We report a study of the simultaneous equilibria existing in aqueous MCl2-pyrazole (M = Cu2+, Ni2+) solutions. We collected concentration-dependent UV-visible spectra by varying the metal, pyrazole, and chloride concentrations. Statistical deconvolution of the spectra provide the number of observed absorbers, the absorption profile of each, and the free energies of the ligand addition reactions. For Cu2+, the MLn (n = 0 - 4) complexes were observed, with free energies for the sequential ligand addition reactions decreasing from -21.0 kJ/mol to -5.0 kJ/mol. For Ni2+, the MLn (n = 0 - 3) complexes were observed, with free energies decreasing from -45.2 kJ/mol to -5.3 kJ/mol. Mass spectra suggest that the observed complexes carry an associated Cl- ion in addition to the pyrazole ligand.

Characterization of aqueous metal-pyrazole complexes

249th National Meeting (2015)

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