SPECTROSCOPIC INVESTIGATION OF CONCENTRATED-SOLUTIONS OF GALLIUM(III)CHLORIDE IN MESITYLENE AND BENZENE

The metal-arene interaction in concentrated binary mixtures of GaCl3 a nd mesitylene or benzene has been investigated using multinuclear (H-1 ,C-13,Ga-71) NMR, Raman and UV/VIS spectroscopy as well as liquid X-ra y scattering. The effects of hydrolysis and radiolysis of such mixture s have also been studied using UV/VIS, EPR and IR spectroscopy. Galliu m(III) chloride has been found to be monomeric in mesitylene and to fo rm eta(6) complexes with this arene. A structural determination of thi s complex in solution yielded a Ga-C distance of 2.20 Angstrom and a G aCl3 moiety with C-3V symmetry and Ga-Cl distances of 2.10 Angstrom. I n benzene. GaCl3 exists as a mixture of the Cl2Ga(mu-Cl)(2)GaCl2 dimer and one or several other species, containing terminal GaCl3 groups of C-3V symmetry, e.g. the dimer isomer Cl2Ga(mu-Cl)GaCl3 and monomeric GaCl3. The complex with benzene is weaker than with mesitylene and the co-ordination mode cannot be unambiguously elucidated. Hydrolysis of the GaCl3-C6H6 system produced a darkly coloured precipitate showed by IR spectroscopy to be a mixture of poly(p-phenylene) and other polyme ric species, probably meta-substituted, chlorinated and hydroxylated p olyphenylenes. On the basis of Ga-71 NMR results, it is suggested that the formation of this polymer proceeds via protonated Wheland interme diates, rather than direct oxidation of benzene by Ga-III. Radiolysis of the mixtures of GaCl3 with mesitylene and benzene yielded radicals, according to EPR spectroscopy. In benzene solution the formation of r adicals is accompanied by reduction of Ga-III to Ga-I. No formation of solid polymers could be detected.