Heteroleptic Samarium(III) Chalcogenide Complexes: Opportunities for Giant Exchange Coupling in Bridging σ- and π-Radical Lanthanide Dichalcogenides

Abstract

The introduction of (N₂)^3–• radicals into multinuclear lanthanide molecular magnets raised hysteresis temperatures by stimulating strong exchange coupling between spin centers. Radical ligands with larger donor atoms could promote more efficient magnetic coupling between lanthanides to provide superior magnetic properties. Here, we show that heavy chalcogens (S, Se, Te) are primed to fulfill these criteria. The moderately reducing Sm(II) complex, [Sm(N^††)₂], where N^†† is the bulky bis(triisopropylsilyl)amide ligand, can be oxidized (i) by diphenyldichalcogenides E₂Ph₂ (E = S, Se, Te) to form the mononuclear series [Sm(N^††)₂(EPh)] (E = S, 1-S; Se, 1-Se, Te, 1-Te); (ii) S₈ or Se₈ to give dinuclear [{Sm(N^††)₂}₂(μ-η²:η²-E₂)] (E = S, 2-S₂; Se, 2-Se₂); or (iii) with Te═PEt₃ to yield [{Sm(N^††)₂}(μ-Te)] (3). These complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, FTIR, and electronic spectroscopy; the steric bulk of N^†† dictates the formation of mononuclear complexes with chalcogenate ligands and dinuclear species with the chalcogenides. The Lα₁ fluorescence-detected X-ray absorption spectra at the Sm L₃-edge yielded resolved pre-edge and white-line peaks for 1-S and 2-E₂, which served to calibrate our computational protocol in the successful reproduction of the spectral features. This method was employed to elucidate the ground state electronic structures for proposed oxidized and reduced variants of 2-E₂. Reactivity is ligand-based, forming species with bridging superchalcogenide (E₂)^−• and subchalcogenide (E₂)^3–• radical ligands. The extraordinarily large exchange couplings provided by these dichalcogenide radicals reveal their suitability as potential successors to the benchmark (N₂)^3–• complexes in molecular magnets.