Metal–organic frameworks from novel flexible triptycene- and pentiptycene-based ligands

Abstract

Four distinct iptycene-containing metal–organic frameworks (MOFs) were synthesized and characterized using two new organic ligands. By varying the reaction conditions a series of 1-D, 2-D, and 3-D frameworks was synthesized with a range of secondary building units (SBUs) using the same triptycene-derived ligand. Furthermore, the first example of a pentiptycene-containing MOF is reported as an interpenetrated 3-D framework containing pseudo-[Zn₄O]⁶⁺ clusters. The structural integrity of the MOFs upon guest solvent removal varies depending on the framework, and was tracked using powder X-ray diffraction and thermogravimetric analysis. Gas adsorption experiments were conducted on the robust frameworks and revealed no appreciable surface area. Iptycenyl groups and flexible moieties incorporated into the MOF ligand system appear to enhance structural diversity, but also crowd the pores of the MOF or facilitate framework collapse upon solvent removal, reducing accessible surface area.