Metallo-hydrogen bonded organic frameworks with nitrogen tridentate ligands: exploring inclusion and dye adsorption properties†

In this research, we've synthesized a remarkable series of charge-assisted hydrogen-bonded host frameworks. These frameworks are like intricate molecular “houses” built using a unique bowl-shaped nitrogen tridentate ligand L (2,4,6-trimethyl-1,3,5-tris(morpholinomethyl)benzene) and metal ions (M = Cu, Zn, Cd). Through the second sphere coordination approach, we've created networks with varying void sizes or tightly packed structures. The water molecules nestled within these voids play a crucial role as hydrogen bonding bridges, and they can be released while the voids remain stable even at the melting point. Once the guest water molecules are removed, these frameworks become selective “sieves” for different liquid solvents, depending on their molecular size. What's more, they show impressive dye adsorption capabilities, with 31.5 mg g⁻¹ for SY (78.8%), 32.6 mg g⁻¹ for MB (81.5%), and 36.4 mg g⁻¹ for CR (91.0%) in methanol solutions within just 24 hours. This research could pave the way for new applications in areas like environmental remediation and chemical separation.