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

Compounds with the composition Bi₆(Bi_1−yM_y)X₂O_16−z, M = transition metal or Pb, X = P, V, As, display pseudo-tetragonal crystal systems. They are, however, monoclinic with space group I2 and the heavy atom positions mimic the δ-Bi₂O₃ structure. The title compound is monoclinic, a = 11.284(2) Å, b = 5.4259(11) Å, c = 11.112(2) Å, β = 96.25(3)°, I2, Z = 2. Least-squares refinement of single-crystal X-ray diffraction data on F² converged to R1 = 0.050, wR2 = 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 (OBi₄) tetrahedra parallel to [1 0 −1]. The chains are bridged parallel to [1 0 1] by linked PO₄ tetrahedra and (Mn/Bi)O₆ 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 BiO bond lengths vary from 2.08(5) to 3.05(2) Å. The Mn/Bi atoms are disordered around the two-fold axis. Three oxygen atom sites contain vacancies.