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Themetal-carbon bonds in metal carbonyls have both ╧Г and ╧А characters. A ╧Г bond isformed when the carbonyl carbon donates a lone pair of electrons to the vacantorbital of the metal. A ╧А bond is formed by the donation of a pair of electronsfrom the filled metal┬аd┬аorbital into the vacant anti-bonding╧А* orbital (also known as back bonding of the carbonyl group). The ╧Г bondstrengthens the ╧А bond and vice-versa. Thus, a synergic effect is created dueto this metal-ligand bonding. This synergic effect strengthens the bond betweenCO and the metal.
