One-dimensional decavanadate chains in the crystal structure of Rb4[Na(H2O)6][HV10O28]·4H2O.

New decavanadate minerals, the products of the leaching or metasomatic processes, are possible in nature via Na/Rb removal/inclusion reactions. As part of our search for novel vanadate phases with varying functionalities, a new phase, tetrarubidium hexaaquasodium hydrogen decavanadate tetrahydrate, Rb4[Na(H2O)6][HV10O28]·4H2O, has been synthesized by the hydrothermal technique at 553 K. Ten shared edges of V-centred octahedra form monoprotonated decavanadate cages, which are joined together via hydrogen bonds into one-dimensional chains parallel to the [101] direction. Within these chains, H atoms are sandwiched between neighbouring polyanions. Na and Rb atoms and H2O molecules occupy interstices flanked by the anionic chains providing additional crosslinking in the structure. This compound is the second decavanadate with P2/n symmetry. Structural relationships among protonated and deprotonated decavanadates with inorganic cations, including minerals of the pascoite group, are discussed.

The first vanadate-carbonate, K2Mn3(VO4)2(CO3): crystal structure and physical properties.

Mixed potassium-manganese vanadate-carbonate, K(2)Mn(3)(VO(4))(2)(CO(3)), represents a novel structure type; it has been synthesized hydrothermally from the system MnCl(2)-K(2)CO(3)-V(2)O(5)-H(2)O. Its hexagonal crystal structure was determined by single-crystal X-ray diffraction with a = 5.201(1) Å, c = 22.406(3) Å, space group P6(3)/m, Z = 2, ρ(c) = 3.371 g/cm(3), and R = 0.022. The layered structure of the compound can be described as a combination of honeycomb-type modules of [MnO(6)] octahedra and [VO(4)] tetrahedra, alternating in the [001] direction with layers of [MnCO(3)] built by [MnO(5)] trigonal bipyramids and [CO(3)] planar triangles, sharing oxygen vertices. The K(+) ions are placed along channels of the framework, elongated in the [100], [010], and [110] directions. The title compound exhibits rich physical properties reflected in a phase transition of presumably Jahn-Teller origin at T(3) = 80-100 K as well as two successive magnetic phase transitions at T(2) = 3 K and T(1) = 2 K into a weakly ferromagnetic ground state, as evidenced in magnetization, specific heat, and X-band electron spin resonance measurements. A negative Weiss temperature Θ = -114 K and strongly reduced effective magnetic moment µ(eff)(2) ~ 70 µ(B)(2) per formula unit suggest that antiferromagnetic exchange interactions dominate in the system. Divalent manganese is present in a high-spin state, S = 5/2, in the octahedral environment and a low-spin state, S = ½, in the trigonal-bipyramidal coordination.