BOND STRENGTHS IN 1ST-ROW-METAL CARBONYL ANIONS

Energy-resolved collision-induced dissociation of metal carbonyl anion s M(CO)n-(M = V, Cr, Mn, and Co) is used to determine sequential metal -carbonyl bond energies. The derived thermochemistry can be used in co njunction with literature measurements of neutral chromium carbonyl el ectron affinities to provide (CO)(n)Cr-CO bond strengths, which are co mpared to previous experimental determinations. Literature observation s of ligand exchange reactions are used to derive other metal-ligand b ond strengths. Analysis of the present data and previous values for th e iron and nickel carbonyl anions shows that most metal-carbonyl ligan d bond strengths are ca. 40 kcal/mol, which is apparently the intrinsi c metal-carbonyl bond strength in anions. Several of the values for D[ M--2CO] are significantly lower than average; these bond strengths cor relate with the energy needed to promote the metal anion into a state suitable for bonding. The electronic promotion is apparently complete after the addition of two carbonyl ligands. Comparisons of isoelectron ic species confirm the general order of metal-carbonyl bond strengths, anion greater-than-or-equal-to neutral greater-than-or-equal-to catio n.