Luminescent Er³⁺ based single molecule magnets with fluorinated alkoxide or aryloxide ligands

We report the synthesis, structures, and magnetic and luminescence properties of a series of new mono- and dinuclear Er³⁺ complexes derived from sterically demanding aryloxide and fluorinated alkoxide ligands: [4-tBu-2,6-(Ph₂CH)₂C₆H₂O]₃Er(THF) (1), [(C₆F₅)₃CO]₃Er(Me₃SiOH) (2), [(C₆F₅)₃CO]₃Er[(Me₃Si)₂NH] (3), [(C₆F₅)₃CO]₃Er(C₆H₅CH₃) (4), [(C₆F₅)₃CO]₃Er(o-Me₂NC₆H₄CH₃) (5) and {[Ph(CF₃)₂CO]₂Er(μ²-OC(CF₃)₂Ph)}₂ (6). In compounds 1, 2, and 4, the Er³⁺ ion is four-coordinated and adopts a distorted trigonal pyramidal geometry, while in 3, 5, and 6, the coordination geometry of Er³⁺ is impacted by the presence of several relatively short Er⋯F distances, making them rather 6-coordinated. All compounds behave as field-induced Single Molecule Magnets (SMMs) and exhibit an Er³⁺ characteristic near infrared (NIR) emission associated with the ⁴I_13/2 → ⁴I_15/2 transition with a remarkably long lifetime going up to 73 μs, which makes them multifunctional luminescent SMMs. The deconvolution of the NIR emission spectra allowed us to provide a direct probe of the crystal field splitting in these compounds, which was correlated with magnetic data.