Please use this identifier to cite or link to this item: http://dspace.library.iitb.ac.in/xmlui/handle/100/15857
Title: Application of a Structure/Oxidation-State Correlation to Complexes of Bridging Azo Ligands
Authors: DAS, A
SCHERER, TM
MOBIN, SM
KAIM, W
LAHIRI, GK
Keywords: Azo Compounds
Electrochemistry
Epr Spectroscopy
Noninnocent Ligands
Ruthenium
Issue Date: 2012
Publisher: WILEY-V C H VERLAG GMBH
Citation: CHEMISTRY-A EUROPEAN JOURNAL, 18(35)11007-11018
Abstract: Based on data from more than 40 crystal structures of metal complexes with azo-based bridging ligands (2,2'-azobispyridine, 2,2'-azobis(5-chloropyrimidine), azodicarbonyl derivatives), a correlation between the N-N bond lengths (dNN) and the oxidation state of the ligand (neutral, neutral/back-donating, radical-anionic, dianionic) was derived. This correlation was applied to the analysis of four ruthenium compounds of 2,2'-azobispyridine (abpy), that is, the new asymmetrical rac-[(acac)2Ru1(mu-abpy)Ru2(bpy)2](ClO4)2 ([1](ClO4)2), [Ru(acac)2(abpy)] (2), [Ru(bpy)2(abpy)](ClO4)2 ([3](ClO4)2), and meso-[(bpy)2Ru(mu-abpy)Ru(bpy)2](ClO4)3 ([4](ClO4)3; acac-=2,4-pentanedionato, bpy=2,2'-bipyridine). In agreement with DFT calculations, both mononuclear species 2 and 32+ can be described as ruthenium(II) complexes of unreduced abpy0, with 1.295(5)<dNN<1.320(3) angstrom, thereby exhibiting effects from p back-donation. However, the abpy ligand in both the asymmetrical diamagnetic compound 12+ (dNN=1.374(6)angstrom) and the symmetrical compound 43+ (dNN=1.360(7), 1.368(8) angstrom) must be formulated as abpy.-. Remarkably, the addition of [RuII(bpy)2]2+ to mononuclear [RuII(acac)2(abpy0)] induces intracomplex electron-transfer under participation of the noninnocent abpy bridge to yield rac-[(acac)2Ru1III(mu-abpy.-)Ru2II(bpy)2]2+ (12+) with strong antiferromagnetic coupling between abpy.- and RuIII (DFT (B3LYP/LANL2DZ/6-31G*)-calculated tripletsinglet energy separation ES=1-ES=0=11739 cm-1). Stepwise one-electron transfer was studied for compound 1n, n=1-, 0, 1+, 2+, 3+, by UV/Vis/NIR spectroelectrochemistry, EPR spectroscopy, and by DFT calculations. Whereas the first oxidation of compound 12+ was found to mainly involve the central ligand to produce an (abpy0)-bridged Class I mixed-valent Ru1IIIRu2II species, the first reduction of compound 12+ affected both the bridge and Ru1 atom to form a radical complex (1+), with considerable metal participation in the spin-distribution. Further reduction moves the spin towards the {Ru2(bpy)2} entity.
URI: http://dx.doi.org/10.1002/chem.201201049
http://dspace.library.iitb.ac.in/jspui/handle/100/15857
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