Donor–Acceptor Bond in Nontransition and Transition Element Complexes: Studies with Natural Bonding Orbital Approach

Electronic structures of tin, antimony, titanium, and niobium chloride complexes were analyzed using density functional theory. Parameters of nuclear quadrupole resonance spectra calculated using pseudopotential and all-electron basis states were compared with the experimental values. It was shown that the use of the central atom pseudopotential leads to a significant deviation of the atomic quadrupole coupling constants from their experimental values. The bonding in complexes was analyzed by making use of the natural orbitals of metal–chlorine and metal–ligand bonds. Donor–aceptor interactions in complexes of main group elements are described within the framework of sp-hybridization, while those in the transition element complexes, within the sd-hybridization framework.