[Eddzzz_2012]

Hi. I'm trying to determine whether the C-O stretching frequency will increase or decrease in energy if the M-CO bond was weakened. So:

Stronger M-CO pi-backbonding interaction corresponds to strongest backbonder to C-O ligand
Longest C-O bond length corresponds to lowest oxi state because of being a stronger backbonder
C-o Stretching frequency corresponds to longest C-O bond length
Therefore the C-O stretching frequency will if the M-CO bond was weakened.

Is this correct?

[Schrödinger]

Therefore the C-O stretching frequency will if the M-CO bond was weakened.
Is this correct?

Is what correct?

[Enthalpy]

What about the stiffness of the M-C bond? We're speaking about mechanical vibrations, and C is lighter than O, so any stiff mass bound to C would decrease the frequency.

This is a question from me, not a suggestion.