Synthesis, crystal structures and magnetic properties of organically templated new layered vanadates:: [C4H8NH2]V3O7, [(CH3)2NH2]V3O7, [C5H10NH2]V3O7 and [C2H5NH3]V3O7

Four new layered mixed-valance vanadium oxides, which contain the interlamellar organic cations pyrolidinium, dimethylammonium, piperidinium, and ethylammonium, have been prepared under hydrothermal conditions and their structures determined. All four structures contain vanadium oxide layers constructed from V5+O4 tetrahedra and pairs of V4+O5 square pyramids with the protonated organic amines occupying the interlayer space. The materials are further characterized by thermal analysis, FTIR and scanning electron microscopy. Magnetic susceptibility studies of the first three compounds reveal a spin-gap behavior explained by an isolated antiferromagnetic dimers model. Large values of the exchange constants J = 325 - 480 K were found and the dependence of J upon the structural parameters was analyzed assuming a kinetic exchange mechanism.