Two New Members of the Lanthanoid Bismuth Oxide Oxidosilicates LnBiO[SiO₄] with Ln=La and Gd

Abstract

The isostructural lanthanoid bismuth oxide oxidosilicates with the formula LnBiO[SiO4] (Ln = La and Gd) crystallize in the triclinic space group P with Z = 2 for both. Colorless single crystals were serendipitously obtained from the reaction of bismuth sesquioxide, bismuth trifluoride and the lanthanoid sesquioxides at 850 °C in unprotected torch‐sealed silica ampoules as SiO2 source. Their crystal structure features Ln3+ cations surrounded by eight oxygen atoms as distorted square antiprisms [LnO8]13–, which are linked via edges with three further polyhedra of this kind to form layers {[LnOO]7–} within the (010) plane. The oxygen environment of the Bi3+ cations has to be described as ψ1‐octahedral (square pyramids [BiO5]7–) with five oxide ligands and the stereochemically active lone pair. Two of them are edge‐linked to form ψ1‐bioctahedra [Bi2O8]10–. Four out of five oxygen atoms belong to discrete [SiO4]4– tetrahedra, which separate {[OLnBi]4+} chains of trans‐edge connected [OLn2Bi4]10+ tetrahedral, centered by the fifth oxygen atom propagating along [100] for charge compensation. Furthermore, the magnetic properties of GdBiO[SiO4] were investigated, showing Curie‐Weiss behavior without any magnetic ordering phenomena down to lowest temperatures.