Metal Node Control of Coordinatively Unsaturated Sites in Heterobimetallic MOFs for Stable and High Ammonia Adsorption

The escalating demand for ammonia (NH₃) as an energy vector and chemical feedstock, coupled with its toxic and corrosive nature, has raised serious environmental and health concerns due to widespread emissions. The development of sorbents with both high capacity and stability, particularly under ambient conditions, remains a critical challenge. Herein, we report a novel multivariate (MTV) metal-organic framework (MOF), MUV-102(Cu-Ti), engineered through precise integration of heterometallic Cu^(2-δ)+-Ti⁴⁺ clusters, which demonstrates exceptional NH₃ adsorption performance and reversible stability under both low and high concentrations. Under static exposure to 100 ppm of NH₃, MUV-102(Cu-Ti) achieves 3.9 mmol g^-1 uptake, while at dynamic equilibrium (1 bar), it reaches 22.4 mmol g^-1, surpassing monometallic and other heterobimetallic titanium-based analogs (Co, Ni, Zn, Mn), ranking among the top in current record of MOFs. The framework retains its integrity and adsorption capacity after nine adsorption-desorption cycles. Experimental and theoretical analyses reveal that the heterometallic Cu^(2-δ)+-Ti⁴⁺ unit enhances thermodynamic stability by strengthening metal-ligand (M-L) bonds and dynamically modulating Lewis acidic sites to generate abundant open metal sites (OMS) for NH₃ molecules. These findings provide a design strategy for multivariate MOFs (MTV-MOFs) with complementary metal reactivity, offering promise for efficient NH₃ capture in environmental remediation and energy applications.