Studies of Fe(111) with IHP were carried out oat pH 3.0,5.0 and 8.0. The predominant stocihiometry of the complexes were found out to be ML, M2L and ML2 dependent pH and the related concentration of metal and ligand. The stability constants of complexes were calculated through spectrophotometric and potentiometric methods and found to be comparable. The work yielded the stability constants in the range of 1012 for ML complexes, 1022 for ML2 complexes M2L complexes. For the potentiometric study computer program “BEST” was used to get more reliable results.
The proposed structure of the various species of the complexes were proposed and the structural confirmation was made by and I.R study of the complex.
Thermodynamic stability of ht complexes was assessed by working out various thermodynamic parameters. Preliminary data was gathered by pH titration at temperatures ranging from 25oC to 65 oC. The data was ten processed and analyze by computer program BEST for the refinement of the logβ values. Graphs were plotted with InK versus 1/T which gave ∆H/R as slope and ∆S/R as intercept.
Change in enthalpy values were found to be -5.12x103 KJmol-1 for ML complexes, -6.32x102 KJmol-1 for M2L complexes and 8.07x102 KJmol-1 for ML2 complexes. Change in entropy values were found to be 4.192J-1 for ML complexes, 5.182 J-1 for M2L complexes and 2.828 J-1 for ML2 complexes.
The reduction of the complex was performed by ascorbic acid dithionite and hydroquinone at pH 4.5 and at 30oC. The redox potential(εº ox)values with different reductants were found to be -1.58x10-1V with ascorbate, 1.338V with dithionite, and -6.89x10-1V with hydroquinone.
The rate of the of the reduction was deduced by using computer program “Rate 2” and “spectrokinetics” using diode array spectrometer. The rate of reduction was found to be 2.74x10-1 sec-1 with ascorbate dithionite and 1.79x10-1 sec-1 with hydroquinone.
Interaction of Fe(111)-IHP complex with other chelathors of the biological environment like gallic acid, tannic acid and salicylhydroxamic acid was observed. The general trend was found to be:
Saliclhydroxamic Acid > Gallic Acid > Tannic Acid
The rates of replacement show that the fastest replacement is accompanied by salicylhydroxamic acid rate of 2.71x10-1 sec-1followed by Gallic Acid rate being 0.47x10-1 sec-1, and then by tannic acid its rate being 0.44 x10-1 sec-1.
Interaction of the Fe(111)-IHP complex with copper, zinc and calcium was also observed to see for the replacement of Fe(111). It was noted that zinc and calcium have the tendency to form binuclear complex when in limiting concentration and remove iron from the complex when present in excess concentration. The structures of the related complexes were also proposed.