CRYSTAL STRUCTURES AND LATTICE DISTORTIONS OF alpha-TYPE LAYERED VANADIUM BRONZES: sigma-M0.25V2O5.H2O (M=Mg, Co, Ni)

摘要

New sigma-type layered vanadium bronzes M0.25V2O5.H2O were hydrothermally synthesized for divalent metals of M=Mg, Co, Ni in addition to the first-reported M=Zn compound. The sigma-type structures, consisting of V2O5 layers with three octahedral and one tetrahedral V atoms and interlayer M(H2O)4 rectangles, were confirmed by single-crystal XRD. The Ni compound crystallizes in the same P-1 phase as the Zn compound while the Mg and Co compounds crystallize in the new P21/a phase of higher symmetry. The P21/a phases is an undistorted form of the P-1 phases, where the distortion is caused by the locations of interlayer water molecules. Among four V atoms one octahedral atom is tetravalent and others are pentavalent, being consistent with the average V4.75+ valence. The M(H2O)4 is held by two apical oxygens of VO4 tetrahedra to form a regular MO6 octahedron and thus M2+ ions must fit for the octahedral O coordination. 11 refs.