π-Complexes of p-block elements: (η6-Mesitylene)tin(II) chloride tetrachloroaluminate(III), a coordination polymer

(η⁶-1,3,5-Trimethylbenzene)tin(II) chloride tetrachloroaluminate(III), (η⁶-1,3,5-C₆H₃Me₃)SnCl (AlCl₄), has been obtained from the reaction of anhydrous SnCl₂ and AlCl₃ in the molar ratio 1 : 2 in excess mesitylene as a solvent. The compound crystallizes in monoclinic needles, space group P2₁/n, containing a coordination polymer with planar four-membered rings Sn-Cl-Sn-Cl as the fundamental structural units. Each tin(II) atom of these rings is η⁶-bonded to a mesitylene ring, with the metal approximately centered over the aromatic hydrocarbon at a distance of 2.71 Å. Each of the tin(II) atoms is further connected to two tetrachloroaluminate counter ions, one of these monodentate and one bidentate. Through this mono/bidentate contacts a one-dimensional coordination polymer is generated with crystallographic centers of inversion in the middle of the Sn(Cl)₂Sn and Sn(AlCl₄)₂Sn rings. The structure is similar to that of the analogous benzene complex, but not identical owing to a different connectivity pattern. Also, the arene-Sn(II) distance is much shorter in the mesitylene complex (2.71 Å) than in the benzene complex (2.90 Å), indicating that the trimethylbenzene molecule is a much better donor than benzene.