| Abstrakt: |
Structural analysis of electron diffraction data on trimethylstannylacetylene, (CH3)3SnC/math>CH (1), obtained in the previous investigation (the nozzle temperature being 22°C), has been performed with consideration of nonlinear kinematic effects at the first-order level of perturbation theory (h1). The geometry and force field of 1 have been calculated by the RHF and MP2 (frozen core) methods. The effective core potential in SBK form and the optimized 31G* valence basis set have been applied in the case of Sn atom. The 6-311G** basis set have been used for carbon and hydrogen atoms. Vibrational spectra of the light and two deuterated isotopomers of 1 have been interpreted using the C3v equilibrium molecular symmetry. For this purpose, the procedure of scaling the quantum-chemical force field by fitting the calculated frequencies to the experimental ones has been employed. The root-mean-square (RMS) vibrational amplitudes and shrinkage corrections used in the electron diffraction analysis have been calculated from the scaled quantum-chemical force field. It has been shown that flexibility of the linear fragment in 1 decreases considerably compared to that of the symmetrically substituted acetylene fragment in the (CH3)3SnC/math>CSn(CH3)3 molecule (2). Using these data, we refined the geometrical parameters of 1 in terms of a static C3v symmetry molecular model. The following rh1 values have been obtained (the bond distances are given in Å and the valence angles in degrees): Sn\bondCMe 2.147(7), Sn\bondC/math>2.096(17), C/math>C 1.237(11), CMe\bondH (av.) 1.091(4), CMe\bondSn-C/math>107.1(7), Sn\bondCMe\bondH (av.) 113.4(6). The values in parentheses are experimental total errors including least-squares standard deviation values and scale uncertainties. The structural parameters of linear fragments in both ethynyl derivatives of Sn 1 and 2 are found to be virtually equal. [ABSTRACT FROM AUTHOR] |
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