Decomposition of high-oxygen content organoaluminum compounds. The formation and structure of the [Al7O6Me16]- anion

Article abstract of DOI:10.1021/om50002a008

The unusual anion [Al₇O₆Me₁₆]^- has been encountered in the decomposition pathways of two different high-oxygen content organoaluminum compounds, K[Al₂Me₆O₂] and presumably Cs₂[Al₂Me₆O]. It is likely that these two compounds pass through the same intermediate and that the [Al₇O₆Me₁₆]^- ion is a thermodynamic sink. In both cases crystalline material has been isolated, and X-ray structural determinations have been carried out. K[Al₇O₆Me₁₆]·C₆H₆ crystalizes in the triclinic space group P1 with lattice parameters a = 12.095 (5) A?, b = 12.222 (5) A?, c = 13.893 (5) A?, α = 105.56 (3)°, β = 94.52 (2)°, γ = 83.98 (2)°, and ρ_calcd = 1.09 g cm^-3 for Z = 2. Least-squares refinement gave a final R value of 0.042 for 2509 independent observed reflections. Cs[Al₇O₆Me₁₆]·3C₆H ₅Me belongs to the cubic space group P2₁3 with a = 17.512 (8) A? and ρ_calcd = 1.16 g cm^-3 for Z = 4. Refinement based on 460 observed reflections gave a final R of 0.075. The anion for the cesium salt lies on a crystallographic threefold axis. The structure consists of an open Al₆O₆ cage capped by the seventh Al atom which is bonded to three alternate O atoms in the cage. The six Al atoms are bonded to two terminal methyl groups each, while the unique Al is bonded to only one methyl group. Each O atom is three coordinate: the ones on the exterior (not bonded to the unique Al atom) bridge two Al atoms and are also bonded to one methyl group each.