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Two binuclear complexes of cobalt(III) have been prepared with 3,3′,4,4′-tetrahydroxy-5,5′-di- tert -butylbenzaldazine (H 4 thBu) as bis(catecholate) ligand and two different ancillary ligands, 2,2′-bipyridine (bpy) or 2,2′-dipyridylamine (dpa). These compounds were characterized by 1 H NMR spectra, electrochemical measurements and UV–Vis spectra. In one case, [Co 2 (dpa) 4 (thBu)] 2+ , electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples ( E 1/2 = 1 mV and 168 mV versus Fc/Fc + ). Chemical oxidation of [Co 2 (dpa) 4 (thBu)] 2+ using Ag + is observed to occur as a stepwise two-electron process forming [Co 2 (dpa) 4 (thBu Cat,SQ )] 3+ or [Co 2 (dpa) 4 (thBu SQ,SQ )] 4+ by UV–Vis spectrum. However, [Co 2 (bpy) 4 (thBu)] 2+ shows no change in electronic spectrum under the same conditions of oxidation. This illustrates the dependence of redox properties of the binuclear Co(III) complexes on the nature of the nitrogen-donor ancillary ligands. In this report we discuss the effect of two different nitrogen-donor ancillary ligands on the0 oxidation behavior of binuclear Co(III) complexes. |
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