Crystal structures of GaX 3 (X = Cl, Br, I) and AlI3

Abstract

Abstract Crystal structures of GaX 3 (X = Cl (I), Br (II), and I (III)) and AlI3 (IV) were determined at low temperature by single crystal X-ray crystallography. I is monoclinic, space group C2/m with a = 11.948(4), b = 6.855(3), c = 7.050(3) Å, β = 125.69(3)°, Z = 4, R 1 = 0.038. II–IV are isotypic to each other: II is monoclinic, space group P21/c with a = 8.874(4), b = 5.637(2), c = 11.006(4) Å, β = 107.81(4)°, Z = 4, R 1 = 0.056; III: a = 9.584(3), b = 6.084(2), c = 11.839(4) Å, β = 107.78(3)°, R 1 = 0.044; IV: a = 9.591(3), b = 6.069(2), c = 11.902(3) Å, β = 108.05(3)°, R 1 = 0.046. The crystal structures I–IV are built of dimeric M 2 X 6 molecules consisting of two MX 4 tetrahedra sharing a common XX edge with shorter M-X (terminal) and longer M-X(bridging) distances. The structure of I can not be described in terms of the closest Cl packing, whereas the structures of II–IV are based on slightly distorted cubic closest packing of halogen atoms, which accounts for their strong tendency to twinning.