Magnetic Transition in Organic Radicals: The Crystal Engineering Aspects

Abstract

Spin–Spin interactions between unpaired electrons in organic radicals are of utter importance from the viewpoint of molecular magnetism and the development of smart materials. The diamagnetic to paramagnetic phase transition observed in some radicals often leads to “magnetic bistability,” sometimes associated with a thermally accessible structural phase transition. The noncovalent interactions determining the solid-state packing arrangement are highly susceptible to external stimuli (temperature, pressure, light, electric field, etc.) and allow the radicals to respond reversibly. Thus, a qualitative understanding of the communication pathway of the spin centers and factors determining the solid-state packing arrangement for the radicals is most important. In this perspective, we mainly discuss the effect of noncovalent interactions rearranging the radicals’ position with temperature determining the mechanistic pathway of such phase transitions. We focus on the importance of electronic parameters stabilizing different polymorphic phases of the radicals, secondary dynamic effects arising from the π-stacking in solid-state, and their role in a magnetic phase transition, along with the consequences of different external stimuli in fine-tuning the magnetic bistable states.