in compound 1. Since the structure of compound 1 shows the presence of alternating bpym and triple FHS bridges, we can, in principle, assume that the magnetic properties of 1 correspond to an alternating chain. It is well-known that bpym bridges in Cu(II) complexes give rise to moderate/strong antiferromagnetic coupling (see Table 4). Although our triple FHS bridge is unprecedented, the reported Cu(II) complexes with triple oxygen-based bridges containing μ-carboxylato-1κO:2κO′ and

Table 4. Relevant Data for All the Structurally and Magnetically Characterized Copper(II) Alternating Chains Containing Bis(bidentate) bpym Bridges compd

alternating bridge

PEMPIG10 YIKMOU YIKMUA HIWBUK

(μ-OH)2 (μ-OH)2 (μ-OH)2 oxpn

NASLOJ BAWKIW BAWKOW BAWKUH KODLAS

tcpd (μ-OH)2 (μ-OH)2 (μ-F)2 (μ-OH2) (μ-pz)2 (μ-OH2) (μ-3-Mepz)2 (μ-OH) (μ-3,5-Me2pz)2 (μ-OH) (μ-HCO2) (μ-OSO3)

KODLEW KODLIA 1

donor set

geoma

Nbpymb

Cu−Cuc (Å)

Cu−Cud (Å)

γe (deg)

ϕf,g (deg)

N2O3 N2O3 N2O4 N2O3 N2O4 N4O2 N2O4 N2O4 F3N2O N4O2

SPY SPY EO SPY EO EO EO EO EO EO

eq−eq eq−eq eq−eq eq−ax

5.473 5.461 5.452 5.766

2.866 2.854 2.860 5.225

6.5 0 0 69.5

10.7 2.7 0.9 82.8

−140 −135 −145 −82

+105 +98 +160 −340

35 35 35 36

eq−eq eq−eq eq−eq eq−ax eq−eq

5.505 5.428 5.449 5.925 5.544

7.020 2.832 2.824 3.303 3.313

0 0 0.3 0 3.5

3.9 4.7 4.1 89.2 7.3

−90 −149 −141 −0.30 −211

≈0 +194 +176 −8.1 −217

37 39 39 39 40

N4O2

SPY

eq−eq

5.538

3.235

7.1

8.8

−213

−215

40

N4O

SPY TBP EO

h

5.767

3.322

h

h

−44

−153

40

eq−eq

5.485

3.004

1.8

7.5

−139

+116

this work

N2O4

Jbpym (cm‑1)

JX (cm‑1)

ref

a

Geometry: SP = square-planar; SPY = square pyramidal, EO = elongated octahedral; TBP = trigonal bypiramidal. bCoordination site of the bpym nitrogen atoms. cCu−Cu separation across the bpym bridge. dCu−Cu separation across the alternating bridge. eAngle between equatorial planes (bpym bridge). fAngle between equatorial planes and mean plane of the bpym molecule. gMean values. hIn this compound the geometry is intermediate between SPY and TBP and the position of the Nbpym cannot be easily determined. oxpn = N,N′-bis(3-aminopropyl)oxamidate; tcpd = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide; H-3-Mepz = 3-methylpyrazolato; 3,5-Me2pz = 3,5-dimethylpyrazolato. E


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Inorganic Chemistry

Table 5. Relevant Structural and Magnetic Data for All the Copper(II) Compounds Triply Bridged Containing Both μHydroxido-1κO:2κO and μ-Carboxylato-1κO:2κO′ Bridging Ligands in Equatorial Positions

a

compd

geometry

ϕa(deg)

τb(deg)

Cu···Cu (Å)

Cu−OH−Cu (deg)

J (cm‑1)

ref

AGIZEW CITLOH CITLUN DEQFOU DORSAF ELAZAT GIKMUJ JEJCIC10 KAMVID LELZUZ LEMBAI LEMBEM LEMBIQ LEMBOW LEMBUC LEMCAJ NEQGIZ NEQGOF OCERIY PATFOG QAQTUZ QAQVAH RELMOK SAQWOW UJIGAV XAFCEM XUGFEK XUGFIO YAFZOU YAFZUA YEMNEK YEMNIO ZEGYAN ZEGYOB ZOJSIA 1

SPY SPY SPY EO SPY/SP EO SPY/SP SPY SPY SPY SPY SPY SPY SPY SPY SPY SPY SPY SP SPY/EO SPY SPY SPY EO SPY/EO SPY/EO SPY/SQ SPY/EO SPY SPY SP SP SPY SPY EO EO

120.7 115.0 123.0 105.8 120.5 92.8 121.0 118.1 117.5 119.0 122.1 120.2 122.1 115.0 118.7 112.3 147.7 150.2 180.0 122.8 119.1 154.8 139.3 143.6 118.6 128.0 121.8 125.6 122.8 122.7 120.1 114.0 150.9 180.0 141.6 108.9

173.1 146.7 176.3 164.6 177.9 166.6 169.1 174.5 177.7 176.1 173.1 177.9 175.9 172.3 178.8 173.3 170.6 168.6 177.2 176.5 173.5 178.1 173.2 168.9 169.9 177.9 175.1 176.9 177.5 178.6 176.4 161.8 175.8 167.5 172.7 175.8

3.08 3.00 3.04 3.33 3.13 3.16 3.08 3.04 3.16 3.02 3.08 3.06 2.98 3.01 3.01 2.98 3.39 3.37 3.28 3.36 3.02 3.34 3.25 3.49 3.12 3.20 3.16 3.17 3.02 3.01 3.04 2.99 3.42 3.37 3.46 3.00

107.4 102.5 103.3 122.0 109.8 111.5 108.0 103.8 109.3 103.4 107.3 105.6 101.1 102.4 102.6 100.8 124.0 123.3 122.4 128.3 104.6 122.3 114.9 131.2 119.9 115.0 112.6 113.3 103.3 103.6 104.5 101.3 132.2 126.2 123.6 103.5

82.2 120.5 145.3 −29.0 76.0 −33.9 0.2 19.3 1.3 102.1 72.6 90.2 104.3 98.7 92.1 103.1 −10.0 −10.0 −30.2 29.1 151.2 104.5 45.1 −152.0 7.0 9.0 59.1 94.0 111.0 109.0 149.0 120.0 −103.6 −34.0 −66.0 +116

72 54 54 73 74 75 76 77 78 61 61 61 61 61 61 61 79 79 80 81 60 60 82 83 84 67 85 85 86 86 87 87 88 88 89 this work

ϕ = angle between equatorial planes. bτ = mean value of the Cu−O−C−C′ (or Cu−O−C−H) torsion angles.

as far as we know, no satisfactory correlation has been obtained. In fact, from the structural and magnetic data reported in Table 4 no straightforward correlation between the J coupling constant and any structural parameters can be observed. With regard to the exchange interaction through the triple bridge, the observed behavior may be understood in terms of the nature of the orbitals involved in the exchange interactions together with structural considerations of the triple bridge. As has been discussed above, in the title compound the unpaired electron of the copper(II) ions is essentially located in a magnetic orbital mainly built from the dx2−y2 metallic orbital. So, the contribution of the exchange pathway through the μsulfato-1κO:2κO bridge, which occupies an axial position in both Cu(II) coordination polyhedra is expected to lead to a very weak or negligible magnetic interaction. Consequently, the observed ferromagnetic behavior has to be attributed to the exchange interactions propagated by the μ-hydroxo-1κO:2κO and μ-formato-1κO:2κO′ bridges. In a previous magneto-structural correlation in triply bridged dinuclear pentacoordinated Cu(II) compounds containing both carboxylato and hydroxido bridges, Moreira et al.59−61

established that the intensity and sign of the exchange constant coupling arises from the countercomplementarity of both bridges. Thus, in systems with two different bridging ligands, they may either add or counterbalance their effects. These phenomena, which are known as orbital complementarity or countercomplementarity, were treated by Nishida et al.,62,63 Mckee et al.,64,65 and Cano et al.66−68 As it is well-known, in hydroxido-bridged Cu(II) dinuclear complexes the observed magnetic exchange is ferromagnetic or antiferromagnetic depending on the [Cu−OH−Cu] core topology, in particular the Cu−O−Cu bond angle (θ).69,70 On the other hand, the syn−syn μ-carboxylato-1κO:2κO′ bridges propagate moderate antiferromagnetic interactions between the bridged metal atoms.71 We have extended the comparative study to copper(II) complexes where both μ-carboxylato-1κO:2κO′ and μ-hydroxido-1κO:2κO bridges occupy equatorial coordination positions, as observed in 1 (Table 5). The analysis of these data shows a considerable dispersion of the J values with respect to several structural and topological parameters, as for instance the Cu··· Cu distances, the dihedral angle between the equatorial Cu(II) F


Inorganic Chemistry

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planes, or the Cu-OCO-Cu torsion angles. However, an approximate correlation could be obtained between the J values and the Cu−O−Cu angle (see Figure 5) in agreement

Article

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 We thank the Spanish MINECO (Projects CONSOLIDERINGENIO CSD 2010-00065, CTQ201-26507, CTQ201452758-P, and MAT2014-56143-R), the Generalitat Valenciana (Prometeo-II2014/076 and ISIC projects), and the University of Valencia (project UV-INV-AE-14-268562) for financial support. Thanks are given to the Consejo Superior de ́ Investigaciones Cientificas (CSIC) of Spain for the award of a license for the use of the Cambridge Crystallographic Data Base (CSD).

Figure 5. Variation of the J parameter as a function of the Cu−OH− Cu bond angle for the compounds gathered in Table 5 (see text). Red point corresponds to compound 1.

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with previous experimental and theoretical studies69,70 and with the fact that, among the three bridges, this is the most important one in determining the magnetic coupling (see above). Notwithstanding, it must be stressed that significant deviations of the outlined correlation are observed for some compounds, suggesting that the carboxylato bridge and other factors may also play an important role in determining the global magnetic coupling in this kind of triply bridged copper complex. With this rough correlation and a Cu−OH−Cu bond angle of 103.53(8)° in 1, we can estimate a ferromagnetic coupling constant of ca. 100 cm−1 for the triple bridge in 1, in agreement with the experimental value (JF = 116 cm−1).

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CONCLUSIONS Here we have reported the crystal structure and magnetic characterization of compound [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1) that contains the first example of a triple formato/hydroxido/sulfato (FHS) bridge for any metal. Compound 1 presents a chain structure with triple FHS bridges alternating with 2,2′-bipyrimidine ones. Although the structure of this compound showed the unexpected and serendipitous presence of μ-sulfato-1κO:2κO bridges, a posterior rational design of the synthesis allowed us to obtain compound 1 as a pure phase in large quantities. The magnetic properties of 1 show that it is an alternating ferro/antiferromagnetic S = 1/2 chain compound with predominant antiferromagnetic interactions that can be well-reproduced with JAF = −139 cm−1 for the bpym bridge and JF = 116 cm−1 for the triple FHS bridge (α = JF/|JAF| = 0.83). The antiferromagnetic coupling constant is within the range found in many other bpym-bridged Cu(II) complexes, and the ferromagnetic coupling is very close to the estimated one from magneto-structural correlations in triply Cu−Cu bridged compounds with hydroxido and carboxylato bridges located in equatorial positions.

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REFERENCES

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00105. X-ray crystallographic data for 1 (CIF) X-ray crystallographic data for 1′ (CIF) G


Article

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