3-Pyridylmethanol vs. N,N′-diethylnicotinamide in copper(II) complex formation – A comparative EPR study

Copper(II) complexes, formed from 4-chlorosalicylic acid anion A (A = 4-Clsal−), different copper(II) salts (Cu(ac)2 or CuSO4) and different N-donor ligands B (B = 3-pyridylmethanol (ron) or N,N′-diethylnicotinamide (denia)) with varying N-donor ligand-to-metal ratio (x), were studied by EPR spectroscopy in the frozen water/methanol (1:3 v/v) solutions. The number of ligand B molecules coordinated to Cu(II) central ion was determined from the nitrogen perpendicular and parallel superhyperfine splitting multiplets of Cu(II) EPR spectra. It was found for both N-donor ligands: (i) At lower ligand B concentrations (x = 1, 2), [CuB] and/or [CuB2] species having one and/or two molecules of ligands B in equatorial position were dominant. The dominant ternary complex particles were [CuA2B2] species. (ii) At higher ligand B concentrations (x ⩾ 4) the formation of [CuB3] and/or [CuB4] species having three and/or four molecules of ligands B in equatorial position was confirmed. Such information is not possible to get from Cu(II) EPR spectra of powdered samples of given copper(II) complexes.