Metal-Organic Frameworks (MOFs) self-assemble from metal ions and ligands, forming higher order structures.1 These materials have gained increased attention as synthetic approaches for target applications have been uncovered.2 The use of nitrogen donor pillar ligands and carboxylic acid functionalised ligands to construct these materials are an interesting aspect of MOF design. They can be used to vary the level of interpenetration thereby altering the final topology as well as providing a scaffold for interactions with guest molecules such as gases.
Our work has focused on the formation and characterisation, via single crystal X-ray diffraction and powder diffraction, of a series of MOFs synthesised using pillar and carboxylic acid ligands in combination with zinc(II). The pillar ligands are functionalised with bulky groups such as triazole esters, trimethyl silanes and alkynes. The functionality impacts MOF assembly as well as providing sites for interaction of adsorbing molecules. An extension of pillaring ligands in literature, these materials utilise the bulkiness of the pillar ligand to synthesise non-interpenetrated 3D MOFs and investigate their impact on the MOFs nodes.
The synthesised MOFs, [Zn3(bdc)3(L)], are composed of 2D sheets stacked together by pillar ligands forming a 3D framework. These sheets are made up of zinc(II) trimer nodes coordinated via the carboxylate groups of 1,4-dicarboxylic acid. The 3D framework is then formed via the nitrogen donor ligands, acting as pillars between the sheets. Gas adsorption techniques were used to uncover the surface area and potential for selective CO2 adsorption.