Syntheses and crystal structures of di-μ-chloro-bis [dithiocyanatoselenate(II)] and di-μ-bromo-bis [dithiocyanatoselenate(II)] salts

The compounds were prepared by oxidation of elemental selenium with halogen and addition of [C6H5(CH3)(3)N]SCN or [(CH3)(3)NH]SCN. The crystal structures have been determined by X-ray methods. [C6H5(CH3)(3)N](2)[Se-2(mu -Cl)(2)(SCN)(4)] (1) and [C6H5(CH3)(3)N](2)[Se-2(mu -Br)(2)(SCN)(4)] (2) are isotypic, and so are [(CH3)(3)NH](2)[Se-2(mu -Cl)(2)(SCN)(4)] (3) and [(CH3)(3)NH](2)[Se-2(mu -Br)(2)(SCN)(4)] (4) The anions are cis-SeX2(SCN)(2) squares (X = Cl or Br) dimerised b the halogen atoms. The terminal bonds, Se-S, are in the narrow range 2.252(1) - 2.295(2) Angstrom whereas the bridging bonds are in the wider range; Se-Cl = 2.885(1) - 3.041(1) Angstrom and Se-Br = 2.971(1) - 3.117(1) Angstrom. In the structures of the isotypic pair 3 and 4 there are N-H . . .X hydrogen bonds between the (CH3)(3)NH(+)cations and the halogen atoms, N . . . Cl = 3.114(3) Angstrom and N . . . Br 3.270(3) Angstrom. The bridging bonds of these compounds are increased by an average of 0.087 compared to the corresponding bonds of the isotypic pair 1 and 2.