(708a) Control of Metal-Organic Framework Crystal Structure By Ligand Functionalization: Functionalized HKUST-1 Derivatives

Control of Metal-Organic Framework Crystal Structure by Ligand Functionalization: Functionalized HKUST-1 Derivatives

Ambarish R. Kulkarni, Yang Cai, Krista S. Walton and David S. Sholl*

School of Chemical & Biomolecular Engineering, Georgia Institute of Technology.

Metal-Organic Frameworks (MOFs) are a novel class of materials consisting of metal centers bonded to organic ligands to form a 3-dimensional porous network. Recent computational and experimental approaches have focused on functionalization of the organic linker to alter the local chemical environment of the framework, which in turn can be used to tune macroscopic properties such as diffusion and adsorption. These studies inherently assume that functionalization of the linker will not affect the topology of the parent MOF.

Previously, we have reported the synthesis of a new topology for CuBTC MOF using methyl and ethyl functionalized BTC (BTC = 1,3,5-benzenetricarbozylate) precursors [Cryst. Growth Des., 2012, 12 (7), pp 3709–3713]. In this work, we study a set of six functionalized BTC precursors (methyl, ethyl, methoxy, nitro, acetamide and bromo) to experimentally show that the use of functionalized ligands within the CuBTC family leads to multiple distinct crystal structures. Further, we perform periodic Density Functional Theory (DFT) calculations to explain the experimental observations. Our DFT calculations show that show that the preference of a particular topology for a given functionalized CuBTC polymorph can be explained and rationalized using computational methods. Specifically, using a cluster model to study the secondary building unit, we assess the thermodynamic stability of the polymorphs in terms of energy penalties associated with the distortion of both the BTC linker and the framework. This molecular level insight of the interactions between the functional group and the topology allows the prediction of topology for a given functionalized ligand and opens the possibility of controlling the topology of a MOF by an appropriate choice of the functionalized precursor.