Chelating (pyrazolylmethyl)pyridine ligands: Coordination chemistry and binding properties with zinc(II) and cadmium(II) cations

Reactions of 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L2) and 2-(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L3) with either Zn(NO3) or Cd(NO3) produced monometallic complexes [Zn(NO3)2(L2)] (1), [Zn(NO3)2(L3)] (2), [Cd(NO3)2(L2)] (3) and [Cd(NO3)2(L3)] (4). In the solid state structures of complexes 1, 3 and 4, L2 and L3 ligate to the zinc and cadmium atoms in a bidentate fashion. The pyrazolyl compounds 2-(pyrazol-1-ylmethyl)pyridine (L1), (L2) and (L3) were also used as model chelating agents for liquid–liquid removal of zinc(II), cadmium(II) and lead(II) cations from water using dichloromethane as the organic solvent. L1–L3 showed extraction efficiencies of 70–88% for zinc(II), 50–55% for lead(II) and (19–31%) for cadmium(II). Theoretical results obtained from density functional theory calculations were consistent with the experimental extraction trends.