Multidentate bis(pyrazolylmethyl) pyridine ligands: coordination chemistry and binding properties with zinc(II) and cadmium(II) cations

The coordination chemistry and cationic binding properties of 2,6-bis(pyrazol-1-ylmethyl) pyridine (L1), 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl) pyridine (L2), and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl) pyridine (L3) with zinc(II) and cadmium(II) have been investigated. Reactions of L2 with zinc(II) and cadmium(II) nitrate or chloride salts produced monometallic complexes [Zn(NO3)(2)(L2)] (1), [ZnCl2(L2)] (2), [Cd(NO3)(2)(L2)] (3), and [CdCl2(L2)] (4). Solid state structures of 1 and 3 confirmed that L2 binds in a tridentate mode. While the nitrates in the zinc complex (1) adopt monodentate binding fashion, in cadmium complex (3), they exhibit bidentate mode. L1-L3 show binding efficiencies of 99% for zinc(II), 60% for lead(II), and 30% for cadmium(II) cations from aqueous solutions of the metal ions. Theoretical studies using Density Functional Theory were consistent with the observed extraction results.