Solvatomorphs of dimeric transition metal complexes based on the V₄O₁₂ cyclic anion as building block: Crystalline packing and magnetic properties

Dinuclear [{M(phen)₂}₂V₄O₁₂] · C₆H₁₂O · H₂O (M = Co^II 1, Mn^II 2, Ni^II 3 and Cu^II 4) and [{Cu(phen)₂}₂V₄O₁₂] · 3.5H₂O 5 has been prepared by biphasic and hydrothermal syntheses, respectively. All five structures exhibit the {V₄O₁₂}^4- cluster in a chair-like configuration, covalently bonded to two [M(phen)₂]²⁺ fragments, producing a super-exchange magnetic phenomenon. The magnetic study of complexes 1-5 shows that they are very weak antiferromagnetically coupled systems, with J values of -0.14, 2; -0.64, 3 and -0.23, 4 cm^-1. Complexes 1 to 3 correspond to isostructural compounds in which the cyclovanadate group acts as a bidentate bridged ligand. In the copper complexes (4 and 5) the {V₄O₁₂}^4- anion presents the novel monodentate bridging mode, and therefore a more significant distortion from the chair-like configuration. The mentioned complexes, together with that reported in the literature, permit to conclude that it is quite common for a single molecular species to exist in more than one crystalline arrangement. A detailed analysis of the structures of 1-4 shows that the crystal symmetry cannot be strictly centrosymmetric, due to the presence of the cyclohexanol molecule with a single -OH group in the lattice.