Infrared Spectroscopy - Chemistry LibreTexts

Maybe your like

For cis-M(CO)2L4, the symmetry point group of this molecule is C2v.

C2v	E	C2	\({\sigma}\)(xz)	\({\sigma}\)(yz)
\({\gamma}\)co	2	0	2	0

\({\gamma}\)co = A1 + B1

Since A1 has a basis on z axis and B1 has a basis on x axis, there are two IR vibrational bands observed in the spectrum.

For trans-M(CO)2L4, the symmetry point group of this molecule is D4h.

D4h	E	C4	C2	C2'	C2"	i	S4	\({\sigma_h}\)	\({\sigma_v}\)	\({\sigma_d}\)
\({\gamma}\)co	2	2	2	0	0	0	0	0	2	2

\({\gamma}\)co = A1g + A2u

Since A2u has a basis on z axis, there is only one IR vibrational band observed in the spectrum.

Therefore, from what have been discussed above, we can distinguish these two structures based on the number of IR bands.