ABSTRACT
In all three cases it is the carbon atolll which is illlmediately linked to the metal atoin or atoms. The linear bonding is realized owing to the overlap of filled 30 orbital of CO 1110lecule with the empty a orbital of the metal atom, d z2 orbital with the simultaneous back-donation of electrons from the filled d1T orbitals (e.g., dxz and d yz ) to the overlapping empty 21Ty and 21Tx antibonding orbitals. This back donation contributes to the strengthening of M-C bond by the cOlllpensation of the polarization of 0 bond. The shift of electron density to the 2'IT antibonding orbitals ,veakens the c-o bond in carbon 111onoxide molecule thus decreasing its stretching frequency from 2143 c1n-1 in free CO 1110lecule to 2100-2000 cm-1 for neutral, unsubstituted linearly bonded one [3].
