Performance of ONIOM in the investigations of tri-n-butyltin compounds

The performance of ONIOM was systematically assessed in the calculations of various properties for six conformers of tri-n-butyltin chloride and tri-n-butylmethyltin. Three ONIOM combinations of levels of theory, namely ONIOM(B3PW91/IGLO:HF/3-21G*), ONIOM(B3PW91/IGLO:PM3) and ONIOM(B3PW91/IGLO:UFF), were used and for each combination three ONIOM partitioning schemes of the investigated molecules were probed. The results of such molecular properties as structural parameters, relative conformational energies, dipole moments, vibrational frequencies and chemical shifts obtained by the ONIOM combinations were compared in a statistical manner with the reference data calculated using B3PW91/IGLO. It was found that ONIOM(B3PW91/IGLO:HF/3-21G*) and ONIOM(B3PW91/IGLO:PM3) reproduce the structural parameters of the investigated conformers accurately when the core layer contains the (–CH2CH2CH2)3SnX or (–CH2CH2)3SnX fragment (X = Cl, Me). ONIOM(B3PW91/IGLO:HF/3-21G*) with the (–CH2CH2)3SnX core is recommended for fast predictions of relative conformational energies, dipole moments and vibrational frequencies. A good agreement with the reference results of 119Sn, 13C and 1H NMR chemical shifts was obtained only in one case, namely for ONIOM(B3PW91/IGLO:HF/3-21G*) and the largest possible core layer.