Cluster bond enthalpies, EL(BB), and orders, n̄(BB), for the structurally characterised closo anions, BnHn2− (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships EL(BB) (kJ mol−1) = 1.766 × 1011 [L(BB)]−4.0 and EL(BB) (kJ mol−1) = 318.8[n̄(BB)]0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, EI, have been calculated using the relationships EI(BB) = 297.9 I(BB) and EI(BH) = 374.8I(BH) (enthalpies in kJ mol−1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of EL and Σ EL generally exceed those of EI and Σ EI by some 8% and calculated values of I generally exceed those of n̄ by a greater amount, the trends in these parameters for the series of BnHn2− anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ EI values suggest that the anions are all of comparable stability, the ΣEL values clearly show B6H62−, B10H102− and B12H122− to be more stable than B8H82−, B9H92− and B11H112−. The interatomic distances in B7H72− and in the unknown B5 H52− are estimated and used to assess their relative stabilities. The EL values suggest that B7 H72− is of comparable stability to B8H82− etc., but show B5H52− as relatively unstable. The EI values suggest that both of these anions should be relatively stable members of the series of closo anions.
- cluster bonding
- borane anions
- closo anions
- bond enthal
HOUSECROFT, C. E., SNAITH, R., MOSS, K., Mulvey, R., ONEILL, M. E., & WADE, K. (1985). Cluster bonding and energetics of the borane anions, BnHn2− (n = 5–12): A comparative study using bond length—bond enthal. Polyhedron, 4(11), 1875-1881. https://doi.org/10.1016/S0277-5387(00)86704-2