Chemistry of selenium and tellurium tetrahalides: ionisation of the chlorides and bromides in solution and the constitution of their adducts

Abstract

Tellurium tetrachloride and tetrabromide are ionised as 1 : 1 electrolytes in a range of solvents. Selenium halides are only partially ionised unless the solvent, e.g., dimethylformamide, has marked electron-donor properties. The diphenylselenium and diphenyltellurium dihalides are still less readily dissociated than the tetrahalides. Conductimetric titration of halides with ligands provides evidence on donor–acceptor interactions and co-ordination numbers.

The tetrahalides of both elements form compounds of the types MX₄,2py and MX₄,bipy, which are 1 : 1 electrolytes. Spectroscopic and molecular-weight data confirm ionisation to free halide rather than a halogeno-anion. Tellurium tetrachloride also forms ionised complexes TeCl₄,L (L = pyridine, pyridine N-oxide), TeCl₄,terpy, and 2TeCl₄,terpy (terpy = 2,2′:6′2″-terpyridyl). Selenium alone yields bis-complexes [SeCl₂,2L″]²⁺ 2Cl^– with bidentate ligands. Evidence on the various co-ordination numbers of these lenium and tellurium in these compounds is discussed.