LAUSR

Abstract The hexagonal and heptagonal holes of B 39 - allow its complexation with a half sandwich complex ECp∗+ (E Si, Ge, Sn, Pb). Structure and the nature of bonding of (η6/7-B39)E(η5-Cp∗) are explored through the density functional theory based computation. (η6-B39)E(η5-Cp∗) isomers are more stable than (η7-B39)E(η5-Cp∗) and the energy difference between these two isomers decreases down the group from Si to Pb. The dissociation path, (η6/7-B39)E(η5-Cp∗) →  B 39 - + ECp∗+ is studied. For all E, (η6/7-B39)E(η5-Cp∗) is formed exergonically at 298 K temperature as given by the ΔG values of dissociation path [60.1(Si) to 68.3(Pb) kcal/mol for (η6-B39)E(η5-Cp∗) and 58.3(Si) to 67.8(Pb) kcal/mol for (η7-B39)E(η5-Cp∗)]. The adduct becomes bent around the central E atom when B 39 - gets attached to ECp∗+ and the amount of bending increases gradually down the group from Si to Pb. Bonding analysis of the stable isomer, (η6-B39)E(η5-Cp∗) has been done by natural bonding orbital (NBO) and energy decomposition analyses (EDA). The electron density from B 39 - is transferred to the ECp∗+ moiety as revealed by the NBO analysis. All the complexes are mainly stabilized by the electrostatic and orbital interactions between B 39 - and ECp∗+ fragments as highlighted by the EDA results.