A Multifunctional Ca^II-Eu^III Heterometallic Organic Framework with Sensing and Selective Adsorption in Water

With increasing global industrialization, it is urgent and challenging to develop multifunctional species for detection and adsorption in the environment. For this purpose, a novel anionic heterometallic organic framework, [(CH₃)₂NH₂][CaEu(CAM)₂(H₂O)₂]·4H₂O·4DMF (CaEuCAM), is hydrothermally synthesized based on chelidamic acid (H₃CAM). Single crystal analysis shows that CaEuCAM features two different oxygen-rich channels along the c-axis in which one CAM^3- bridges two sextuple-coordinated Ca²⁺ and two octuple-coordinated Eu³⁺ with a μ₄-η¹: η¹: η¹: η¹: η¹: η¹ new chelating and bridging mode. The characteristic bright red emission and superior hydrostability of CaEuCAM under harsh acidic and basic conditions benefit it by acting as a highly sensitive sensor for Fe³⁺ and 3-nitrophenol (3-NP) with extremely low LODs through remarkable quenching. The combination of experiments and theoretical calculations for sensing mechanisms shows that the competitive absorption and interaction are responsible for Fe³⁺-induced selective emission quenching, while that for 3-NP is the result of the synergism of host-guest chemistry and the inner filter effect. Meanwhile, the assimilation of negative charge plus channels renders CaEuCAM a highly selective adsorbent for methylene blue (MB) due to a synergy of electrostatic affinity, ion-dipole interaction, and size matching. Of note is the reusability of CaEuCAM toward Fe³⁺/3-NP sensing and MB adsorption besides its fast response. These findings could be very useful in guiding the development of multifunctional Ln-MOFs for sensing and adsorption applications in water media.