Cu(II) Complex Derived from N

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Unprecedented Mixed-Valence Cu(I)/Cu(II) Complex Derived from N‑Methyl-1,3,5-triaza-7-phosphaadamantane: Synthesis, Structural Features, and Magnetic Properties Alexander M. Kirillov,*,† Małgorzata Filipowicz,‡ M. Fátima C. Guedes da Silva,†,§ Julia Kłak,‡ Piotr Smoleński,*,‡ and Armando J. L. Pombeiro*,† †

Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Avenida Rovisco Pais, 1049-001 Lisbon, Portugal ‡ Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383, Wroclaw, Poland § Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Avenida do Campo Grande, 376, 1749-024, Lisbon, Portugal S Supporting Information *

ABSTRACT: The unique mixed-valence tetracopper(I/II) complex [Cu4I4(μ-N3)2(N3)4(μ-PTA-Me)2(PTA-Me)2]·2H2O (1), composed of the hexaazido dicopper(II) core {Cu2(μ-N3)2(N3)4}2− and two copper(I) {CuI2(μ-PTA-Me)(PTA-Me)}+ units, has been easily generated by self-assembly in water from copper(II) nitrate, Nmethyl-1,3,5-triaza-7-phosphaadamantane iodide, [PTA-Me]I, and sodium azide. It has been characterized by IR, 1H and 31P{H} NMR, and EPR spectroscopies and elemental and single-crystal X-ray diffraction analyses. Apart from representing the first mixed-valence metal compound bearing PTA or any cage-like aminophosphine derivative, 1 also discloses a rare P,N-coordination mode of PTA-Me ligands, which act, for the first time, as spacers between the Cu(I) and Cu(II) centers. Magnetic susceptibility and EPR studies reveal a ferromagnetic interaction (2J = +17.1 cm−1) between the Cu(II) atoms through μ-1,1-azido ligands.

N

been described, 2a−d there was still no example of a homometallic mixed-valence complex bearing PTA or any related aminophosphine ligand, among over 300 structurally characterized PTA derivatives.9 The filling of this gap thus constitutes the main objective of the present study, while the second objective consists in probing the still unexplored coordination ability of the N-methyl-1,3,5-triaza-7-phosphaadamantane [PTA-Me]+ ligand to a copper(II) center. Hence, we describe herein the easy synthesis, full characterization, X-ray crystal structure, and magnetic properties of the unprecedented tetracopper(I/II) complex [Cu 4 I 4 (μN3)2(N3)4(μ-PTA-Me)2(PTA-Me)2] (1), which represents the first mixed-valence compound bearing PTA or any related cage-like aminophosphine. The combination in water of copper nitrate, [PTA-Me]I, and sodium azide results in the selfassembly formation of 1 (Scheme 1), wherein the hexaazido dicopper(II) {Cu2(μ-N3)2(N3)4}2− core is linked to two copper(I) {CuI2(μ-PTA-Me)(PTA-Me)}+ units through P,Ncoordinated PTA-Me spacers. Interestingly, the same reagents,

owadays, the cage-like aminophosphine 1,3,5-triaza-7phosphaadamantane (PTA) and its various derivatives are particularly important ligands in aqueous organometallic chemistry due to their solubility and stability in water and rich coordination chemistry.1 This research field has recently gained further impetus from the observation of unusual N,Pcoordination modes of PTA cores2 and the development of new synthetic strategies3,4 that allow the rational use of such aminophosphine ligands as multidentate building blocks. With regard to copper, a number of complexes and coordination polymers derived from PTA or N-alkyl-1,3,5triaza-7-phosphaadamantanes, [PTA-R]X (R = Me, Et, nPr, n Bu; X = I, Br), have emerged in recent years,4−8 also finding interest in medicinal chemistry,6 photoluminescence,7 and crystal engineering.4,8 Owing to the reducing ability of PTA cores, the majority of the obtained compounds were Cu(I) complexes, although their syntheses were usually based on a Cu(II) starting material.4−8 Moreover, the presence of soft Pand hard N-donor atoms within the PTA cages, along with their already recognized ability to act as P,N-spacers,4 can allow the synthesis of heterometallic or mixed-valence complexes. These can potentially show a synergic effect in biological, catalytic, or any other activity. Although a few heterometallic compounds (mainly coordination polymers) with PTA spacers have already © XXXX American Chemical Society

Special Issue: Copper Organometallic Chemistry Received: June 19, 2012

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instead of [PTA-Me]I furnished the 1D Cu(I) coordination polymer [Cu(μ-N3)(μ-PTA)]n.4b These observations indicate that the coordination modes of the PTA-Me cages and the resulting self-assembled products therefrom depend on the presence of iodide and azide ions playing the role of auxiliary ligands. Compound 1 has been isolated in 78% yield as an airstable, brownish-green crystalline solid, and its molecular structure has been established by single-crystal X-ray diffraction and supported by elemental analysis and IR, NMR, and EPR spectroscopies. An interesting feature of 1 concerns its solution NMR spectra. In spite of the presence of Cu(II) ions, the terminal PTA-Me ligands coordinated to diamagnetic Cu(I) atoms appear to be far from paramagnetic centers and could be detectable by NMR techniques. Hence, the 1H NMR spectrum of 1 in DMSO-d6 is typical for nonequivalent methylene protons of the NCH2N, NCH2N+, and PCH2N moieties within the PTA-Me cages, except for the PCH2N+ group, which appears as a singlet at δ 4.39.10 Apart from the methylene protons, a broad singlet due to the methyl groups of PTA-Me is detected at δ 2.67. The 31P{1H} NMR spectrum of 1 in DMSO-d6 shows a very broad singlet at δ −65 with a

Scheme 1. Aqueous Medium Self-Assembly Synthesis and Structural Formula of 1

but in the absence of NaN3, resulted in the generation of a monomeric Cu(I) product, [CuI(PTA-Me)3](I)3,7 bearing only P-coordinated PTA-Me moieties, whereas the use of PTA

Figure 1. Crystal structure of 1: (a) ellipsoid plot (50% probability) with partial atom-labeling scheme; (b) ball-and-stick plot with polyhedral representation of the coordination environments around the Cu1 and Cu2 atoms. All H atoms and crystallization H2O molecules are omitted for clarity. Color codes: Cu (green), N (blue), P (orange), I (purple), C (cyan). Selected distances (Å) and angles (deg): Cu1−P1 2.2314(12), Cu1−P2 2.2259(11), Cu1−I1 2.6438(9), Cu1−I2 2.6756(7), Cu2−N1 1.948(4), Cu2−N4 1.955(3), Cu2−N7 2.021(3), Cu2−N7i 2.014(3), Cu2−N23 2.509(3), Cu2···Cu2i 3.1589(10), Cu1···Cu2 6.626(1), Cu1···Cu1i 14.063(2); P2−Cu1−P1 126.83(5), P2−Cu1−I1 115.38(4), P1−Cu1−I1 100.82(4), P2−Cu1−I2 93.23(4), P1−Cu1−I2 105.69(4), I1−Cu1−I2 115.01(4), N1−Cu2−N4 98.64(15), N1−Cu2−N7 90.76(14), N4−Cu2− N7 163.67(16), N7i−Cu2−N7 76.94(14), N1−Cu2−N7i 167.16(15), N4−Cu2−N7i 92.52(14), N7−Cu2−N23 95.60(13), N1−Cu2−N23 96.49(14), N4−Cu2−N23 96.57(14), N23−Cu2−N7i 88.41(14), Cu2−N7−Cu2i 103.06(14), N1−N2−N3 175.7(5), N7−N8−N9 179.4(5). Symmetry code: (i) 2−x, 2−y, 2−z. B

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coordination shift (Δδ = δcomplex 1 − δ[PTA‑Me]I = 31) that is in agreement with P-bound aminophosphine.10 In general, the NMR data are comparable to those of previously reported Cu(I) complexes with P- and P,N-coordinated PTA-Me ligands.4a,7 In contrast to 1, no PTA signals were observed in the NMR spectra of the Cu(II)/Re(III) cluster [Re6Cu(μ3Se)8(PEt3)5(NO3)3(PTA)]SbF6·2MeCN due to the closeness of the PTA ligand to the Cu(II) center, despite the detection of resonances of PEt3 groups coordinated to Re(III) atoms.8a The IR spectrum of 1 exhibits a set of bands in the 1450− 550 cm−1 range typical for PTA-Me moieties.4a,7,10 In addition, there are weak ν(CH) vibrations in the 2970−2930 cm−1 interval and a strong, broad ν(H2O) band with a maximum at 3456 cm−1 due to crystallization water molecules.11 The most characteristic feature concerns two very strong and partially overlapping νas(N3) bands with maxima at 2054 and 2025 cm−1, which are in good agreement with the terminal and bridging nature of azido ligands coordinated to Cu(II) atoms.11−13 The X-ray crystal structure of 1 bears the neutral [Cu4I4(μN3)2(N3)4(μ-PTA-Me)2(PTA-Me)2] tetranuclear complex and two crystallization water molecules per formula unit (Figure 1). The complex is centrosymmetric with the inversion center situated at the midpoint of the hexaazido dicopper(II) unit, {Cu2(μ-N3)2(N3)4}2−, which binds two copper(I) {CuI2(μPTA-Me)(PTA-Me)}+ fragments through μ-PTA-Me spacers. The “side” four-coordinate Cu1 atoms adopt the {CuI2P2} trigonal pyramidal environments (τ4 = 0.84),14a filled by two iodide ligands [Cu1−I1 2.6438(9), Cu1−I2 2.6756(7) Å] and the P1 and P2 atoms of terminal and bridging PTA-Me moieties [Cu1−P1 2.2314(12), Cu1−P2 2.2259(11) Å], respectively (Figure 1). The major deviations from the idealized tetrahedral geometry concern the P2−Cu1−P1 [126.83(5)°] and P2−Cu1−I2 [93.23(4)°] angles, with the average bond angle around the Cu1 atom being ∼109.49°. The “central” fivecoordinate Cu2 atoms exhibit slightly distorted {CuN5} square pyramidal geometries (τ5 = 0.06),14b formed by the N1 and N4 atoms of terminal azido groups [Cu2−N1 1.948(4), Cu2−N4 1.955(3) Å] and the N7 and N7i atoms of μ-1,1-azido ligands [Cu2−N7 2.021(3), Cu2−N7i 2.014(3) Å] in basal positions, while the apical site is taken by the N23 atom [Cu2−N23 2.509(3) Å] from the bidentate P,N-coordinated PTA-Me spacers. Within the planar Cu2−N7−Cu2i−N7i core the Cu2 atoms are separated by 3.1589(10) Å, while the representative N7−Cu2−N7i and Cu2−N7−Cu2i angles are 76.94(14)° and 103.06(14)°, respectively. Both the terminal and bridging azido ligands are essentially linear, as attested by the N1−N2−N3 [175.7(5)°] and N7−N8−N9 [179.4(5)°] bond angles. In general, the bonding parameters of 1 are comparable to those reported for related copper compounds bearing azido13 or Nalkyl PTA moieties.4a,7 Although the unconventional P,Ncoordination mode of PTA cores has already been observed in some other Cu(I) compounds,4a,7 1 is a unique example wherein PTA-Me or any other cage-like PTA derivative acts as a spacer between the homometallic centers of different valences. In addition, a noteworthy feature of 1 concerns the presence of both terminal and bridging PTA-Me ligands, since mixed coordination modes have not yet been detected in Nalkyl PTA derivatives.9 Furthermore, complex 1 and the previously reported tetrairidium carbonyl derivative15 represent the only examples of tetranuclear complexes bearing cage-like PTA ligands.

The EPR powder spectra of 1 recorded in the X-band at 293 and 77 K indicate two poorly resolved lines related to g⊥ = 2.06 and g∥ = 2.26 parameters (Figure S1). The observed EPR spectrum is the average pattern of two copper(II) centers in the ligand field of the distorted square pyramidal symmetry. Moreover, in a low-field part of the spectrum the ΔMS = 2 transition has been detected, confirming the exchange interaction between the Cu(II) centers in the {Cu2(μN3)2(N3)4}2− units. Compared with the spectrum at 77 K, the signals at 293 K are much sharper and stronger. The magnetic properties of 1 were determined over the temperature range of 1.8−300 K. Plots of magnetic susceptibility χm−1 and χmT product versus T are given in Figure 2. The value χmT at 300 K equals 0.775 cm3 mol−1 K,

Figure 2. Temperature dependence of experimental χmT (○) and χm−1 (●) for complex 1. The solid line is the calculated curve derived from eqs 1 and 2.

which roughly corresponds to the value expected for the two noncoupled copper(II) ions (χmT = 0.749 cm3 mol−1 K). Upon cooling, the χmT product increases significantly, attaining a value of 1.04 cm3 mol−1 K at 1.8 K. This is slightly higher than the spin-only value (μeff = 2.83 μB) calculated for the S = 1 ground state expected for the two ferromagnetically coupled Cu(II) atoms with g = 2.00. The increase of χmT upon cooling indicates that the triplet is the ground state, and the interactions between the copper(II) ions are transmitted by azido bridges being of ferromagnetic nature. The values of the Curie and Weiss constants determined from the relation χm−1 = f(T) over the 1.8−300 K temperature range are equal to 0.778 cm3 mol−1 K and 3.3 K, respectively. A positive value of the Weiss constant also confirms the occurrence of ferromagnetic interactions between the copper centers in the {Cu2(μ-N3)2(N3)4}2− core. To confirm the nature of the ground state of 1, we investigated the variation of the magnetization, M, with respect to the field, at 2 K. The results are shown in Figure 3, where the molar magnetization M is expressed in μB units. The compound does not reach saturation in the applied field range, and the magnetization at 5 T is equal to 1.90 μB. The magnetization data have been compared with the sum of the Brillouin functions of two isolated Cu(II) atoms, as well as with the Brillouin function of the S = 1 pair state. The experimental magnetization of 1 is greater than that for two independent S = 1 /2 systems, being very close to the Brillouin function of the S = C

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nearly total magnetic isolation of the dicopper(II) subunits in the crystal lattice. Literature examples show that in dibridged complexes with symmetric end-on azido ligands the interaction between the copper(II) ions is usually strongly ferromagnetic, whereas in compounds with asymmetric end-on azido bridges the interaction is either weakly ferromagnetic or antiferromagnetic.18 In complexes with two symmetric end-on azido bridges, the Cu−Nazido bond lengths are usually shorter than 2.10 Å and the interaction between the metal ions is often strongly ferromagnetic. In contrast, compounds bridged by asymmetric end-on azido groups with both short (2.10 Å) and long (2.20 Å) Cu−Nazido bond lengths are rare, and the interaction between metal centers is weakly ferromagnetic or even antiferromagnetic.19 At the same time, for copper(II) complexes with symmetric end-on azido bridges, Ruiz et al. found that the ferromagnetic coupling decreases upon increasing the Cu−N−Cu (θ) bond angle, eventually reaching an antiferromagnetic behavior for θ ≥ 104°.20 For 1, both the θ value [103.06(14)°] and the Cu−Nμ‑azido distances [2.021(3), 2.014(3) Å] are close to those of other related compounds and smaller than the critical value proposed by Ruiz et al.20 Some structural distortions may result in the reduction of orthogonality between the magnetic orbitals, decreasing the ferromagnetic coupling constant. In summary, the present study has widened the family of cage-like aminophosphine metal complexes to a new example, [Cu 4 I 4 (μ-N 3 ) 2 (N 3 ) 4 (μ-PTA-Me) 2 (PTA-Me) 2 ]·2H 2 O (1), which has been easily self-assembled in aqueous medium. This compound shows a number of novel features, namely, it (i) represents the first mixed-valence metal complex bearing PTA or any derived ligand, (ii) discloses the rare P,Ncoordination mode of PTA-Me moieties that act, for the first time, as spacers between the Cu(I) and Cu(II) centers, and (iii) shows the mixed P- and P,N-coordination modes of PTA-Me ligands that have not been reported previously. Moreover, the magnetic behavior of 1 has been studied by magnetic susceptibility and EPR methods, revealing its ferromagnetic nature and thus contributing to the still limited application of PTA-based materials in molecular magnetism.1 Further research toward the exploration of cage-like aminophosphine ligands as multidentate building blocks in the design of functional metal−organic materials and the search for their expected diverse applications will be pursued.

Figure 3. Field dependence of the magnetization for complex 1. The solid line is the Brillouin function curve for the S = 1 state of the Cu(II)/Cu(II) unit; the dashed line is the Brillouin function for two uncoupled S = 1/2 systems.

1 state. These results also confirm the ferromagnetic coupling between the copper(II) atoms. The crystal structure of 1 reveals a tetracopper Cu(I)Cu(II)Cu(II)Cu(I) arrangement, in which two “side” Cu(I) atoms are four-coordinate, while two “central” Cu(II) atoms assume the square pyramidal geometry. Since the “side” Cu(I) ions are diamagnetic, the magnetization in this sample results only from the two Cu(II) (d9, S = 1/2) ions. Hence, from the magnetic point of view, this compound will be considered as a Cu(II)/ Cu(II) dimer. The energy separation (2J) between the ground triplet and excited singlet states can be derived from the Bleaney−Bowers expression (eq 1) for the magnetic susceptibility for two exchange-coupled copper(II) ions.16 The data have been fit to a model that assumes the exchange Hamiltonian H = −2JS⃗1·S⃗2 for S1 = S2 = 1/2.16 To elucidate the significance of exchange between the dicopper(II) subunits in the crystal lattice, a molecular field correction term was also included (eq 2).17 χm = χmcorr

⎤ 2Nβ 2g 2 ⎡ 1 ⎢⎣1 + exp( − 2J /kT )⎥⎦ 3kT 3

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(1)

χm

= 1−

2zJ ′ χ Nβ 2g 2 m

EXPERIMENTAL SECTION

Synthesis of [Cu4I4(μ-N3)2(N3)4(μ-PTA-Me)2(PTA-Me)2]·2H2O (1). To an aqueous solution (8 mL) containing Cu(NO3)2·3H2O (5.0 mmol, 1.208 g) was added an aqueous solution (40 mL) of [PTAMe]I (10.0 mmol, 2.991 g) and solid NaN3 (50.0 mmol, 3.250 g). The resulting deep greenish-brown suspension was stirred at 45 °C for 1 h and then filtered off. The deep green filtrate was kept for several days at room temperature (rt, ∼25 °C), resulting in the formation of brownish-green X-ray quality crystals, which were collected and dried in air to give 1 (∼30% yield). The remaining part of the filtrate was stored in a refrigerator at +4 °C for several days, resulting in the formation of a precipitate. This was filtered off, washed with cold water (2 × 2.5 mL) and acetone (2 × 10 mL), and dried in air to furnish the second crop of 1 as a microcrystalline brownish-green solid (∼48% yield). The total yield was 78% (1.711 g), based on the copper(II) nitrate. Compound 1 is soluble in DMSO and barely soluble in water (S25 °C ≈ 1.5 mg mL−1). Anal. Calcd for C28H64Cu4I4N30O2P4 (Mr = 1738.7 g/mol): C, 19.34; H, 3.71; N, 24.17. Found: C, 19.83; H, 3.41; N, 24.30. 1H NMR (DMSO-d6, rt, Me4Si): δ/ppm 2.67 (s, br, 6H, N+CH3), 3.83 and 4.01 (br, J(HAHB) = 7 Hz, 8H, PCHAHBN), 4.39 (s,

(2)

In eqs 1 and 2, N is Avogadro’s number, g the spectroscopic splitting factor, β the Bohr magneton, k the Boltzmann constant, J the exchange parameter, and zJ′ the molecular field correction (interdimer interaction). A least-squares fitting of the experimental data in the whole temperature range leads to 2J = 17.7 cm−1, zJ′ = 0.04 cm−1, and g = 2.02, as indicated by the solid curve in Figure 2. The criterion used in determination of the best fit was based on minimization of the sum of squares of the deviation, R = ∑(χexpT − χcalcT)2/∑(χexpT)2 (R = 1.68 × 10−5). Results of the magnetic data calculations indicate a ferromagnetic interaction between the “central” copper(II) ions bridged by two end-on azido groups, with the value of the singlet−triplet separation 2J of +17.1 cm−1. Additionally, the value of molecular field corrections (zJ′ ≈ 0 cm−1) points out D

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br, 4H, PCH2N+), 4.29 and 4.56 (br, J(HAHB) = 10 Hz, 4H, NCHAHBN), 4.83 and 5.01 (br, J(HAHB) = 8 Hz, 8H, NCHAHBN+). 31 1 P{ H} NMR (DMSO-d6, rt, 85% H3PO4): δ/ppm −65.0 (s, br). IR (KBr, cm−1): 3456 vs br ν(H2O), 2954 w and 2944 w ν(CH), 2054 vs and 2025 vs νas(N3), 1600 w, 1445 m, 1420 w, 1384 w, 1292 m, 1245 m, 1119 m, 1092 m, 1028 m, 980 m, 926 m, 898 w, 810 m, 768 m, 745 m, and 557 w. Crystal data for 1: C28H64Cu4I4N30O2P4, M = 1738.73, triclinic, space group P1̅, a = 7.589(4) Å, b = 13.7459(12) Å, c = 14.8097(18) Å, α = 109.430(8)°, β = 101.394(5)°, γ = 98.230(7)°, V = 1391.2(8) Å3, T = 150(2) K, Z = 1, Dcalcd = 2.075 Mg m−3, μ = 3.903 mm−1, 12 877 reflections collected, 5054 unique, I > 2σ(I) (Rint = 0.0330), R1 = 0.0294, wR2 = 0.0716, GOF 1.020.

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(5) (a) Kirillov, A. M.; Smoleński, P.; Guedes da Silva, M. F. C.; Pombeiro, A. J. L. Eur. J. Inorg. Chem. 2007, 2686. (b) Wanke, R.; Smoleński, P.; Guedes da Silva, M. F. C.; Martins, L. M. D. R. S.; Pombeiro, A. J. L. Inorg. Chem. 2008, 47, 10158. (c) Pellei, M.; Alidori, S.; Camalli, M.; Campi, G.; Lobbia, G. G.; Mancini, M.; Papini, G.; Spagna, R.; Santini, C. Inorg. Chim. Acta 2008, 361, 1456. (6) (a) Santini, C.; Pellei, M.; Papini, G.; Morresi, B.; Galassi, R.; Ricci, S.; Tisato, F.; Porchia, M.; Rigobello, M. P.; Gandin, V.; Marzano, C. J. Inorg. Biochem. 2011, 105, 232. (b) Porchia, M.; Benetollo, F.; Refosco, R.; Tisato, F.; Marzano, C.; Gandin, V. J. Inorg. Biochem. 2009, 103, 1644. (c) Alidori, S.; Lobbia, G. Gioia; Papini, G.; Pellei, M.; Porchia, M.; Refosco, F.; Tisato, F.; Lewis, J. S.; Santini, C. J. Biol. Inorg. Chem. 2008, 13, 307. (7) Kirillov, A. M.; Smoleński, P.; Ma, Z.; Guedes da Silva, M. F. C.; Haukka, M.; Pombeiro, A. J. L. Organometallics 2009, 28, 6425. (8) (a) Tu, X.; Nichol, G. S.; Zheng, Z. J. Cluster Sci. 2009, 20, 93. (b) Kirillov, A. M.; Smoleński, P.; Guedes da Silva, M. F. C.; Kopylovich, M. N.; Pombeiro, A. J. L. Acta Crystallogr. 2008, E64, m603. (9) See the Cambridge Structural Database (CSD, version 5.33, May 2012): Allen, F. H. Acta Crystallogr. 2002, B58, 380. (10) Smoleński, P.; Pruchnik, F. P.; Ciunik, Z.; Lis, T. Inorg. Chem. 2003, 42, 3318. (11) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.; Wiley: New York, 1997. (12) Escuer, A.; Goher, M. A. S.; Mautner, F. A.; Vicente, R. Inorg. Chem. 2000, 39, 2107. (13) (a) Jia, Q.-X.; Bonnet, M.-L.; Gao, E.-Q.; Robert, V. Eur. J. Inorg. Chem. 2009, 3008. (b) Song, Y.-F.; Kitson, P. J.; Long, D.-L.; Parenty, A. D. C.; Thatcher, R. J.; Cronin, L. CrystEngComm 2008, 10, 1243. (c) Li, L.; Liao, D.; Jiang, Z.; Mouesca, J.-M.; Rey, P. Inorg. Chem. 2006, 45, 7665. (14) (a) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955. (b) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349. (15) Darensbourg, D. J.; Beckford, F. A.; Reibenspies, J. H. J. Cluster Sci. 2000, 11, 95. (16) (a) Kahn, O. Molecular Magnetism; VCH Publishers: New York, 1993. (b) Bleaney, B.; Bowers, K. D. Proc. R. Soc. London, Ser. A 1952, 214, 451. (17) Samuel Smart, J. Effective Field Theories of Magnetism; W.B. Saunders Co.: Philadelphia, 1966. (18) (a) Wang, Q.-L.; Jia, X.-Q.; Liao, D.-Z.; Yan, S.-P.; Cheng, P.; Yang, G.-M.; Ren, H.-X.; Jiang, Z.-H. Trans. Met. Chem. 2006, 31, 434. (b) Comarmond, J.; Plumere, P.; Lehn, J.-M.; Agnus, I.; Louis, R.; Weiss, R.; Kahn, O.; Morgenstern-Badarau, I. J. Am. Chem. Soc. 1982, 104, 6330. (c) Sikorav, S.; Bkouche-Waksman, I.; Kahn, O. Inorg. Chem. 1984, 23, 490. (d) Tandon, S. S.; Thompson, L. K.; Manuel, M. E.; Bridson, J. N. Inorg. Chem. 1994, 33, 5555. (e) Albada, G. A.; van; Lakin, M. T.; Veldman, N.; Spek, A. L; Reedijk, J. Inorg. Chem. 1995, 34, 4910. (f) Graham, B.; Hearn, M. T. W.; Junk, P. C.; Kepert, C. M.; Mabbs, F. E.; Moubaraki, B.; Murray, K. S.; Spiccia, L. Inorg. Chem. 2001, 40, 1536. (g) Woodward, J. D.; Backov, R. V.; Abboud, K. A.; Dai, D.; Koo, H.-J.; Whangbo, M.-H.; Meisel, M. W.; Talham, D. R. Inorg. Chem. 2005, 44, 638. (19) (a) Costes, J. P.; Dahan, F.; Ruiz, J.; Laurent, J. P. Inorg. Chim. Acta 1995, 239, 53. (b) Manikandan, P.; Muthukumaran, R.; Thomas, K. R. J.; Varghese, B.; Chandramouli, G. V. R.; Manoharan, P. T. Inorg. Chem. 2001, 40, 2378. (c) Koner, S.; Saha, S.; Mallah, T.; Okamoto, K.-I. Inorg. Chem. 2004, 3, 840. (d) Cortés, R.; Urtiaga, M. K.; Lezama, L.; Larramendi, J. I. R.; Arriortua, M. I.; Rojo, T. J. Chem. Soc., Dalton Trans. 1993, 3685. (20) Ruiz, E.; Cano, J.; Alvarez, S.; Alemany, P. J. Am. Chem. Soc. 1998, 120, 11122.

ASSOCIATED CONTENT

S Supporting Information *

Materials and methods, refinement details for X-ray analysis, supporting references, EPR spectra (Figure S1), and crystallographic file in CIF format for 1. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (A.M.K.), piotr.smolenski@chem. uni.wroc.pl (P.S.), [email protected] (A.J.L.P.). Phone: +351 218419207/37. Fax: +351 218464455. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the KBN program (Grant No. N204 280438), Poland, and by the Foundation for Science and Technology (FCT) (projects PTDC/QUI-QUI/121526/2010 and PEst-OE/QUI/UI0100/2011), Portugal.

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dx.doi.org/10.1021/om3005564 | Organometallics XXXX, XXX, XXX−XXX