Molecular complexes between silicon derivatives and electron-rich groups

Theoretical calculations on a series of SiXY3. . . ZW complexes, where X an d Y are H, F, and Cl, and Z corresponds to an electron donor atom (ZW = NH3 , NCH, CNH, OH2, FH), were performed. The calculations were carried out usi ng B3LYP/6-311++G**, MP2/6-311++G** and MP2/6-311++G(2d,2p) computational m ethods. The electron density was characterized by means of the atoms in mol ecules (AIM) methodology, and the interaction nature was studied with the N BO method. Finally, the effect of the complexation on the nuclear chemical shieldings was evaluated with the GIAO method. The results display a wide r ange of interaction distances that vary from 2.1 to 4.1 Angstrom. The compl exes with shorter interaction distances (similar to2.1 Angstrom) show impor tant distortion effects and large dipole moment enhancements. The NBO analy sis indicates that in those complexes an ionic interaction is formed betwee n the Si and Z atoms. Comparison of the chemical shieldings of the complexe s and the monomers indicates that these interactions could be detected expe rimentally using Si-29 NMR. In addition, in the case of the complexes with NH3 and OH2, the use of N-15 NMR and O-17 NMR could be adequate to check th e potential formation of the corresponding complexes.