The trigonal polymorph of strontium tetra-borate, ß-SrB(4)O(7).

ABSTRACT

The asymmetric unit of the title compound, ß-SrB(4)O(7), contains five Sr atoms (three located on a threefold rotation axis), twelve B and 21 O atoms. The structure is made up from BO(3) triangles and BO(4) tetra-hedra in a 11 ratio. Pairs of BO(3) triangles are linked to BO(4) 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 Sr(2+) ions reside in the channels and exhibit strongly distorted polyhedra The density of the ß-polymorph is considerably lower than that of α-SrB(4)O(7), which is constructed solely from BO(4) tetra-hedra.