Electron spin resonance spectra of the triple ions [Na₂-pyrazine]⁺ and [Na₂-tetramethylpyrazine]⁺

Abstract

Reduction of pyrazine (P) and tetramethylpyrazine (TMP) by sodium in the presence of sodium tetraphenylboride produces Na2P+ and Na2TMP+, respectively. The electron spin resonance spectra of these species are presented and compared with those of the corresponding ion pairs. From linebroadening effects within the sodium hyperfine multiplets of the triple ion spectra, it is deduced that the sodium ions occupy positions close to the N-N axes of the ring systems. IntroductionThe detection, by electron spin resonance spectroscopy, of triple ions of the formula Na,Q+ has been reported (1, 2) for Q equals p-benzoquinone, 2,3-, 2,5-, 2,6-dimethyl-p-benzoquinone, and duroquinone. The proton hyperfine splitting constants of the triple ion indicate that one sodium associates with each oxygen of the semiquinone. Molecular tumbling does not completely average the anisotropies within the hyperfine and g tensors of the triple ion with the result that asymmetric broadening of the sodium hyperfine septets was observable. From this broadening it was deduced (2) that the sodium ions occupy positions close to the 0-0 axis of the semiquinone. It is of interest to determine whether these effects are limited to semiquinones, or whether the experiment has more general application to the structure of other ionic associates.A number of papers (3-10) have concerned themselves with the structure of ion pairs formed between pyrazine anions and alkali metal cations. The observation of line-width alternation for sodium-pyrazine in tetrahydrofuran (4) and 1,2-dimethoxyethane and of two non-equivalent nitrogen nuclei for lithium-pyrazine in tetrahydrofuran (5) makes it clear that these cations associate with one of the nitrogens of pyrazine, rendering the anion asymmetric. Calculations on the structure of these ion pairs (5,8,10) indicate that at realistic interionic distances the most stable position for the cation is above the center of the pyrazine ring, which obviously does not agree with the experimental results. Calculations on the structure of the protonated pyrazine anion (9) predict an asymmetric structure with the proton

Electron Spin Resonance Spectra of Azine – Alkali Metal Triple Ions in Ethereal Solvents

“…2 deserve little comment since they follow the expectations of our previous discussion (2,3); a more negative value is obtained for the unsubstituted pyrazine because the counter-ion can approach closer to the molecular plane of the anion. Similarly, in spin density units, the lithium splitting is more negative than the sodium splitting, suggesting that the lithium cation forms a "tighter" triple ion than does sodium.…”

“…spectroscopy has been used to demonstrate the existence, in ethereal solvents, of triple ions of the general formula Na2A+ where A may be p-benzosemiquinone, pyrazine or their methylated derivatives (1)(2)(3). From the hyperfine splitting patterns of the e.s.r.…”

Electron spin resonance study of some polycyclic nitrogen heterocyclic radical anions

“…These effects are often very apparent in radical anions of nitrogen heterocycles and many well known examples have been reported. [15][16] Our preliminary investigations clearly showed this to be the case. We hoped to compare our results with similar results for the two parent molecules, quinoxaline and phenazine.…”

Koordinationschemie reduzierter N-Heterozyklen. Komplexe des Pyrazin-Radikalanions mit Phenylmetallkationen +MPh von Beryllium, Magnesium und Zink / Coordination Chemistry of Reduced N-Heterocycles. Complexes of Pyrazine Anion Radical with Phenyl Metal Cations +MPh of Beryllium, Magnesium and Zinc

“…Die drei Radikalkomplexe (1) weisen im Rahmen der Meß-genauigkeit identische Proton-Kopplungen auf, der Wert von an ~ 0,284 mT offenbart eine Mittelstellung sowohl zwischen Pz 7 und PzH2t als auch zwischen den Alkalimetall-Tripelionen [Pz(M)2]t [11] und den Komplexen [Pz(AlR2)2]t [13,14] [30]) und des Chlorophylls a 1 (a25Mg < 0,1 mT, [31]) verwendet.…”

“…Als Beispiele seien die Radikalanionen zweizähniger Komplexbildner wie etwa des 2.2'-Bipyridins [1][2][3], der Diazabutadiene [2,4,5] oder der o-Semichinonimine [6] genannt, hierzu zählen aber ebenso die n-Kationen und -Anionen vierzähniger Makrozyklen [7], insbesondere der biochemisch relevanten Porphyrin-Derivate [8]. Ein einfach gebauter, nicht chelatbildender Radikalligand liegt dagegen in dem Pyrazin-Radikalanion Pz" vor: Während die Alkalimetall-Ionenpaare [Pz 7 , M + ] und -Tripelionen [M + , Pz~, M + ] seit länge-rem bekannt sind [9][10][11], ist erst kürzlich über silicium- [12] und aluminiumorganische [12][13][14] Radikalkomplexe des reduzierten Pyrazins sowie über dessen Koordinationsverbindungen mit Metallcarbonylfragmenten [15] und metallorganische Kationen der 3. Hauptgruppe berichtet worden [16].…”