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Low-spin octahedral cobalt(II) complexes of CoN6 and CoN4P2 chromophores. Synthesis, spectroscopic characterisation and electron-transfer properties

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Title Low-spin octahedral cobalt(II) complexes of CoN6 and CoN4P2 chromophores. Synthesis, spectroscopic characterisation and electron-transfer properties
 
Creator SANTRA, BK
LAHIRI, GK
 
Subject chemistry
ruthenium(ii)
spectra
ligands
co(ii)
 
Description The reaction of 2-(arylazo)pyridines (NC5H4)N=NC6H4R L-1-L-7 (R=H, o-Me/Cl, m-Me/Cl, p-Me/Cl) with cobalt(II) perchlorate hexahydrate in absolute ethanol under anaerobic conditions afforded low-spin [(CoL3)-L-II](2+) complexes, isolated as ClO4- salts. At room temperature the complexes are one-electron paramagnetic in nature, low-spin Co-II, t(2g)(6)e(g)(1), S=1/2 and behave as 1:2 electrolytes in acetonitrile solvent. In acetonitrile solvent they show a ligand-to-metal charge-transfer (LMCT) band near 400 nm, an intraligand transition near 300 nm and ligand-field d-d transitions in the range 860-600 nm. The complexes exhibit quasi-reversible Co-II-Co-III couples near 1 V and six sequential ligand reductions (N=N groups) in the range 0.2 to -1.8 V versus saturated calomel electrode (SCE). At room temperature in the solid state they exhibit isotropic EPR spectra but at 77 K, both in the polycrystalline state and in the dichloromethane solution, display rhombic spectra. Reaction of [(CoL3)-L-II](2+) with 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) resulted in complete ligand-exchanged products with concomitant metal oxidation, low-spin [Co-III(bpy)(3)](3+) and low-spin [Co-III(phen)(3)](3+) respectively. The reaction of PPh3 with the [Ca-II(L-7)(3)](2+) [L-7=2-(p-chlorophenylazo)pyridine] yielded a partial ligand-exchanged product, low-spin [Co-II(L-7)(2)(PPh3)(2)](2+), isolated as its ClO4- salt. The complex is one-electron paramagnet and a 1 :2 electrolyte in acetonitrile solvent. It displays an LMCT band at 401 nm, an intraligand transition at 305 nm and four d-d transitions in the range 870-640 nm. It exhibits irreversible Co-II to Co-III oxidation at 1.33 V (E-pa) and four successive ligand reductions in the range -0.30 to -1.1 V versus SCE. At 77 K the complex displays an axial EPR spectrum.
 
Publisher ROYAL SOC CHEMISTRY
 
Date 2011-08-28T12:54:23Z
2011-12-26T12:58:02Z
2011-12-27T05:47:03Z
2011-08-28T12:54:23Z
2011-12-26T12:58:02Z
2011-12-27T05:47:03Z
1998
 
Type Article
 
Identifier JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, (1), 139-145
0300-9246
http://dx.doi.org/10.1039/a706587f
http://dspace.library.iitb.ac.in/xmlui/handle/10054/11744
http://hdl.handle.net/10054/11744
 
Language en