A theoretical study on electron donor-acceptor complexes of Et2O, Et2S and Me3N with interhalogens, I-X (X = Cl and Br)

The electron donor-acceptor complexes of diethyl ether, diethyl sulfide and trimethyl amine with ICl and IBr are studied by ab initio molecular orbital and density functional methods. Frontier molecular orbital (FMO) analysis reveals that the interaction occurs between the sigma* orbital of iodine in I-X (X = Cl and Br) and the lone pair of donors. Based on this, computed ether . . . IX and amine . . . IX complexes yield C-2v and C-3v geometries respectively, whereas sulfide IX achieves a C-s structure. The natural bond orbital (NBO) analysis confirms the stabilization interaction through the quantified orbital occupancies as anticipated in FMO; the least occupancy in donor orbital and the highest in acceptor predict a greater charge transfer. Computed geometries, corrected interaction energies, NBO and frequency analyses show the sulfide complex to be favorable over ether case, while amine complex is the most efficient one because the complex strength increases this order. Calculations further establish that ICI is a stronger acceptor than I- Br for such complex formation by virtue of greater sigma -withdrawal of Cl over Br. (C) 2001 Published by Elsevier Science B.V.