INFRARED-SPECTRA OF ALUMINUM CARBONYL-COMPLEXES IN SOLID ARGON

Infrared spectra of aluminium carbonyl complexes generated in argon ma trices 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 const ant (F(CO) almost-equal-to 14 mdyn angstrom-1) markedly smaller than i n Al(CO)2 (15.5 mdyn angstrom-1), thus contradicting earlier studies c oncluding that an AlCO complex should be unbound or, at most, a weak v an der Waals complex. The new features in the low-frequency region for the previously characterized AI(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 C2v symmetry with bent Al-C=O groups. The existence of isocarbonyl structures could not be confirmed, but the bimetallic species Al2CO and Al2(CO)4 were ident ified.