Crystallographic characterisation of dihalogenodimethylselenium compounds, Me2SeX2 (X = Cl, Br or I) and the dependence of their structures on the nature of the halogen

Abstract

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) Å, 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 ₂ to produce the regular trigonal-bipyramidal molecule Me ₂ SeBr ₂ with Se–Br bond lengths of 2.546(4) and 2.551(4) Å, i.e. virtually identical. However, the dichloro-compound, Me ₂ SeCl ₂ , prepared from the reaction of SO ₂ Cl ₂ with Me ₂ Se, shows significant variations in Se–Cl bonds [2.349(5), 2.408(6), 2.351(6) and 2.405(5) Å (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.