K6Bi13(PO4)15, K5Bi(P2O7)2, A5Bi5(PO4)4(P2O7)2 (A=K, Rb): New bismuth phosphates with different condensed phosphate groups

Four new Bi(III) phosphates, K6Bi13(PO4)15, K5Bi(P2O7)2, and A5Bi5(PO4)4(P2O7)2 (A= K, Rb) with the different condensed P-O groups have been successfully synthesized via the solid-state reactions. The single crystals X-ray diffractions show that they crystallize in the different space groups (K6Bi13(PO4)15: C2; K5Bi(P2O7)2: P 1¯; K5Bi5(PO4)4(P2O7)2 and Rb5Bi5(PO4)4(P2O7)2: P21/c). The structure of K6Bi13(PO4)15 can be described as a three-dimensional (3D) network composed of the Bi-O polyhedra and PO4 tetrahedra with K atoms filling in the space to balance the residual charges. K5Bi(P2O7)2 features 2D [BiP4O14]∞ layers built by the BiO6 octahedra and P2O7 dimers and the adjacent [BiP4O14]∞ layers are bridged by the K atoms. A5Bi5(PO4)4(P2O7)2 (A = K, Rb) contain two different condensed P-O groups, PO4 tetrahedra and P2O7 dimers, which are connected by Bi-O polyhedra to construct the complicated 3D framework with K/Rb atoms located in the tunnels. Note that, the compounds that simultaneously contain two different types of P-O groups are still rare in phosphates. Detailed structural comparisons of Bi3+-containing phosphates indicate that the Bi/P ratios have a significant effect on the condensed degrees of PO4 groups. Furthermore, TG-DSC, IR, UV-Vis-NIR diffuse reflectance spectra and SHG test for title compounds have also been reported.