Synthesis, stability constant determination, and structural study of some complexes of a zinc triad containing pyridyl-amine-quinoline and pyridyl-thio-quinoline

The potentially fluorescent and terdentate ligands containing nitrogen or sulfur as coordinating atom were synthesized and used in the formation of perchlorate or chloride complexes of the metals of the Zn triad. The reaction of the ligands with metal perchlorate salts yields the corresponding bis-chelate derivatives, whereas the same ligands react with metal chloride salts to give monochelate complexes. All of these complexes undergo NMR-scale fast fluxional rearrangement in solution. Some structural X-ray diffractometric studies were also performed and the ensuing data confirm the surmised structures and the solution rearrangement in the case of monochelate substrates and of one Hg derivative, respectively. The equilibrium constants of formation in the case of monochelate derivatives were also determined in water by means of spectrophotometric titration of the studied ligand with the metal ions. The values of the equilibrium constants were confirmed by supplementary determination taking into account the exchange between two different metals and/or dissociation equilibria. The fluorescence activity of ligands and complexes was eventually studied and notably one fluorescent silent ligand gives rise to fluorescent zinc derivatives.