Experimental and ab initio structural study of estertin compounds, X_3SnCH_2CH_2CO_2Me: Crystal structures of C1_3SnCH_2CH_2CO_2Me at 120 K and Br_3SnCH_2CH_2CO_2Me at 120 and 291 K

摘要

The Me0_2CCH_2CH_2 ligand in X_3SnCH_2CH_2C0_2Me, (X = Cl, Br or I), acts as a C,0-chelating group, via the car_bonyl 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 Sn_O bond lengths in solid 1 (X = Cl, Br or I) indicates that the strength of the Sn_O interaction increases in the order X = 1< Br < Cl. Furthermore, the strength of the Sn-0 bond is greater in CI_3SnCH_2CH_2C0_2Me than in the corresponding ketotin compound, Cl_3SnCMe_2CH_2COMe, another chelated complex. Mixtures of 1 (X = CI) and 1 (X = Br or I) undergo exchange reactions in solution, as shown by NMR spectra, to give all possible halide derivatives, (Cl_nX_(3-n)SnCH_2CH_2CO_2Me: n = 0-3: X = Br or I). A ser_ies of electronic structure calculations on (1: X = F, CI, Br, I, SCN; R = Me) have been carried out at various levels of theory, including RHF and M 2. 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 = CI, Br and I) are reported.