Pb2BiO2PO4, a new oxyphosphate

Pb2BiO2PO4 is orthorhombic with space group Pnma, a = 5.930(4), b = 9.079(10), c = 11.473 (6) Angstrom at room temperature, Z = 4, and a congruent melting point of 860 degrees C. The structure was solved from single crystal and powder diffraction data, The PO4 ion can occupy two energetically equivalent positions causing two oxygen atoms to be disordered, The structure can be described on the basis of several motifs, Infinite chains of BiO2 rectangular pyramids formed by edge-sharing parallel to the a axis that are linked by lead atoms and phosphate anions, Bi can also be considered as present in a trigonal prismatic environment of oxygen atoms in which one corner of a triangular face is unoccupied, Presumably the 6s(2) lone pair extends toward that apex, Pb is bonded to sis oxygen atoms forming a distorted octahedron when distances less than 3 Angstrom are considered, When two additional oxygen ions at 3.20(9) and 3.24(5) Angstrom are considered part of the coordination polyhedron it can be described as a bisdisphenoid, This structure is related to structures found in many (M2BiXO6)-Bi-II phases, The Raman spectrum shows the expected frequencies for PO4. In addition frequencies are observed that can be assigned to P-O-Bi and P-O-Pb linkages, Intense bands at 143 and 150 cm(-1) are attributed to internal vibrational modes of the BiO4 pyramid. (C) 1997 Academic Press.