SO3 complexes with nitrogen containing ligands as the object of nuclear quadrupole interactions and density functional theory calculations

We have analyzed by means of DFT calculations of nitrogen nuclear quadrupole coupling constants of a range of SO3⋯B complexes (n aπ type in Mulliken notation) formed between molecules SO3 and Lewis bases B. The geometrical parameters, the rotational constants and the nitrogen nuclear quadrupole coupling constants obtained by these calculations substantially agree with the data from microwave spectroscopy in the gas phase. A good correlation is found between the calculated bond strengths of these complexes and the lengthening of the S-O bond. The NBO partitioning scheme and the stabilizing orbital interaction term suggest that there are excellent correlations between the charge transfer and the bond strength. From electron partitioning analyses and Klopman's approach, it follows that for the SO3⋯B complexes the electrostatic contribution to the bonding is comparable to the covalent contribution.