Isolation and Crystal Structure of (Hexamethylbenzene)gallium(I) Tetrachlorogallate(III), a Mono(arene) Complex of Gallium(I)

Ga₂Cl₄ reacts with hexamethylbenzene in benzene to give (hexamethylbenzene)gallium(I)-tetrachlorogallate(III), (CH₃)₆C₆Ga' GaCl₄, in high yield. The complex crystallizes in the rhombohedral space group R3m with four formula units per cell. Cell constants are a = 12.449(3) A and a = 91.01(2)°. In the structure tetrameric clusters can be identified containing two crystallographically independent formula units, one having 3 m and the other three having m symmetry. In both types of (arene)Ga” cations the Ga atoms are symmetrically positioned over the arene ring, 2.43(3) and 2.51(3) A. respectively, away from the ring plane. Four (arene)Ga⁺ cations and four GaCl₄ anions are aggregated in such a way that the Ga¹ atoms are surrounded by six or seven chlorine atoms, respectively, at distances in the range 3.16(1) to 3.67(1) A. The four hexamethylbenzene molecules form an efficient cover around the inorganic [Ga GaCl₄]₄ framework. Between the tetrameric clusters there are no contacts of the Ga¹…Cl Type.