Dihydrogen Phosphate Clusters: Trapping H₂PO₄^– Tetramers and Hexamers in Urea-Functionalized Molecular Crystals

Co-crystallization of two urea-functionalized ligands with tetrabutylammonium (TBA) dihydrogen phosphate resulted in the isolation of discrete (H₂PO₄^–)₄ and (H₂PO₄^–)₆ clusters stabilized in the crystalline state by multiple urea hydrogen bonds. Structural analysis by single-crystal X-ray diffraction, combined with a Cambridge Structural Database survey of (H₂PO₄^–)_<i>n</i> aggregates, established that these clusters display unique topologies and hydrogen-bonding connectivities

Dihydrogen Phosphate Clusters: Trapping H₂PO₄^– Tetramers and Hexamers in Urea-Functionalized Molecular Crystals

Co-crystallization of two urea-functionalized ligands with tetrabutylammonium (TBA) dihydrogen phosphate resulted in the isolation of discrete (H₂PO₄^–)₄ and (H₂PO₄^–)₆ clusters stabilized in the crystalline state by multiple urea hydrogen bonds. Structural analysis by single-crystal X-ray diffraction, combined with a Cambridge Structural Database survey of (H₂PO₄^–)_<i>n</i> aggregates, established that these clusters display unique topologies and hydrogen-bonding connectivities

De Novo Structure-Based Design of Ion-Pair Triple-Stranded Helicates

We present a generalized approach toward the design of ion-pair ML₃A helicates assembled by coordination of metal cations (M) and anions (A) by ditopic chelating ligands (L). This computational approach, based on de novo structure-based design principles implemented in the HostDesigner software, led to identification of synthetically accessible ditopic ligands that are structurally encoded to form charge-neutral ion-pair helicates with FeSO₄ or LnPO₄

Direct Air Capture of CO₂ via Reactive Crystallization

Atmospheric CO2 removal using engineered chemical processes, aka direct air capture (DAC), has become an essential component of our available portfolio for mitigating climate change. Here we describe a promising approach to DAC based on reactive crystallization of atmospheric CO2 (RC-DAC) with aqueous guanidine and amino acid. Compared to the previously studied phase-changing DAC processes involving initial CO2 absorption by an aqueous alkaline solvent followed by carbonate crystallization in a second step, RC-DAC combines the CO2 absorption and carbonate crystallization into a single step. Thus, as the insoluble carbonate salts are removed from solution by crystallization, more CO2 is pulled from the air into solution, further driving the DAC process. The RC-DAC was performed in a household humidifier as the air–liquid contactor, which can handle solid–liquid slurries effectively. The crystallization was monitored in situ by pH measurements, real-time imaging with a microscope probe, and by Raman spectroscopy, and ex situ by NMR spectroscopy, powder X-ray diffraction, and total inorganic carbonate analysis. The investigation provided a detailed mechanistic picture of the RC-DAC process, involving formation of carbamate and carbonate anions in solution, followed by sequential crystallization of different guanidinium carbonate phases

Liberalization Of Account Of Operations With Capital And Violation Of Financial Stability

У статті досліджено вплив процесів фінансової лібералізації на стан макроекономічної та фінансової стійкості, альтернативні позиції щодо використання інструментів контролю над капіталом з метою нейтралізації проциклічного впливу міжнародних потоків капіталу.In the article influence of processes of financial liberalization is investigational on the state of macroeconomic and financial firmness, alternative positions in relation to the use of control instruments above a capital with the aim of neutralization of проциклічного influence of international streams of capital

Computer-Aided Design of Interpenetrated Tetrahydrofuran-Functionalized 3D Covalent Organic Frameworks for CO₂ Capture

Using computer-aided design, several interpenetrated imine-linked 3D covalent organic frameworks with diamondoid structures were assembled from tetrakis-4-formylphenylsilane as the tetrahedral node, and 3<i>R</i>,4<i>R</i>-diaminotetrahydrofuran as the link. Subsequently, the adsorption capacity of CO₂ in each framework was predicted using grand canonical Monte Carlo simulations. At ambient conditions, the 4-fold interpenetrated framework, with disrotatory orientation of the tetrahedral nodes and diaxial conformation of the linker, displayed the highest adsorption capacity (∼4.6 mmol/g). At lower pressure, the more stable 5-fold interpenetrated framework showed higher uptake due to stronger interaction of CO₂ with the framework. The contribution of framework charges to CO₂ uptake was found to increase as the pore size decreases. The effect of functional group was further explored by replacing the ether oxygen with the CH₂ group. Although no change was observed in the 1-fold framework, the CO₂ capacity at 1 bar decreased by ∼32% in the 5-fold interpenetrated framework. This work highlights the need for a synergistic effect of a narrow pore size and a high density of ether-oxygen groups for high-capacity CO₂ adsorption

Sodium Sulfate Separation from Aqueous Alkaline Solutions via Crystalline Urea-Functionalized Capsules: Thermodynamics and Kinetics of Crystallization

The thermodynamics and kinetics of crystallization of sodium sulfate with a tripodal tris-urea receptor (L1) from aqueous alkaline solutions have been measured in the 15–55 °C temperature range for a fundamental understanding of the elementary steps involved in this sulfate separation method. The use of radiolabeled Na₂³⁵SO₄ provided a practical way to monitor the sulfate concentration in solution by β liquid scintillation counting. Our results are consistent with a two-step crystallization mechanism, involving relatively quick dissolution of crystalline L1 followed by the rate-limiting crystallization of the Na₂SO₄(L1)₂­(H₂O)₄ capsules. We found that temperature exerted relatively little influence over the equilibrium sulfate concentration, which ranged between 0.004 and 0.011 M. This corresponds to 77–91% removal of sulfate from a solution containing 0.0475 M initial sulfate concentration, as found in a typical Hanford waste tank. The apparent pseudo-first-order rate constant for sulfate removal increased 20-fold from 15 to 55 °C, corresponding to an activation energy of 14.1 kcal/mol. At the highest measured temperature of 55 °C, 63% and 75% of sulfate was removed from solution within 8 and 24 h, respectively. These results indicate the capsule crystallization method is a viable approach to sulfate separation from nuclear wastes

How Amidoximate Binds the Uranyl Cation

This study identifies how the amidoximate anion, AO, interacts with the uranyl cation, UO₂²⁺. Density functional theory calculations have been used to evaluate possible binding motifs in a series of [UO₂(AO)_<i>x</i>(OH₂)_<i>y</i>]^2–<i>x</i> (<i>x</i> = 1–3) complexes. These motifs include monodentate binding to either the oxygen or the nitrogen atom of the oxime group, bidentate chelation involving the oxime oxygen atom and the amide nitrogen atom, and η² binding with the N–O bond. The theoretical results establish the η² motif to be the most stable form. This prediction is confirmed by single-crystal X-ray diffraction of UO₂²⁺ complexes with acetamidoxime and benzamidoxime anions

Degradation of CYANEX 301 in Contact with Nitric Acid Media

The nature of the degradation product obtained upon contacting CYANEX 301 (bis­(2,4,4-trimethylpentyl)­dithiophosphinic acid) with nitric acid has been elucidated and found to be a disulfide derivative. The first step to the degradation of CYANEX 301 in toluene has been studied using ³¹P­{¹H} NMR after being contacted with nitric acid media. The spectrum of the degradation product exhibits a complex multiplet around δ_P = 80 ppm. A succession of purifications of CYANEX 301 has resulted in single crystals of the acidic form and the corresponding ammonium salt. Unlike the original CYANEX 301, which consists of a complex diastereomeric mixture displaying all possible combinations of chiral orientations at the 2-methyl positions, the purified crystals were shown by single-crystal X-ray diffraction to be racemates, containing 50:50 mixtures of the [<i>R</i>;<i>R</i>] and [<i>S</i>;<i>S</i>] diastereomers. The comparison between the ³¹P {¹H} NMR spectra of the degradation products resulting from the diastereomerically pure CYANEX 301 and the original diastereomeric mixture has elucidated the influence of the isomeric composition on the multiplicity of the ³¹P {¹H} NMR peak. These NMR data indicate the initial degradation leads to a disulfide-bridged condensation product displaying multiple resonances due to phosphorus–phosphorus coupling, which is caused by the inequivalence of the two P atoms as a result of their different chirality. A total of nine different NMR resonances, six of which display phosphorus–phosphorus coupling, could be assigned, and the identity of the peaks corresponding to phosphorus atoms coupled to each other was confirmed by ³¹P {¹H} homodecoupled NMR analysis

Degradation of CYANEX 301 in Contact with Nitric Acid Media

The nature of the degradation product obtained upon contacting CYANEX 301 (bis­(2,4,4-trimethylpentyl)­dithiophosphinic acid) with nitric acid has been elucidated and found to be a disulfide derivative. The first step to the degradation of CYANEX 301 in toluene has been studied using ³¹P­{¹H} NMR after being contacted with nitric acid media. The spectrum of the degradation product exhibits a complex multiplet around δ_P = 80 ppm. A succession of purifications of CYANEX 301 has resulted in single crystals of the acidic form and the corresponding ammonium salt. Unlike the original CYANEX 301, which consists of a complex diastereomeric mixture displaying all possible combinations of chiral orientations at the 2-methyl positions, the purified crystals were shown by single-crystal X-ray diffraction to be racemates, containing 50:50 mixtures of the [<i>R</i>;<i>R</i>] and [<i>S</i>;<i>S</i>] diastereomers. The comparison between the ³¹P {¹H} NMR spectra of the degradation products resulting from the diastereomerically pure CYANEX 301 and the original diastereomeric mixture has elucidated the influence of the isomeric composition on the multiplicity of the ³¹P {¹H} NMR peak. These NMR data indicate the initial degradation leads to a disulfide-bridged condensation product displaying multiple resonances due to phosphorus–phosphorus coupling, which is caused by the inequivalence of the two P atoms as a result of their different chirality. A total of nine different NMR resonances, six of which display phosphorus–phosphorus coupling, could be assigned, and the identity of the peaks corresponding to phosphorus atoms coupled to each other was confirmed by ³¹P {¹H} homodecoupled NMR analysis