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Efforts to limit rising concentrations of CO2 have motivated the development of negative emission technologies. Direct air capture (DAC) of CO2 is one of the negative emissions technologies that ha...

We report a bench-scale direct air capture (DAC) process comprising CO2 absorption with aqueous amino acid salts (i.e., potassium glycinate, potassium sarcosinate), followed by room-temperature reg...

We report a hybrid solvent/solid-state approach to CO2 separation from flue gas, consisting of absorption with aqueous glycine or sarcosine amino acids, followed by crystallization of the bicarbona...

We report a structure-properties relationship study of DAC by crystallization of bis-iminoguanidine (BIG) carbonate salts. The study focuses on a series of basic BIG structures including the glyoxal-bis(iminoguanidine) prototype (GBIG) and its simple analogs methylglyoxal-bis(iminoguanidine) (MGBIG) and diacetyl-bis(iminoguanidine) (DABIG). We find that minor structural modifications in the molecular structure of GBIG, such as substituting one or two hydrogen atoms with methyl groups, result in major changes in the crystal structures, induced by the increased conformational flexibility and steric hindrance. As a result, the corresponding aqueous solubilities within the series increase significantly, leading in turn to enhanced DAC performances.

Crystal truncation rod (CTR) measurements and density functional theory (DFT) calculations were performed to determine the atomic structure of the mineral–water interface of the {100} surface of xenotime (nominally YPO4). This mineral is important, because it incorporates a variety of rare earth elements (REEs) in its crystal structure. REEs are critical materials necessary for a variety of renewable and energy efficient technologies. Current beneficiation techniques are not highly selective for REE ore minerals, and large amounts go to waste; this is a first step toward designing more efficient beneficiation. Evidence is found for minor relaxation of the surface within the topmost monolayer with little or no relaxation in subsurface layers. Justification for ordered water at the interface is found, where water binds to surface cations and donates hydrogen bonds to surface phosphates. The average bond lengths between cations and oxygens on water are 228 pm in the best fit to the CTR data, versus 243 and 2...

A bench-scale direct air capture process is reported, based on CO2 absorption with aqueous amino acids and carbonate crystallization with a guanidine compound.

A hybrid solvent/solid-state approach to carbon capture is demonstrated based on absorption with glycine or sarcosine, followed by crystallization of a guanidinium bicarbonate salt.

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 increase...

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.

Co-crystallization of two urea-functionalized ligandswith 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–)n aggregates, established that these clusters display unique topologies and hydrogen-bonding connectivities.

In this paper, we present the case for molecular-recognition approaches for sulfate removal from radioactive wastes via the use of anion-sequestering systems selective for sulfate, using either liquid-liquid extraction or crystallization. Potential benefits of removing sulfate from the waste include improved vitrification of the waste, reduced waste-form volume, and higher waste-form performance, all of which lead to potential cleanup schedule acceleration and cost savings. The need for sulfate removal from radioactive waste, especially legacy tank wastes stored at the Hanford site, is reviewed in detail and primarily relates to the low solubility of sulfate in borosilicate glass. Traditional methods applicable to the separation of sulfate from radioactive wastes are also reviewed, with the finding that currently no technology has been identified and successfully demonstrated to meet this need. Fundamental research in the authors' laboratories targeting sulfate as an important representative of the class of oxoanions is based on the hypothesis that designed receptors may provide the needed ability to recognize sulfate under highly competitive conditions, in particular where the nitrate anion concentration is high. Receptors that have been shown to have promising affinity for sulfate, either in extraction or in crystallization experiments, include hexaurea tripods, tetraamide macrocycles, cyclo[8]pyrroles, calixpyrroles, and self-assembled urea-lined cages. Good sulfate selectivity observed in the laboratory provides experimental support for the proposed molecular-recognition approach.

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 3R,4R-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 decrease...

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 δP = 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 [R;R] and [S;S] diastereomers. The comparison between the 31P {1H} NMR spectra of the degradation products resulting from the diastereomerically pure CYANEX 301 and the ...

Six members of a new family of cerium-halide-based materials with promising scintillation behavior have been synthesized in single crystal form, and their crystal structures were determined. Specifically, these new compounds are [(CeCl(3))(7)(BuOH)(16)(H(2)O)(2)]·(BuOH)(2) (1), (CeBr(3))(14)(BuOH)(36) (2), [(CeCl(3))(7)(1-PrOH)(16)(H(2)O)(2)]·(1-PrOH)(2) (3), [(CeBr(3))(7)(1-PrOH)(18)]·(1-PrOH)(2) (4), [(CeCl(3))(6)(iBuOH)(15)]·(iBuOH)(2) (5), and CeCl(3)(sec-BuOH)(2)(H(2)O) (6). Additionally, the scintillation ability of compound 1 was established. The structures of these cerium-halide-based materials consist of catenated tetradecanuclear rings that arrange themselves into three distinct structural motifs which contain the largest lanthanide-based ring structures reported to date; the different motifs are obtained by involving specific alcohols during synthesis. Specifically, n-butanol and n-propanol lead to 1-D chains of tetradecanuclear rings, and iso-butanol leads to 2-D parquet-patterned sheets of rectangular tetradecanuclear rings, while sec-butanol results in a zigzag 1-D chain structure. One of the compounds, [(CeCl(3))(6)(iBuOH)(15)]·(iBuOH)(2), has been shown to scintillate with a light yield of up to 1920 photons/MeV, and due to the presence of protons, it should be capable of detecting high energy neutrons without the necessity of prior thermalization. Furthermore, it also appears to be the first cerium-based compound that scintillates in spite of the fact that water coordinates to two of the Ce(III) centers within the structure.

Poly(acrylamidoximes) play an important role in the uranium extraction from seawater. The present work reports solution studies of simple analogues to address the formation and stability of two binding sites present in these polymers, open-chain amidoximes and cyclic imide dioximes, including: (1) conditions that maximize the formation of the cyclic form, (2) the existence of a base-induced conversion from open-chain to cyclic form, and (3) degradation under acid and base conditions.

This study identifies how the amidoximate anion, AO, interacts with the uranyl cation, UO(2)(2+). Density functional theory calculations have been used to evaluate possible binding motifs in a series of [UO(2)(AO)(x)(OH(2))(y)](2-x) (x = 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 η(2) binding with the N-O bond. The theoretical results establish the η(2) motif to be the most stable form. This prediction is confirmed by single-crystal X-ray diffraction of UO(2)(2+) complexes with acetamidoxime and benzamidoxime anions.

Single crystals of CaMg(2)Bi(2), EuMg(2)Bi(2), and YbMg(2)Bi(2) were obtained from a Mg-Bi flux cooled to 650 °C. These materials crystallize in the CaAl(2)Si(2) structure-type (P ̅3m1, No. 164), and crystal structures are reported from refinements of single crystal and powder X-ray diffraction data. EuMg(2)Bi(2) displays an antiferromagnetic transition near 7 K, which is observed via electrical resistivity, magnetization, and specific heat capacity measurements. Magnetization measurements on YbMg(2)Bi(2) reveal a weak diamagnetic moment consistent with divalent Yb. Despite charge-balanced empirical formulas, all three compounds are p-type conductors with Hall carrier concentrations of 2.0(3) × 10(19) cm(-3) for CaMg(2)Bi(2), 1.7(1) × 10(19) cm(-3) for EuMg(2)Bi(2), and 4.6(7) × 10(19) cm(-3) for YbMg(2)Bi(2), which are independent of temperature to 5 K. The electrical resistivity decreases with decreasing temperature and the resistivity ratios ρ(300 K)/ρ(10 K) ≤ 1.6 in all cases, indicating significant defect scattering.

Self-assembly of a tris(urea) anion receptor with Na2SO4 or K2SO4 yields crystalline capsules held together by coordinating Na+ or K+ cations and hydrogen-bonding water bridges, with the sulfate anions encapsulated inside urea-lined cavities. The sodium-based capsules can be selectively crystallized in excellent yield from highly competitive aqueous alkaline solutions (∼6 M Na+, pH 14), thereby providing for the first time a viable approach to sulfate separation from nuclear wastes.

An in-depth analysis of the distribution of anions about planar six-membered rings in the Cambridge Structural Database reveals anion−π interactions with charge-neutral π systems to be extremely rare in crystal structures. The predominant interaction motif is C−H···anion hydrogen bonding.

Herein we report crystallization of self-assembled capsules functionalized with urea hydrogen-bonding groups as a means for selective separation of sulfate anion. The high complementarity and the rigid environment found in such crystalline systems impart strong discrimination between anions of different shape, like sulfate and sulfite, or anions of the same shape but slightly different size, like sulfate and selenate, with selectivity that exceeds that observed in sulfate-binding protein. Similar to natural receptors, these crystalline capsules completely isolate the anions from the aqueous solvent by encapsulating them inside rigid cavities lined with complementary hydrogen-bonding groups. Furthermore, the capsules are made from flexible building blocks, whose structure and relative orientation in the crystal can be allosterically regulated to fine-tune the anion selectivity. These characteristics suggest that crystallization of such urea-functionalized capsules from simple and flexible components repres...

Herein we report the competitive crystallization of urea-functionalized hydrogen-bonded helical frameworks as a new approach to separating anions from aqueous mixtures. N,N′-Bis( m-pyridylurea) ( 1) containing orthogonal pyridine and urea hydrogen-bonding functionalities forms upon monoprotonation with 1 equiv of HX acids (X = Cl −, Br −, I −, NO 3 −, and ClO 4 −) an isomorphous series of crystalline hydrogen-bonded helices assembled by pyridinium···pyridine hydrogen bonds, with the urea functional groups binding the anions through chelate hydrogen bonding. The helices are further connected in the crystals by CH···X − and pyridinium···X − interactions, as well as π-stacking interactions. Competitive crystallization experiments and lattice energy calculations of the 1·HX crystals showed the solvation-based Hofmeister bias that typically dominates anion separation selectivities from water was attenuated, but not completely overturned. The observed selectivity is apparently a result of the relatively soft an...

A series of metal−organic frameworks (MOFs) functionalized with urea hydrogen-bonding groups has been synthesized and structurally analyzed by single-crystal X-ray diffraction to evaluate the efficacy of anion coordination by urea within the structural constraints of the MOFs. We found that urea-based functionalities may be used for anion binding within metal−organic frameworks when the tendency for urea···urea self-association is decreased by strengthening the intramolecular CH···O hydrogen bonding of N-phenyl substituents to the carbonyl oxygen atom. Theoretical calculations indicate that N,N‘-bis(m-pyridyl)urea (BPU) and N,N‘-bis(m-cyanophenyl)urea (BCPU) should have enhanced hydrogen-bonding donor abilities toward anions and decreased tendencies to self-associate into hydrogen-bonded tapes compared to other disubstituted ureas. Accordingly, BPU and BCPU were incorporated in MOFs as linkers through coordination of various Zn, Cu, and Ag transition metal salts, including Zn(ClO4)2, ZnSO4, Cu(NO3)2, Cu(C...

The chiral organization in the host frameworks of 16 crystalline inclusion compounds, assembled from guanidinium ions and racemic mixtures of various substituted 4,4‘-biphenyldisulfonates or 4,4‘-binaphthyldisulfonate, was examined with single-crystal X-ray diffraction. These inclusion compounds adopt lamellar architectures as a consequence of hydrogen-bonded sheets consisting of complementary sulfonate moieties (S) and guanidinium (G) ions arranged in a quasihexagonal motif, which has proven pervasive in numerous other guanidinium organodisulfonates. The GS sheets were connected by the chiral organosulfonate “pillars,” which support inclusion cavities occupied by the guests. Only one of the 16 compounds crystallized as a conglomerate of enantiomorphs. Of the remaining 15 compounds, 5 crystallized as racemates, and 10 crystallized as pseudoracemates in which each crystal contained equal amounts of crystallographically disordered left- and right-handed pillars. This preference for pseudoracemates, which is...

The effects of high pressures (up to 40 kbar) on the dihydrogen-bonded BH3NH3 molecular crystal were investigated using Raman spectroscopy in diamond and moissanite anvil cells. The stretching mode frequencies of the NH3 proton donor groups exhibited moderate red shifts with increasing pressures, as found in many conventional hydrogen-bonded systems of weak to medium strength. The stretching modes corresponding to the BH3 proton acceptor group, on the other hand, showed large blue shifts with increasing pressure, which, however, are not related to the changes in the N−H···H−B interactions. The BH3NH3 crystals undergo a pressure-induced disorder−order phase transition around 8 kbar, which is facilitated by the presence of dihydrogen bonds.

The first mechanistic investigation of a topochemical dihydrogen to covalent bonding conversion is presented. Solid-state decomposition of the LiBH4·TEA (TEA = triethanolamine) dihydrogen-bonded complex into a covalent material was studied using 11B solid-state MAS NMR, FT-IR, XRD, and optical microscopy. The majority of this solid-state reaction occurs by nucleation and two-dimensional growth of the covalent product nuclei. Variable-temperature kinetics and H/D exchange experiments established that proton transfer between the OH groups of the TEA and the BH4- anions, at the reactant/product interface, is the rate-limiting step, with an associated activation barrier of 21.0 ± 2.4 kcal/mol. The activation parameters ΔH⧧ and ΔS⧧ for the same process were calculated to be 20.1 ± 2.4 kcal/mol and −16.8 ± 6.2 eu, respectively, comparable with the analogous values found for the aqueous hydrolysis of BH4- in neutral water, suggesting similar mechanisms for the solid and solution decompositions.

A new methanol adduct of cerium trichloride of composition CeCl3(CH3OH)4 was crystallized from a solution growth in methanol. Large single crystals (more than several cubic centimeters) have been grown in controlled temperature baths. The molecular adduct of composition Ce2Cl6(CH3OH)8 is determined from X-ray crystal structure analysis, and this molecule undoubtedly persists in solution as well. Motivations for studying these compounds are their promising unique scintillation properties for radiation detection applications and the model structural systems they provide for the realization of new low-dimensional quantum magnets. This material apparently represents the first example of a metal-organic scintillator that is applicable to X-ray, γ-ray, and neutron detection.

A metal-organic framework with one-dimensional channels decorated with -COOH binding sites was synthesized under aqueous acidic conditions, which inhibited the participation of these groups to metal coordination or self-association by hydrogen bonding. This material selectively includes Cl(H2O)4- clusters in its channels, as revealed by single-crystal X-ray diffraction analysis, which represents the first structural characterization of such a water-chloride cluster.