Switching Closed-Shell to Open-Shell Phenalenyl: Toward Designing Electroactive Materials

Open-shell phenalenyl chemistry started more than half a century back, and the first solid-state phenalenyl radical was realized only 15 years ago highlighting the synthetic challenges associated in stabilizing carbon-based radical chemistry, though it has great promise as building blocks for molecular electronics and multifunctional materials. Alternatively, stable closed-shell phenalenyl has tremendous potential as it can be utilized to create an in situ open-shell state by external spin injection. In the present study, we have designed a closed-shell phenalenyl-based iron­(III) complex, FeIII(PLY)3 (PLY-H = 9-hydroxyphenalenone) displaying an excellent electrocatalytic property as cathode material for one compartment membraneless H2O2 fuel cell. The power density output of FeIII(PLY)3 is nearly 15-fold higher than the structurally related model compound FeIII(acac)3 (acac = acetylacetonate) and nearly 140-fold higher than an earlier reported mononuclear Fe­(III) complex, FeIII(Pc)Cl (Pc = pthalocyaninate), highlighting the role of switchable closed-shell phenalenyl moiety for electron-transfer process in designing electroactive materials.