A Quantum Mechanical Investigation of the Nature of the Dative Bond in Crystalline 1-Chlorosilatrane

Abstract

The molecular geometry of crystalline 1-chlorosilatrane is computed at the self-consistent field (SCF) and density functional theory (DFT) levels of theory with the 6-31G* basis set and compared with experiment. The calculations reproduce the shortening of the Si-N distance in the crystal relative to the gas phase, in agreement with existing experimental data for methyl-and fluorosilatrane. The bond shortening is shown to be the result of a combination of a conformational change in the molecule and dipole-dipole interactions with the surrounding molecules in the crystal. The importance of the need to include long-range interactions in the calculation is demonstrated. The calculated electron density of chlorosilatrane is analyzed in terms of the natural bond orbital formalism (NBO), natural resonance theory (NRT), and the theory of atoms in molecules (AIM).

On the nature of the B⋯N interaction and the conformational flexibility of arylboronic azaesters

“…However, it has to be noted that, similarly to the study of the SiÁ Á ÁN bond, 26 the use of the MP2 method may result in an overestimation of the dispersion-type interactions which can give significant contributions to the energy of the open conformer. Therefore, in accordance with literature devoted to the SiÁ Á ÁN bond properties, [26][27] we have also performed calculations using an efficient DFT method [RI-DFT(BP86)/SV(P)] 37-39 -again obtaining similar results to those computed with DFT(B3LYP)/aug-cc-pVDZ level of theory, thus validating the method used in all further stages.…”

“…The B-N bond is often compared with the Si-N one. 27 However, the formation of the donor-acceptor interaction between the silicon and nitrogen atoms leads to the 5-or 6-coordinated Si atom with a Si-N distance in the range from 1.95 up to 2.75 A ˚.26,31 The Si-N interaction is thus much weaker than the B-N one. Consequently, the electron density found at the BCP is smaller (about 0.15-0.50 e A ˚À3 ).…”

“…26 Moreover, theoretical calculations and gas electron diffraction (GED) studies show that also some silatrane derivatives can exist in two different forms: the exo conformer in which an electron lone pair of the nitrogen atom is directed outward from the silatrane cage, and the endo form with an Si-N dative bond. 27 It was recently shown that substitution via metalation of the N-butyl isomer of 6-butyl-2-(3 0 ,5 0 -difluorophenyl)-(N-B)-1,3,6,2-dioxazaborocane (1 0 ) proceeds well with high yields. 8 However, when the N-tert-butyl derivative, namely 6-tertbutyl-2-(3 0 ,5 0 -difluoro-phenyl)-(N-B)-1,3,6,2-dioxazaborocane (hereafter abbreviated as 1), is used, the reaction results in a mixture of products containing borinic acids.…”

Hexacoordinate Bonding and Aromaticity in Silicon Phthalocyanine

“…The molecular properties of a large number of pentacoordinate and hexacoordinate silicon molecules have been studied both theoretically and experimentally. − Such molecules are viewed to be hypervalent because the central silicons are thought to bear more than eight electrons in the valence shell. − The Si−N bonding in pentacoordinate silatrane has been extensively studied. , The properties of this bonding are strongly related to the cage effect. It was pointed out that silatrane can exist in an exo form in which the Si−N bonding is unnecessary to support the molecular framework because of the cage effect . Si−N bondings in silicon phthalocyanine are affected by probably an even stronger ring effect and thus are different from most other Si−N bondings.…”