CT complexes based on TEMPO radicals

A series of CT (charge-transfer) complexes have been prepared, in which TEMPO (2,2,6,6-tetramethylpiperidinyloxyl) radical 1 and its derivatives (2 and 6-10) act as donors using TCNQF(4) (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyanobenzo-1,4-quinone) as acceptors. A sharp difference was observed in magnetic properties between the charge-transfer complexes derived from the TEMPO radicals 1 or 2 and amino-TEMPO radicals 6-10 and the distinct difference observed in the molecular/crystal structures in the complexes is thought to reflect the difference in their magnetic behaviour. The CT complexes from 4-dimethylamino- or 4-azetidino-TEMPO and DDQ formed salt-like complexes of protonated 4-dialkylamino-TEMPO and the substituted benzo-1,4-quinonehydroxylate upon recrystallization from moist acetone.