Two complexes: Os(CO)3(PPh3)2 and Os(CO)2(PPh3)3 both have this single intense CO band in the IR around 1895 cm-1. So how can I use group theoretical arguments to find out which isomer is present for each complex? Also, how ( or is there a way?) to confirm this kind of analysis? The only thing I know for sure is that osmium(0) compounds are usually trigonal bipyramidal shapes.