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

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 σ* 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 C2v and C3v geometries respectively, whereas sulfide ⋯ IX achieves a Cs 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 ICl is a stronger acceptor than I–Br for such complex formation by virtue of greater σ-withdrawal of Cl over Br.