High-Connectivity Triazolate-Based Metal-Organic Framework for Water Harvesting

Increasing the connectivity of structural units presents a potentially valuable approach to improve hydrolytic stability in metal-organic frameworks (MOFs). We herein leverage this strategy by synthesizing the first tritopic benzotriazolate MOF, Zn₅(OAc)₄(TBTT)₂ (H₃TBTT = 2,4,6-tris(1H-benzo[d][1,2,3]triazol-5-yl)-1,3,5-triazine), which exhibits open metal sites, high connectivity, high porosity, and significant water uptake capacity. The MOF adopts a previously unknown topology with (3,6,6)-connectivity, which is supported by single-crystal electron diffraction and elemental analysis. The framework undergoes postsynthetic metal and anion exchange with NiCl₂, which increases the accessible pore volume and the net hydrophilicity of the framework. With this exchange, the apparent BET surface area increases from 1994 to 3034 m²/g, and the water uptake step shifts from 56 to 33% relative humidity (RH). The high gravimetric capacity of the Ni-rich MOF, 0.98 g/g, translates to a working capacity of 0.64 g/g during a pressure swing cycle between 20 and 40% RH at 25 °C. Combining this performance with a less than 2% loss in working capacity over 100 cycles, the new material rivals the best MOF water sorbents to date.