1. Center for Reticular Chemistry, Department of Chemistry and Biochemistry, University of California-Los Angeles, 607 East Charles E. Young Drive, Los Angeles, California 90095, USA
2. Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA

Correspondence to: Omar M. Yaghi¹ Correspondence and requests for materials should be addressed to O.M.Y. (Email: yaghi@chem.ucla.edu).

Zeolitic imidazolate frameworks (ZIFs) are porous crystalline materials with tetrahedral networks that resemble those of zeolites: transition metals (Zn, Co) replace tetrahedrally coordinated atoms (for example, Si), and imidazolate links replace oxygen bridges¹. A striking feature of these materials is that the structure adopted by a given ZIF is determined by link–link interactions, rather than by the structure directing agents used in zeolite synthesis². As a result, systematic variations of linker substituents have yielded many different ZIFs that exhibit known or predicted zeolite topologies. The materials are chemically and thermally stable, yet have the long-sought-after design flexibility offered by functionalized organic links and a high density of transition metal ions^{1, 2, 3, 4, 5, 6, 7}. Here we report the synthesis and characterization of two porous ZIFs—ZIF-95 and ZIF-100—with structures of a scale and complexity previously unknown in zeolites^{8, 9, 10}. The materials have complex cages that contain up to 264 vertices, and are constructed from as many as 7,524 atoms. As expected from the adsorption selectivity recently documented for other members of this materials family³, both ZIFs selectively capture carbon dioxide from several different gas mixtures at room temperature, with ZIF-100 capable of storing 28 litres per litre of material at standard temperature and pressure. These characteristics, combined with their high thermal and chemical stability and ease of fabrication, make ZIFs promising candidate materials for strategies aimed at ameliorating increasing atmospheric carbon dioxide levels.