Synthesis of Pyrazole‐Based Pyridine Ligands and Their Use as Extractants for Nickel(II) and Copper(II): Crystal Structure of a Copper(II)–Ligand Complex

Abstract

Three pyrazole‐based pyridine ligands, 2‐(3‐butyl‐1H‐pyrazol‐5‐yl)pyridine (1), 2‐[3‐(tert‐butyl)‐1H‐pyrazol‐5‐yl]pyridine (2) and 2‐(3‐octyl‐1H‐pyrazol‐5‐yl)pyridine (3) were synthesised and fully characterised using conventional means. We then carried out a comprehensive solvent‐extraction study of NiII and CuII in the presence and absence of a synergist (sodium p‐dodecylbenzenesulfonate). The solvent extraction of only NiII in the presence of a synergist produced extraction values between 72 and 73 %. The competitive extraction of NiII and CuII from a base‐metal ion mix (Co2+, Ni2+, Zn2+, Cu2+, Pb2+ and Cd2+) produced extraction values of 85–90 % extraction of CuII for two ligands without synergists and values for CuII and NiII with synergists were in the range 38–45 %. Selectivity studies in favour of the targeted CuII, where the metal ion's concentration was 10 and 100 times lower than the concentration of the other base‐metal ions, showed extremely good selectivity for CuII. Metal‐ion stripping studies were carried out at pH 1.00, producing moderate results. pH isotherms for NiII and CuII were very broad, with CuII showing higher extraction results than NiII. Time‐dependent extraction studies showed equilibration after 2–8 h. Finally, single crystals of the aqua{2‐[3‐(tert‐butyl)‐1H‐pyrazol‐5‐yl]pyridine}dinitratocopper(II) complex were obtained. The coordination around the copper(II) centre is pseudo‐square‐pyramidal.