Experimental and ab initio structural study of estertin compounds, X3SnCH2CH2CO2Me: Crystal structures of Cl3SnCH2CH2CO2Me at 120 K and Br3SnCH2CH2CO2Me at 120 and 291 K

The MeO2CCH2CH2 ligand in X3SnCH2CH2CO2Me, (X = Cl, Br or I), acts as a C,O-chelating group, via the carbonyl group, both in the solid state and in solutions in non-coordinating solvents. The crystal structures of 1 (X = Cl), a redetermination at 120 K and of I (X = Br), at 298 and 120 K, are reported. Comparison of the intramolecular SnO bond lengths in solid 1 (X = Cl, Br or I) indicates that the strength of the SnO interaction increases in the order X = I < Br < Cl. Furthermore, the strength of the SnO bond is greater in Cl3SnCH2CH2CO2Me than in the corresponding ketotin compound, Cl3SnCMe2CH2COMe, another chelated complex. Mixtures of 1 (X = Cl) and 1 (X = Br or I) undergo exchange reactions in solution, as shown by NMR spectra, to give all possible halide derivatives, (ClnX3−nSnCH2CH2CO2Me: n = 0–3: X = Br or I). A series of electronic structure calculations on (1: X = F, Cl, Br, I, SCN; R = Me) have been carried out at various levels of theory, including RHF and MP2. Hessian calculations have also been performed on these optimized geometries in order to obtain internal coordinate force constants. Comparisons of the theoretical and experimental structures of 1 (X = Cl, Br and I) are reported.