# Effects on Stretching Frequencies in Organometallic Complexes

If you added a negative charge to $\ce{Mo(CO)_6}$ how would this effect the $\ce{CO}$ stretching frequency in an IR spectrum?

My thoughts are that it would lower the $\ce{CO}$ stretching frequency because the metal would be able to donate electron density to the $\pi^*$ orbitals of $\ce{CO}$. Does this reasoning sound plausible?

• That is a reasonable answer. You may want to explicitly mention why back-bonding into $\pi^\ast$ would lead to a lower IR stretching frequency. – SendersReagent Jan 30 '16 at 18:50