Cobalt(II) complexes with a novel 2,6-diacetylpyridine-adamantane-1-carbohydrazide ligand

A new Schiff base of 2,6-diacetylpyridine and adamantane-1-carbohydrazide—<b>L</b>, as well as two of its solvatomorphic complexes with Co(II), viz. [Co(L)(H₂O)(EtOH)][CoCl₄] ∙ EtOH ∙ H₂O (<b>1</b>) and [Co(L)(MeCN)₂][CoCl₄] ∙ MeCN (<b>2</b>), were synthesized. The reaction of CoCl₂ ∙ 6H₂O with the ligand in a molar ratio 2:1 in ethanol–acetone solvents gives complex <b>1</b>, while the same reaction in acetonitrile–acetone solvents gives complex <b>2</b>. Characterization involved elemental analysis, Fourier transform infrared spectroscopy (FTIR), conductometric measurements, thermogravimetric analysis, single-crystal X-ray diffraction (SC-XRD), and antioxidant tests. Structural analysis revealed ligand coordination in its neutral form as N₃O₂ pentadentate. The cobalt(II) is placed in a pentagonal bipyramidal environment in both complexes, where the donor atoms of the ligand (one pyridine nitrogen, two azomethine nitrogen, and two carbonyl oxygen atoms) form the base of this polyhedron, and solvent donor atoms occupy the axial positions. Detailed comparative analysis of the structural parameters of free ligands and the complexes, as well as their thermal characterization, is given, enabling a better understanding of the measured antioxidant activity. The results suggest the potential these compounds have in further examination of their biological activity, with the complexes being more active than the ligand itself.