The trigonal polymorph of strontium tetraborate, Β-SrB 4O7

Abstract

The asymmetric unit of the title compound, Β- SrB4O 7, contains five Sr atoms (three located on a threefold rotation axis), twelve B and 21 O atoms. The structure is made up from BO3 triangles and BO4 tetra-hedra in a 1:1 ratio. Pairs of BO3 triangles are linked to BO4 tetra-hedra via common corners, forming chains. These chains are further linked to adjacent chains through corner-sharing, leading to a three-dimensional framework with channels running parallel to [001]. The Sr2+ ions reside in the channels and exhibit strongly distorted polyhedra The density of the Β-polymorph is considerably lower than that of α- SrB4O7, which is constructed solely from BO 4 tetra-hedra.