Inorganic−Organic Hybrid Materials with Novel Framework Structures: Synthesis, Structure, and Magnetic Properties of [Ni(py)4]2V10O29 and [Ni2(py)5(H2O)3]V4O12

Inorganic−organic hybrid materials [Ni(py)4]2V10O29 (1) and [Ni2(py)5(H2O)3]V4O12 (2) have been synthesized and characterized by infrared spectroscopy, thermogravimetry, magnetometry, and complete single crystal structure analysis. The crystal structures of 1 and 2 exhibit novel three-dimensional covalent networks. The framework structure in 1 contains polyoxometallate groupings of stoichiometry {V10O29} which are constructed from two cyclic {V4O12} units bound to centrosymmetric {V2O7} species. V−O−Ni bridges in the a- and b-directions join these units to two crystallographically independent trans-[Ni(py)4O2] octahedra. The nickel- and vanadium-based moieties occupy alternating channels along the c-direction. The structure of 2 consists of octahedral species [Ni(py)3(H2O)O2] and [Ni(py)2(H2O)2O2] which are linked into a three-dimensional covalent network by the sharing of oxygen atom vertices with tetrahedral {VO4} groups. Compounds 1 and 2 are thermally stable up to 200 and 175 °C, respectively. Both compounds show Curie−Weiss type magnetic behavior over the temperature range 1.9−300 K. The effective magnetic moment in both cases is 3.0 μB, revealing the presence of significant orbital contribution. Single ion magnetization as a function of magnetic field showed linear behavior for 1 and 2 over the range of 0−1 T. At a magnetic field of 9 T, 1 approaches saturation at 2 μB per Ni2+ ion, whereas 2 does not approach saturation well.