Mononuclear manganese(II) and manganese(III) complexes of N2O donors involving amine and phenolate ligands: absorption spectra, electrochemistry and crystal structure of [Mn(L3)2](ClO4)

• Published in: Transition metal chemistry (Weinheim) 2005-05, Vol.30 (4), p.393-398
• Main Authors: Biswas, Subhendu, Mitra, Kamala, Chattopadhyay, Shyamal K., Adhikary, Bibhutosh, Lucas, C. Robert
• Format: Article
• Language: English
• Subjects: Crystal structure; Oxidation; Spectrum analysis
• ISSN: 0340-4285; 1572-901X
• DOI: 10.1007/s11243-004-7542-6

A number of mononuclear manganese(II) and manganese(III) complexes have been synthesized from tridentate N^sub 2^O aminophenol ligands (HL^sub 1^-HL^sub 5^) formed by reduction of corresponding Schiff bases with NaBH^sub 4^. Three types of tridentate N^sub 2^O aminophenols have been prepared by reducing with NaBH^sub 4^which are (a) Schiff bases obtained by bromo salicylaldehyde reaction with N,N-dimethyl/N,N-diethyl ethylene diamine (HL^sub 1^, HL^sub 2^), (b) Schiff bases obtained by condensing salicylaldehyde/bromo salicylaldehyde and picolyl amine (HL^sub 3^, HL^sub 4^), (c) pyridine-2-aldehyde and 2-aminophenol (HL^sub 5^). All the manganese complexes have been prepared by direct addition of manganese perchlorate to the corresponding ligands and were characterized by the combination of i.r., u.v.-vis spectroscopy, magnetic moments and electrochemical studies. The u.v.-vis spectra of all of the manganese(III) complexes show two weak d-d transitions in the 630-520 nm region, which support a distorted octahedral geometry. The electron transfer properties of all of the manganese(III) complexes (1-4 and 6) exhibit mostly similar characteristics consisting two redox couples corresponding to the Mn^sup III^ [arrow right] Mn^sup II^ reductions and Mn^sup III^ [arrow right] Mn^sup IV^ oxidations. The electronic effect on the potential has also been studied by changing different substituents in the ligands. In all cases, an electron-donating group stabilizes the higher oxidation state and electron withdrawing group prefers the lower oxidation state. The cyclic voltammogram of [Mn^sup II^(L^sub 5^)^sub 2^] shows an irreversible oxidation Mn^sup II^ [arrow right] Mn^sup III^ at -0.88 V, followed by another quasi-reversible oxidation Mn^sup III^ [arrow right] Mn^sup IV^ at +0.48 V. The manganese(III) complex (3) [Mn(L^sub 3^)^sub 2^]ClO^sub 4^has been characterized by X-ray crystallography.[PUBLICATION ABSTRACT]