Tuning the Electric Field Response of MOFs by Rotatable Dipolar Linkers

Abstract

Recently the possibility of using electric fields as a further stimulus to trigger structural changes in metal-organic frameworks (MOFs) has been investigated. In general, rotatable groups or other types of mechanical motion can be driven by electric fields. In this study we demonstrate how the electric response of MOFs can be tuned by adding rotatable dipolar linkers, generating a material that exhibits paralectric behavior in two dimensions and dielectric behavior in one dimension. The suitability of four different methods to compute the relative permittivity κ by means of molecular dynamics simulations was validated. The dependency of the permittivity on temperature T and dipole strength μ was determined. It was found that the herein investigated systems exhibit a high degree of tunability and substantially larger dielectric constants as expected for MOFs in general. The temperature dependency of κ obeys the Curie-Weiss law. In addition, the influence of dipolar linkers on the electric field induced breathing behavior was investigated. With increasing dipole moment, lower field strength are required to trigger the contraction. These investigations set the stage for an application of such systems as dielectric sensors, order-disorder ferroelectrics or any scenario where movable dipolar fragments respond to external electric fields.

Molecular Dynamics Simulations of the “Breathing” Phase Transformation of MOF Nanocrystallites

“…[39] The DMOF-1 Zn 2 (bdc) 2 (dabco) system was described by the first principles parameterized MOF-FF force field. [40,41] Force field parameters were assigned automatically using our hierarchical automated parameter assignment (HAPA) strategy, [42] where building blocks are detected by substructure search based on the connectivity graph and force field parameters are automatically assigned from an SQLdatabase hosted at the MOF+ website (http://www.mofplus.org). As a reference for the NC simulations, a periodic model was also constructed as 2 × 2 × 2 supercell from system rotated by 45 • around the z-axis to maintain a mainly orthorhombic unit cell during transformation.…”