μ-Methyl-ene-bis-[di-bromido(diethyl ether-κO)aluminium(III)]: crystal structure and chemical exchange in solution.

In the title compound, [Al2Br4(CH2)(C4H10O)2], the mol-ecule lies on a crystallographic twofold axis passing through the bridging C atom. Each AlIII atom is four-coordinate, being bonded to two bromide ions, bridging the CH2 group as well as the oxygen atom of a diethyl ether ligand in a slightly distorted tetra-hedral arrangement with angles ranging from 101.52 (8) to 116.44 (5)°. The Al-CH2-Al angle, 118.4 (2)°, is the smallest observed for a structure where this moiety is not part of a ring. In the crystal, weak C-H⋯Br inter-actions, characterized as R 2 2(12) rings, link the mol-ecules into ribbons in the [101] direction. The title compound is monomeric and coordinatively saturated in the solid state, as each aluminum is four-coordinate, but in solution the ether mol-ecules from either or both Al atoms can dissociate, and would be expected to rapidly exchange, and this is supported by NMR data.