Rbvopo₄ and csvopo₄, two vanadyl(iv) orthophosphates with an intersecting tunnel structure and discrete vo₅ pyramids

Two new ternary vanadyl(IV) orthophosphates, RbVOPO₄ and CsVOPO₄, have been prepared and their structures have been determined from single-crystal X-ray diffraction data. They crystallize in the orthorhombic space group P2₁2₁2₁ with a = 7.8669(9), b = 7.5848(8), c = 8.3771(10) Å, V = 499.8(1) ų, Z = 4, and R = 0.029 for RbVOPO₄, and a = 7.3665(15), b = 7.6146(15), c = 9.8035(17) Å, V = 549.9(2) ų, Z = 4, and R = 0.029 for CsVOPO₄. These two compounds consist of intersecting tunnels running along each axis, and the alkali metal cations are located at the intersection of these tunnels. Unlike other AM OPO₄ structures (A = alkali metals; M = Ti, V), the frameworks of the title compounds are built up from discrete VO₅ pyramids and PO₄ tetrahedra. Each VO₅ pyramid shares its four basal oxygen atom vertices with three different PO₄ tetrahedra. One of the phosphate groups is coordinated to the V atom as a bidentale ligand. These two closely related structures are not isomorphous, differing in the orientation of vanadyl oxygens.