The synthesis and magnetic properties of carboxylic acid-derived 1,2,4-benzotriazinyl radicals and their coordination particles

Abstract

Organic conjugated radicals are promising materials for organic magnets and spintronics; however, their solid-state properties are difficult to control and predict. We report the synthesis and magnetic properties of carboxylic acid-functionalized 1,2,4-benzotriazinyl radicals DAR, TAR and their corresponding coordination particles. These hydrogen bond containing compounds exhibit a typical antiferromagnetic behavior and good thermal stability up to 300 °C. Moreover, DAR and TAR possess stronger intermolecular spin–spin interactions than their ester counterparts as supported by their wider ESR line widths. Nanosize coordination particles are obtained upon sonication of these two radicals with metal ions at 0 °C. Diamagnetic Zn²⁺-based cubic UD-Zn and spherical UT-Zn show stronger spin–spin interactions than their corresponding ligands, along with the retained forbidden transition signal Δm_s = ±2. In sharp contrast, paramagnetic Cu²⁺-derived CPs display very weak magnetic signals due to the redox reaction between Cu²⁺ and radicals. This work is useful for the future design of conjugated radicals and radical ligand-based magnetic coordination particles.