AM1 AND PM3 SEMIEMPIRICAL MOLECULAR-ORBITAL STUDY OF SILATRANES .3. 1-CHLOROSILATRANE

The AMI and PM3 semiempirical models have been employed to study the bonding and structure of 1-chlorosilatrane using full geometry optimization. The heats of formation were calculated at different Si-N distances between 200 and 360 pm. Two minima have been found on the energy profile when C3 symmetry was retained. A third local energy minimum has been found, in an asymmetrical conformation. The energy cost of shortening the Si-N distance has been found to be small; the energy hypersurface is rather flat, with the silatrane skeleton being flexible. The calculations show that the crystal forces could easily distort the gas-phase structure. The comparison of the published X-ray diffraction structure with the calculated geometry and with the experimental geometries of other silatranes leads to the conclusion that the ethoxy links should be disordered.