Synthesis,spectroscopy and redox properties of mononuclear manganese(II) and manganese(IV) complexes with N-(aryl)-pyridine-2-aIdimine (L) and its amide derivatives.X-ray structural characterization of [Mn(MeL)_2(NCS)_2] (MeL = N-(4-methylphenyl)-pyr

摘要

A series of mononuclear Mn~(II) and Mn~(IV) complexes of general formulae [MnL_2(NCS)_2] (1a-1d) and [Mn(L')_2(NCS)_2] (2a-2c) have been prepared where L are Schiff bases obtained by the condensation of pyridine-2-aldehyde with para-alkyl-substituted aniline,and L' are the corresponding amide ligands.The room temperature magnetic susceptibility data of (1a-1d) indicate that Mn~(II) is in a high spin state.The cyclic voltammograms of (1a-1d) exhibit a one-electron quasi-reversible Mn~(II)->Mn~(III) oxidation.A linear correlation has been found when E~0[Mn~(III)/Mn~(II)] is plotted against Hammett sigma_p parameters.X-ray crystallographic data of (1b) shows that the central Mn~(II) ion adopts a distorted octahedral geometry with six different Mn-N distances.Upon oxidation of Mn~(II) complexes (Ib-ld) by H_2O_2,the corresponding Mn~(IV) complexes (2a-2c) were obtained,and the Schiff base ligands were oxidized to the corresponding amides.The lowest energy LMCT bands of these Mn~(IV) complexes correlate linearly with Hammett sigma_p parameters.The redox behavior of the Mn~(IV) complexes has been investigated by cyclic voltammetry.E.p.r.spectra of the Mn~(II) and Mn~(IV) complexes are also reported.