A novel family of layered bismuth compounds II: the crystal structures of Pb_0.6Bi_1.4Rb_0.6O₂Z₂, Z=Cl, Br, and I

Using various synthetic approaches, we have prepared over 50 new multinary bismuth oxyhalides which crystallize in four layered structure types. Most of the compounds belong to the three previously reported structure types involving fluorite- and CsCl-like metal-oxygen vs. metal-halogen layers as well as single or double halide ion sheets. The majority of Bi(2-x)A(x)Q(0.6)O(2)Z(2) (A-Li, Na, K, Ca, Sr, Ba, Pb; Q=Rb Cs; Z=Cl, Br, I) compounds crystallize in the tetragonal structure of Pb0.6Bi1.4Cs0.60Cl2 (Y2) while both Bi(1.4)Ba(0.6)Q(0.6)O(2)I(2) (Q = Rb, Cs) oxyiodides adopt its orthorhombically distorted, partially ordered version. Due to the lower degree of substitution, the fluorite-like layers in the Y2 structure accommodate more A cations than previously known for related Bi compounds. However, very large Tl+ or Rb+ give compounds with another, as yet unknown, structure. We discuss the influence of size and charge of A cations and stoichiometry of [Bi(2-x)A(x)O(2)] fluorite layers on structure and stability of layered oxyhalides of bismuth. Also, we predict formation of isostructural compounds with smaller Q cations like Tl+ and K+. (C) 2003 Elsevier Science (USA). All rights reserved.