Redox‐Switchable Optical and Magnetic Properties in a Self‐Assembled Hexanuclear Ni(II) Double‐Decker Complex

ABSTRACT We report the synthesis, crystal structure, and properties of a self‐assembled hexanuclear Ni 6 complex of formula [{(TMEDANi) 2 OH} 3 (HHTP) 2 ](OH) 3 , where H 6 HHTP is hexahydroxytriphenylene and TMEDA is N,N,N′,N′‐tetramethylethylenediamine. Single‐crystal x‐ray crystallography reveals a trigonal architecture with three hydroxo‐bridged binuclear Ni(II) units assembled by a diamagnetic (HHTP) 2 double‐decker unit, HHTP are in the tris‐semiquinone oxidation state. Cyclic voltammetry reveals four reversible one‐electron redox processes, and spectro‐electrochemical studies confirm that both oxidized and reduced species are HHTP‐centered, with strong near‐infrared (NIR) optical responses. The one‐electron oxidized species was isolated and characterized by UV–vis spectroscopy, EPR, and DC magnetic measurements. Wave function‐based calculations establish that the HHTP moieties are in the tris‐semiquinone state undergoing a strong covalent interaction. The calculations rationalize the weak exchange coupling within the binuclear Ni(II) centers through the hydroxo bridge. It allows proposing a model to fit the magnetic data. Oxidation generates an S = ½ radical on the (HHTP) 2 unit that couples strongly and asymmetrically to one Ni(II) binuclear unit, yielding an effective spin S eff = ½ as demonstrated from the analysis of the magnetic data. This work demonstrates that redox‐active HHTP scaffolds offer a powerful platform for achieving multistate magnetic and NIR optical switching in polynuclear complexes.