Linear, Electron-Rich Erbium Single-Molecule Magnet with Dibenzocyclooctatetraene Ligands

Abstract

High Resolution Image Download MS PowerPoint Slide Judicious design of ligand scaffolds to highly anisotropic lanthanide ions led to substantial advances in molecular spintronics and single-molecule magnetism. Erbium-based single-molecule magnets (SMMs) are rare, which is attributed to the prolate-shaped Er III ion requiring an equatorial ligand field for enhancing its single-ion magnetic anisotropy. Here, we present an electron-rich mononuclear Er SMM, [K(crypt-222)][Er(dbCOT) 2 ], 1 (where dbCOT = dibenzocyclooctatetraene), that was obtained from a salt metathesis reaction of ErCl 3 and K 2 dbCOT. The dipotassium salt, K 2 dbCOT, was generated through a two-electron reduction of the bare dbCOT 0 ligand employing potassium graphite and was crystallized from DME to give the new solvated complex, [K(DME)] 2 [dbCOT] n, 2 . 1 was analyzed through crystallography, electrochemistry, spectroscopy, magnetometry, and CASSCF calculations. The structure of 1 consists of an anionic metallocene complex featuring a linear (180.0°) geometry with an Er III ion sandwiched between dianionic dbCOT ligands and an outer-sphere K + ion encapsulated in 2.2.2-cryptand. Two pronounced redox events at negative potentials allude to the formation of a trianionic erbocene complex, [Er(dbCOT) 2 ] 3–, on the electrochemical time scale. 1 shows slow magnetic relaxation with an effective spin-reversal barrier of U eff = 114(2) cm –1, which is close in magnitude to the calculated energies of the first and second excited states of 96.9 and 109.13 cm –1, respectively. 1 exhibits waist-constricted hysteresis loops below 4 K and constitutes the first example of an erbocene-SMM bearing fused aromatic rings to the central COT ligand. Notably, 1 comprises the largest COT scaffold implemented in erbocene SMMs, yielding the most electron-rich homoleptic erbium metallocene SMM.

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