Investigation of mesitylene-solvated group 13 mixed-metal halides: syntheses and crystal structures of bis(1,3,5-trimethylbenzene)gallium(I) tetrachlorido- and tetrabromidoaluminate(III) and (1,3,5-trimethylbenzene)gallium(I) tetraiodidoaluminate(III). Variation of the gallium-π-arene bond strength

Abstract

Abstract Bis(1,3,5-trimethylbenzene)gallium(I) tetra­chloridoaluminate(III), [(1,3,5-(CH3)3C6H3)2Ga][AlCl4] (1), bis(1,3,5-trimethylbenzene)gallium(I) tetrabromido­aluminate(III), [(1,3,5-(CH3)3C6H3)2Ga][AlBr4] (2) and (1,3,5-trimethylbenzene)gallium(I) tetraiodidoaluminate(III), [1,3,5-(CH3)3C6H3Ga][AlI4] (3) were synthesized from the corresponding subvalent GaI/AlIII mixed metal halides and characterized via C,H analysis, Raman spectroscopy, X-ray powder diffraction and X-ray single crystal diffraction. Compound 1 crystallizes in the noncentrosymmetric monoclinic space group Cc isotypic to [(1,3,5-(CH3)3C6H3)2Ga][GaCl4]. For 2 and 3 the monoclinic space group P21/n is found, however, they are neither isotypic nor homotypic. While 2 is isotypic to [(1,3,5-(CH3)3C6H3)2In][InBr4], 3 establishes a new structure type. In the solids of all three title compounds coordination polymeric chains are found, in 1 and 2 built up from bis(arene)-coordinated, in 3 from mono(arene)-coordinated Ga+ ions and the corresponding AlX 4 − anions in a 1κCl:2κCl′ (1), 1κCl,Cl′:2κCl″ (2) or 1κCl,Cl′:2κCl″:3κCl‴ (3) bridging mode. Taking into account the weaker coordinating character of the AlCl4 − as compared to the AlBr4 − anion, in line with expectations the number of gallium halogen contacts is increased and the strength of the π-arene bonding is reduced in the bromide 2 as compared to the chloride 1. Finally, with the even more strongly coordinating AlI4 − anion the arene coordination is limited to one molecule. Considering mesitylene complexes of gallium, the formation of a mono(arene) complex is unprecedented and even considering group 13 elements in general, the formation of a mono(mesitylene) complex like 3 is unusual. Furthermore, compound 3 is the first structurally characterized arene solvate of a main group metal tetraiodidometallate.