Impact of Host–Guest Interactions on the Dielectric Properties of MFM-300 Materials

[Image: see text] Metal–organic framework (MOF) materials are attracting increasing interest in the field of electronics due to their structural diversity, intrinsic porosity, and designable host–guest interactions. Here, we report the dielectric properties of a series of robust materials, MFM-300(M) (M = Al, Sc, Cr, Fe, Ga, In), when exposed to different guest molecules. MFM-300(Fe) exhibits the most notable increase in dielectric constant to 35.3 ± 0.3 at 10 kHz upon adsorption of NH(3). Structural analysis suggests that the electron delocalization induced by host–guest interactions between NH(3) and the MOF host, as confirmed by neutron powder diffraction studies, leads to structural polarization, resulting in a high dielectric constant for NH(3)@MFM-300(Fe). This is further supported by ligand-to-metal charge-transfer transitions observed by solid-state UV/vis spectroscopy. The high detection sensitivity and stability to NH(3) suggest that MFM-300(Fe) may act as a powerful dielectric-based sensor for NH(3).