Synthesis, characterization and electrochemical properties of the transition metal (Fe-Zn) complexes of 2,4-di-tert-butyl-6-(pyridin-2-ylazo)-phenol ligand

Herein we report five homoleptic, six-coordinated 3d metal complexes [Fe-II(L)(2)], 1; [Co-III(L)(2)]CIO4, [2]CIO4; [Ni-II(L)(2)], 3; [Cu-II(L)(2)], 4; [Zn-II(L)(2)], 5 containing tridentate anionic azo-aromatic NNO donor ligand 2,4-di-tert-butyl-6-(pyridin-2-ylazo)-phenol (HL). The complexes are synthesized from the reactions between hydrated metal perchlorates and the ligand, HL in 1:2 molar ratio in methanol. One-electron oxidation of the iron complex, 1 by iodine resulted in the isolation of respective cationic complex [Fe-III(L)(2)]I-3, [1]I-3. All these six complexes are characterized by single crystal X-ray diffraction as well as several spectroscopic techniques and magnetic measurements. While complexes 1, [2]ClO4 and 5 are diamagnetic the other three complexes [1]I-3, 3 and 4 behave as simple paramagnets. Redox properties of both HL and metal complexes are studied by cyclic voltammetry. Analysis of three-dimensional X-ray structure together with Fe-57 Mossbauer spectrum for 1 established a low spin bis-ligated Fe-II configuration. The oxidized iron complex [1]I-3 displayed a metal centered axial EPR signal at g(perpendicular to)= 1.995 and g(II) = 1.993 and its Mossbauer spectrum together with magnetic moment established a low-spin Fe-III configuration revealing that redox events in case of iron are metal centered. One electron reduction of the Co-complex, [2]ClO4 produced a Co-III-complex, which showed 8-lines EPR spectrum at g(av.) = 1.997.