CaNb2P2O11: A new calcium niobium (V) oxophosphate with a quasi-one-dimensional structure

The crystal structure of a new calcium niobium (V) oxophosphate, CaNb2P2O11, has been determined by single crystal X-ray diffraction. The title compound crystallizes in the monoclinic crystal system with the space group C2c (No. 15) and Z = 4. The lattice parameters are a = 14.930 (3)Å, b = 10.824 (3)Å, c = 5.214 (2)Å, β = 93.59 (2) Å, and V = 840.9 (4)Å3. The structure contains a double layer of zig-zag corner-sharing NbO6 octahedral chains. These octahedral chains are structurally isolated by PO4 tetrahedral groups, each of which shares three oxygen atoms with NbO6 octahedra to form a quasi-low-dimensional network structure. The interconnected octahedral chains are arranged parallel to each other so that channel structures are formed. The fourth oxygen atoms of the PO4 tetrahedra are pointing into the channel where the calcium atoms are located. A structure comparison with the isotypic compound BaNb2P2O11 and a discussion of the NbO framework formation related to that in the purple molybdenum bronze are presented.