Pb6(AsO4)[B(AsO4)4] - ein neuartiger Kristallstrukturtyp im System PbO/B2O3/As2O5 mit einem Beitrag über Pb(BAsO5)/Pb6(AsO4)[B(AsO4)4] - a New Crystal Structure Type in the System PbO/B2O3/As2O5 with Remarks about Pb(BAsO5)

Abstract

Abstract Single crystals of Pb6(AsO4)[B(AsO4)4] (I) and Pb(BAsO5) (II) were obtained by melting B2O3, As2O5 and PbO at 800 °C. X-ray investigation led to the space group (I): S4 1 -P4̄ (Nr. 81) with a = 715.4(1), c = 976.2(3) pm, Z = 1 and (II): C3 2 -P31 (Nr. 144) with a = 712.2(1), c = 693.5(2) pm, Z = 3. While (II) is isotypic to the Stillwellite structure, Pb6(AsO4)[B(AsO4)4] represents a completely novel type of crystal structure. Boron and arsenic are tetrahedrally coordinated by oxygen. These polyhedra form two kinds of isolated anions: AsO4 3- and B(AsO4)4 9-. Lead is eightfold coordinated by oxygen.