Deuterium NMR studies of framework and guest mobility in the metal-organic framework compound MOF-5, Zn4O(O2CC6H4CO2)3

Variable temperature wideline H-2 NMR investigations of the mobility of aromatic rings in the framework of desolvated samples of the metal organic framework compound MOF-5 (Zn4O(O2CC6H4CO2)(3)) and the closely related solid MOCP-L have been performed. The aromatic rings in MOF-5 are stationary at temperatures lower than room temperature but perform 180 degrees (71) flips at higher temperatures until all framework aromatic groups execute this motion at 373 K. The aromatic groups in MOCP-L demonstrate a higher degree of mobility with some motion even below 170 K. H-2 NMR of perdeuterobenzene adsorbed onto MOF-5 at a loading of two molecules per Zn4O13 inorganic unit shows that upon cooling below 140 K the motion of benzene changes from isotropic reorientation to rotation about its six-fold axis. Computational simulation suggests that benzene occupies a site close to the Zn4O13 unit at low temperatures. (c) 2005 Elsevier Inc. All rights reserved.