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Stabilization of oxidovanadium(iv) by organic radicals.
MedLine Citation:
PMID:  23353872     Owner:  NLM     Status:  Publisher    
o-Imino-p-R'-benzosemiquinone anion radical (L(R')(IS)˙(-)) complexes of oxidovanadium(iv) of type [(L(1)(R-))(VO(2+))(L(R')(IS)˙(-))] (R = H, R' = H, ; R = H, R' = -CMe(3), ; R = -CMe(3), R' = H, and R = -CMe(3), R' = -CMe(3), ) incorporating the redox-innocent tridentate NNO-donor L(1)(R-) ligands (L(1)(R)H = 2,4-di-R-6-{(2-(pyridin-2-yl)hydrazono)methyl}phenol) were isolated and substantiated by elemental analyses, IR, mass, NMR and UV-vis spectra including the single crystal X-ray structure determinations. The V-O(phenolato) (cis to the V[double bond, length as m-dash]O) lengths spanning 1.905(3)-1.9355(15) Å in are consistent with the coordination to the [VO](2+) state. The V-O(IS) (trans to the V[double bond, length as m-dash]O) lengths, 2.1505(17)-2.1869(15) Å, in are longer due to the trans influence of the V[double bond, length as m-dash]O bond. The V-N(IS) lengths, 1.906(3)-1.924(2) Å, in are comparatively shorter due to the higher affinity of the paramagnetic [VO](2+) ion towards the L(R')(IS)˙(-) anion radicals. Density functional theory (DFT) calculations using B3LYP, B3PW91 and PBE1PBE functionals on and authenticated that the closed shell singlet (CSS) solutions (dianionic o-amido-p-R'-phenolates (L(R')(AP)(2-)) coordinated to VO(3+), Type I) of are unstable with respect to the open shell singlet (OSS) perturbations. Broken symmetry, BS (1,1) M(s) = 0 (L(R')(IS)˙(-) coordinated to the VO(2+) ion, Type III) solutions of are stable and reproduce the experimental bond parameters. Frozen glasses EPR spectra of [](+) ions (e.g. g(||) = 1.948, g(⊥) = 1.978, A(||) = 184 (22 G), A(⊥) = 62(15 G) for [](+)) and unrestricted DFT calculations on [](+), [](+), [](-) and [](-) ions using doublet spin state elucidated that the reversible anodic waves at [0.15-0.31] V of complexes are due to the oxidation of L(R')(IS)˙(-) generating [(L(1)(R-))(VO(2+))(L(R')(IQ))](+) complexes (L(R')(IQ) = o-imino-p-R'-benzoquinone) coordinated to the [VO](2+) ion (Type V) while the irreversible cathodic waves at -[1.08-1.49] V are due to the formation of unstable [(L(1)(R-))(VO(2+))(L(R')(AP)(2-))](-) complexes (Type II). The second anodic waves at [0.76-0.89] V are assigned to a [VO](3+)-[VO](2+) couple affording diamagnetic [(L(1)(R-))(VO(3+))(L(R')(IQ))](2+), [](2+) complexes (Type VI) which are identified by UV-vis spectra, DFT and time dependent (TD) DFT calculations. Spectro-electrochemical measurements and TD DFT calculations on and disclosed that lower energy electronic absorption bands of are due to the LMCT and CSS-OSS perturbation which disappear in [](+) ions. [](+) absorb at 600-650 nm due to d-d transitions and MLCT which are absent in VO(3+) complexes, [](2+).
Suman Kundu; Suvendu Maity; Amarendra Nath Maity; Shyue-Chu Ke; Prasanta Ghosh
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-1-28
Journal Detail:
Title:  Dalton transactions (Cambridge, England : 2003)     Volume:  -     ISSN:  1477-9234     ISO Abbreviation:  Dalton Trans     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-1-28     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101176026     Medline TA:  Dalton Trans     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Department of Chemistry, R. K. Mission Residential College, Narendrapur, Kolkata 700 103, India.
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