Bond indices (I) have been calculated, using the CNDO-based molecular-orbital bond index method, for real and hypothetical closo borane species, BnHc−n (n = 5–12; c = 0, 2 or 4), and used to infer their relative stabilities by means of the bond index (I)bond enthalpy [E (kJ mol−1)] equations E(BB) = 297.9I(BB) and E(BH) = 374.8I(BH). For the species able to tolerate n + 2 skeletal electron pairs (n = 8, 9 or 11) in closed-shell electronic configurations, estimates of the relative stabilities of alternative nido structures for the anions BnH4−n have been made. Detailed assessments of the changes in bond index with electron numbers of particular edge types for BnHc−n species (n = 8, 9 or 11; c = 0, 2 or 4) have been carried out, providing quantitative confirmation of earlier qualitative predictions, and showing that generally for the “normal” closo BnH2−n species addition or removal of an electron pair leads to the same type of polyhedral distortion, because, where the HOMO of BnH2−n is bonding for a particular edge, the LUMO is antibonding.
- bond indices
- molecular-orbital bond index method
Mulvey, R., ONEILL, M. E., WADE, K., & SNAITH, R. (1986). Bond indices, enthalpies and relative stabilities of real and hypothetical closo-BnHc−n clusters (n = 5–12; c = 0, 2 or 4) as revealed by the molecular-orbital bond index method. Polyhedron, 5(9), 1437-1447. https://doi.org/10.1016/S0277-5387(00)83505-6