Blurring the lines between MOF and HOF: Permanently porous hydrogen-bonded framework UNAM-2 based on a Cu13 metal- organic anion and a diamidinium cation

Hydrogen-Bonded Frameworks ( HBFs ) have emerged as a class of porous supramolecular materials with myriad applications; however, achieving stability and structural control is challenging due to the fragility of hydrogen bonds. Here, we present an HBF UNAM-2 constructed from metal-organic [Cu II Cu I 12 (HL) 12 ] 8– Molecular Building Block ( MBB ) (obtained by dissolving another HBF UNAM-1 ) and terephthalamidinium chloride in water/formamide mixture. The Cu 13 MBBs engage in multiple charged-assisted hydrogen bonds, half of which correspond to carboxylate-amidinium salt bridges that account for the high stability of UNAM-2 , as it does not dissolve in water, formamide or other highly polar solvents and retains crystallinity even when heated to 473 K. Indeed, UNAM-2 retains its structure even after reversible N 2 , CO 2 , or corrosive SO 2 adsorption. We demonstrate for the first time that polynuclear complexes can be used as rigid, directional, and robust molecular building blocks, suggesting the great potential of MBBs for the development of hydrogen-bonded crystalline materials with predetermined structures and properties, similar to the use of secondary building units for MOF synthesis. • Robust Hydrogen-Bonded Framework UNAM-2 was obtained from another HBF UNAM-1 . • It contains Cu 13 and terephtalamidinium building blocks ( MBB ) and a unique topology. • The Cu 13 MBB is rigid, directional, robust and akin to SBUs used in MOFs . • UNAM-2 can be fully activated and reversibly adsorbs CO 2 and SO 2 without collapsing. • This underscores the potential of MBBs in the development of stable and porous HBFs .