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Four-Center Oxidation State Combinations and Near-Infrared Absorption in [Ru(pap)(Q)2]n (Q=3,5-Di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, pap=2-Phenylazopyridine)

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Title Four-Center Oxidation State Combinations and Near-Infrared Absorption in [Ru(pap)(Q)2]n (Q=3,5-Di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, pap=2-Phenylazopyridine)
 
Creator DAS, D
AGARWALA, H
CHOWDHURY, AD
PATRA, T
MOBIN, SM
SARKAR, B
KAIM, W
LAHIRI, GK
 
Subject density functional calculations
electronic structure
non-innocent ligands
ruthenium
spectroelectrochemistry
structure elucidation
TRANSITION-METAL-COMPLEXES
DENSITY-FUNCTIONAL THEORY
MIXED-VALENCE COMPLEXES
QUINONE-RELATED LIGANDS
NON-INNOCENT LIGANDS
REDOX SERIES
ELECTRONIC-STRUCTURE
RUTHENIUM COMPLEXES
CHARGE-DISTRIBUTION
PI-RADICALS
 
Description The complex series [Ru(pap)(Q)2]n ([1]n[4]n; n=+2, +1, 0, 1, 2) contains four redox non-innocent entities: one ruthenium ion, 2-phenylazopyridine (pap), and two o-iminoquinone moieties, Q=3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine (aryl=C6H5 (1+); m-(Cl)2C6H3 (2+); m-(OCH3)2C6H3 (3+); m-(tBu)2C6H3 (4+)). A crystal structure determination of the representative compound, [1]ClO4, established the crystallization of the ctt-isomeric form, that is, cis and trans with respect to the mutual orientations of O and N donors of two Q ligands, and the coordinating azo N atom trans to the O donor of Q. The sensitive CO (average: 1.299(3)angstrom), CN (average: 1.346(4)angstrom) and intra-ring CC (meta; average: 1.373(4)angstrom) bond lengths of the coordinated iminoquinone moieties in corroboration with the NN length (1.292(3)angstrom) of pap in 1+ establish [RuIII(pap0)(Q.)2]+ as the most appropriate electronic structural form. The coupling of three spins from one low-spin ruthenium(III) (t2g5) and two Q. radicals in 1+4+ gives a ground state with one unpaired electron on Q., as evident from g=1.995 radical-type EPR signals for 1+4+. Accordingly, the DFT-calculated Mulliken spin densities of 1+ (1.152 for two Q, Ru: 0.179, pap: 0.031) confirm Q-based spin. Complex ions 1+4+ exhibit two near-IR absorption bands at about =2000 and 920nm in addition to intense multiple transitions covering the visible to UV regions; compounds [1]ClO4[4]ClO4 undergo one oxidation and three separate reduction processes within +/- 2.0V versus SCE. The crystal structure of the neutral (one-electron reduced) state (2) was determined to show metal-based reduction and an EPR signal at g=1.996. The electronic transitions of the complexes 1n4n (n=+2, +1, 0, 1, 2) in the UV, visible, and NIR regions, as determined by using spectroelectrochemistry, have been analyzed by TD-DFT calculations and reveal significant low-energy absorbance (max>1000nm) for cations, anions, and neutral forms. The experimental studies in combination with DFT calculations suggest the dominant valence configurations of 1n4n in the accessible redox states to be [RuIII(pap0)(Q.)(Q0)]2+ (12+42+)[RuIII(pap0)(Q.)2]+ (1+4+)[RuII(pap0)(Q.)2] (14)[RuII(pap.)(Q.)2] (14)[RuIII(pap.)(Q2)2]2 (1242).
 
Publisher WILEY-V C H VERLAG GMBH
 
Date 2014-10-16T15:02:59Z
2014-10-16T15:02:59Z
2013
 
Type Article
 
Identifier CHEMISTRY-A EUROPEAN JOURNAL, 19(23)7384-7394
http://dx.doi.org/10.1002/chem.201204620
http://dspace.library.iitb.ac.in/jspui/handle/100/15853
 
Language en