pH-metric and spectroscopic studies on some ternary complex systems of nickel(II)

Equilibrium based computer models using MINIQUAD-75 computer program on eig hteen ternary complex systems viz. Ni (II)-histamine(hist)/L-histidine(his) (A) aminobutyric acid (2aba), DL-3-aminobutyric acid (3aba), 4-aminobutyric acid(4aba), DL-4-amino-3-hydroxybutyric acid (ahba), 1,2-diaminopropane (d p), 1,3-diaminopropane(tp), DL-2,3-diaminopropio-nic acid(dapa), DL-2,4-dia minobutyric acid(daba) and DL-ornithine(orn) (B) at 37 degrees C and I=0.15 mol dm(-3) (NaClO4) have demonstrated the formation of the ternary complex species of the type NiAB, NiABH or NiABH(2). The results suggest that the Ni (II) ternary chelates containing five and six membered chelate rings are more stable than those with six membered rings, there is a general agreeme nt between the results obtained by the pH-metric and spectral measurements in the systems under investigation. In the NiABH type of species the result s indicate the possibility of the attachment of the extra proton to be with the respective secondary ligand. The trends hi the results for the NiABH(2 ) complexes indicate that one proton resides with the primary ligand and th e other with the secondary ligand. The computer-simulated distribution of t he complexes in solution has also been evaluated.