Single-Component Charge-Transfer Crystals Based on Spin-Carrying TCNQ (7,7,8,8-Tetracyanoquinodimethane) Derivatives

Abstract

Three TCNQ derivatives carrying nitroxide radicals (3a-3c) were prepared and were found to form single-component charge-transfer (CT) complexes by self-assembly, in which outer nitroxide groups of a couple of different molecules work as donors and the inner TCNQ unit of another molecule as an acceptor. While the CT interactions found for the TEMPO (2,2,6,6-tetramethylpiperidin-1-oxy) derivative 3a and the PROXYL (2,2,5,5-tetramethylpirrolidin-1-oxy) derivative 3b are point-to-face fashion between the oxygen atom of each nitroxide group and the six-membered ring of inner TCNQ unit, the CT interactions found for the PO (2,2,5,5-tetramethyl-3-pyrrolin-1-oxy) derivative 3c are point-to-point contacts between the oxygen atoms of outer nitroxide groups and the carbon atoms of a couple of cyano groups.

2-(9,10-Anthraquinon-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl: polymorphism in a conjugated anthraquinone-substituted nitronylnitroxide

“…There has been much research on crystal engineering and magneto-structural analysis of organic nitronylnitroxide radicals as molecular magnetic materials. 1 But, little of this work has used electron acceptor quinones and close analogues, aside from a few systems 2,3 having TEMPO or bis-TEMPO radicals tethered to benzoquinone by nonconjugating linkers. Nitronylnitroxides have promise in organic batteries, 4 and structural conjugation between quinones and nitronylnitroxide units could enable redox manipulation of spin and charge states in both moieties.…”