Search

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...

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.

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...

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...

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...

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.