Cr<sup>III</sup>−Cr<sup>III</sup> Interactions in Two Alkoxo-Bridged Heterometallic Zn<sub>2</sub>Cr<sub>2</sub> Complexes Self-Assembled from Zinc Oxide, Reinecke’s Salt, and Diethanolamine
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Two new tetranuclear complexes, [Zn2Cr2(NCS)4(Dea)2(HDea)2]·4DMSO (1; DMSO = dimethyl sulfoxide) and [Zn2Cr2(NCS)4(Dea)2(HDea)2]·2CH3CN (2), were prepared from zinc oxide, Reinecke’s salt, NH4[Cr(NCS)4(NH3)2]·H2O, ammonium thiocyanate, and a nonaqueous solution of diethanolamine (H2Dea) in a reaction carried out under open air. Both compounds have similar centrosymmetric crystal structures based on a tetranuclear {Zn2Cr2(μ3-O)2(μ-O)4} core. Variable-temperature magnetic susceptibility measurements of 1 and 2 show weak antiferromagnetic coupling between chromium centers. The magnetic data and high-field, high-frequency electron paramagnetic resonance spectra were analyzed in terms of the spin HamiltonianĤ=JŜ1·Ŝ2−j(Ŝ1·Ŝ2)2+μBB{g1}Ŝ1+DCr{Ŝz12−S1(S1+1)/3}+ECr(Ŝx12−Ŝy12)+μBB{g2}Ŝ2+DCr{Ŝz22−S2(S2+1)/3}+ECr(Ŝx22−Ŝy22)+D12{Ŝz1Ŝz2−Ŝ1·Ŝ2/3}+E12(Ŝx1Ŝx2−Ŝy1Ŝy2)with J = 13.7 cm−1, j = 1.1 cm−1, DCr = 0.3864 cm−1, ECr = −0.1104 cm−1, D12 = −0.1873 cm−1, and E12 = −0.0155 cm−1 for 1 and J = 9.4 cm−1, j = 0.8 cm−1, DCr = 0.3564 cm−1, ECr = −0.0647 cm−1, D12 = −0.1850 cm−1, and E12 = −0.0112 cm−1 for 2. Density functional theory (DFT) calculations were employed to calculate the zero-field splitting on Cr3+ ions. Calculations of the exchange integrals J were attempted by using the “broken-symmetry” DFT method.
