Chemistry: Gas adsorption sites in a large-pore metal-organic framework

The primary adsorption sites for Ar and N₂ within metal-organic framework-5, a cubic structure composed of Zn₄O(CO₂) ₆ units and phenylene links defining large pores 12 and 15 angstroms in diameter, have been identified by single-crystal x-ray diffraction. Refinement of data collected between 293 and 30 kelvin revealed a total of eight symmetry-independent adsorption sites. Five of these are sites on the zinc oxide unit and the organic link; the remaining three sites form a second layer in the pores. The structural integrity and high symmetry of the framework are retained throughout, with negligible changes resulting from gas adsorption.