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Issue 12, 2016
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Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate, 4,4′-di-tert-butyl-2,2′-bipyridine and 1,10-phenanthroline anion radicals to oxidovanadium(IV)

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Abstract

This article reports on the stabilization of organic radical anions promoted by the oxidovanadium(IV) ion. A 3,5-di-tert-butylcatecholate (tBucatH) complex of oxidovanadium(V) of the type [(LaONO2−)(VO3+)(tBucatH)] (1) was isolated using tridentate (E)-N′-((3-hydroxynaphthalen-2-yl)methylene)benzohydrazide (LaONOH2) as a coligand, whereas o-benzosemiquinonate (sq˙) and p-nitro-o-iminobenzosemiquinonate (NO2isq˙) radical anion complexes of oxidovanadium(IV) of the types [(LNNO)(VO2+)(sq˙)] (2) and [(LNNO)(VO2+)(NO2isq˙)] (3) were successfully isolated using (1Z,NE)-N′-(phenyl(pyridin-2-yl)methylene)benzohydrazonic acid (LNNOH) as a coligand. Oxidovanadium(IV) complexes of the types [(LbONO2−)(VO2+)(phen)] (4) and [(LbONO2−)(VO2+)(tBubpy)] (5), which undergo reversible reduction to the 4,4′-di-tert-butyl-2,2′-bipyridine radical anion (tBubpy˙) and the 1,10-phenanthroline radical anion (phen˙) to afford the coupled states [(LbONO2−)(VO2+)(phen˙)] (4) and [(LbONO2−)(VO2+)(tBubpy˙)] (5), respectively, were isolated (LbONOH2 = (E)-N′-(2-hydroxybenzylidene)benzohydrazide). The molecular geometries of the complexes were confirmed by the single-crystal X-ray structure determinations of 1, 3 and 4. In 1, the V–Ophenolato length cis to V[double bond, length as m-dash]O is 1.879(2) Å and the dissimilar V–O and V–OH lengths corresponding to the tBucatH ligand are 1.832(2) and 2.312(2) Å, respectively. In 1, the average C–O lengths in tBucatH are 1.351(3) Å, whereas in 3 the average C–O and C–N lengths in NO2isq˙ are 1.293(4) and 1.355(5) Å, respectively. In 4, the V–Ophenolato length cis to V[double bond, length as m-dash]O (1.937(3) Å) is relatively longer. The 51V NMR spectrum of 1 displays a signal at −337.2 ppm, whereas the signals for 2 and 3 are deshielded to +382.4 and +71.8 ppm, respectively. The closed-shell singlet (CSS) solutions of 3 and 5 at the B3LYP/DFT level are unstable and the open-shell singlet (OSS) solutions are 0.5 and 7.3 kcal mol−1 lower in energy, respectively, than the CSS solutions. In 3 and 5 the alpha spin (100%) is localized on the vanadium ion, whereas the beta spin is delocalized across the aminophenol and bipyridine fragments. 2 and 3 exhibit lower-energy absorption bands at 785 and 585 nm, which are defined as CSS → OSS perturbation transitions.

Graphical abstract: Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate, 4,4′-di-tert-butyl-2,2′-bipyridine and 1,10-phenanthroline anion radicals to oxidovanadium(iv)

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Publication details

The article was received on 15 Jul 2016, accepted on 18 Oct 2016 and first published on 19 Oct 2016


Article type: Paper
DOI: 10.1039/C6NJ02220K
Citation: New J. Chem., 2016,40, 10305-10315
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    Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate, 4,4′-di-tert-butyl-2,2′-bipyridine and 1,10-phenanthroline anion radicals to oxidovanadium(IV)

    M. Shit, S. Maity, S. Bera, T. Weyhermüller and P. Ghosh, New J. Chem., 2016, 40, 10305
    DOI: 10.1039/C6NJ02220K

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