DFT calculations of 119Sn chemical shifts using gauge-including atomic orbitals and their interpretation via group properties

Nonrelativistic DFT calculations of the Sn-119 chemical shift are presented for a large series of tetracoordinated Sri compounds, of the type CH3SnRR'R", where R, R', R" are halogens, alkyl, halogenated alkyl, alkoxy, or alkyl thio groups. The B3PW91 functional is used in conjunction with the IGLO III basis set. Leaving out compounds associating in solution and thus changing the Sn coordination, a correlation coefficient r(2) of 0.978 +/- 0.023 is obtained between solvent NMR shifts and calculated values, with a slope of 0.984. These results indicate that this methodology yields excellent results both in the absolute and relative sense for the majority of the cases studied, where cancellation of errors (solvent and relativistic effects) occurs. The results were interpreted in terms of calculated electronegativity, hardness, and softness of the groups SnRR'R", applying a methodology previously developed by us (J. Phys. Chem. 1993, 97, 1826) and using the 6-311++G** basis set fur H, C, Cl, Br, O, and S and 3-21G for Sn and I. Sequences of group electronegativities and hardnesses could be rationalized via previously calculated or experimental first and second row atomic or functional group values reflecting the interplay of qualitative and quantitative changes in groups on the central Sn atom. The evolution of the Sn-119 chemical shift can be successfully interpreted on the basis of group electronegativities for groups introduced in the beta position of the Sn atom, whereas changes in alpha position (i.e., groups directly bonded to Sn) turn out to be essentially hardness related, especially when changes in the row of the periodic table are involved.