Adsorbate-dependent phase switching in the square lattice topology coordination network [Ni(4,40 -bipyridine)2(NCS)2]n

Switching coordination networks (CNs) featuring stepped sorption isotherms that are accompanied by phase changes offer promise for gas storage and separation applications. However, their responsiveness to different adsorbates remains largely understudied. Herein, we report the variable switching behaviour of a previously known square lattice (sql) topology CN, [Ni(4,4′-bipyridine)2(NCS)2] (sql-1-Ni-NCS), with respect to nine gaseous adsorbates.</p

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

The selection and optimization of synthesis routes for porous metal–organic materials are critical for their large-scale manufacture but remain largely underexplored. In this study, we compare mechanochemistry vs. slurry vs. solution methods for the synthesis of a 1D chain coordination polymer {[Co(bpy)(NCS)2(H2O)2]·bpy}n (chn-1-Co-NCS-H2O) that is an intermediate to the 2D switching coordination network [Co(bpy)2(NCS)2]n, sql-1-Co-NCS (1 = bpy = 4,4′-bipyridine). Although neat mechanosynthesis using Co(NCS)2 and bpy as the starting materials failed, both water slurry and water-assisted mechanochemical syntheses afforded the desired intermediate, chn-1-Co-NCS-H2O, in high yield. Nevertheless, the resulting sql-1-Co-NCS products were observed to exhibit different CO2 sorption profiles depending on the synthesis methods used to prepare chn-1-Co-NCS-H2O. This study reveals that water can play an important role in mechanosynthesis, not only by inducing and accelerating the reaction process, but also by enhancing product quality in a manner that is not readily detectable by PXRD.</p

Dinuclear copper sulfate-based square lattice topology network with high alkyne selectivity

ABSTRACT: Porous coordination networks (PCNs) sustained by inorganic anions that serve as linker ligands can offer high selectivity toward specific gases or vapors in gas mixtures. Such inorganic anions are best exemplified by electron-rich fluorinated anions, e.g., SiF6 2−, TiF6 2−, and NbOF5 2−, although sulfate anions have recently been highlighted as inexpensive and earth-friendly alternatives. Herein, we report the use of a rare copper sulfate dimer molecular building block to generate two square lattice, sql, coordination networks which can be prepared via solvent layering or slurrying, CuSO4(1,4-bib)1.5, 1, (1,4-bib = 1,4-bisimidazole benzene) and CuSO4(1,4-bin)1.5, 2, (1,4-bin = 1,4-bisimidazole naphthalene). Variable-temperature SCXRD and PXRD experiments revealed that both sql networks underwent reversible structural transformations due to linker rotations or internetwork displacements. Gas sorption studies conducted upon the narrow-pore phase of CuSO4(1,4-bin)1.5, 2np, found a high calculated 1:99 selectivity for C2H2 over C2H4 (33.01) and CO2 (15.18), as well as strong breakthrough performance. Across-the-board, C3H4 selectivity vs C3H6, CO2, and C3H8 was also observed. Sulfate-based PCNs, although still understudied, appear increasingly likely to offer utility in gas and vapor separations.</p

Highly selective, high capacity separation of o-xylene from C8 aromatics by a switching adsorbent layered material

Purification of the C8 aromatics (xylenes and ethylbenzene) is particularly challenging because of their similar physical properties. It is also relevant because of their industrial utility. Physisorptive separation of C8 aromatics has long been suggested as an energy efficient solution but no physisorbent has yet combined high selectivity (>5) with high adsorption capacity (>50 wt %). Now a counterintuitive approach to the adsorptive separation of o‐xylene from other C8 aromatics involves the study of a known nonporous layered material, [Co(bipy)2(NCS)2]n (sql‐1‐Co‐NCS), which can reversibly switch to C8 aromatics loaded phases with different switching pressures and kinetics, manifesting benchmark o‐xylene selectivity (SOX/EB≈60) and high saturation capacity (>80 wt %). Structural insight into the observed selectivity and capacity is gained by analysis of the crystal structures of C8 aromatics loaded phases

A new 1:1 drug-drug cocrystal of theophylline and aspirin: discovery,characterization and construction of ternary phase diagrams

A new 1:1 drug-drug cocrystal of theophylline (THP) and aspirin (ASP) was successfully prepared by liquid assisted grinding, evaporative crystallization and slurry conversion crystallization. The obtained cocrystal was comprehensively characterized by Single Crystal X-ray Diffraction, Powder X-ray diffraction, Differential Scanning Calorimetry, Thermogravimetric analysis, Scanning Electron Microscopy and Fourier Transform Infrared analysis. Ternary phase diagrams (TPDs) were constructed for the obtained cocrystal in isopropyl alcohol at two different temperatures, i.e. 20 and 40°C. A narrow stability region was found for the pure THP-ASP cocrystal in the phase diagram at both temperatures. By proper selection of the ratios between THP, ASP and IPA from the stability region, THP-ASP cocrystals could be purely produced by isothermal slurry conversion in IPA. In addition, molecular modelling was deployed to provide mechanistic insights into the formation of this THP-ASP cocrystal syste

Metal-organic frameworks as regeneration optimized sorbents for atmospheric water harvesting

As the freshwater crisis looms, metal-organic frameworks (MOFs) with stepped isotherms lie at the forefront of desiccant development for atmospheric water harvesting (AWH). Despite numerous studies on water sorption kinetics in MOF desiccants, the kinetics of AWH sorbents  are a challenge to quantify. Here, we report that the AWH kinetics of  seven known MOFs and the industry-standard desiccant Syloid are limited  by diffusion  to the sorbent bed surface. A quantitative model that exploits isotherm  shape enables simulation of sorption cycling to evaluate sorbent  performance through productivity contour plots  (“heatmaps”). These heatmaps reveal two key findings: steady-state  oscillation around partial loading optimizes productivity, and dense  ultramicroporous MOFs with a step at low relative humidity afford superior volumetric  performance under practically relevant temperature swing conditions  (27°C, 30% relative humidity [RH] − 60°C, 5.4% RH). Cellulose-desiccant  composites of two such regeneration optimized sorbents retain the  kinetics of powders, producing up to 7.3 L/kg/day of water under these  conditions.</p

A robust molecular porous material for C2H2/CO2 separation

A molecular porous material, MPM-2, comprised of cationic [Ni2(AlF6) (pzH)8(H2O)2] and anionic [Ni2Al2F11(pzH)8(H2O)2] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. The packing in MPM-2 is sustained by multiple interionic hydrogen bonding interactions that afford ultramicroporous channels between dense layers of anionic units. MPM-2 is found to exhibit excellent stability in water (>1 year). Unlike most hydrogen-bonded organic frameworks which typically show poor  stability in organic solvents, MPM-2 exhibited excellent stability with respect to various organic solvents for at least two days. MPM-2 is found to be permanently porous with gas sorption isotherms at 298 K revealing a strong affinity for C2H2 over CO2 thanks to a high (ΔQst)AC [Qst (C2H2) − Qst (CO2)] of 13.7 kJ mol−1 at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C2H2 from a 1:1 C2H2/CO2 mixture at 298 K with effluent CO2 purity of 99.995% and C2H2 purity of >95% after temperature-programmed desorption. C-H···F interactions between C2H2 molecules and F atoms of AlF6 3− are found to enable high selectivity toward C2H2, as determined by density functional theory simulations.</p

Structural phase transformations induced by guest molecules in a nickel-based 2D Square lattice coordination network

Herein, we report the crystal structure and guest binding properties of a new two-dimensional (2D) square lattice (sql) topology coordination network, sql-(azpy)(pdia)-Ni, which is comprised of two linker ligands with diazene (azo) moieties, (E)-1,2-di(pyridin-4-yl)diazene(azpy) and (E)-5-(phenyldiazenyl)isophthallate(pdia). sql-(azpy)(pdia)-Ni underwent guest-induced switching between a closed (nonporous) β phase and several open (porous) α phases, but unlike the clay-like layer expansion to distinct phases previously reported in switching sql networks, a continuum of phases was formed. In effect, sql-(azpy)(pdia)-Ni exhibited elastic-like properties induced by adaptive guest binding. Single-crystal X-ray diffraction (SCXRD) studies of the α phases revealed that the structural transformations were enabled by the pendant phenyldiazenyl moiety on the pdia2– ligand. This moiety functioned as a type of hinge to enable parallel slippage of layers and interlayer expansion for the following guests: N,N-dimethylformamide, water, dichloromethane, para-xylene, and ethylbenzene. The slippage angle (interplanar distances) ranged from 54.133° (4.442 Å) in the β phase to 69.497° (5.492 Å) in the ethylbenzene-included phase. Insight into the accompanying phase transformations was also gained from variable temperature powder XRD studies. Dynamic water vapor sorption studies revealed a stepped isotherm with little hysteresis that was reversible for at least 100 cycles. The isotherm step occurred at ca. 50% relative humidity (RH), the optimal RH value for humidity control.</p

Ultramicroporous lonsdaleite topology MOF with high propane uptake and propane/ methane selectivity for propane capture from simulated natural gas

Propane (C3H8) is a widely used fuel gas. Metal–organic framework (MOF) physisorbents that are C3H8 selective offer the potential to significantly reduce the energy footprint for capturing C3H8 from natural gas, where C3H8 is typically present as a minor component. Here we report the C3H8 recovery performance of a previously unreported lonsdaleite, lon, topology MOF, a chiral metal–organic material, [Ni(S-IEDC)(bipy)(SCN)]n, CMOM-7. CMOM-7 was prepared from three low-cost precursors: Ni(SCN)2, S-indoline-2-carboxylic acid (S-IDECH), and 4,4′-bipyridine (bipy), and its structure was determined by single crystal X-ray crystallography. Pure gas adsorption isotherms revealed that CMOM-7 exhibited high C3H8 uptake (2.71 mmol g–1) at 0.05 bar, an indication of a higher affinity for C3H8 than both C2H6 and CH4. Dynamic column breakthrough experiments afforded high purity C3H8 capture from a gas mixture comprising C3H8/C2H6/CH4 (v/v/v = 5/10/85). Despite the dilute C3H8 stream, CMOM-7 registered a high dynamic uptake of C3H8 and a breakthrough time difference between C3H8 and C2H6 of 79.5 min g–1, superior to those of previous MOF physisorbents studied under the same flow rate. Analysis of crystallographic data and Grand Canonical Monte Carlo simulations provides insight into the two C3H8 binding sites in CMOM-7, both of which are driven by C–H···π and hydrogen bonding interactions.</p

Developing ANN-Kriging hybrid model based on process parameters for prediction of mean residence time distribution in twin-screw wet granulation

Artificial neural network (ANN) modelling is applied to predict the mean residence time of pharmaceutical formulation in a twin-screw granulator. Process parameters including feed flow rate, screw speed, and liquid to solid ratio are correlated with the obtained values of mean residence time to build a predictive tool. In order to improve the ANN predictive capability, a kriging interpolation approach is utilised and both ANN models (before and after kriging) are compared. Experimental data is obtained for wet granulation of microcrystalline cellulose using a bench-scale 12 mm twin-screw granulator. In addition, the effect of screw configurations on mean residence time is investigated by the developed ANN. The ANN model is made of two hidden layers with 2 linear nodes in each layer, and the linear system of equations is derived for the improved ANN model. The results revealed that the developed model was capable of predicting the mean residence time in the granulator more accurately after applying kriging interpolation, with an R2 value of about 0.92 for both training and validation. ANN model after kriging shows a dramatic improvement of R2 by 4% and 22% in training and validating phases, respectively. Also, the RMSE was improved by 40% and 61.5% in training and validating phases, respectively. Furthermore, this improvement was reflected in the contour profiles of the ANN models before and after kriging interpolation, where the model that uses the interpolated data points shows a smoother contour profiles and wider prediction areas. Screw configuration has the most significant effect on the residence time of granules inside the granulator where adding more kneading zones results in a substantial increase in the mean residence time compared to other process parameters