A magnesium-based bifunctional MOF: Studies on proton conductivity, gas and water adsorption

• A magnesium-based bifunctional metal-organic framework.
• Mg based 2D coordination polymer.
• Proton conductivity study.
• N2, CO2 and H2O adsorption and desorption studies.

An alkaline earth metal ion based bi-functional metal-organic framework {[Mg(4,4′-bpdc)(H2O)3](H2O)}n (where 4,4′-bpdc = 4,4′-biphenyl dicarboxylate) has been synthesized by simply stirring the precursors in water. The framework crystallizes in orthorhombic Pbca space group. The metal nodes of the complex are bridged by dicarboxylates in μ3-fashion to form corrugated 2D coordination sheets. The neighbouring 2D sheets are further connected by hydrogen bonding interactions between the coordinated water molecules and the carboxylate oxygen atoms to form a 3D supramolecular structure. The small hydrophilic supramolecular pockets of the 3D supramolecular structure are filled by guest water molecules through hydrogen bonding interactions. The framework exhibits proton conductivity of 1.44 × 10−5 S m−1 at 303 K under vacuum and the proton transport in the framework follows the Grotthuss mechanism where the hydrogen bonded network acts as the proton transport pathway. The evacuated material, after removal of both coordinated and guest water molecules, retains its crystallinity but is not isostructural with the original framework. According to N2 adsorption study the BET surface area and the total pore volume of the evacuated material are 39 m2 g−1 and 0.133 cc g−1, respectively. The evacuated material can adsorb (175 cc g−1 at P/P0 ∼ 0.99) and store (154 cc g−1 at P/P0 = 0.1) a decent amount of water molecules.

The proton transport, gas and water adsorption properties of a Mg based metal organic framework{[Mg(4,4′-bpdc)(H2O)3](H2O)}n (where 4,4′-bpdc = 4,4′-biphenyl dicarboxylate) has been studied. The framework exhibits moderate proton conductivity of 1.44 × 10−5 S m−1 at 303 K under vacuum. The proton transport in the framework follows the Grotthuss mechanism. The evacuated material obtained after removal of guest and coordinated water molecules can adsorb (175 cc g−1 at P/P0 ∼ 0.99) and store (154 cc g−1 at P/P0 = 0.1) a decent amount of water molecules.Figure optionsDownload as PowerPoint slide