Structure and properties of cocrystals of phenazine and fumaric-, 2,3-dihydroxyfumaric-, and oxalic acid.
In: Journal fuer Praktische Chemie (Weinheim, Germany), Jg. 342 (2000) ; Nr. 5, S. 465-472
Zeitschriftenaufsatz / Fach: Chemie
Phenazine and the dicarboxylic acids fumaric-, 2,3-dihydroxyfumaric-, and oxalic acid form 1: 1 cocrystals. X-ray anal. shows that the mols. are arranged as linear tapes, mainly held together by strong O-H.tplbond.N and weak C(sp2)-H.tplbond.O H bonds. Individual mols. form staples which are surrounded by staples of the other mols. The angle between neighboring tapes varies from .apprx.90 Deg in the cocrystal of phenazine and fumaric acid to .apprx.70 Deg in the cocrystal of phenazine and 2,3-dihydroxyfumaric acid, and .apprx.25 Deg in the cocrystal of phenazine and oxalic acid. The mols. assume an offset face-to-face arrangement in individual phenazine staples. Negligible p-stacking is obsd. in the cocrystals of phenazine with fumaric- and 2,3-dihydroxyfumaric acid. The absence of the CC double bond as spacer in oxalic acid leads to appreciable p-overlap of phenazine mols. in the cocrystal. As a consequence, the latter cocrystal displays special properties. An irreversible light-induced electron transfer generates initially singlet and triplet biradicals with the unpaired electrons positioned on neighboring phenazine mols. Partially, the electrons are transformed to magnetically independent electrons which show strong exchange narrowing in the EPR spectrum at temps.>0 Deg. The proposed model is supported by UV/visible-ESR-, and SQUID measurements.
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