We report the results of quantum-chemical calculations at RHF/6-31G(d), MP2/6-31G(d) and MP2/6-31+G(d) levels made for 1-chlorosilatran molecule with total optimization of its geometry including calculations made at the MP2/6-31G(d) level at different Si…N distances (from 2.0 to 3.7 Å). It is shown that coordination bond in silatranes is a result of joint participation of different atomic orbitals of the Si and N atoms in some molecular orbitals. The number of these orbitals increases as Si and N atoms converge. This leads to a decrease in total energy value of the molecule. Сoordination and covalent bonds in such molecules have the same nature. These bonds differ only in length and strength. On reduction of the Si…N distance, a shift of electron density from the O and Si atoms to the Cl atom, and increase in the Si-Cl bond length take place. At this point, noticeable variations in populations of valence s- and pz-orbitals of the N atom are conditioned mainly by a variation in its valence angles.
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