Discuss brifly the nature of bonding in metal carbonyls.

Explanation

(i) In metal carbonyls , the bond between metal atom and the carbonyl ligand consists of two components.
(ii) The first component is an electron pair donation from the carbon atom of carbonyl ligand into a vacant d-orbital of central metal atom.
(iii) This electron pair donation forms ` M overset(sigma " bond ")leftarrowCO ` sigma bond .
(iv) This sigma bond formation increases the electron density in metal d orbitals and makes the metal electron rich.
(v) In order to compensate for this increased electron density ,a filled metal d-orbital interacts with the empty `pi^(**) ` orbital on the carboyl ligand and transfers the added electron density back to the ligand
(vi) This second component is called `pi- ` back bonding ,Thus in metal carbonyls. electron dentisity moves from ligand to metal through sigma bonding and from metal to ligand through pi bonding this synergic effect accounts for strong ` M right Co ` bond in metal corbonyls
(vii) This phenomenon is shown diagrammatically as follows.
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