Synthesis and structure of Bi14O20(SO4), a new bismuth oxide sulfate

A new bismuth oxide sulfate of stoichiometry Bi14O20(SO4) has been synthesized from thermal treatment of an intimate mixture of alpha-Bi2O3 and (NH4)(2)SO4 in the mole ratio 1:0.14, and its structure determined using a combination of electron diffraction, X-ray powder diffraction, and neutron powder diffraction. The body-centered tetragonal unit cell (I4/m; a = 8.664(1) Angstrom, c = 17.282(2) Angstrom) is a commensurate superstructure of the cubic fluorite subcell of delta-Bi2O3 (a(0)): a = (root 10/2)a(0), c = 3a(0). The structure contains discrete sulfate anions at the unit cell corners and body center, and a Bi-O framework of linked BiO(4)e (e = lone pair of electrons) square pyramids and trigonal bipyramids. The square pyramids are aggregated into clusters of composition Bi6O8, comprising O2- ions arranged in the form of a cube, the faces of which are capped by Bi3+ ions. In contrast, the trigonal bipyramids are corner linked to form layers perpendicular to [001]. The structure is thought to represent just one of several related phases in this system.