Infrared spectra of aluminium carbonyl complexes in solid argon

Abstract

Infrared spectra of aluminium carbonyl complexes generated in argon matrices by co-condensation of aluminium atoms and carbon monoxide have been observed and analysed. AlCO, aluminium monocarbonyl, was isolated and clearly identified. It is characterized by a carbonyl force constant (F_co≈ 14 mdyn Å^–1) markedly smaller than in Al(CO)₂(15.5 mdyn Å^–1), thus contradicting earlier studies concluding that an AlCO complex should be unbound or, at most, a weak van der Waals complex.

The new features in the low-frequency region for the previously characterized Al(CO)₂ species are analysed based on a harmonic force field. The experimental results are consistent with the prediction of an aluminium dicarbonyl structure of C_2v symmetry with bent Al—CO groups. The existence of isocarbonyl structures could not be confirmed, but the bimetallic species Al₂CO and Al₂(CO)₄ were identified.