CT complexes based on TEMPO radicals

Abstract

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.TEMPO radicals are a well-known class of stable radicals mainly used as spin probes for biological studies and a number of derivatives have been prepared for the purpose until now. ¹ On the other hand, it is of current interest to develop new molecular-based magnetic materials especially organomagnetic materials and numerous compounds carrying TEMPO radicals as the key building blocks have been prepared and their magnetic behaviour has been elucidated in recent years. ² During the course of our studies to develop new organomagnetic materials, we have been interested in preparing some donor or acceptor molecules carrying stable radicals and the CT complexes derived therefrom to build up and to arrange the spins in the solid state/crystal structures ⁴ and we found recently that some TEMPO radicals (A) ⁵ or verdazyl radicals (B) ⁶