The complex formation between Cu(Ⅱ) and chitosan was studied in aqueous solution at different pH values.The composition and structure of chitosan-Cu(Ⅱ) complexes were characterized by elemental analysis

infrared spectra

thermograms and X-ray diffraction.The ratios of glucosamine residue of chitosan molecule to Cu(Ⅱ) are 8∶3

4∶3 and 1∶1 at pH=5

6 and 7

respectively.The results of IR spectra indicated that the —NH2 and —OH of the secondary alcohol of chitosan molecules are coordinated to Cu(Ⅱ). New peaks at 555

532 and 551

551cm-1 appear in the chitosan-Cu(Ⅱ) complexes at pH=6 and 7

respectively.The absorption at 550cm-1 si suggested to be the asymmetric Cu-O vibration and absorption at 511cm-1 could be related to hydroxy-bridged compounds.The marked difference of X-ray diffraction patterns between the chitosan and its complexes indicated thaat the coordination of chitosan to Cu(Ⅱ) could be correlated with the conformation change of chitosan molecules at pH=6 and 7.Chitosan has three steps in the thermal weight loss process

but the complexes have four steps.Considering chitosan being a linear truck poolysaccharide of anti-appeal arrangement

together with its other physical properties

such as solubility and crystallinity

it can be concluded that the complexes of chitosan with Cu(Ⅱ) in the dilute formic acid solution of pH=7have the hydroxy-bridged structure.