The bonding in M(CO)n groups (where n= 1, 2, 3, and 4)

The bonding within M(CO)n groups (n= 1,2,3, and 4) in cylindrically symmetric environments is considered using perturbation theory. The case where n= 3, for which there is abundant structural data, is considered in detail, and the treatment is extended to molecules with non-cylindrical symmetry.