Photoacoustic spectroscopy has been used to measure the optical absorption
of a pair of hydrate isomers of dinuclear copper (II) complexes with 26-mem
bered hexa-aza-macrocycle. It is found that the absorptions of both isomers
in the visible region are quite different, which indicates the diversity o
f their crystal structures. It is also shows that the difference on absorpt
ion properties of the studied isomers is difficult to distinguish by using
other conventional spectroscopies.