Abstract
Here we report four post-synthetic modifications, including the first ever example of a high pressure-induced post-synthetic modification, of a porous copper-based metal-organic framework. Ligand exchange with a water ligand at the axial metal site occurs with methanol, acetonitrile, methylamine and ethylamine within a single-crystal and without the need to expose a free metal site prior to modification, resulting in significant changes in the pore size, shape and functionality. Pressure experiments carried out using isopropylalcohol and acetaldehyde, however, results in no ligand exchange. By using these solvents as hydrostatic media for high-pressure single-crystal X-ray diffraction experiments, we have investigated the effect of ligand exchange on the stability and compressibility of the framework and demonstrate that post-synthetic ligand exchange is very sensitive to both the molecular size and functionality of the exchanged ligand. We also demonstrate the ability to force hydrophilic molecules into hydrophobic pores using high pressures which results in a pressure-induced chemical decomposition of the Cu-framework.
Highlights
Nanoporous metal–organic frameworks (MOFs) have an array of potential applications including gas storage,[1,2,3] separation processes[4,5,6] and molecular recognition.[7,8] As such, MOFthemed research papers number in the hundreds per annum,[9] with many reporting synthetic or crystal engineering approaches to making more sophisticated, novel frameworks
We show that the selection of a hydrostatic medium of appropriate molecular size and functionality can be of paramount importance when investigating the high pressure postsynthetic modi cation (PSM) behaviour of MOFs
We propose that the shorter bond and resulting lability of the axial water ligands is caused by the secondary structure, i.e. the framework topology of STAM-1, where the hydrophilic channel is relatively constrained compared to HKUST-1 which is composed of much larger pores
Summary
Nanoporous metal–organic frameworks (MOFs) have an array of potential applications including gas storage,[1,2,3] separation processes[4,5,6] and molecular recognition.[7,8] As such, MOFthemed research papers number in the hundreds per annum,[9] with many reporting synthetic or crystal engineering approaches to making more sophisticated, novel frameworks. Single-crystal X-ray diffraction data has been used to show that the water ligands in the axial position of the Cu paddle wheel of STAM-1 can exchange with various organic solvents, both at ambient and above-ambient pressure, causing signi cant changes in the hydrophilic pore size and functionality.
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