Record Details

A five-center redox system: molecular coupling of two noninnocent imino-o-benzoquinonato-ruthenium functions through a pi acceptor bridge

DSpace at IIT Bombay

View Archive Info
 
 
Field Value
 
Title A five-center redox system: molecular coupling of two noninnocent imino-o-benzoquinonato-ruthenium functions through a pi acceptor bridge
 
Creator DAS, AK
SARKAR, B
FIEDLER, J
ZALIS, S
HARTENBACH, I
STROBEL, S
LAHIRI, GK
KAIM, W
 
Subject transition-metal-complexes
creutz-taube ion
quinone-related ligands
order regular approximation
mixed-valence chemistry
electron-transfer
diruthenium complexes
oxidation-states
ab-initio
g-tensors
 
Description Combining the concepts of noninnocent behavior of metal/ligand entities and the coupling of redox-active moieties via an electronically mediating bridge led to the synthesis and the structural, electrochemical, and spectroscopic characterization of [Cl(Q)Ru(mu-tppz)Ru(Q)Cl](n) where Q(o) is 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone and tppz(o) is 2,3,5,6-tetrakis(2-pyridyl)pyrazine, the available oxidation states being Ru(II,III,IV), Q(o,center dot-,2-), and tppz(o,center dot-,2-). One-electron transfer steps between the n = (2-) and (4+) states were studied by cyclic voltammetry and by EPR, UV-vis-NIR spectroelectrochemistry for the structurally characterized anti isomer of [Cl(Q)Ru(mu-tppz)Ru(Q)Cl](PF(6))(2), 2(PF(6))(2), the only configuration obtained. The combined investigations reveal that 2(2+) is best described as [Cl(Q(center dot-))Ru(III)(mu-tppz(o))Ru(III)(Q(center dot-))Cl](2+) with antiferromagnetic coupling between the ruthenium(III) and the iminosemiquinone components at each end. A metal-based spin as evident from large g factor anisotropy (EPR) and an intense intervalence absorption band at 1850 nm in the near-infrared (NIR) suggest that oxidation occurs at both iminosemiquinones to yield two Ru(II,III)-bonded quinones, implying redox-induced electron transfer. Reduction takes place stepwise at the metal centers yielding iminosemiquinone complexes of Ru(III,II) as evident from radical complex EPR spectra with small (99,101)Ru hyperfine contributions. After complete metal reduction to ruthenium(II) the bridging ligand tppz is being reduced stepwise as apparent from typical NIR absorption bands around 1000 nm and from small g anisotropy of the monoanion [Cl(Q(center dot-))Ru(II)(mu-tppz(center dot-))Ru(II)(Q(center dot-))Cl](-). A structure-based DFT calculation confirms the Ru-Cl character of the HOMO and the iminoquinone-dominated LUMO and illustrates the orbital interaction pattern of the five electron transfer active components in this new system.
 
Publisher AMER CHEMICAL SOC
 
Date 2011-10-15T08:18:32Z
2011-12-15T09:16:24Z
2011-10-15T08:18:32Z
2011-12-15T09:16:24Z
2009
 
Type Review
 
Identifier JOURNAL OF THE AMERICAN CHEMICAL SOCIETY,131(25)8895-8902
0002-7863
http://dx.doi.org/10.1021/ja901746x
http://dspace.library.iitb.ac.in/xmlui/handle/10054/13958
http://hdl.handle.net/100/3150
 
Language en