scholarly journals Coordination Environment of Copper Sites in Cu-CHA Zeolite Investigated by Electron Paramagnetic Resonance

2014 ◽  
Vol 118 (40) ◽  
pp. 23126-23138 ◽  
Author(s):  
Anita Godiksen ◽  
Frederick N. Stappen ◽  
Peter N. R. Vennestrøm ◽  
Filippo Giordanino ◽  
Søren Birk Rasmussen ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Paramagnetic Resonance ◽  
Coordination Environment ◽  
Copper Sites ◽  
Electron Paramagnetic

Structural and electron paramagnetic resonance (EPR) characterization of novel vanadium(V/IV) complexes with hydroquinonate-iminodiacetate ligands exhibiting “noninnocent” activity

2012 ◽  
Vol 85 (2) ◽  
pp. 329-342 ◽  
Author(s):  
Chryssoula Drouza ◽  
Marios Stylianou ◽  
Petri Papaphilippou ◽  
Anastasios D. Keramidas
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Continuous Wave ◽  
Semiquinone Radical ◽  
Paramagnetic Resonance ◽  
Amine Nitrogen ◽  
Coordination Environment ◽  
X Ray Crystallography ◽  
X Band ◽  
Electron Paramagnetic

Reaction of KVO3 with 2-[N,N'-(carboxymethyl)aminomethyl]-5-methylhydroquinone (H4mecah) in aqueous solution at pH 8.2 results in the isolation of mononuclear K2[VV(O)2{Hmecah(-3)}]·2H2O complex. On the other hand, reaction with the 2-[N,N'-(carboxymethyl)aminomethyl]-5-tert-butylhydroquinone (H4tbutcah) under the same conditions gives the tetranuclear mixed-valent complex K6[{VVO(μ-O)VIVO}{μ-tbutbicah(-6)}]2·10.5H2O (H6tbutbicah, 2,2'-({2-[bis(carboxymethyl)amino]-3,6-dihydroxy-4-methylbenzyl}azanediyl)diacetic acid). The structures of both complexes were determined by single-crystal X-ray crystallography. The coordination environment of vanadium ions in both complexes is octahedral, with four out of the six positions to be occupied by the two cis carboxylate oxygens, one hydroquinonate oxygen, and one amine nitrogen atoms of the ligands’ tripod binding sites. The importance of the chelate ring strains in the stabilization of the p-semiquinone radical is also discussed. A protonation of the ligated to vanadium(IV) ion hydroquinonate oxygen at low pH was revealed by continuous wave (cw) X-band electron paramagnetic resonance (EPR) and UV–vis spectroscopies.

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