Methane Sorption and Structural Characterization of the Sorption Sites in Zn 2 (bdc) 2 (dabco) by Single Crystal X‐ray Crystallography

Store it away : Methane adsorption isotherms of Zn 2 (bdc) 2 (dabco) ( 1 ) are measured up to a pressure of 35 bar. X‐ray structure analysis of methane‐adsorbed 1 at 90 K reveals that methane molecules occupy three independent sorption sites A, B , and C while interacting with the framework as well as each other through van der Waals interactions.Sorption isotherms of methane in Zn 2 (bdc) 2 (dabco) are measured up to a pressure of 35 bar in the temperature range between 198–296 K. The methane sorption measurements at 296 K showed an uptake of 137 cm 3  cm −3 at 35 bar. The enthalpy of methane adsorption for Zn 2 (bdc) 2 (dabco) estimated by the virial equation is 13.6 kJ mol −1 at zero coverage. X‐ray structure analysis of methane‐adsorbed Zn 2 (bdc) 2 (dabco) by synchrotron radiation at 90 K revealed that methane molecules occupy three independent sorption sites ( A , B , and C ) with a stoichiometry of Zn 2 (bdc) 2 (dabco)⋅6.69CH 4 , which is consistent with the results of the gas sorption measurements at 198 K. In a cavity, eight symmetry‐related methane sorption sites A are located near the {Zn 2 (CO 2 ) 4 } paddle‐wheel units, while four symmetry‐related methane sorption sites B are near the center of the small windows along the a and b axes. Both A and B sites are half‐occupied. Methane molecules occupying sites A are not only in van der Waals contact with the paddle‐wheel units, but also interact with the phenyl rings of bdc ligands through partial π‐HC interactions. Methane molecules in B sites interact with the side of the phenyl rings through van der Waals interaction. The site C , located at the center of the cavity, is a secondary sorption site; methane molecules occupying sites C are in van der Waals contact with those in sites A and B .