Metal-organic frameworks based on previously unknown Zr8/Hf8 cubic clusters.

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.