Hydrothermal synthesis and crystal structure of the Ni2(C4H4N2)(V4O12)(H2O)2 and Ni3(C4H4N2)3(V8O23) inorganic–organic hybrid compounds. Thermal, spectroscopic and magnetic studies of the hydrated phase

Ni2(C4H4N2)(V4O12)(H2O)2, 1, and Ni3(C4H4N2)3(V8O23), 2, have been synthesized using mild hydrothermal conditions at 170 °C under autogenous pressure. Both phases crystallize in the P-1 triclinic space group, with the unit-cell parameters, a=7.437(7), b=7.571(3), c=7.564(4) Å, α=65.64(4), β=76.09(4), γ=86.25(3)° for 1 and a=8.566(2), b=9.117(2), c=12.619(3) Å, α=71.05(2), β=83.48(4), γ=61.32(3)° for 2, being Z=2 for both compounds. The crystal structure of the three-dimensional 1 is constructed from layers linked between them through the pyrazine molecules. The sheets are formed by edge-shared [Ni2O6(H2O)2N2] nickel(II) dimers octahedra and rings composed by four [V4O12] vanadium(V) tetrahedra linked through vertices. The crystal structure of 2 is formed from vertex shared [VO4] tetrahedra that give rise to twelve member rings. [NiO4(C4H4N2)2]∞ chains, resulting from [NiO4N2] octahedra and pyrazine molecules, give rise to a 3D skeleton when connecting to [VO4] tetrahedra. Diffuse reflectance measurements of 1 indicate a slightly distorted octahedral geometry with values of Dq=880, B=980 and C=2700 cm−1. Magnetic measurements of 1, carried out in the 5.0–300 K range, indicate the existence of antiferromagnetic couplings with a Neel temperature near to 38 K.