A spectroscopic study of some halogeno-complexes of tellurium (IV)

Abstract

The aim of this work was to prepare and structurally characterise a series of halogeno- complexes of tellurium (IV). The principal technique used in the structural determination was to have been tellurium-125 nuclear magnetic resonance spectroscopy, used in conjunction with the method of pairwise interactions. Unfortunately, although this method has been used elsewhere with great success, the chemical shifts obtained in the present study did not yield any consistent results, and the presence of a pair of electrons, not formally involved in bonding, is presented as a possible cause of this behaviour. Far-infrared and laser Raman spectroscopy were used in a qualitative manner to determine the configurations of the penta- and hexachlorobromo complexes and the results obtained were found to agree with those predicted by a stereo chemical model developed for complexes of tin. Assignments of new species were made, as far as possible, by analogy with published results for the corresponding complexes of selenium (IV) or antimony (V) and, in some cases, different assignments are given for previously reported species of tellurium (IV). Complexes containing iodine were found to give more ccnv-2_plicated results but the new species TeI(_4)X(_2)(^2-) (X=F, C1, Br) were prepared and characterised as well as the TeBr(_4)F(^-)anion. The attempted preparation of novel fluoro- species generally led to the isolation of the pentafluorotellurate anion, although the TeBr(_4)F(^-) ion is reported for the first time. The preparation of the unknown hexafluorotellurate anion was also attempted, and although it could not be isolated, some evidence was obtained for its presence in an excess of starting materials. Finally, the behaviour of tellurium dioxide in anhydrous hydrogen chloride and hydrogen bromide has been studied. In both cases tellurium tetrahalide is formed and, for the chlorine compound, further reaction occurs to yield a chloroxo- species. A possible reaction pathway is proposed. The analagous aqueous systems were also investigated.