Hi,
I was wondering if anybody could help with the following:
Explain for the differences in CO stretching frequencies shown below
Complex
Frequency
[Mn(CO)6]+
2090
Cr(CO)6
2000
[V(CO)6]-
1860
[Ti(CO)6]2-
1750
Evidently, they decrease as the central metal ion goes down period 4.
I know the following is true:
- For CO, the stretching frequency is lowered as other e- rich donators are added to the metal ion. however, all of the ligands in each of the complexes are CO ligands, so this can't be the reason.
- "Bridging" of M ions by the CO group lowers in stretching frequency. As the CO is bonded to more and more Metal ions, the frequency lowers. However, I dont think there is any bridging in any of the complexes above?
I know it has something to do with M ion and the bonding in the complex. Is it because the M-L bond is stronger progressively? Because I know this weakens the C-O bond. Please can somebody give me the reason behind the drop in CO stretch frequency as we go along the period.
THANK YOU!