Mixed-ligand complexes of nickel(II) involving sulphur-containing ligands and diaminocarboxylic acids

Abstract

Stability constants for mixed-ligand complexes of the types [NiABH2], [NiABH] and [NiAB] formed by Ni n with L-cysteine (cys), D-penicillamine (pen) or L-cysteic acid (cya) as ligand A and DL-2,3-diaminopropionic acid (dapa), DL-2,4-diaminobutyric acid (daba) or DL-ornithine (orn) as ligand B have been determined by the computerbased analysis of pH titration data obtained at 37 ~ and I = 0.15 tool dm-3 (NaC10~). In the [NiABH] species, for all three secondary ligands (B), when A = pen or cya the labile proton appears to be attached to the terminal amino group of ligand B, whereas when A = cys it is not clear where the proton is located. In all the systems in the [NiABH2] species, one proton resides with the primary ligand (A) and the other with the secondary ligand (B). In the [NiAB]-type complexes, cys and pen chelate through the amino and thiolato groups, while cya binds in a glycine-like mode and the secondary ligands (B) coordinate in a terdentate manner.

Solution Equilibria of Ni(II), Cu(II), and Zn(II) Complexes Involving Pyridoxine and Imidazole Containing Ligands: pH Metric, Spectral, Electrochemical, and Biological Studies

“…The maximum percentage of concentration for MA and MA 2 species were ∼35% and ∼15%, respectively, at pH 6.5 (Figure ). The M(II)-him, bim, hist, and his(B) complexation equilibria have been taken from the literature. − …”

“…In continuation of our earlier works on amino acid ternary complexes, − we report here the solution equilibria and stability of ternary complexes of Ni(II), Cu(II), and Zn(II) with pyridoxine (PN) in the presence of imidazole containing ligands, namely, imidazole (him), benzimidazole (bim), histamine (hist), and l -histidine (his). pH metric, spectrophotometric, and cyclic voltammetric studies on these systems were carried out.…”

“…All other chemicals used were of reagent grade purity. Metal perchlorates and other reagents were prepared and estimated as described elsewhere. − The dilute solutions were prepared from doubly distilled deionized water which was previously boiled to remove dissolved CO 2 . Alkali titer concentrations and the absence of carbonate were periodically checked by means of the appropriate Gran titrations against potassium hydrogen phthalate.…”