Substituents Effects of Organic Linkers on Rotational Energy Barriers in Metal-Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) are a new kind of solid porous materials built from metal cations and organic bridging linkers or ligands. We considered a model MOF system using various organic linkers with Zn2+ cations, and studied their equilibrium geometry, structure, potential energy curves (PECs), rotational dynamics, and rotational barriers of the linkers by employing first-principles based DFT methods. We investigated the rotational and dynamical behaviors of the organic linkers in the MOFs. We found that the structural parameters and rotational barrier of the model MOF containing 1,4-benzendicarboxylate (BDC) linker are in excellent agreement with previous experiments. The B3LYP rotational energy barrier of the model MOF containing 1,4-naphthalenedicarboxylate (NDC) linker makes a replica of the previous experimental value. The present computation found that the rotational energy barriers differ considerably depending on the linkers and the substituent effects on them, oscillating from the largest barrier 56.5 kJ/mol (for BDC) to the lowest one 15.3 kJ/mol (for 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylate (TFBDC)). This study expands the opportunity of innovative reticular material chemistry to design novel flexible MOFs with ultrahigh working capacity and small rotational barrier to include linkers having the common acrylate connectivity. We envisage that this new class of MOFs with small rotational energy barrier will be beneficial in a variety of applications including H2-storage, gas storage and separation, adsorption, sensors, and many others. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim