The low-temperature structure of diethyl ether magnesium oxybromide

The crystal structure of the title compound, hexa-μ(2)-bromido-μ(4)-oxido-tetra-kis-[(diethyl ether)magnesium], [Mg(4)Br(6)O(C(4)H(10)O)(4)], determined from data measured at 173 K, differs from the previously known structure of diethyl ether magnesium oxybromide, which was determined from room-temperature data [Stucky & Rundle (1964 ▶). J. Am. Chem. Soc. 86, 4821-4825]. The title compound crystallizes in the tetra-gonal space group I[Formula: see text], whereas the previously known structure crystallizes in a different tetra-gonal space group, namely P[Formula: see text]2(1)c. Both molecules have crystallographic [Formula: see text] symmetry and show almost identical geometric parameters for the Mg, Br and O atoms. The crystal of the title compound turned out to be a merohedral twin emulating a structure with apparent Laue symmetry 4/mmm, whereas the correct Laue group is just 4/m. The fractional contribution of the minor twin component converged to 0.462 (1).