Tunable Anisotropic Thermal Expansion of a Porous Zinc(II) Metal–Organic Framework

Abstract

A novel three-dimensional metal-organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, n-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host-guest interactions and temperature.

Modulation of Thermal Expansion by Guests and Polymorphism in a Hydrogen Bonded Host

“…This clearly indicates that the guest molecules can influence and increase the thermal expansion of a host network. 15 54,19 But one important difference with these reported systems is that these MOF host−guest systems have been compared with the apo-host, i.e., after removal of the guests from the host lattice without changing the network, whereas in the present report the guest-free form was obtained via crystallization through slow evaporation of solvent. The MOF apo-hosts, reported earlier, were thermodynamically unstable species, but this guest-free form is a stable entity.…”

“…Very recently, Barbour et al 15 reported an interesting case of tuning of thermal expansion of a Zn(II) based metal organic framework (MOF) by changing guest molecules. They used methanol, ethanol, n-propanol, and isopropanol as the guest and showed that PTE along the major principal axis decreases with increasing length of the guest molecules.…”

“…In our work, we have shown much higher NTE and PTE values along the principal axes in the three isostructural solvates. The thermal expansion coefficient values along the minor and major principal axes of the isostructural 1-ph, 1-pc, and 1-mc solvates are −100(8), −50(2), 29(3) MK −1 and 276 (15), 176(4), 68(2) MK −1 respectively, and the volumetric thermal expansion coefficients for these systems are 228 (8), 179(5), and 160 (7) MK −1 respectively. Therefore, the 1-ph system exhibits more prominent uniaxial NTE and PTE as well as higher average volumetric thermal expansion coefficient values compared to the other two isostructural solvates.…”

Switching Between Giant Positive and Negative Thermal Expansions of a YFe(CN)6‐based Prussian Blue Analogue Induced by Guest Species

“…Notably,the presence of guest ions (K + )and molecules (H 2 O) can substantially switch thermal expansion of YFe(CN) 6 from negative (a v = À33.67 10 À6 K À1 )t op ositive (a v =+42.72 10 À6 K À1 )-a range that covers the thermal expansion of most inorganic compounds.T he mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X-ray diffraction, X-rayabsorption fine structure,n eutron powder diffraction, and density functional theory calculations.T he presence of guest ions or molecules plays ac ritical damping effect on transverse vibrations,t hus inhibiting negative thermal expansion. Subsequently,m any more NTE framework materials were found, such as oxides containing MÀOÀMo xygen atom bridges with the general chemical formulae AMO 5 , [7] A 2 M 3 O 12 , [8,9] AO 3 , [10] AM 2 O 7 , [11] and AM 2 O 8 ; [1,12] ReO 3 -type fluorides, [13][14][15][16] cyanides,a nd the Prussian blue analogues formed by double atom M-CN-M bridges in Zn(CN) 2 , [17] Ag 3 Co(CN) 6 , [18] LnCo(CN) 6 , [19] and FeCo(CN) 6 ; [20] and metal-organic frameworks (MOFs) [21][22][23][24] with carboxylate linkages.Thec ontrol of thermal expansion in NTE materials was mainly achieved by chemical substitution, as reported in previous studies. [1][2][3][4][5] Theo ccurrence of negative thermal expansion (NTE) materials offers ap romising possibility.I n 1968, Hummel et al first observed the NTE phenomenon in the framework material ZrW 2 O 8 .…”

Giant negative linear compression positively coupled to massive thermal expansion in a metal–organic framework

“…The uptake of guest molecules strongly interacting with the host framework considerably enhances the linear responses of exceptional positive thermal expansion (PTE) coupled to NTE in Zn(II)MOF (ref. 18), FMOF-1 (ref. 19) and other porous coordination polymers 20,21 .…”