Preparation and structure of soluble complexes of the ternary compounds GaSBr and GaSeBr

Abstract

[GaSBr] and [GaSeBr] can be prepared from Ga[GaBr₄] and elemental sulfur/selenium in toluene or tetrahydrofuran, respectively. GaBr₃(thf)₂ is a by-product of these reactions. Its structure (a trigonal-bipyramidal array of ligands with the bromine atoms in equatorial positions) has been determined. The two ternary gallium bromides are insoluble in most common organic solvents, but are readily dissolved in pyridine and substituted pyridines (L) to give trinuclear complexes [GaSBr(L)]₃ with L = 3,5-dimethylpyridine (1), 4-tert-butylpyridine (2) and 4-dimethylaminopyridine, and [GaSeBr(L)]₃ with L = 3,5-dimethylpyridine (5), respectively. The molecular structures of 1, 2 and 5 have been determined. The core units are six-membered rings with different substitution patterns depending largely on the steric requirements of the ligands L, and on the mode of crystallization. The reaction of [GaSBr] with the strongly basic 4-Me₂NC₅H₄N in refluxing acetonitrile leads to partial degradation of the trinuclear units to give an ionic product [Ga₄S₅(L)₄]²⁺2Br⁻ (4). The dications have a bicyclic structure of the well-known borax-type. The reactions and structures are discussed in the light of previous findings in the corresponding chloride series [GaSCl(L)]₃ and [GaSeCl(L)]₃. For comparison the structure of [GaSCl(L)]₃ with L = 3,5-dimethylpyridine has also been determined for the solvate-free crystal and for a tetrahydrofuran solvate, where different conformations are observed.