Localized molecular orbital studies on B4Cl4, 1,5‐C2B3H5 and BH2‐(n = 6–10, 12)

Abstract

AbstractThe wave functions, level energies and Mülliken population analysis of localized molecular orbitals (LMO's) for B4Cl4, 1,5‐C2B3H5 and the closo‐BnH2‐n (n = 6–10, 12) are calculated by using the Edmiston‐Reudenberg energy localisation scheme under the CNDO/2 approximation in order to reveal the nature of quasi‐aromaticity of the closo‐BnH2‐n (n > 5). It has been found that all the B‐H or B‐Cl LMO's are highly localised between the B and H (or Cl) atoms, corresponding to B—H or B—Cl σ‐bond, while the Bn framework bonding is formed mainly by the three‐centered two‐electron B‐B‐B bonds on the polyhedral faces. In the cases of B4Cl4 and 1,5‐C2B3H5, these three‐centered B‐B‐B bonds just fill their polyhedral faces; however, for the framework bonding of the closo‐BnKn2‐ (n > 5), the valence electron deficiency leads to the delocalisation of their three‐centered B‐B‐B bonds, and as delocalisability of this three‐centered B‐B‐B bond increases, some three‐centered B‐B‐B bonds are farther delocalized to become a four‐centered B‐B‐B‐B bond. It is important that for the closo‐BnHn2‐ (n > 5), the sequence of this delocalisability of the three‐centered B—B—B bond is consistent with the degree of quasiaromaticity of the closo‐boranes.