E. Belogolova, V. Sidorkin
2004
Citations
0
Influential Citations
27
Citations
Journal
Journal of Molecular Structure-theochem
Abstract
Abstract The structure and thermodynamic stability of Si-substituted (O–Si)dimethyl(N-acetylacetamidomethyl)silanes were studied at the ab initio (HF, MP2 with different basis sets) and DFT (B3LYP/6-31G*) levels of theory. Performed calculations have demonstrated that these compounds exist explicitly in chelate forms with pentacoordinate silicon atom with energetic advantage of these forms over nonchelate structures equal to ∼3–6 kcal/mol (at T=0 and 298 K) depending on the nature of axial substituent at the silicon atom (X=OCOCH3, OCOCF3, F, Cl, Br). According to the Bader analysis of electron distribution, chelate cycles SiCNCO in the compounds studied are closed by weakly covalent Si–O bonds. A decrease in the Si–O bond distance upon variation of X is accompanied by increasing the stability of the (O–Si)chelate complexes and the extent of electron density transfer from the donor oxygen atom to the acceptor XSiC3 fragment. The negative sign of the multi-center bond indices calculated for the X–Si–O fragment of Si-substituted (O–Si)dimethyl(N-acetylacetamidomethyl)silanes is suggestive of the (3c-4e) character of bonding in this fragment.