The asymmetry parameter of the electric field gradient tensor of TiCl 4 and its complexes studied by NQR nutation spectroscopy

Abstract

Nuclear Quadrupole Resonance (NQR) Nutation Spectroscopy studies and INDO calculations of the electronic structure of TiCl 4 and its complexes have been performed. An explanation of the changes of the NQR frequencies and asymmetry parameters upon complex formation have been proposed. The populations of the TiCl 4 orbitals have been estimated for different crystallographic structures and compared with the population of the TiCl 4·2CH 3CN orbitals. The values of the experimental 35 Cl NQR frequencies correlated with the calculated ones. Moreover, there is good agreement between the experimentally determined and calculated nutation spectra asymmetry parameter for TiCl 4. The results of the INDO calculations showed that the Ti–Cl bond order decreases upon complex formation and consequently the 35 Cl NQR frequencies decrease and the asymmetry parameter increases. On the basis of the results of the quantum chemical calculations the population of the 3p π chlorine orbital decreases when the molecular structure changes from TiCl 4 (T d) to TiCl 4 (D 4 h). The electron density transfer from the p π orbital of the chlorine atom to the d π orbital of the Ti atom decreases due to complex formation. It was found that the INDO method is suitable for determining the electron distribution in TiCl 4 and its complexes.