Metal–Organic Frameworks Based on Previously Unknown Zr8/Hf8 Cubic Clusters

Abstract

The ongoing study of zirconium– and hafnium–porphyrinic metal–organic frameworks (MOFs) led to the discovery of isostructural MOFs based on Zr₈ and Hf₈ clusters, which are unknown in both cluster and MOF chemistry. The Zr₈O₆ cluster features an idealized Zr₈ cube, in which each Zr atom resides on one vertex and each face of the cube is capped by one μ₄-oxygen atom. On each edge of the cube, a carboxylate from a porphyrinic ligand bridges two Zr atoms to afford a 3D MOF with a very rare (4,12)-connected ftw topology, in which two types of polyhedral cages with diameters of ～1.1 and ～2.0 nm and a cage opening of ～0.8 nm are found. The isostructural Zr– and Hf–MOFs exhibit high surface areas, gas uptakes, and catalytic selectivity for cyclohexane oxidation.