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

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.