Lanthanum(III) chloroaluminate and chlorogallate complexes with toluene and hexamethylbenzene: The effect of arene methylation on the structure

Two new lanthanum(III) chloroaluminate complexes with neutral arenes, [La(eta(6)-C6H5Me)(AlCl4)(3)] (1) and [La(eta(6)-C6Me6)(AlCl4)(3)].1/2C(6)H(6) (2), as well as the first lanthanide chlorogallate complex [La(eta(6)- C6Me6)(GaCl4)(3).1/2C(6)H(6) (3) have been synthesized and structurally characterized. The coordination polyhedron around the central lanthanum ion in 1-3 is a distorted pentagonal bipyramid formed by six Cl-atoms and an eta(6)-bound arene. In contrast to the mononuclear complex 1 with toluene, 2 and 3 form dimers in the solid state via pi-pi stacking interactions of the coordinated hexamethylbenzene ligands with a sandwiched benzene molecule. Such dimerization has not been seen in the crystal structures of other known lanthanide chloroaluminate pi-complexes, including those with C6Me6. The reasons for the dinner formation in the lanthanum(III)-hexamethylbenzene-benzene systems are discussed based on DFT calculations and H-1 NMR experiments. (C) 2008 Elsevier B.V. All rights reserved.