Interaction of pyridoxal-derived hydrazones with anions and Co2+, Co3+, Ni2+, Zn2+ cations

Present paper reports on the interactions between four hydrazones derived from pyridoxal and hydrazides of 2-furoic, thiophene-2-carboxylic, pyrazinoic and pyridine-3-carboxylic acids and 10 different anions (F−, Cl−, I−, PO43-, HPO42-, H2PO43-, NO3−, SO32-, SO42-, CH3COO−) and three cations (Co2+, Ni2+, Zn2+). Hydrazones are sensitive towards anion presence in non-buffered DMSO only, thus, indicating that the proton transfer from ligand towards anion is responsible for the changes in colour, UV-Vis and fluorescent spectra. Buffered solutions of ligand mixture with any anion are indistinguishable from free hydrazone. The addition of d-metal ions to pyridoxal-derived hydrazones dissolved in buffered DMSO changes the solution colour, UV-Vis and fluorescent spectra. Conditional rate constants of Co2+ oxidation, as well as the apparent stability constants of Co2+, Co3+ complexes with Schiff bases, were determined from kinetic experiments, while Ni2+, Zn2+ complexes stability constants were calculated from UV-Vis and fluorimetry titration data.