The structures of carbonyls and related compounds

The structures of carbonyls and related compounds The main features are as follows. 

The CO molecule is bonded to the metal atom(s) through C this has been proved for Fe(CO)j and Cr(CO)g and is assumed to be true in all other molecules. 

The CO molecule behaves as a monodentate ligand, (a), as a bridge between two metal atoms, (b), or (less frequently) between three metal atoms, (c). 

The formulae of most simple carbonyls and related compounds are consistent with the view that in many of these compounds the metal atom acquires a share in sufficient electrons to attain a noble gas configuration. Assuming that CO bonded as at (a) contributes 2 electrons, and NO 3 electrons, then in all the following compounds the metal would have the Kr configuration  

In Fe2(CO)9 the same electronic configuration would be reached by the formation of a metal-metal bond metal-metal bonds are an important feature of the polynuclear carbonyls. This simple electron counting is consistent with the formation of mononuclear carbonyls by the even-numbered elements, Ct(CO)6, Fe(CO)s, and Ni(CO)4, and of polynuclear carbonyls by Mn and Co it is not, however, consistent with the formation of V(CO)g. 

---