Facile in Situ Halogen Functionalization via Triple-Bond Hydrohalogenation: Enhancing Sorption Capacities through Halogenation to Halofumarate-Based Zr(IV)-Metal-Organic Frameworks

Surface halogenation is an important means to tune or improve functionalities of solid-state materials. However, this concept has been hardly explored and exploited in the engineering of metal-organic frameworks (MOFs). Here, a facile approach to obtain halo-functionalized derivatives of zirconium fumarate (MOF-801) is developed by reacting zirconium halides (ZrX₄; X = Cl, Br, I) in water with acetylenedicarboxylic acid. The latter quantitatively undergoes an unusual in situ linker transformation into halofumarate via trans addition of HX to the −CC– triple bond. This HX addition and MOF formation happen in a one-pot reaction, that is, the in situ generated halogenated linker reacts with zirconium ions in solution to yield three microporous HHU-2-X MOFs (X = Cl, Br, I) with an fcu topology, containing UiO-type [Zr₆O₄(OH)₄] secondary building units 12-fold connected by halofumarate linkers. The halogen (Cl) groups in HHU-2-Cl result in increased hydrophilicity for water vapor sorption as well as increased gas uptakes of 21% SO₂, 24% CH₄, 44% CO₂, and 154% N₂ when compared to the non-halogenated MOF-801. The tuning of the inner surface chemistry is realized to yield multipurpose adsorbent materials for enhanced gas and vapor uptakes over their non-halogenated analogues. The gas sorption properties of the chlorinated HHU-2-Cl material indicate its suitability for CO₂, N₂, and SO₂ capture and separation, while its water sorption profile yields a high heat storage capacity of 500 kJ kg^–1, making it promising for adsorption-based thermal batteries and dehumidification applications.