Heats of formation and bond energies in group III compounds

Abstract
We present heats of formation and bond energies for Group-III compounds obtained from calculations of molecular ground-state electronic energies. Data for compounds of the form MX₀ are presented, where M = B, Al, Ga, and In, X = H, Cl, and CH₃, and n = 1-3. Energies for the B, Al, and Ga compounds are obtained from G2 predictions, while those for the In compounds are obtained from CCSD(T)/CBS calculations ; these are the most accurate calculations for indium-containing compounds published to date. In most cases, the calculated thermochemistry is in good agreement with published values derived from experiments for those species that have well-established heats of formation. Bond energies obtained from the heats of formation follow the expected trend (Cl >> CH₃ - H). However, the CH₃M-(CH₃)₂ bond energies obtained for trimethylgallium and trimethylindium are considerably stronger (> 15 kcal mol^-1) than currently accepted values.