N,N′-Bis(aryl)pyridine-2,6-dicarboxamide complexes of ruthenium: Synthesis, structure and redox properties
作者:Moutusi Dasgupta、Sumon Nag、Gopal Das、Munirathinam Nethaji、Samaresh Bhattacharya
DOI:10.1016/j.poly.2007.08.042
日期:2008.1
Reaction of five N,N'-bis(aryl)pyridine-2,6-dicarboxamides (H2L-R, where H-2 denotes the two acidic protons and R (R = OCH3, CH3, H, Cl and NO2) the para substituent in the aryl fragment) with [Ru(trpy)Cl-3](trpy = 2,2',2"-terpyridine) in refluxing ethanol in the presence of a base (NEW affords a group of complexes of the type [Ru-II(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [Ru-II(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic H-1 NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru-II(trpy)(L-R)] complexes shows a Ru(II)-Ru(III) oxidation within 0.16-0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94-1.33 V versus SCE and a reduction of coordinated terpyridine ligand within -1.10 to -1.15 V versus SCE. Constant potential coulometric oxidation of the [Ru-II(trpy)(L-R)] complexes produces the corresponding [Ru-II(trpy)(L-R)](+) complexes, which have been isolated as the perchlorate salts. Structure of the [Ru-III(trpy)(L-CH3)ClO4 complex has been determined by X-ray crystallography. All the Ru(Ill) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [Ru-III(trpy)(L-R)]ClO4 complexes near 1600 nm. (C) 2007 Elsevier Ltd. All rights reserved.