Polar Molecule Confinement Effects on Dielectric Modulations of Sr-Based Metal–Organic Frameworks

The dielectric behavior
of metal–organic frameworks is highly dependent on the polarity
of molecules that are confined in their structure. Hence, it is of
fundamental importance to examine the influence of polar molecules
in a well-designed framework. Herein, we clearly distinguish the role
of polar molecular confinement on dielectric modulations in three
isostructural Sr-based MOFs [Sr2(1,3-bdc)2­(H2O)­(DMF)]n (1D), [Sr2(1,3-bdc)2­(H2O)2·H2O]n (1W), and their
dehydrated analogue [Sr2(1,3-bdc)2]n (1). The synthesis of Sr-based MOF
[Sr2(1,3-bdc)2­(H2O)­(DMF)]n (1D) was performed by the solvothermal
reaction of SrCl2·6H2O and benzene-1,3-dicarboxylic
acid (1,3-bdc) at 110 °C. The effective dielectric constant (κeff) of the DMF-containing compound 1D was found
to be 22.4 (κ = 39.3, where κ is the intrinsic dielectric
constant) at 1 MHz (295 K) which serves to highlight the significant
function of the coordinated DMF when compared with its isostructural
MOF having coordinated and guest H2O molecules (1W; κeff = 7.9, κ = 13.0) and the dehydrated
analogue (1; κeff = 2.4, κ = 3.2).
The presence of DMF molecules between the 2D layers of compound 1D instead of H2O molecules or a vacuum resulted
in a high dielectric constant due to the large kinetic diameter and
dipole moment of DMF molecules. The significance of this study is
the design of an elegant model with a stable core structure, which
can be used to clearly distinguish the role of polar molecules as
well as the presence and absence of guest molecules on the dielectric
behavior of electronic materials. This is of fundamental significance
in chemistry, which will pave the way for the design of dielectric
MOFs in the future for the microelectronics applications.