Arene-mercury complexes stabilized aluminum and gallium chloride: Synthesis and structural characterization

Reaction Of HgCl2 with 2 equiv Of MCl3 in an aromatic solvent yields Hg(arene)(2)(MCl4)(2) where, arene = C6H5Me, M = Al (1), Ga (2); arene = C6H5Et, M = At (3) and Ga (4); o-C6H4Me2, M = Al (5), Ga (6); C6H3-1,2,3-Me-3, M = Al (7) and Ga (8). The solid-state structures of compounds 1-5 and 7 have been determined by X-ray crystallography. In the solid state, compounds 1-4 and 7 exist as neutral complexes in which two arenes are bound to the mercury, and the MCl3 groups are bound through bridging chlorides to the mercury; compound 5 exists as a cation-anion pair [Hg(o-C6H4Me2)(2)(AlCl4)][AlCl4]. However, in solution compounds 1-8 all exist as neutral complexes. The structures of Hg(arene)(2)(AlCl4)(2) and [Hg(arene)(2)(AlCl4)](+) have been determined by DFT calculations {B3LYP level} to facilitate the assignment of the C-13 CPMAS NMR spectra and are in good agreement with the X-ray diffraction structures of compounds 1 and 5. Reaction of HgCl2 with MCl3 in benzene, m-xylene, and p-xylene results in the formation of liquid clathrates whose spectroscopic characterization is consistent with ionic structures, [Hg(arene)(2)(MCl4)][MCl4]. The calculated energy difference between Hg(C6H5Me)(2)(AlCl4)(2) and [Hg(C6H5Me)(2)(AlCl4)][AlCl4] is discussed with respect to the structure of compound 5 in the solid state versus solution state and the proposed speciation in the liquid clathrates.