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

Reaction of HgCl(2) with 2 equiv of MCl(3) in an aromatic solvent yields Hg(arene)(2)(MCl(4))(2) where, arene = C(6)H(5)Me, M = Al (1), Ga (2); arene = C(6)H(5)Et, M = Al (3) and Ga (4); o-C(6)H(4)Me(2), M = Al (5), Ga (6); C(6)H(3)-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 MCl(3) groups are bound through bridging chlorides to the mercury; compound 5 exists as a cation-anion pair [Hg(o-C(6)H(4)Me(2))(2)(AlCl(4))][AlCl(4)]. However, in solution compounds 1-8 all exist as neutral complexes. The structures of Hg(arene)(2)(AlCl(4))(2) and [Hg(arene)(2)(AlCl(4))](+) have been determined by DFT calculations [B3LYP level] to facilitate the assignment of the (13)C CPMAS NMR spectra and are in good agreement with the X-ray diffraction structures of compounds 1 and 5. Reaction of HgCl(2) with MCl(3) 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)(MCl(4))][MCl(4)]. The calculated energy difference between Hg(C(6)H(5)Me)(2)(AlCl(4))(2) and [Hg(C(6)H(5)Me)(2)(AlCl(4))][AlCl(4)] 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.