Compounds with the composition Bi-6(Bi1-yMy)X2O16-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 delta-Bi2O3 Structure. The title compound is monoclinic, a=11.284(2) angstrom, b=5.4259(11) angstrom, c=11.112(2) angstrom, beta = 96.25(3)degrees, I2, Z=2. Least-squares refinement of single-crystal X-ray diffraction data on F-2 converged to R1 = 0.050, wR2 = 0.130. The crystal is twinned by two-fold rotation about [0 10] and each twin consists of its inverted component forming a racemate. The structure consists of chains of edge sharing (OBi4) tetrahedra parallel to [10 - 1]. The chains are bridged parallel to [10 1] by linked PO4 tetrahedra and (Mn/ Bi)O-6 octahedra parallel to [10 -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) angstrom. The Mn/Bi atoms are disordered around the two-fold axis. Three oxygen atom sites contain vacancies. (C) 2006 Elsevier Ltd. All rights reserved.