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Insight into the gas-induced phase transformations in a 2D switching coordination network via coincident gas sorption and in situ PXRD

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journal contribution
posted on 2024-02-02, 09:32 authored by Shi-Qiang WangShi-Qiang Wang, Volodymyr Bon, Shaza DarwishShaza Darwish, Shao-Min Wang, Qing‐Yuan Yang, Zhengtao Xu, Stefan Kaskel, MICHAEL ZAWOROTKOMICHAEL ZAWOROTKO

ABSTRACT: Switching coordination networks (CNs) that reversibly transform between narrow or closed pore (cp) and large pore (lp) phases, though fewer than their rigid counter-parts, offer opportunities for sorption-related applications. However, their structural transformations and switching mechanisms remain underexplored at the molecular level. In this study, we conducted a systematic investigation into a 2D switching CN, [Ni(bpy)2(NCS)2]n, sql-1-Ni-NCS (1 = bpy = 4,4′-bipyridine), using coincident gas sorption and in situ powder X-ray diffraction (PXRD) under low-temperature conditions. Gas adsorption measurements revealed that C2H4 (169 K) and C2H6 (185 K) exhibited single-step type F−IVs sorption isotherms with sorption uptakes of around 180−185 cm3 g−1 , equivalent to four sorbate molecules per formula unit. Furthermore, parallel in situ PXRD experiments provided insight into sorbate-dependent phase switching during the sorption process. Specifically, CO2 sorption induced single-step phase switching (path I) solely between cp and lp phases consistent with the observed single-step type F−IVs sorption isotherm. By contrast, intermediate pore (ip) phases emerged during C2H4 and C2H6 desorption as well as C3H6 adsorption, although they remained undetectable in the sorption isotherms. To our knowledge, such a cp-lp-ip-cp transformation (path II) induced by C2H4/6 and accompanied by single-step type F−IVs sorption isotherms represents a novel type of phase transition mechanism in switching CNs. By virtue of Rietveld refinements and molecular simulations, we elucidated that the phase transformations are governed by cooperative local and global structural changes involving NCS− ligand reorientation, bpy ligand twist and rotation, cavity edge (Ni-bpy-Ni) deformation, and interlayer expansion and sliding.


Green Adsorbents for Clean Energy (GrACE)

Science Foundation Ireland

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ACS Materials Letters 6, pp. 666-673


American Chemical Society

Other Funding information

Irish Research Council (IRCLA/2019/167) German Federal Ministry of Research and Education (Projects No. 05K22OD1 and 05K22OD2) Science Technology and Research (SC25/22-119116).

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