Crystal structures of phenyltrimethylammonium salts of hexabromodiselenate(II), [C6H5(CH3)3N]2[Se2Br6], hexachlorodiselenate(II), [C6H5(CH3)3N]2[Se2Cl6], and a mixed bromo/chlorodiselenate(II), [C6H5(CH3)3N]2[Se2Br5Cl]

The title compounds were prepared from elemental selenium and halogen and phenyltrimethylammonium halide. The crystal structures of [C6H5(CH3)(3)N](2)-[Se2Br6] (1), [C6H5(CH3)(3)N](2)[Se2Br5Cl] (2) and [C6H5(CH3)(3)N](2)[Se2Cl6] (3) have been determined by X-ray methods. Crystals of 1, and 2 are monoclinic, space group P2(1)/c with Z=4 and a=9.366(2), b=10.095(2), c=28.748(6) Angstrom, beta=91.54(3)degrees for 1, and a=9.371(2), b=10.054(2), c=28.685(6) Angstrom, beta= 91.99(3)degrees for 2. Crystals of 3 are monoclinic, space group P2(1)/n with Z=2 and a=9.086(2), b=10.306(2), c=14.110(3) Angstrom, beta=96.89(3)degrees. The Se2X62- ions consist of two edge-sharing distorted SeX4 squares. The terminal bonds are 2.404(2)-2.439(2) Angstrom in 1 and 2.260(2)-2.261(2) Angstrom in 3, whereas the bridging bonds are 2.792(2)-2.899(2) Angstrom in 1 and 2.590(4)-2.899(4) Angstrom in 3. In 2 each halogen position is partly occupied by bromine and partly by chlorine, the content of chlorine in one position varying from 7 to 28%. The observed effect on bond lengths by replacing some of the bromine by chlorine is small.