Basic Zinc Cubane-1,4-Dicarboxylate: A New MOF-5 Analogous with High Porosity and Robust Dynamics

A new metal-organic framework, basic zinc cubane-1,4-dicarboxylate, (1) was synthesized. 1 is a cubic framework of the same underlying topology, as basic zinc terephthalate, MOF-5, with similar lattice parameters, unique dynamics and competitive adsorption properties. It has a highsymmetry space group, Pm3,¯m with a lattice parameter of 12.776 Å, as determined by X-ray diffraction at 100 K. The structure consists of a random distribution of two perpendicular basic zinc carboxylate nodes and axially disordered cubylene spacers, so the observed high-symmetry structure is an average of several lower-symmetry unit cells. The binary orientational disorder of the nodes has significant influence on the uniaxial rotation of the edges, realizing a previous idea of robust dynamics1. The structural and dynamical ifferences of 1 and MOF-5 are based on the local symmetry and the electronic structure of the organic components: i) the lack of conjugation in cubane-1,4-dicarboxylate does not fix the orientation of the nodes; and ii) the incomplete match of the cubylene (rotor) and dicarboxylate (stator) units facilitates the rotation of the cubylene units even at 100 K. The calculated rotation barrier is unusually low, and it depends on the orientation of the adjacent carboxylate units. The crystals of 1 can be activated either at elevated temperature in vacuum or at ambient conditions by solvent exchange. The high surface area (3160 m2g-1) and the high capacity of hydrogen uptake promise future practical applications.