Synthesis, molecular structure, and spectral analysis of copper(II) complexes derived from pyridinediols

<div><p>A series of mononuclear copper(II) complexes was synthesized by reaction of different 2,6-disubstituted pyridines with elemental Cu in a CCl₄/DMSO solvent system. Physical properties were analyzed using IR, optical spectroscopy, mass spectrometry, and EPR. Single-crystal X-ray diffraction for complexes <b>2a</b> and <b>4a</b> revealed that the molecular structure of <b>2a</b> is composed of a six-coordinate unit in which two ligands are linked to Cu(II) by oxygen and nitrogen donors. Conversely, in the molecular structure of <b>4a</b>, the Cu(II) has a slightly distorted trigonal bipyramidal arrangement, where the coordination environment around the copper ion is five-coordinate. EPR spectra of Cu(II) complexes were illustrated elaborately and some theoretical data were abstracted from EPR curves to support the proposed structures.</p>