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Ruthenium(II)/(III) bipyridine heterochelates incorporating phenolato imine functionalities. Synthesis, crystal structure, spectroscopic and electron-transfer properties and solution reactivities

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Title Ruthenium(II)/(III) bipyridine heterochelates incorporating phenolato imine functionalities. Synthesis, crystal structure, spectroscopic and electron-transfer properties and solution reactivities
 
Creator CHAKRABORTY, S
WALAWALKAR, MG
LAHIRI, GK
 
Subject redox properties
ruthenium complexes
electrochemical properties
variable-temperature
bidentate ligands
chemistry
oxidation
2,2'-bipyridine
family
states
 
Description A new class of ruthenium-bipyridine complexes of the type [Ru(bpy)(2)(L')]ClO4 [bpy=2,2'-bipyridine; L'=-OC6H3(R)C(R')=NH; R=R'=H 1a; R=H, R'=CH3 1b; R=NO2, R'=H 1c] have been synthesized via cleavage of N-N and N-C (aliphatic and aromatic) bonds of binucleating imine functionalities. The formation of 1 has been authenticated by the single crystal structure determination of 1a. The complexes exhibit strong MLCT transitions in the visible region and intraligand transitions in the UV region and display moderately strong emission near 700 nm. The quantum yield (phi) of the emission process at 77 K (EtOH-MeOH, 4:1 glass) varies in the range 2.2x10(-2)-6.5x10(-3) depending on L' in 1. The complexes show ruthenium(III)-ruthenium(II) and ruthenium(IV)-ruthenium(III) oxidations in the ranges 0.52-0.77 and 1.71-1.97 V versus SCE respectively. For 1a and 1b, one ligand centred oxidation near 2 V and for all the complexes two bipyridine based reductions have been detected in the ranges -1.51 to -1.56 V and -1.72 to -1.79 V versus SCE. Coulometric oxidation of 1 initially generates the unstable trivalent one-electron paramagnetic [Ru-III(bpy)(2)(L')](2+) congener, 1(+). The complexes 1(+) display one broad and moderately strong LMCT band near 750 nm and intraligand transitions in the UV region. The oxidised complexes 1(+) exhibit rhombic EPR spectra at 77 K which have been analysed to furnish values of distortion parameters (Delta=4543-5923 cm(-1), V=3251-5127 cm(-1)) and energy of the expected ligand field transitions (nu(1) 3086-3508, nu(2) 6409-8669 cm(-1)) within the t(2) shell. One of the ligand field transitions has been experimentally observed (nu(2) 7092-7812 cm(-1)). The oxidised species 1(+) slowly changes to diamagnetic dimeric species of the type [(bpy)(2)Ru-III{-OC6H3(R)C(R')=NNC(R')(R)C6H3O-}Ru-III(bpy)(2)](4+) 2 where the ruthenium(III) centres are antiferromagnetically coupled. In the presence of water 1(+) as well as 2 return to the parent bivalent species 1. The second order rate constants (k) of the conversion process 1(+)-->2 in dry acetonitrile and first order rate constants (k') of 1(+)-->1 in ordinary acetonitrile and the thermodynamic parameters (Delta H double dagger and Delta S double dagger) of both have been determined spectrophotometrically in the temperature range 303-333 K.
 
Publisher ROYAL SOC CHEMISTRY
 
Date 2011-08-28T17:50:55Z
2011-12-26T12:58:08Z
2011-12-27T05:47:36Z
2011-08-28T17:50:55Z
2011-12-26T12:58:08Z
2011-12-27T05:47:36Z
2000
 
Type Article
 
Identifier JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, (16), 2875-2883
1470-479X
http://dx.doi.org/10.1039/b001663m
http://dspace.library.iitb.ac.in/xmlui/handle/10054/11804
http://hdl.handle.net/10054/11804
 
Language en