Raman spectroscopic structural studies on the stepwise dehydration of Zn(BrO₃)₂ · 6H₂O

Abstract

Abstract Raman spectra of single‐crystal Zn(BrO 3 ) 2 · 6H 2 O were examined at 298, 338 and 378 K from the fully hydrated to the totally anhydrous state. At 298 K, the presence of only one set of OH stretching bands in the Raman spectrum confirmed the structural equivalence of the six water molecules. At 338 K, the spectrum of the dihydrate indicated splittings in the OH stretching region attributable to the non‐equivalent H 2 O groups. Thechanges in the internal modes of the BrO 3 − revealed lifting of degeneracy as a consequence of lowering of site symmetry. Conclusions drawn from Raman spectral investigations conformed to the change in site symmetry of BrO 3 − from C 3 to C 1 . Differential scanning calorimetric data indicated the formation of dihydrate and anhydrous compound of Zn(BrO 3 ) 2 involving a two‐step dehydration process. X‐ray powder diffraction patterns recorded at different temperatures were analysed and indexed on unit cells of cubic symmetry. The results from Raman studies with reference to change in the site symmetry of BrO 3 − in conjunction with x‐ray powder pattern analysis led to the deduction of the space group for the anhydrous compound. Vibrational selection rules for the anhydrous compound were determined on a proposed space group P 23( T 1 ).