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

The structure of BaBiO2Cl has been determined from single crystal X-ra y diffraction data. It crystallizes in the orthorhombic space group Cm cm 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 bet ween the layers. The structure differs from other bismuth oxyhalides i n that the barium and bismuth cations are found to be ordered in two d istinct coordination environments. The cation ordering and fourfold co ordination environment of bismuth is seen as a structural expression o f the stereochemically active bismuth 6s lone pair of electrons. (C) 1 995 Academic Press, Inc.