Crystallographic characterisation of dihalogenodimethylselenium compounds, Me(2)SeX(2) (X=Cl, Br or I) and the dependence of their structures on the nature of the halogen

The reaction of Me(2)Se with I-2 in diethyl ether produced the charge-transfer complex Me(2)Se-I-I, which has a short I-I distance of 2.916(3) Angstrom, when compared to the analogous Group 16 compound Me(3)As-I-I, reflecting the weaker donor power of Se compared to As towards diiodine. Dimethyl selenide reacted with Br, to produce the regular trigonal-bipyramidal molecule Me(2)SeBr(2) with. Sr-Br bond lengths of 2.546(4) and 2.551(4) Angstrom, i.e. virtually identical. However, the dichloro-compound, Me(2)SeCl(2), prepared from the reaction of SO2Cl2 with Me(2)Se, shows significant variations in Se-Cl bonds [2.349(5), 2.408(6), 2.351(6) and 2.405(5) A (two inequivalent molecules in the asymmetric unit)]. This is due to significant long Se . Cl contacts which lie within the van der Waals radii. These results illustrate the structural changes observed for the Me(2)SeX(2) (X = I, Br or Cl) series in the solid state upon changing the nature of the halogen.