92413-13-3Relevant articles and documents
Structures and Molecular Properties of Charge-Perturbed Molecules. 2,3-Diphenylquinoxaline Radical Anions in Solution and in Crystals
Bock, Hans,John, Andreas,Naether, Christian,Ruppert, Klaus
, p. 1505 - 1519 (1994)
The Na+ and K+ radical-ion salts of 2,3-diphenylquinoxyline seem to be (according to a structural database search) among the first ones of N-heterocyclic radical anions in crystals.The one-electron reduction in aprotic 1,2-dimethoxyethan (DME) solution at metal mirrors and the crystallization under Ar have been preceded by cyclovoltammetric (CV) and ESR/ENDOR measurement.The first electron insertion at -1.63 V proves to be reversible, whereas the irreversible second step, which is accompained by an overcrossing of the CV line, can be rationalized by an "ECE-DISP" mechanism via a dianion redox disproportination.The ENDOR spectrum resolves four 1H couplings and allows to simulate the ESR spectrum including the 14N hyperfine splittings.Both dark-blue single crystals of the radical ion salts .- Met+ (DME)> show unexpected similarities for Met+ = Na+, K+ despite the 36-pm difference in their ionic radii.The largest structural changes inflicted by the one-electron reduction of the N-heterocyclic molecule are observed in the vicinity of the N-centers bearing the highest effective nuclear charge.The DME-chelated metal cations coordinate at the N electron pairs and form Met+(DME)-bridged polymer chains of the radical anion, which are differently ondulated in the Na+ and K+ radical anion salts.The take-home lesson suggests that many more N-heterocyclic molecules might be analogously reduced under optimized conditions and isolated as single crystals.
