This article describes LCAO–Hartree–Fock–Slater calculations on the binuclear metal carbonyls Mn₂(CO)₁₀, Fe₂(CO)₉ and Co₂(CO)₈. The calculations, which are carried out within a double zeta STO basis, are used to investigate the electronic structure of the carbonyls and to calculate a number of physical properties.

It is found that in Mn₂(CO)₁₀ the two Mn(CO)₅ fragments are bonded by a single Mn—Mn bond, but that in Fe₂(CO)₉ and Co₂(CO)₈ the bonding effects arise from a strong interaction between metal d-orbitals and π* levels of the bridging ligands. Neither in the iron complex, nor in the cobalt complex, is there any evidence for a direct metal–metal bond. The calculated ionisation potentials and u.v. data agree reasonably well with experimental values when these are available. π* Populations of bridging and terminal carbonyls fit well into a correlation with i.r. stretching frequencies previously obtained.