Molecular Structures of Acetylene Derivatives of Tin. VIII Trimethylstannylacetylene: Use of Results of Quantum-Chemical Calculations and Spectroscopic Measurements in Analysis of Gas-Phase Electron Diffraction Data |
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Authors: | Khaikin L. S. Grikina O. E. Granovsky A. A. Nikitin V. S. Vilkov L. V. |
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Affiliation: | (1) Department of Chemistry, M. V. Lomonosov Moscow State University, 119992 Moscow, Russian Federation |
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Abstract: | Structural analysis of electron diffraction data on trimethylstannylacetylene, (CH3)3SnCCH (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)3SnCCSn(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—CMe 2.147(7), Sn—C2.096(17), CC 1.237(11), CMe—H (av.) 1.091(4), CMe—Sn-C107.1(7), Sn—CMe—H (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. |
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Keywords: | Trimethylstannylacetylene gas-phase electron diffraction quantum-chemical calculations molecular structure force field scaling normal coordinate analysis |
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