Abstract
The elastic properties of a zeolitic metal-azolate framework, Zn(mtz)2 (MAF-7, mtz− = 3-methyl-1,2,4-triazolate), have been examined from the view point of the first principles calculations and experiments. Our results demonstrate that the three independent elastic constants of MAF-7 are about 5.0–73.3% higher than those of ZIF-8, though they are isomorphic. The electron-donating effect of the nitrogen atom at the 2-position in mtz- ring dominantly accounts for such a prominent difference. The detailed analysis of the full elastic tensors reveals that the volume moduli, shear moduli, and Poisson’s ratios of MAF-7 are about 3.4% to 20.1%, 3.2% to 20.6%, and −30.3% to 12.3% higher than those of ZIF-8. The underlying structural reasons were discussed to explain the anisotropic difference of those properties. Moreover, the conclusion deduced from first-principle calculations was also been verified by nanoindentation and high-pressure synchrotron X-ray diffraction measurements.
Highlights
Zeolitic metal-azolate frameworks (MAFs), a subclass of porous MOFs, have been attracting particular attention due to their potential application [1] superior to traditional zeolites in many fields, such as gas storage/separation [2,3,4], catalysis [5], sensing, and drug delivery [6,7]
Work, we present a systematic study on the elastic properties of a zeolitic triazolate, Zn(mtz)22 (MAF-7 (MAF-7 [16], mtz = 3-methyl-1,2,4-triazolate), which is isomorphous to zeolitic imidazolate frameworks frameworks (ZIFs)-8
The elastic properties of MAF-7 were studied by first-principles calculation and experiment
Summary
Zeolitic metal-azolate frameworks (MAFs), a subclass of porous MOFs, have been attracting particular attention due to their potential application [1] superior to traditional zeolites in many fields, such as gas storage/separation [2,3,4], catalysis [5], sensing, and drug delivery [6,7]. The zeolitic MAFs would experience several rounds of mechanical manufacturing processes. Much study has revealed that significant difference exists between zeolitic MAFs and zeolites in terms of mechanical robustness [8,9,10]. In 2009, Moggach et al performed high pressure single-crystal X-ray diffraction studies on (ZIF), Zn(mim) (ZIF-8 [11], mim = 2-methylimidazolate), a zeolitic imidazolte framework, and discovered that the exertion of pressure can increase the accessible surface area and its absorption performance [12]. A follow-up high-pressure powder X-ray diffraction study reveals similar results and shows that the hydrostatic behavior of ZIF-8 strongly depends on the Crystals 2017, 7, 99; doi:10.3390/cryst7040099 www.mdpi.com/journal/crystals depends on the size of different pressure-transmitting mediumsTan [13]
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