Typical values of different compounds and groups

 
Group v(CO) / cm-1
free CO (g) 2143
COT 2000 +/- 100
COB 1800 +/- 75

Here are the values of XMo(CO)3 where X are various groups.

 
X v(CO)
PF3 2074
PCl3 2041
PPh3 1949
PEt3 1937
PY 1888


 
V(CO)6- Cr(CO)6 Mn(CO)6+
v(CO) / cm-1 1860 1980 2090
v(MC) / cm-1 460 441 416