Cobalt(III) complexes using in-plane tetradentate pyridinecarboxamide ligands and two monodentate axial ligands: spectroelectrochemical correlation

Ray, M. ; Mukherjee, R. N. (1992) Cobalt(III) complexes using in-plane tetradentate pyridinecarboxamide ligands and two monodentate axial ligands: spectroelectrochemical correlation Polyhedron, 11 (22). pp. 2929-2937. ISSN 0277-5387

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S02775...

Related URL: http://dx.doi.org/10.1016/S0277-5387(00)83597-4

Abstract

A series of diamagnetic cobalt(III) complexes of bpb and bpc ligands [H2bpb = 1,2-bis(2-pyridinecarboxamido)benzene; H2bpc = 4,5-dichloro-1,2-bis(2-pyridinecarboxamido) benzene] with axial ligands (Cl-, N3-, SCN-, NO2- or MeCO2-) has been synthesized. The trans geometry has been shown by 1H NMR spectroscopy. The brown or green crystalline complexes display dominant ligand-to-metal charge-transfer transitions at ca 400 nm, while in the low-energy region ligand field transitions are observed. From an analysis of the d-d transition(s) ligand field parameters of the in-plane and axial ligands have been determined. In acetonitrile solution the complexes exhibit an irreversible CoIII-CoII couple [Epc -0.42 to -1.18 V vs saturated calomel electrode (S.C.E.)] and a quasi-reversible CoII-CoI couple (Ef -1.12 to - 1.27 V vs S.C.E.). When X = SCN- this couple is irreversible (Epc = -1.40 V vs S.C.E.). These complexes display an additional quasi-reversible oxidative response (0.69-0.92 V vs S.C.E.) of primarily ligand oxidation origin. When X = NO2- and SCN- this couple is irreversible [Epa = 0.88 V (NO2-); Epa = 1.00 V (SCN-)]. A linear spectroelectrochemical correlation has been obtained between the ligand field strength of the axial ligands and the cathodic peak potential for the CoIII-CoII couple.

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