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 con gruent melting point of 860 degrees C. The structure was solved from s ingle crystal and powder diffraction data, The PO4 ion can occupy two energetically equivalent positions causing two oxygen atoms to be diso rdered, The structure can be described on the basis of several motifs, Infinite chains of BiO2 rectangular pyramids formed by edge-sharing p arallel to the a axis that are linked by lead atoms and phosphate anio ns, Bi can also be considered as present in a trigonal prismatic envir onment of oxygen atoms in which one corner of a triangular face is uno ccupied, Presumably the 6s(2) lone pair extends toward that apex, Pb i s bonded to sis oxygen atoms forming a distorted octahedron when dista nces less than 3 Angstrom are considered, When two additional oxygen i ons at 3.20(9) and 3.24(5) Angstrom are considered part of the coordin ation polyhedron it can be described as a bisdisphenoid, This structur e is related to structures found in many (M2BiXO6)-Bi-II phases, The R aman spectrum shows the expected frequencies for PO4. In addition freq uencies are observed that can be assigned to P-O-Bi and P-O-Pb linkage s, Intense bands at 143 and 150 cm(-1) are attributed to internal vibr ational modes of the BiO4 pyramid. (C) 1997 Academic Press.