Carlos

New anhydrous lanthanide metal–organic frameworks (MOFs) [Pr(tip)_1.5]_2n (tip-Pr), [Nd(tip)_1.5]_2n (tip-Nd), [Eu(tip)_1.5]_2n (tip-Eu), and [Eu(OH)(mip)]_n (mip-Eu) (tip=5-tert-butylisophthalate anion, mip=5-methylisophthalate ion), have been hydrothermally synthesized and structurally characterized by elemental analyses, FT-IR spectroscopy, single-crystal X-ray diffraction, thermal gravimetric analysis/differential thermal analysis (TG/DTA), and X-ray powder diffraction (XRPD) techniques. MOFs tip-Pr, tip-Nd, and tip-Eu are isostructural anhydrous compounds, and exhibit an unprecedented 3D microporous structure with hexagonal channel arrays. The selectively prepared MOF mip-Eu presents an interpenetrated 3D microporous architecture containing the hydroxyl cluster chains. Solid-state photoluminescence properties at room temperature indicate that both tip-Eu and mip-Eu display the characteristic of the Eu³⁺ ion spectrum dominated by the ⁵D₀→⁷F_J (J=0-4) transition. Compared with mip-Eu, tip-Eu displays the very high solid-state quantum yield (0.62±0.03) and longer lifetime value (0.94±0.01 ms), which is due to the absence of the hydroxyl groups from the solid-state structure of tip-Eu. More importantly, a new method to directly investigate the potential of solid-state lanthanide MOFs for ionic sensing in aqueous solutions has been developed, and successfully applied it to study the potential sensing function of tip-Eu for polyoxometalates (POMs). The possible mechanism for the quenching effect of POMs on the fluorescence of tip-Eu is elucidated by the strongly competitive absorption of the excited light source energy between POMs and tip ligands. The very promise for the highly sensitive sensing for polyoxometalates, together with the characteristic of the reversible fluorescence response, suggest that solid-state tip-Eu can be an excellent candidate for the directly photoluminescent detection of POMs in aqueous solutions.

Tip for detection: New anhydrous 3D microporous lanthanide metal–organic frameworks (MOFs) with hexagonal channel arrays were synthesized based on the 5-tert-butylisophthalate ligand (tip; see figure). The potential sensing function of the Eu-based MOF for polyoxometalates (POMs) in an aqueous solution is investigated for the first time.