Experimental evidence of negative linear compressibility in the MIL-53 metal–organic framework family

Abstract

We report a series of powder X-ray diffraction experiments performed on the soft porous crystals MIL-53(Al) and NH-MIL-53(Al) in a diamond anvil cell under different pressurization media. Systematic refinements of the obtained powder patterns demonstrate that these materials expand along a specific direction while undergoing total volume reduction under an increase in hydrostatic pressure. The results confirm for the first time the Negative Linear Compressibility behaviour of this family of materials recently predicted from quantum chemical calculations.

The Direct Heat Measurement of Mechanical Energy Storage Metal–Organic Frameworks

“…Furthermore, structural studies with other systems confirm such a transition with pressure. [6,14] This compression step occurs at a pressure which is smaller than that observed either for MIL-53(Cr) (around 55 MPa [4] ) or MIL-47(V) (around 85 MPa). [5] The volume variation during this step (0.24 mL g À1 ) is comparable to that calculated from structure parameters obtained by XRD of approximately 0.3 mL g À1 (calculated from a volume variation of 29 % from LP to NP and a density of 0.98 g mL À1 for LP form).…”

“…[17] Mechanical systems can be classified as either shock absorbers (irreversible compression), dampers (compressiondecompression with hysteresis), or molecular springs (compression-decompression without hysteresis). [18] For any application, mercury cannot be retained as a pressure transmission fluid for safety reasons, and alternative fluids have already been proposed including silicon oil, [6] mineral oil, [14,19] fluorinert, [20] and 2-propanol. [21] Here, silicon oil was used to perform the compression-depression cycles with the sample placed inside a calorimeter.…”

Research Update: Mechanical properties of metal-organic frameworks – Influence of structure and chemical bonding

“…40,41 Furthermore, the structural anisotropy of many MOFs often gives rise to large mechanical anisotropy and, correspondingly, unique mechanics. For a Electronic addresses: dearweili@gmail.com and shenke738@gmail.com b W. Li instance, some MOFs have been reported to exhibit negative linear compressibility (NLC) [42][43][44] and massive positive or negative thermal expansion (PTE and NTE). [45][46][47][48] Considering that MOF research is mainly dominated by synthetic chemists, a general introduction to the intrinsic links between chemistry and mechanics is of particular interest, as it will bridge the gap between chemistry and mechanical engineering.…”

Computational characterization and prediction of metal–organic framework properties

“…This property of materials expanding in one or two directions under hydrostatic compression is considered rather exotic in inorganic solids, [152] but has been observed in a relatively large number of framework materials [153,154,155,156] and MOFs. [157,158,159] On the strain δεi Figure 12: Determination of the four-rank tensor C of second-order elastic constants, by quantum chemistry calculations, and its analysis to obtain physical properties such as Young's modulus (E), shear modulus (G), linear compressibility (β ), and Poisson's ratio (ν).…”

“…In the linear elasticity regime, it can be studied through the computation of the elastic stiffness tensor as described above, as was done for the prediction and subsequent experimental confirmation of negative linear compressibility in the MIL-53 family. [158] It can also be performed by in silico compression experiments, studying the influence of finite increments of pressure on a MOF structure, either through enthalpy minimization calculations under pressure, [157] or through constant-pressure constanttemperature (N, σ , T ) molecular dynamics studies. [149] Because computational compression experiments allow the determination of structure (unit cell parameters and atomic positions) as a function of applied mechanical pressure, it yields information outside of the elastic regime and can provide insight into the occurrence of pressure-induced structural transitions.…”