Magnetic properties of phosphate-bridged copper(II) organic-inorganic hybrid compounds
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Hydrothermal synthesis has allowed us to isolate and characterize three new inorganic organic hybrid materials, the compounds [Cu-2(phen)(2)(H2O)(2)(H2PO4)(2)](NO3)(2).2H(2)O (1), [(Cu(2)bipy(2))(2)(V4O9)(PO4)(2)(HPO4)(H2P2O7)](n).nH(2)O (2) and [Cu-2(dpa)(2)(V2P2O12)](n), (4), which have been magneto-structurally characterized. In addition, the magnetic behaviour of the related compound [Cu-2(bipy)(2)(VO2)(2)(PO4)(2)](n) (3), has been measured. Compound 1 has a dimeric structure, while compound 2 and 4 have dimer chain structures. The dependence of the magnetic susceptibility on temperature suggests antiferromagnetic coupling for 1, 2 and 3, while compound 4 can be well understood in terms of the Curie-Weiss law with theta = -23 K. The fitting of the magnetic behaviour to the Bleaney-Bowers spin-dimer coupling expression leads to J = -8.0 cm(-1) for 1, J = -28.8 cm(-1) for 2 and J = -29.0 cm(-1) for 3. The use of alternating chain expressions leads to J = -28.8 cm(-1), alpha = -0.03 for 2 and J = -29.4 cm(-1), alpha = -0.027 for 3. Although a variety of coordination geometries are exhibited by the compounds in the series, all of them have O-P-O bridges connecting the cupric centres. It was possible to identify the role of the vanadyl groups of the phosphovanadate framework as an important factor affecting the ability of the phosphate groups to transmit magnetic interactions.
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