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Abstract: The magnetic properties of [(VO)3(μ-PO4)2(2,2′-bpy)(μ-OH2)]1/3H2O (1) and (VO)2H4P2O9 (2), a tubular and a layered vanadium(IV) phosphates containing triply oxido bridged VIV dimers, are analyzed considering the Bleaney–Bowers S =1/2 dimer model. In compound 1 the presence of an additional VIV connected with the VIV dimers through μ1,2-PO4 3− bridges is described with a Curie–Weiss type correction. This model reproduces the magnetic properties of compound 1 with g =1.956, J dim =−102.1cm−1, θ =−0.4cm−1 and Nα =278×10−6 emumol−1. In compound 2, the presence of a small percentage of paramagnetic impurity has to be considered to account for the divergence of χm at low temperatures. This simple model reproduces the magnetic data of compound 2 with g =1.99, J =−62.4cm−1 and a 1.2% of monomeric impurity. The moderate antiferromagnetic coupling found in the triply oxido bridges VIV dimers is justified from the structural parameters of the bridge. These studies confirm that the coupling through –O–P–O– bridges is antiferromagnetic and relatively weak, as well as previous magneto-structural correlations in this kind of oxido bridges. DFT calculations on a dinuclear fragment model for the two systems gave the following values of J calc =−72.4cm−1 for 1 and J calc =−5.2cm−1 for 2. These values reproduce the antiferromagnetic nature of the superexchange interactions between the VIV centers. [Copyright &y& Elsevier]

Abstract: Dinuclear [{M(phen)2}2V4O12]·C6H12O·H2O (M=CoII 1, MnII 2, NiII 3 and CuII 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. [Copyright &y& Elsevier]