Near IR luminescent rare earth 3,4,5,6-tetrafluoro-2-nitrophenoxide complexes: Synthesis,X-ray crystallography and spectroscopy

3,4,5,6-Tetrafluoro-2-nitrophenoxide (L⁻) forms complexes with rare earth M³⁺ ions. X-ray crystal structures of substances with the stoichiometry Cs₂ML₅ · mEt₂O (M = Er, m = 0; M = Er, m = 1; M = Y, m = 1.5; M = Yb, m = 1) have been determined. Each M³⁺ ion is coordinated to two bidentate and three monodentate L⁻ ions; Et₂O does not coordinate to M³⁺. The complexes absorb both visible and ultraviolet light. The solid Er³⁺ and Yb³⁺ complexes have unusually long lifetimes (τ = 20.2 μs and 142 μs, respectively) for the decay of their luminescence in the near-infrared region following photoexcitation; this is attributed to the lack of C–H bonds and other high frequency oscillators that could cause vibrational quenching.