Main group monocarbonyls

Non-local density functional calculations are used to investigate the properties and bonding of the monocarbonyl complexes of the s- and p-block main group elements of the first five periods. There is good agreement between the calculated properties and those of experimentally observed monocarbonyls. Predictions of the vibrational frequencies and stabilities of, as yet, unknown complexes are given. A bonding model involving synergistic M←CO σ-donation and M→CO π-backbonding analogous to that used for transition metal carbonyls is described. It is used to describe the variations in the properties of these systems within the groups and periods of the main group elements. The limitations of this description when applied to electron-poor and electron-rich main group MCO molecules are outlined. The bonding in the s-block monocarbonyls is dominated by the repulsive σ-interaction between the metal s-electrons and the CO lone pair. In the monocarbonyls of electronegative elements, there is significant involvement of the filled π-level on CO.