Pressure-Induced Structural Effects in the Square Lattice (sql) Topology Coordination Network Sql-1-Co-NCS·4OX

Abstract

A high-pressure study of a switching coordination network of square lattice topology (sql) loaded with o-xylene (OX), [Co(4,4′-bipyridine) 2 (NCS) 2 ] n •4nC 8 H 10 (sql-1-Co-NCS•4OX), was conducted up to approximately 1 GPa to investigate pressure-induced structural changes. Previous reports revealed that sql-1-Co-NCS exhibits multiple phases thanks to its ability to switch between closed (nonporous) and several open (porous) phases in the presence of various gases, vapors, and liquids. Networks of such properties are of topical interest because they can offer high working capacity and improved recyclability for gas adsorption. The monoclinic crystal structure of sql-1-Co-NCS•4OX at 100 K was previously reported to show an increase in interlayer separation of more than 100% compared to the corresponding closed phase, sql-1-Co-NCS, when exposed to gases or vapors under ambient conditions. Herein, a tetragonal crystal form of sql-1-Co-NCS•4OX (space group I4/mmm, Phase I) that exists at 0.1 MPa/303 K is reported. Exposure of Phase I to high pressure using penetrable pressure transmitting media (OX and 1:1 vol MeOH/EtOH) did not result in further separation of the sql networks. Rather, compression of the crystals and release of adsorbed OX molecules occurred. These pressure-induced changes are discussed in terms of structural voids, framework conformation, and molecular packing of the sql layers. Although Phase I retained tetragonal symmetry throughout the investigated pressure range, the interlayer voids occupied by OX molecules were significantly reduced between 0.3 and 0.5 GPa; further compression above 0.5 GPa induced structural disorder. Additionally, analysis of the electron count present in the pores of sql-1-Co-NCS confirmed the multistep evacuation of OX molecules from the crystal, and two intermediate phases, Ia and Ib, differing in the OX loading level, are postulated.

The impact of solution vs. slurry vs. mechanochemical syntheses upon the sorption performance of a 2D switching coordination network

“…[29][30][31][32] Recently, we reported that the previously known square lattice (sql) CN, 33,34 [Co(bpy) 2 (NCS) 2 ] n (bpy = 4,4′-bipyridine), sql-1-Co-NCS, exhibits recyclable switching between its "closed" nonporous and "open" porous phases induced by CO 2 or C 8 aromatics. 35,36 We coined the term "switching adsorbent layered materials" (SALMAs) for such sorbents and they hold promise for gas storage and hydrocarbon separations, [36][37][38][39][40][41][42] prompting us to explore the feasibility of their large-scale manufacture. In our previous work, 35 we prepared sql-1-Co-NCS by applying heat under vacuum to its guest-loaded variant sql-1-Co-NCS•2TFT (TFT = α,α,α-trifluorotoluene), which was synthesized by self-assembly of Co(NCS) 2 and bpy using the SD method in the presence of organic solvents (Fig.…”

Insight into the Gas-Induced Phase Transformations in a 2D Switching Coordination Network via Coincident Gas Sorption and In Situ PXRD

“…2D sql CNs with general formula [M­(L) 2 (A) 2 ] n (M = divalent metal cation, L = ditopic linker ligand, A = axial counteranion) are modular from a crystal engineering perspective − and exemplify the “node and linker” design strategy proposed by Hoskins and Robson over three decades ago. , The first reported sorption study for 2D switching sql CNs was conducted on [Cu­(bpy) 2 (BF 4 ) 2 ] (bpy = 4,4′-bipyridine), ELM-11, which was observed to exhibit single (type F–IV s ) or multistep (type F–IV m ) sorption isotherms (Scheme a, d) induced by gases such as N 2 , Ar, CO 2, C 2 H 2 and n -butane. ,,,,− Recently, we studied the sorption properties of three previously known sql CNs [M­(bpy) 2 (NCS) 2 ] n (M = Fe, Co, or Ni), − sql-1-M-NCS, which are closely related to the ELM platform. CO 2 sorption for sql-1-M-NCS resulted in single-step type F–IV s isotherms (Scheme a) and the switching pressures were found to be metal-ion controlled with the Ni version being the “softest”. , It was later reported that sql-1-Ni-NCS exhibited even lower switching pressure and higher sorption uptake for C 2 H 2 than for CO 2 …”

Adsorbate-dependent phase switching in the square lattice topology coordination network [Ni(4,4′-bipyridine)2(NCS)2]n

“…42 Future studies will explore the sorption behaviour of sql-1-Ni-NCS and related switching adsorbent layered materials (SALMAs) for other adsorbates including the effect of pressure. 43…”

“…42 Future studies will explore the sorption behaviour of sql-1-Ni-NCS and related switching adsorbent layered materials (SALMAs) for other adsorbates including the effect of pressure. 43 M. J. Z. gratefully acknowledges the support of the Irish Research Council (IRCLA/2019/167) and Science Foundation Ireland (16/IA/4624).…”