Variants of the Bi6TiP2O16 structure: The preparation and crystal structure of the isomorph Bi6(Mn0.6Bi0.4)P2O15

Abstract Compounds with the composition Bi 6 (Bi 1− y M y )X 2 O 16− z , M = transition metal or Pb, X = P, V, As, display pseudo-tetragonal crystal systems. They are, however, monoclinic with space group I 2 and the heavy atom positions mimic the δ-Bi 2 O 3 structure. The title compound is monoclinic, a  = 11.284(2) A, b  = 5.4259(11) A, c  = 11.112(2) A, β  = 96.25(3)°, I 2, Z  = 2. Least-squares refinement of single-crystal X-ray diffraction data on F 2 converged to R 1 = 0.050, w R 2 = 0.130. The crystal is twinned by two-fold rotation about [0 1 0] and each twin consists of its inverted component forming a racemate. The structure consists of chains of edge sharing (OBi 4 ) tetrahedra parallel to [1 0 −1]. The chains are bridged parallel to [1 0 1] by linked PO 4 tetrahedra and (Mn/Bi)O 6 octahedra parallel to [1 0 −1], into a three-dimensional structure. The lone-pair electrons of adjacent Bi atoms along the chain point in opposite directions along the b -axis. The Bi atoms are in distorted trigonal prismatic coordination that has one or two faces capped. The Bi O bond lengths vary from 2.08(5) to 3.05(2) A. The Mn/Bi atoms are disordered around the two-fold axis. Three oxygen atom sites contain vacancies.