Temperature-Dependent Conductivity, Luminescence and Theoretical Calculations of a Novel Zn(II)-Based Metal-Organic Framework
Anovel four-fold interpenetrating metal-organic framework (MOF) (1) was obtained following reaction between Zn2+ and benzene-1,3,5-tribenzoate (H3BTB). Single crystal analysis demonstrated that the framework featured a three-dimensional (10, 3) net anionic framework with dimethyl formamide (DMF) and H2NMe2 + encapsulated in channels along the b axis. Alternating current impedance measurements revealed an unusual temperature-dependent conductance. As the temperature was increased from 20°C the conductance value increased from 0.36×10-6 S·cm-1 to a maximum value of 2.24×10-5 S·cm-1 at 160°C, and then began to decrease. A combination of molecular dynamics (MD) simulations and dielectric property measurements demonstrated that this conductance behavior could be attributed to the synergic effect of the enhanced mobility of the H2NMe2 + cation and removal of DMF as the temperature was increased. Furthermore, the transporting energy barrier was determined to be 0.20 eV, which confirmed that the conductance was caused by proton conductivity. This work indicated that the confinement of H2NMe2 + within the pores of MOFs is a promising method to induce electrical conductivity. Interestingly, the emission peak of 1 was blue-shifted when compared with that of H3BTB. Density functional theory (DFT) calculations revealed that this phenomenon was caused by the disruption of delocalized π-bonds within the BTB3- ligand in 1.
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