Probing the Mechanochemistry of Metal-Organic Frameworks with Low-Frequency Vibrational Spectroscopy

Abstract

<div>The identification of low-frequency vibrational motions of metal-organic frameworks (MOFs) allows for a full understanding of their mechanical and structural response upon perturbation by external stimuli such as temperature, pressure, and adsorption. Here, we describe the unique combination of an experimental temperature- and pressure-dependent terahertz spectroscopy system with state-of-the-art quantum mechanical simulation to measure and atomistically assign specific low-frequency vibrational modes that directly drive the mechanochemical properties of this important class of porous materials. Our work highlights the complex interplay between structural, vibrational, and mechanochemical phenomena, all of which are key to the effective exploitation of MOFs. We demonstrate the critical importance of terahertz vibrational motions on the function of MOFs, and how this information can be measured and interpreted in a method that can be applied widely to any supramolecular materials. </div><div><br></div>

Pressure-driven mechanical anisotropy and destabilization in zeolitic imidazolate frameworks

“…[18][19][20][21]23,24 The latter has generally been overlooked until it was recently shown to represent the intrinsic "order parameter" of the first-order phase transition occurring in ZIF-8 at high pressure. 30 The computed individual elastic constants of cubic ZIF-8 (C 11 , C 12 and C 44 ) are reported in Figure 1 as a function of pressure, in the 0-0.4 GPa range. At zero pressure, the agreement with the experimental values (black symbols) from room temperature Brillouin scattering measurements is rather satisfactory (the computed values being consistently higher because of neglected thermal effects).…”

Terahertz Spectroscopy of Emerging Materials

“…Temperature-dependent measurements, such as those demonstrated by Dong et al, 43 may be especially useful in this regard. Dynamics have been studied by pressure changes, 45 temperature effects, 46 and the effect of gas adsorption on certain resonant absorptions. 47 These THz-TDS studies highlight the fact that rich structural information can be obtained in MOFs in the THz frequency range, and time- resolved photoinduced structural dynamics may very well be an important future application of TRTS to MOFs.…”

Methyl-rotation dynamics in metal–organic frameworks probed with terahertz spectroscopy

“…[14][15][16] Previous work has demonstrated that in particular, the low-frequency (sub 200 cm À1 ) vibrational motions are clearly related to many properties, such as mechanochemical and gas adsorption phenomena. 17,18 It is therefore highly desirable to develop a complete understanding of the interplay between the structural and dynamical aspects of MOFs in order to optimize their design, and ultimately, their function.…”