Elektronentransfer und Ionenpaar-Bildung, 33 [1, 2]. Die Einelektronen-Reduktion von Tetraphenyl-p-benzochinon mit Alkalimetallen: ENDOR-Spektren von Kontaktionen-Paaren sowie Tripelionen in Lösung und Einkristallstrukturen der Neutralverbindung und ihres Natrium-Salzes / Electron Transfer and Ion Pair Formation, 33 [1,2]. The Single Electron Reduction of Tetraphenyl-p-benzoquinone by Alkali Metals: ENDOR Spectra of Contact Ion Pairs as well as Triple Ions in Solution and Single Crystal Structures of Both the Neutral Compound and its Sodium Salt

1994 ◽  
Vol 49 (4) ◽  
pp. 529-541 ◽  
Author(s):  
Hans Bock ◽  
Andreas John ◽  
Markus Kleine ◽  
Christian Näther ◽  
Jan W. Bats
Keyword(s):  
Single Crystal ◽  
Radical Anion ◽  
Alkali Metals ◽  
Ion Pairs ◽  
Radical Cations ◽  
Chair Conformation ◽  
Reduction Potentials ◽  
Half Wave ◽  
Electron Reduction ◽  
Contact Ion Pairs

Tetraphenyl-p-benzoquinone, according to its single crystal structure, shows some steric congestion: its quinone ring is distorted by 7° to a chair conformation, and its phenyl substituents are twisted around their CC axes between 46° and 72°. The half-wave reduction potentials of -0.57 and -1.25 V in acetonitrile confirm negligible π interaction of the phenyl substituents. Addition of alkalimetal tetraphenylborate salts lowers the second reduction potential due to contact ion formation, which can be confirmed by UV/VIS spectra recorded under aprotic conditions. Extensive ESR/ENDOR investigations prove the formation of the following species in THF solution: Tetraphenyl-p-benzosemiquinone radical anion contact ion pairs [M·⊖ Me⊕solv]' (Me⊕: Li⊕, Na⊕, Rb⊕, Cs⊕) and contact triple ion radical cations both with identical cations [M·⊖ (Me⊕solv)2]·⊕ (Me⊕: Li⊕, Na⊕, Cs⊕) and different cations [M·⊖ (Li⊕solv)(Me⊕solv)]·⊕ (Me⊕: Na⊕, Cs⊕). Addition of crown ethers can lead to external solvation of the Me⊕ counter cations, whereas cryptands form internal solvation complexes. The radical anion of 2,6-diphenyl-p-benzosemiquinone adds cations at its phenyl-free molecular half. The radical anion salt [tetraphenyl-p-benzosemiquinone·⊖ (Na⊕(tetrahydropyrane) 2)] could be crystallized and its structure determined at 200 K. In agreement with the Hirota sign rules for contact radicals in solution, the Na⊕ ion is found 62 pm above the π plane and 29° outside the axis of the CO bound, which is elongated due to one-electron reduction by 5 pm to 127 pm.

Elektronentransfer und Ionenpaare, 15 [ 1– 3] Radikalanion und Radikal-Kontakt-Ionenpaare von Dimesityl-tetraketon / Electron Transfer and Ion Pairing, 15 [1-3] Radical Anion and Radical Ion Pairs of Dimesityl Tetraketone

1990 ◽  
Vol 45 (8) ◽  
pp. 1197-1204 ◽  
Author(s):  
H. Bock ◽  
P. Hänel ◽  
H.-F. Herrmann
Keyword(s):  
Electron Transfer ◽  
Radical Anion ◽  
Ion Pairs ◽  
Ion Pairing ◽  
Single Electron ◽  
Single Electron Transfer ◽  
Temperature Dependent ◽  
Contact Ion Pairs

The radical anion of dimesityltetraketone (ERed, I = -0.40 V) is easily generated in THF by potassium mirror/[2.2.2]-cryptand reduction. Its contact ion pairs with Na⊕, Cs⊕ and Ba⊕⊕ counter cations, prepared in THF solution by single electron transfer from the respective metals, are characterized by their ESR/ENDOR spectra, which exhibit temperature-dependent metal couplings of aNa⊕ = 0.061 mT (190 K), aCs⊕ = 0.021 mT (190 K), and aBa⊕⊕ = 0.145 mT (295 K).

Relative One-Electron Reduction Potentials of Carotenoid Radical Cations and the Interactions of Carotenoids with the Vitamin E Radical Cation

1998 ◽  
Vol 120 (17) ◽  
pp. 4087-4090 ◽  
Author(s):  
Ruth Edge ◽  
Edward J. Land ◽  
David McGarvey ◽  
Louise Mulroy ◽  
T. George Truscott
Keyword(s):  
Vitamin E ◽  
Radical Cation ◽  
Radical Cations ◽  
Reduction Potentials ◽  
Electron Reduction

Elektronentransfer und Ionenpaar-Bildung, 27 [1, 2] Darstellung von Semichinon-Ionenpaaren durch Reduktion von Chinonen mit Tetraalkylammonium-boranat in aprotischen Lösungen: 1,10-Phenanthrolin-5,6-dion / Electron Transfer and Ion Pairing, 27 [1, 2] Preparation of Semiquinone Ion Pairs by Reduction of Quinones Using Tetraalkylammonium Boranate in Aprotic Salt Solutions: 1,10-Phenanthrolin-5,6-dione

1992 ◽  
Vol 47 (2) ◽  
pp. 288-300 ◽  
Author(s):  
H. Bock ◽  
P. Hänel
Keyword(s):  
Radical Anion ◽  
Nuclear Charge ◽  
Ion Pairs ◽  
Radical Cations ◽  
Ion Pair ◽  
Metal Salts ◽  
Multiply Charged ◽  
Counter Cation ◽  
Cation Charge ◽  
Spin Densities

Ion pairs of 1,10-phenanthrolin-5,6-dione radical anion [M · ⊖Me⊕n] ·⊕(n−1) with Me⊕n = Mg⊕⊕, Ca⊕⊕, Sr⊕⊕, Zn⊕⊕, Cd⊕⊕, Pb⊕⊕ and La⊕⊕⊕ are advantageously prepared in aprotic DMF solution containing appropriate metal salts Me⊕nX⊖ by using the ‘mild’ single-electron reducing agent tetra(n-butyl)ammonium-boranate R4N⊕BH4⊖ . For comparison, the ‘naked’ radical anion with the largely interaction-free [K⊕(2.2.2)-cryptand]⊕ counter cation is chosen, which is formed on reduction with potassium in THF solution of (2.2.2)-cryptand. Addition of excess Na⊕[B(C6H5)4]⊖ to the reduction solution only yields a solvent-separated ion pair (M · ⊖)DMF ··· (Na⊕)DMF, whereas in the presence of multiply charged counter cations Me⊕n the respective contact ion pair radical cations [M · ⊖Me⊕n] · ⊕(n−1) are formed. Their g values decrease with increasing nuclear charge of Me⊕n and their metal-s-spin densities increase with the effective counter cation charge n⊕/rMe⊕n. The ESR /ENDOR data recorded suggest Me⊕n complexation by the δ⊖OC -COδ⊖ chelate tongs and the ion pair stability, which is modified by the dielectric properties of the solvent used, may be rationalized by the Coulombic attraction between the radical anion M · ⊖ and the counter cations Me⊕n.

Crystal Structure of 3Ni(N03)2.16C6 H5NH2

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1185-1189
Author(s):  
Michael Mahr ◽  
Inge Pabst ◽  
Konrad G. Weil
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Ion Pairs ◽  
X Ray Diffraction ◽  
Nickel Ion ◽  
Ionic Solutions ◽  
Triclinic Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
Contact Ion Pairs

Abstract The Compound 3Ni(NO3)2 -16C6H5NH2 was obtained by crystallization from solutions of Ni(NO3)2 • 6C6H5NH2 -2H2O in aniline. Its crystal structure was determined by single crystal X-ray diffraction. The crystals are triclinic, space group P1 with lattice constants a = 985.2 pm, ft = 1004.5 pm and c = 2514.3 pm, a = 96.34°, ß = 92.63° and y = 89.82°. The structure shows units of four aniline molecules and two slightly distorted nitrate ions in the coordination sphere of each nickel ion. These units are similar to contact ion pairs in concentrated ionic solutions.

One-electron reduction potentials of dietary carotenoid radical cations in aqueous micellar environments

FEBS Letters ◽  
2001 ◽  
Vol 500 (3) ◽  
pp. 132-136 ◽  
Author(s):  
Marc Burke ◽  
Ruth Edge ◽  
Edward J. Land ◽  
David J. McGarvey ◽  
T.George Truscott
Keyword(s):  
Radical Cations ◽  
Reduction Potentials ◽  
Electron Reduction ◽  
Dietary Carotenoid

Elektronentransfer und Ionenpaar-Bildung, 18 [1 -3] / Electron Transfer and Ion Pairing, 18 [ 1 - 3]

1991 ◽  
Vol 46 (3) ◽  
pp. 326-338 ◽  
Author(s):  
H. Bock ◽  
P. Dickmann ◽  
H.-F. Herrmann
Keyword(s):  
Electron Transfer ◽  
Metal Cation ◽  
Reduction Potential ◽  
Ion Pairs ◽  
Radical Cations ◽  
Membered Ring ◽  
Cation Complexation ◽  
Metal Cation Complexation ◽  
Contact Ion Pairs ◽  
Triple Ion

The redox behaviour of aza-substituted naphtho- and anthraquinones, which offer O=C–C=N– chelate tongs for an advantageous five-membered ring metal cation complexation, is investigated by a combination of cyclovoltammetric and ESR/ENDOR spectroscopic measurements. The formation of paramagnetic contact ion pairs like [(quinoline-5,8-semiquinone)·⊖Me⨁]·, with Me⨁ = Li⨁, Na⨁, Tl⨁, or of triple ion radical cations like [(1,4-diazo-9,10-anthrasemiquinone)eMe⨁]·⨁, with Me⨁ = Li⨁, Na⨁ is corroborated both by shifts of the second reduction potential of up to 0,67 V for e.g. quinoline 5,8-quinone upon addition of Li⨁[B(C6H5)4]⊖ to its DMF solution and by the observation of ESR/ENDOR metal couplings.

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