Selective sorption of oxygen and nitrous oxide by an electron donor-incorporated flexible coordination network

Incorporating strong electron donor functionality into flexible coordination networks is intriguing for sorption applications due to a built-in mechanism for electron-withdrawing guests. Here we report a 2D flexible porous coordination network, [Ni₂(4, 4′-bipyridine)(VTTF)₂]n(1) (where H₂VTTF = 2, 2′-[1, 2-bis(4-benzoic acid)-1, 2ethanediylidene]bis-1, 3-benzodithiole), which exhibits large structural deformation from the as-synthesized or open phase (1α) into the closed phase (1β) after guest removal, as demonstrated by X-ray and electron diffraction. Interestingly, upon exposure to electron-withdrawing species, 1β reversibly undergoes guest accommodation transitions; 1α⊃O₂ (90 K) and 1α⊃N₂O (185 K). Moreover, the 1β phase showed exclusive O₂ sorption over other gases (N₂, Ar, and CO) at 120 K. The phase transformations between the 1α and 1β phases under these gases were carefully investigated by in-situ X-ray diffraction, in-situ spectroscopic studies, and DFT calculations, validating that the unusual sorption was attributed to the combination of flexible frameworks and VTTF (electron-donor) that induces strong interactions with electron-withdrawing species

Benchmark Acetylene Binding Affinity and Separation through Induced Fit in a Flexible Hybrid Ultramicroporous Material

Structural changes at the active site of an enzyme induced by binding to a substrate molecule can result in enhanced activity in biological systems. Herein, we report that the new hybrid ultramicroporous material sql-SIFSIX-bpe-Zn exhibits an induced fit binding mechanism when exposed to acetylene, C₂H₂. The resulting phase change affords exceptionally strong C₂H₂ binding that in turn enables highly selective C₂H₂/C₂H₄ and C₂H₂/CO₂ separation demonstrated by dynamic breakthrough experiments. sql-SIFSIX-bpe-Zn was observed to exhibit at least four phases: as-synthesised (α); activated (β); and C₂H₂ induced phases (β' and γ). sql-SIFSIX-bpe-Zn-β exhibited strong affinity for C₂H₂ at ambient conditions as demonstrated by benchmark isosteric heat of adsorption (Qst ) of 67.5 kJ mol⁻¹ validated through in situ pressure gradient differential scanning calorimetry (PG-DSC). Further, in situ characterisation and DFT calculations provide insight into the mechanism of the C₂H₂ induced fit transformation, binding positions and the nature of host-guest and guest-guest interactions

Crystal engineering of flexible metal organic materials

Crystal engineering is the field of chemistry that studies the design, properties, and application of crystals. An aspect of crystal engineering is the design of coordination networks formed by the rational combination of metal nodes and organic linker ligands. Porous coordination networks, which are also known as porous coordination polymers (PCPs), Metal Organic Materials (MOMs) or Metal Organic Frameworks (MOFs), have captured the interest of researchers worldwide because of their inherent modularity and amenability to crystal engineering principles. PCPs and porous MOMs have been classified into four generations: 1st generation materials collapse on guest removal and lose crystallinity; 2nd generation materials possess a rigid nature upon guest insertion/removal and exhibit a type I isotherm; 3rd generation materials alter their original structure and maintain overall framework connectivity when exposed to external stimuli such as guest incorporation/removal, pressure and heat; 4th generation materials can be fine-tuned via post synthetic modification (PSM), defects or solid solutions. 3 rd generation materials or porous flexible MOMs, have attracted attention owing to  their potential applications in gas storage, separation, drug delivery and catalysis. These flexible MOMs tend to exhibit ‘stepped’ or ‘S-shaped’ isotherm profiles. Herein, we propose classification of such MOMs based on their gas sorption isotherm profiles as follows, i) type F-I (gradual change from open to more open, ii) type F-II (sudden change from open to more open sudden), iii) type F-III (gradual change from closed to open gradual), iv) type F-IV(sudden change from closed to open) and v) type F-V (shape-memory effect). This thesis also examines the three types of network topologies, primitive cubic unit (pcu), diamondiod (dia) and square lattice (sql) networks. The systematic studies we conducted herein offer design principles for future studies of porous flexible coordination networks in terms of understanding their structural transformations and improving the performance of gas storage/separation.  </p

Solvent-Dependent Delamination, Restacking, and Ferroelectric Behavior in a New Charge-Separated Layered Compound: NH4] Ag-3(C9H5NO4S)(2)(C13H14N2)(2)]center dot 8H(2)O

A new anionic coordination polymer, NH4] Ag-3( C9H5NO4S)(2)( C13H14N2)(2)]center dot 8H(2)O, with a two-dimensional structure, has been synthesized by a reaction between silver nitrate, 8-hydroxyquinoline-5-sulfonic acid (HQS), and 4,4'-tri-methylene dipyridine (TMDP). The compound stabilizes in a noncentrosymmetric space group, and the lattice water molecules and the charge-compensating NH4](+) group occupy the inter-lamellar spaces. The lattice water molecules can be fully removed and reinserted, which is accompanied by a crystalline-amorphous-crystalline transformation. This transformation resembles the collapse/delamination and restacking of the layers. To the best of our knowledge, this is the first observation of delamination and restacking in an inorganic coordination polymer that contains silver. The presence of a natural dipole (the anionic framework and cationic ammonium ions) along with the noncentrosymmetric space group gives rise to the room-temperature ferroelectric behavior of the compound. The ferroelectric behavior is also water-dependent and exhibits a ferroelectric-paraelectric transformation. The temperature-dependent dielectric measurements indicate that the ferroelectric/paraelectric transformation occurs at 320 K. This transformation has also been investigated by using in-situ IR spectroscopy and PXRD studies. The second-harmonic generation (SHG) study indicated values that are comparable to some of the known SHG solids, such as potassium dihydrogen phosphate (KDP) and urea

Microwave assisted hydrothermal synthesis of Ag2O/α-Bi2O3 heterostructures with highly enhanced photocatalysis and their environmental interest

A methodological analysis is made in the rational synthesis of the Ag2O/α-Bi2O3, p-n junction heterostructure with significant application, possessing substantial electron-hole recombination acting as solar catalysts through powerful and modest microwave inspired hydrothermal technique. Meanwhile, Ag2O/α-Bi2O3 is intermediary for single step Methyl Red (MR) dye photocatalytic degradation. Additionally, the experimental and characterization findings demonstrated that sunlight-induced surface effects on synthetic materials remove heavy metals such as Lead (Pb) sunder solar irradiation. The research work provides a strategy for excellent and efficient design of photocatalyst as an eco-friendly and biomedical approach. Electrochemical studies, such as photocurrent calculations, band positions and EIS for Ag2O/α-Bi2O3 heterostructures were also carried out. The study helps to broaden the search for and development of new hybrid composites for electrochemical applications and environmental interest

Fabrication of spherical porous pAg(2)O-nWO(3)/Ag/GNS heterostructure with enhanced photocatalytic activity through plasmonic S-scheme mechanism and its complementing biological interest

The synthesis and characterization of Ag2OWO3/Ag/GNS heterostructure with desired modifications has been elucidated in the contemporary study. The fabrication involves a simple hydrothermal method for the configuration of fascinating heterostructures intended to photo-catalytically degrade Eosin Yellow (EY) dye. The toxic dye molecules were converted into non-toxic molecular intermediates, also the elimination of heavy metals from industrial wastewater, being trapped in the pores of heterostructure. The pn junction photocatalyst with plasmonic resonance of Ag for abolition of electron and hole coupling, enhances the photo-response where the catalyst abides S-Scheme mechanism. The work functions of active photocatalysts as calculated for Ag2O is 6.61eV and WO3 is 6.04eV. Furthermore, the Ag2OWO3/Ag/GNS photocatalysts recovery and reuse in several trials without any noticeable loss of photocatalytic activity, complimented the recyclability of the heterostructure. To ensure the safety of the environment on heterostructure being released, toxicity analysis were carried out. These Ag2OWO3/Ag/GNS heterostructures had optimistic result on cytotoxicity assay, and on Musmusculus skin melanoma cells (B16-F10), with anti-microbial/fungal properties. Thereby, the contemporary experiment upholds efficient photocatalysis and ropes multiple errands on biological applications

A dynamic and multi-responsive porous flexible metal–organic material

Stimuli responsive materials (SRMs) respond to environmental changes through chemical and/or structural transformations that can be triggered by interactions at solid-gas or solidliquid interfaces, light, pressure or temperature. SRMs span compositions as diverse as organic polymers and porous inorganic solids such as zeolites. Metal–organic materials (MOMs), sustained by metal nodes and organic linker ligands are of special interest as SRMs. SR-MOMs have thus far tended to exhibit only one type of transformation, e.g. breathing, in response to one stimulus, e.g. pressure change. We report [Zn2(4,4′-biphenyldicarboxylate) 2(4,4′-bis(4-pyridyl)biphenyl)]n, an SR-MOM, which exhibits six distinct phases and four types of structural transformation in response to various stimuli. The observed structural transformations, breathing, structural isomerism, shape memory effect, and change in the level of interpenetration, are previously known individually but have not yet been reported to exist collectively in the same compound. The multi-dynamic nature of this SR-MOM is mainly characterised by using in-situ techniques

Crossover Sorption of C₂H₂/CO₂ and C₂H₆/C₂H₄ in Soft Porous Coordination Networks

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption, ” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn₂(L1)(L2)₂]n (PCP-1) and [Zn₂(L1)(L3)₂]n (PCP-2) (L1= 1, 4-bis(4-pyridyl)benzene, L2=5-methyl-1, 3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1, 3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C₂H₂/CO₂ and C₂H₆/C₂H₄, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C₂H₂, CO₂, C₂H₆, and C₂H₄ gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions

Readily Accessible Shape-Memory Effect in a Porous Interpenetrated Coordination Network

Shape-memory effects are quite well-studied in general, but there is only one reported example in the context of porous materials. We report the second example of a porous coordination network that exhibits a sorbate-induced shape-memory effect and the first in which multiple sorbates, N2, CO2 and CO promote this effect. The material, a new threefold interpenetrated pcu network, [Zn2(4,4′-biphenyldicarboxylate)2(1,4-bis(4-pyridyl)benzene)]n (X-pcu-3-Zn-3i), exhibits three distinct phases: the as-synthesized α phase; a denser-activated β phase; and a shape-memory γ phase, which is intermediate in density between the α and β phases. The γ phase is kinetically stable over multiple adsorption/desorption cycles and only reverts to the β phase when heated at \u3e400 K under vacuum. The α phase can be regenerated by soaking the γ phase in N,N′-dimethylformamide. Single-crystal x-ray crystallography studies of all three phases provide insight into the shape-memory phenomenon by revealing the nature of interactions between interpenetrated networks. The β and γ phases were further investigated by in situ coincidence powder x-ray diffraction, and their sorption isotherms were replicated by density functional theory calculations. Analysis of the structural information concerning the three phases of X-pcu-3-Zn-3i enabled us to understand structure-function relationships and propose crystal engineering principles for the design of more examples of shape-memory porous materials

Comparing the Structures and Photophysical Properties of Two Charge Transfer Co-crystals

In the search for molecular materials for next-generation optoelectronic devices, organic co-crystals have emerged as a promising class of semiconductors for their unique photophysical properties. This paper presents a joint experimental-theoretical study of ground and excited state charge transfer (CT) interactions in two CT co-crystals. Reported herein is a novel CT co-crystal Npe:TCNQ, formed from 4-(1-naphthylvinyl) pyridine (Npe) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules via molecular self-assembly. The electronic structure and photophysical properties of Npe:TCNQ are compared with those of the co-crystal composed of Npe and 1,2,4,5-tetracyanobenzene (TCNB) molecules, Npe:TCNB, reported here with a higher-symmetry (monoclinic) crystal structure than previously published. Npe:TCNB and Npe:TCNQ dimer clusters are used as theoretical model systems for the co-crystals and their electronic structure is compared to that of the extended solids via periodic boundary conditions density functional theory (PBC DFT). UV-Vis absorption spectra of the dimers are computed with time-dependent density functional theory (TD-DFT) and compared to experimental UV-Vis diffuse reflectance spectra. Both Npe:TCNB and Npe:TCNQ are found to exhibit neutral character in the S0 state and ionic character in the S1 state. The degree of CT in the S0 state of Npe:TCNB is found to be slightly smaller than that of Npe:TCNQ, as predicted from differences in electron affinities of the acceptors. Furthermore, the degree of CT in the S1 state of Npe:TCNB is found to be slightly higher than that of Npe:TCNQ, aligning with predictions employing a recently developed orbital similarity metric