Ab initio and natural bond orbital (NBO) study on the strain energy of chlorocyclotrisilane and chlorocyclopropane

A comparative study between hexachlorocyclotrisilane (1) and hexachlorocyclopropane (2) by ab initio method and natural bond orbital (NBO) analysis was carried out using 6-31G∗∗ basis set, implemented in GAUSSIAN 03 program. The s and p character of SiCl and Si-Si bonds obtained for the compounds were then used to examine the rehybridization effect from the strain energy. A higher strain energy in the former can be satisfactorily attributed to the weaker rehybridization capability of silicon relative to carbon in response to the angle strain such that SiCl bond strengthening is less effective. Strained XCl4 and X2Cl6 (X = C, Si) were used as models to show the rehybridization effect on the geometry and bond orbital energy.