Two new porous UiO-66-type zirconium frameworks; open aromatic N-donor sites and their post-synthetic methylation and metallation

Abstract

Two new, isostructural UiO-66-type metal–organic frameworks (MOFs), Zr-PyDC (Zr₆O₄(OH)₅(pyridine-2,5-dicarboxylate)₄(formate)₃(H₂O)₃₄) and Zr-PzDC (Zr₆O₄(OH)_4.75(pyrazine-2,5-dicarboxylate)_4.5(formate)_2.25(H₂O)₃₃) have been synthesised via an unusual high acidity route. Despite the chelating capability of the ligands, which incorporate pyridine and pyrazine N-functionalities, these robust MOFs are linked exclusively through carboxylate donors to leave free Lewis base donor sites. Both MOFs show increased heats of adsorption and higher loadings of CO₂ and H₂ than UiO-66. High-conversion post-synthetic modification of Zr-PyDC and Zr-PzDC yielded charged, N-methylated frameworks with enhanced gas adsorption capacities. Further, the metal binding properties of Zr-PyDC have been probed by post-synthetic metallation with Cu^II.