A Ubiquinol‐Based Charge‐Transfer Complex Obtained from a Solvent‐Free Approach

Abstract

Quinones (¼ cyclohexa-2,5-diene-1,4-diones) and hydroquinones (¼ benzene-1,4-diols) belong to species that are balanced between their redox character and their ability to build supramolecular complexes. Considering the ubiquinol 2,3-dimethoxy-5-methyl-1,4-dihydroquinone (¼ 2,3-dimethoxy-5-methylbenzene-1,4-diol; 1), the tendency to undergo an oxidation side reaction was overcome by combining this electron-donating species 1 with a nonreactive partner, benzene-1,2,4,5-tetracarbonitrile (TCNB; 3), to yield a 2 : 1 charge-transfer (CT) complex 4. This work illustrates how very convenient the solvent-free techniques are to access intermolecular species. X-Ray diffraction studies revealed that pure ubiquinol 1 (structure included) crystallizes in two enantiomeric conformations, while the triads 4 formed with TCNB (3) exist as meso forms assembled via H-bonds in zigzag-chains patterns.

Series of charge transfer complexes obtained as crystals in a confined environment

“…The two apparently degenerate modes, namely b 2u and b 3u , in the D 2h space group of TCNB become discriminated in the C 2h space group of a TCNB molecules where two cyano groups in para positions are different from the two others 16,21 . Both vibrations are b u modes, but correspond to elongations towards the H-bonds direction and along the direction of cyano groups not involved in H-bonds, respectively (Fig.…”

“…Thus, perylene -F x TCNQ (x = 1,2,4) CT single crystals were obtained in a two-zone furnace, where the two partners were set at different temperatures, a physical transport being achieved with an argon flow 15 . In case of ubihydroquinone, CoH 2 Q 0 , we already reported the structure of its CTC with TCNB, with the formula (TCNB)(CoH 2 Q 0 ) 2 , obtained by co-evaporation in a two separated compartments sublimator, both partners being heated at two different temperatures, under primary vacuum 16 . In some cases, the coevaporation of both counterparts can be achieved in a unique closed primary evacuated tube, as reported for the 2:1 2methoxybenzoquinone (BQ OMe ) -H 2 Q CTC 3 .…”

Proton coupled electron transfer of ubiquinone Q2 incorporated in a self-assembled monolayer

“…Furthermore, quinones and their reduced derivatives act as electron donors and acceptors in photosynthesis 3 and as charge transfer complexes. 4,5 Therefore, the electrochemistry of ubiquinone has attracted considerable interest in order to determine their thermodynamic constants. The mechanisms and the thermodynamics depend on the quinones environment and can differ when the molecule is adsorbed on the electrode or in solution due to different effects such as lateral interactions between the adsorbed molecules 6 or differences in solvation.…”