Single-crystal Raman spectrum of strontium dichloride hexahydrate and some related materials

Abstract

Single-crystal Raman spectra at liquid nitrogen temperature are reported for SrCl₂·6H₂O, SrCl₂·6D₂O and SrBr₂·6H₂O. The crystals are trigonal and have a unimolecular primitive cell in which water is coordinated to strontium in both terminal and bridging situations. There are two features of particular note in the assignment. (a) It is shown that although all E modes can in principle show LO–TO splitting, the splitting is likely to be small for those modes originating as Raman-active only in the line group of the chain; this is confirmed by observation. (b) The effect of disorder among the set of terminal water molecules is to relax the selection rules governing Sr—O bond stretching in the plane normal to the chain axis. A complete assignment is offered for all three crystals, except in the ν(OH) region.