The C-O stretching frequency of carbon monoxide changes when the molecule coordinates to a metal centre. Does it increase or decrease? Explain

decrease

Explanation

During the co ordinate bond between the Carbonyl and The metal,

The Carbonyl donates the sigma electrons and through the process of back bonding, it accepts the electrons in its pi star orbitals i. e., the antibonding orbitals, thereby reduces the bond order and which in turns reduces the bond strength and, there fore,

The IR stretching frequency for CO reduces.