π-Complexes of p-Block Elements: [(η⁶-C₆Me₆)Sn(AlCl₄)₂]₂ ·3 C₆H₆ — a Dimeric Coordination Compound of Hexamethylbenzene with Sn(AlCl₄)₂

Dimeric (η⁶-hexamethylbenzene)tin(II)bis(tetrachloroaluminate), [(η⁶-C₆Me₆)Sn(AlCl₄)₂]₂, has been obtained from the reaction of anhydrous SnCl₂, A1Cl₃, and hexamethylbenzene in the molar ratio of 1:2:1 in benzene as a solvent. The complex, which crystallizes in the triclinic space group PI, contains a folded eight-membered ring Al₂Sn₂Cl₄²⁺, with the two tin(II) centers linked by two bidentate bridging A1Cl₄ counterions. Each tin(II) atom is η⁶-bonded to a hexamethylbenzene ring at a distance of 2.45 A — the shortest Sn-to-arene distance ever found in the tin(II)/ arene system. Each tin(II) atom is further connected to another A1Cl₄⁻ anion, also acting as a bidentate ligand, but without contacts to other tin(II) centers. The three crystal benzene molecules show no specific metal contacts.