Characterisation of the oxo-anions of bromine BrOx–(x= 1–4) by infrared, Raman, nuclear magnetic resonance, and bromine K-edge extended X-ray absorption fine structure techniques

Abstract

The bromine oxo-anions BrO_x^–(x= 1–4) have been studied by vibrational and multinuclear n.m.r. spectroscopy and bromine K-edge extended X-ray absorption fine structure (EXAFS) measurements. Raman and/or i.r. data for BrO^– and BrO₂^– are presented, and conflicts in the literature for the latter resolved. Oxygen-17 n.m.r. data for the halogen oxo-anions have been recorded, and an increase in δ(¹⁷O) with formal oxidation state of the halogen noted. Coupling to the halogen nucleus has been observed for ClO₄^–, ¹J(^35/37Cl–¹⁷O)= 85, and for BrO₄^–, ¹J(^79/81Br–¹⁷O)= 420Hz, but could not be resolved for IO₄^–. The ⁸¹Br n.m.r. resonance of BrO₄^–(δ= 2 476) and the ¹²⁷I resonance of IO₄^–(δ= 4 090 p.p.m.) are reported. Bromine K-edge EXAFS data are presented for all four ions in solution, and for all but BrO^– in the solid state, and differences in bond lengths between solid state and solution found to be within experimental error. Bond lengths obtained are: BrO₄^– 1.61, BrO₃^– 1.65, BrO₂^– 1.72, and BrO^– 1.81 Å. This is the first bond length reported for the hypobromite ion.