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Redox-Switchable Optical and Magnetic Properties in a Self-Assembled Hexanuclear Ni(II) Double-Decker Complex
Aristide Colin1, Yiting Wang1, François Lambert1
1Institut de Chimie Moléculaire et des Matériaux D'orsay, CNRS, Université Paris-Saclay UMR 8182, Orsay, France.
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We report the synthesis, crystal structure, and properties of a self-assembled hexanuclear Ni6 complex of formula [{(TMEDANi)2OH}3(HHTP)2](OH)3, where H6HHTP 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 Seff = 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.
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