Infrared spectroscopy
Infrared spectroscopy has been used extensively to distinguish between isomers. Many complexes of divalent metals are "N"-bonded. "O"-bonding has been suggested for complexes of the type [M(OCN)6]"n"−, M = Mo(III), Re(IV) and Re(V). The yellow complex Rh(PPh3)3(NCO) and orange complex Rh(PPh3)3(OCN) are linkage isomers and show differences in their infrared spectra which can be used for diagnosis (PPh3 stands for triphenylphosphine).