The Effect of High Pressure on MOF-5: Guest-Induced Modification of Pore Size and Content at High Pressure

The authors have obsd. the effect of pressure on the metal-org. framework MOF-5 from ambient pressure to 3.2 GPa, and subsequently explored what drives the framework's behavior. Initial compression to 0.8 GPa represents a pressure region where solvent is "squeezed" into the pores. This is highlighted by comparison with computational results which show direct compression of the evacuated framework. Increasing the pressure further to 1.3 GPa results in a decrease in vol. and a sudden marked decrease in solvent content as the solvent is evacuated from the pores. Increasing the pressure to 3.2 GPa results in a gradual and steady redn. in vol. and resoln. of the data as the sample becomes amorphous. Increasing pressure above 3.2 GPa results in complete amorphization of the sample. When compared with a previous pressure study it appears that hydrostatic compression delays the onset of amorphization. This indicates that pressure-induced solvent inclusion makes the framework more resilient to pressure. The compressibility of the framework is mediated through Zn-O bonds. In particular, the Zn-O2 bond (to the carboxyl oxygen atom) shows significantly greater compression than the Zn-Ol bond (to the |j.4-oxygen atom). This is also obsd. in the computational results on the evacuated framework, though interestingly the Zn-Ol bond here compresses significantly more. How the presence of solvent effects the compressibility of Zn-O bonds is still under investigation.