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

Abstract

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.