DFT calculations, structural, and spectroscopic studies on the products formed between IBr and N,N'-dimethylbenzoimidazole-2(3H)-thione and –2(3H)-selone

The NBO charge distribution calculated at DFT level on the [LEX]+ species [LE = N,N′-dimethylbenzoimidazole-2(3H)-thione (3) and -2(3H)-selone (4) (Scheme 1); X = I, Br] suggests that the most likely products from the reaction of 3 and 4 with IBr are the 10-X-2 charge-transfer (CT) adduct and the 10-Se-3 “T-shaped” hypervalent adduct featuring a linear Br–Se–I system, respectively. This prediction is confirmed by the synthesis, and X-ray diffraction analysis of 3·IBr (I) and 4·I0.72Br1.28 (II). In particular, II is a 10-Se-3 “T-shaped” hypervalent adduct containing an almost linear X–Se–X system [X–Se–X 179.07(3)°, X = I0.36/Br0.64], which is roughly perpendicular to the average plane of the benzoimidazole moiety. The FT-Raman spectra of I and II agree very well with their structural features. In particular, the complexity of the FT-Raman spectrum of II reflects the disorder in the X-ray crystal structure of this compound.