CATION ORDERING IN THE SILLEN X(1)-TYPE OXYCHLORIDE, BABIO2CL

The structure of BaBiO2Cl has been determined from single crystal X-ray diffraction data. It crystallizes in the orthorhombic space group Cmcm with a = 5.880(4), b = 12.945(18), c = 5.677(3) Angstrom, V = 432.0(3) Angstrom(3), and Z = 4. BaBiO2Cl is related to a family of bismuth oxyhalides which can be viewed as separate oxygen and chlorine layers stacked along the b axis, with bismuth and barium cations located between the layers. The structure differs from other bismuth oxyhalides in that the barium and bismuth cations are found to be ordered in two distinct coordination environments. The cation ordering and fourfold coordination environment of bismuth is seen as a structural expression of the stereochemically active bismuth 6s lone pair of electrons. (C) 1995 Academic Press, Inc.