Ternary complexes of nickel(II) involving 6-aminopenicillanic acid and some potentially bidentate or tridentate ligands

Multiple equilibrium studies by pH-metric and visible spectral measurements in the ternary nickel(II) complexes with 6-amino-penicillanic acid (6apa) as ligand A and diamines [1,2-diaminopropane(dp), and 1,3-diaminopropane(tp)] and diaminocarboxylic acids [DL-2,3-diaminopropionic acid(dapa), DL-2,4-diaminobutyric acid(daba) and DL-2,5-diaminovaleric acid(dava)) as ligands B show the presence of NiABH(2), NiABH or NiAB ternary complex species. The ligand, 6apa binds the metal ion via 6 amino and 7 carbonyl oxygen atoms in both the NiABH and NiAB species, and the binding of ligand B in NiAB complexes is exactly similar to their binding in the respective binary species. The results indicate the site of protonation in the NiABH species to be with the terminal amino group of the ligand B. In the NiABH, complexes, one proton is attached to the ligand A and other to the ligand B. The computer simulated distribution of the complexes in solution has been evaluated.