Calculation of the relative stability of molecular alumoxanes

Calculations have been performed on a series of alumoxane rings and cages having the formula [HAlO]n (n = 2-10). Results from these calculations are in excellent agreement with previous calculations on methyl alumoxane rings and cages and experimental structures of organic alumoxane rings and cages. Optimized aluminum-oxygen bond lengths of both rings and cages were found to increase with decreasing stability of these compounds. Comparison of the calculated IR spectra for all of these cages with the experimental spectra of methyl alumoxane (MAO) catalyst suggests that the structure of MAO is composed of large cages containing both four- and six-membered rings.