Ab initio study on the structural features of icosahedral carboranes containing heteroatoms

摘要

Icosahedral carboranes containing heteroatoms (Si, P, As) have been investigated by using ab initio methods to study the structure and vibrational spectra at Hartree-Fock level with 6-31G basis set. The results obtained in this work are in good agreement with experimental ones. It is concluded that the substitution of heavy heteroatoms (Si, P, Ge, As) for icosahedral carborane CH groups leads to the appearance in the spectrum of intense of low-frequency bands that is associated with the heteroatom participation in the cage motions, and also to the red-shift of the B-H stretching and cage frame breathing mode frequencies as compared to those of o=C_2B_10H_12, indicating the weakening of the B-B chemical bond. The optimization of both geometry and the atomic populations indicates that in icosahedral carborane containing heteroatoms the increased electron charges at B atoms compared to o-C_2B_10H_12 will occupy boron skeletal antibonding orbital. This is why the B-B bonds are weaker and the bond lengths are longer accordingly.