Impact of Disordered Guest-Framework Interactions on the Crystallography of Metal-Organic Frameworks

Abstract

It is a general and common practice to carry out single-crystal X-ray diffraction experiments at cryogenic temperatures in order to obtain high-resolution data. In this report, we show that this practice is not always applicable to metal-organic frameworks (MOFs), especially when these structures are highly porous. Specifically, two new MOFs are reported here, MOF-1004 and MOF-1005, for which the collection of the diffraction data at lower temperature (100 K) did not give data of sufficient quality to allow structure solution. However, collection of data at higher temperature (290 K) gave atomic-resolution data for MOF-1004 and MOF-1005, allowing for structure solution. We find that this inverse behavior, contrary to normal practice, is also true for some well-established MOFs (MOF-177 and UiO-67). Close examination of the X-ray diffraction data obtained for all four of these MOFs at various temperatures led us to conclude that disordered guest-framework interactions play a profound role in introducing disorder at low temperature, and the diminishing strength of these interactions at high temperatures reduces the disorder and gives high-resolution diffraction data. We believe our finding here is more widely applicable to other highly porous MOFs and crystals containing highly disordered molecules.