Crystallographic characterization of the metal-organic framework Fe[subscript 2](bdp)[subscript 3] upon reductive cation insertion
Abstract not provided
Biggins, Naomi↗
SEARCH · Engineering Papers
Results for “CATIONS”
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A rare 4-fold interpenetrated metal–organic framework constructed from an anionic indium-based node and a cationic dicopper linker
We describe the synthesis and structure of a charged unique 4-fold interpenetrated MOF constructed from a new dicationic Robson-type dicarboxylate linker and a 4-connected In 3+ node.
Pappuru, Sreenath↗
Clarification of mechanisms of protonic photovoltaic action initiated by photoexcitation of strong photoacids covalently bound to hydrated Nafion cation-exchange membranes wetted by aqueous electrolytes
Junctions formed from materials that contain mobile charged species and fixed counterions can assist in photo-induced charge separation and lead to photovoltaic action, irrespective of whether the mobile charges are electronic or protonic.
Luo, Simon↗
Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes
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catalysis (heterogeneous)↗
Density functional theory modeling of cation diffusion in tetragonal bulk Zr O 2 : Effects of humidity and hydrogen defect complexes on cation transport
Not Available
Lee, Yueh-Lin (ORCID:0000000324776412)↗
Polymorphic transformations in Cu{sub 2}Se, Ag{sub 2}Se, AgCuSe and the role of partial cation-cation and anion-anion replacement in stabilizing their modifications
A review of studies of the crystalline structure of copper and silver chalcogenides is given. These materials have diverse physical properties making them promising in practical applications. Physical properties of crystals are determined by chemical composition, crystalline structure, and the influence of external conditions. In this work we carried out the analysis of published results on the crystalline structures of copper and silver chalcogenides at high and low temperatures. The inconsistency of published data on the crystal lattice parameters is noted. We also present our own results on the temperature dependence and the features of phase transitions in copper and silver chalcogenides with different composition.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. I - The naphthalene cation (C10H8/+/)
The ultraviolet, visible, and near-infrared absorption spectra of naphthalene (C10H8) and its radical ion (C10H8/+/), formed by vacuum ultraviolet irradiation, were measured in argon and neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing ion production in the solid phase. The absorption coefficients were calculated for the ion and found lower than previous values, presumably due to the low polarizability of the neon matrix.
Salama, F.↗
The Role of Cation-Water Disorder during Cation Exchange in Small-Pore Zeolite Sodium Natrolite
Abstract Not Provided
CHEM↗
Characterization of Isolated Ga 3+ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl 3
Ga/H-MFI was prepared by vapor-phase reaction of GaCl 3 with Brønsted acid O-H groups in dehydrated H-MFI zeolite. The resulting [GaCl 2 ] + cations in the as-exchanged zeolite are treated in H 2 at 823 K to stoichiometrically remove Cl ligands and form [GaH 2 ] + cations. Subsequent oxidation in O 2 and characterization by IR spectroscopy and NH 3 -temperature-programmed desorption (TPD) suggests that, for Ga/Al ratios ≤0.3, Ga 3+ exists predominantly as [Ga(OH) 2 ] + -H + cation pairs and to a lesser degree as [Ga(OH)] 2+ cations at low Ga/Al ratios (~0.1); while both species are associated with proximate cation-exchange sites, calculated free energies of formation suggest that [Ga(OH)] 2+ cations are more stable on cation-exchange sites associated with NNN (next-nearest neighbor) framework Al atoms than on those associated with NNNN (next-next-nearest neighbor) framework Al atoms. Ga K-edge X-ray Absorption Near Edge Spectroscopy (XANES) measurements indicate that, under oxidizing conditions and for all Ga/Al ratios, all Ga species are in the +3 oxidation state and are tetrahedrally coordinated to 4 O atoms. Fourier analysis of Ga K-edge Extended X-ray Absorption Fine Structure (EXAFS) data supports the conclusion that Ga 3+ is present predominantly as [Ga(OH) 2 ] + cations (or [Ga(OH) 2 ] + -H + cation pairs). For Ga/Al ratios ≤0.3, wavelet analysis of EXAFS data provide evidence for backscattering from nearest neighboring O atoms and from next-nearest neighboring framework Al atoms. For Ga/Al > 0.3, backscattering from next-nearest neighboring Ga atoms is also evident, characteristic of GaO x species. Here, upon reduction in H 2 , the oxidized Ga 3+ species produce [Ga(OH)H] + -H + cation pairs, [GaH 2 ] + -H + cation pairs, and [GaH] 2+ cations. Computed phase diagrams indicate that the thermodynamic stability of the reduced Ga 3+ species depends sensitively on temperature, Al-Al interatomic distance, and H 2 and H 2 O partial pressures. For Ga/Al ratios ≤0.2, it is concluded that [GaH 2 ] + -H + cation pairs and [GaH] 2+ cations are the predominant species present in Ga/H-MFI reduced above 673 K in 10 5 Pa H 2 and in the absence of water vapor.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Tuning the melting point of selected ionic liquids through adjustment of the cation’s dipole moment.
In prior research with thermally robust salts [Cassity et al., PCCP, 2017, 19, 31560] it was noted that an increase in the dipole moment of the cation generally led to a decrease in the melting point. Molecular dynamics simulations of the liquid state revealed that an increased dipole moment reduces cation-cation repulsions through dipole-dipole alignment. This was believed to reduce the liquid phase enthalpy, which would tend to lower the melting point of the IL. Here, we also test this principle by replacing hydrogen atoms with fluorine atoms at selected positions within the cation. This allows us to alter the electrostatics of the cation without substantially affecting the sterics. Furthermore, the strength of the dipole moment can be controlled by choosing different positions within the cation for replacement. We studied variants of four different parent cations paired with bistriflimide and determined their melting points, and enthalpies and entropies of fusion through DSC experiments. The decreases in the melting point were determined to be enthalpically driven. We found that the dipole moment of the cation, as determined by quantum chemical calculations, is inversely correlated with the melting point of the given compound. Molecular dynamics simulations of the crystalline and solid states of two isomers showed differences in their enthalpies of fusion that closely matched those seen experimentally. Moreover, this reduction in the enthalpy of fusion was determined to be caused by an increase in the enthalpy of the crystalline state. We provide evidence that dipole-dipole interactions between cations leads to the formation of cationic domains in the crystalline state. These cationic associations partially block favourable cation–anion interactions, which are recovered upon melting. If, however, the dipole- dipole interactions between cations is too strong they have a tendency to form glasses. This study provides a design rule for lowering the melting point of structurally similar ILs by altering their dipole moment.
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
A Universal Model of Cation Effects in Electrocatalysis
Electrolyte cations are conventionally viewed as inert spectators in electrocatalysis. However, a wealth of observations show that catalytic rates are often highly sensitive to cation identity. Despite their prevalence, these cation effects have resisted a unified mechanistic explanation, with different physical phenomena implicated across reaction chemistries, catalyst compositions, and choice of solvent. In this perspective, we describe a general framework for understanding cation effects in electrocatalysis based on electrostatics. We argue that cations influence reaction rates by modifying the strength of the electric field present at the catalyst surface, which alters the energetics of adsorbed intermediates and transition states according to their dipole moments and polarizabilities. The magnitude of this field depends on how cations arrange at the electrode surface, controlled by their size, shape, solvation, and packing efficiency. Cations that can arrange more densely result in a steeper potential drop at the electrode surface and consequently a stronger electric field. Our model further identifies two criteria for observing cation effects: (1) the operating potential must be negative of the electrode’s potential of zero total charge, ensuring that cations accumulate at the interface, and (2) the energetics of the kinetically relevant elementary step must be field sensitive. This framework reconciles previously inconsistent trends, including why cation effects appear only for some catalysts, why reaction selectivity is sensitive to cation identity, and why activity can increase with cation size on certain metals but decrease on others. Supported by kinetic measurements, spectroscopy, and atomistic simulations, the model provides both conceptual value for building intuition about catalysis at charged interfaces and predictive value for anticipating trends for new reactions, catalysts, and electrolytes. We conclude by highlighting the importance of electric fields across electrochemical, thermochemical, and biological catalysis and propose that considering the electrostatic environment around active sites offers new opportunities for improving activity and selectivity.
cation effects↗
Toggling Stereochemical Activity through Interstitial Positioning of Cations between 2D V 2 O 5 Double Layers
The 5/6s 2 lone-pair electrons of p-block cations in their lower oxidation states are a versatile electronic and geometric structure motif that can underpin lattice anharmonicity and often engender electronic and structural instabilities that underpin the function of active elements in nonlinear optics, thermochromics, thermoelectrics, neuromorphic computing, and photocatalysis. In contrast to periodic solids where lone-pair-bearing cations are part of the structural framework, installing lone-pair-bearing cations in the interstitial sites of intercalation hosts provides a means of a systematically modulating electronic structure through the choice of the group and the period of the inserted cation while preserving the overall framework connectivity. The extent of stereochemical activity and the energy positioning of lone-pair-derived mid-gap states depend on the cation identity, stoichiometry, and strength of anion hybridization. V 2 O 5 polymorphs are versatile insertion hosts that can accommodate a broad range of s-, p-, and d-block cations. However, the insertion of lone-pair-bearing cations remains largely underexplored. In this article, we examine the implications of varying the 6s 2 cations situated in interlayer sites between condensed [V 4 O 10 ] n double layers. Systematic modulations of lattice distortions, electronic structure, and magnetic ordering are observed with increasing strength of stereochemical activity from group 12 to group 14 cations. We compare and contrast p-block-layered M x V 2 O 5 (M = Hg, Tl, and Pb) compounds and map the significance of local off-centering arising from the stereochemical activity of lone-pair cations to the emergence of filled antibonding lone-pair 6s 2 –O 2p-hybridized mid-gap states mediated by second-order Jahn–Teller distortions. Crystallographic studies of cation coordination environments and the resulting modulation of V–V interactions have been used in conjunction with variable-energy hard X-ray photoelectron spectroscopy measurements, first-principles electronic structure calculations, and crystal orbital Hamilton population analyses to decipher the origins of stereochemical activity. Magnetic susceptibility measurements reveal antiferromagnetic signatures for all the three compounds. However, the differences in V–V interactions significantly affect the energy balance of the superexchange interactions, resulting in an ordering temperature of 160 and 260 K for Hg 0.5 V 2 O 5 and δ-Tl 0.5 V 2 O 5 , respectively, as compared to 7 K for δ-Pb 0.5 V 2 O 5 . In δ-Pb 0.5 V 2 O 5 , the strong stereochemical activity of electron lone pairs and the resulting electrostatic repulsions enforce superlattice ordering, which strongly modifies the electronic localization patterns along the [V 4 O 10 ] slabs, resulting in disrupted magnetic ordering and an anomalously low ordering temperature. The results demonstrate a versatile strategy for toggling the stereochemical activity of electron lone pairs to modify the electronic structure near the Fermi level and to mediate superexchange interactions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cation selectivities in zwitterion grafted nanopores: effect of zwitterion architecture
Selective separation of monovalent cations is a critical challenge in applications such as water purification and lithium recovery from salt brines. Cross-linked zwitterionic amphiphilic copolymer (ZAC-X) membranes have gained attention for their exceptional anion permselectivity, attributed to self-assembled zwitterion-lined nanodomains that interact preferentially with anions according to their hydrated radii r hyd . However, these membranes show minimal selectivity among monovalent cations, despite significant differences in their hydration structures, motivating studies on the underlying mechanisms of cation transport and selectivity in this family of materials. In this study, we conducted molecular dynamics simulations of aqueous salt solutions within zwitterion-functionalized nanopores to elucidate the influence of dipole orientation of the zwitterionic (ZI) ligands on cation diffusivities, partitioning, and permeabilities. To this end, we examined two contrasting ZI ligand architectures: Motif A (surface–cation–anion, S–ZI + –ZI − ) and Motif B (surface–anion–cation, S–ZI − –ZI + ). Our results show that in Motif A, the sulfonate groups of the ZI ligands are localized near the pore center radially, leading to strong electrostatic interactions with small bare cations (Mg 2+ and Li + ). This configuration results in high cation partitioning but low cation diffusion, maintaining solution-diffusion tradeoff typical of functionalized membranes. In contrast, Motif B show that sulfonate groups shift radially toward the mid-region of the pore. This shift, especially for small bare cations, introduces steric constraints that weaken their interactions with the sulfonate groups, thereby enhancing hydration and lowering partitioning, while still maintaining their low self-diffusivity. These findings establish zwitterion dipole orientation as a powerful design lever for tuning cation selectivity in membrane systems and offer molecular-level insights for engineering next-generation ion separation materials.
Morishita, Kazuya [Univ. of Texas, Austin, TX (Uni↗
Theoretical constraints on the effects of added cations on clumped, oxygen, and carbon isotope signatures of dissolved inorganic carbon species and minerals
Carbonate clumped isotope thermometry has emerged as a useful tool for the reconstruction of precipitation temperatures for minerals from surface and subsurface environments. Few studies have examined the impact of variable solution chemistry and mineral chemistry on clumping. Therefore, we used theoretical calculations to predict the impact of the presence of cations in a solution on the equilibrium clumped, oxygen ( 18 O/ 16 O and 17 O/ 16 O, θ and κ), and carbon isotopic ( 13 C/ 12 C) compositions of dissolved inorganic carbon species (DIC), and the impact of cation type and stoichiometry on carbonate mineral composition within the calcite-dolomite-magnesite solid solution. We examined the impact of the presence of Mg 2+ , K + , Na + , and Ca 2+ on equilibrium Δ 63 values of carbonate ion groups in DIC species and the composite DIC pool using the B3LYP/6-311++G(2d, 2p) model. We developed new cluster models for dolomite, magnesite, and high-magnesium calcite (Ca 0.83 Mg 0.17 )CO 3 and (Ca 0.67 Mg 0.33 )CO 3 ) and examined the effect of extraneous cations substituted into the crystal lattices of the carbonate minerals. We find the presence of added cations in the DIC pool increases equilibrium Δ 63 values slightly, depending upon their solution concentrations. For the cations examined, the identity of the added cation does not seem to be significant. Cumulative effects may account for small-scale differences (<0.02‰) but are unlikely to be substantial unless cation/anion association and ion pairing are important in the solution that carbonates are growing from. We also find that at a given temperature, stoichiometric dolomite and magnesite Δ 63 values are similar to calcite and less than aragonite. Surprisingly, substitution of an extraneous cation into a carbonate mineral (e.g., as observed in high-magnesium calcite) generally lowered Δ 63 by a slight amount, which suggests that high and low-magnesian calcites may have resolvable differences in equilibrium clumped isotope signatures, potentially providing an explanation for observations of different Δ 47 values in slow-growing minerals. These results imply the cationic composition of the solution may be a minor factor that should be considered for crystals that rapidly grow from solution, and that cationic substitution into carbonate mineral lattices will influence equilibrium compositions of carbonate minerals. Solution chemistry effects on mineral composition are likely to be observed at high growth rates. In contrast, equilibrium isotope compositions arising from cationic substitution in minerals, such as differences between high-Mg calcite and low-Mg calcite, or high-Mg calcite and dolomite, would likely be observed at slow growth rates.
58 GEOSCIENCES↗
Highly conducting divalent Mg{sup 2+} cation solid electrolytes with well-ordered three-dimensional network structure
A three-dimensionally well-ordered NASICON-type Mg{sup 2+} cation conductor, (Mg{sub x}Hf{sub 1−x}){sub 4/(4−2x)}Nb(PO{sub 4}){sub 3}, was firstly developed by partial substitution of lower valent Mg{sup 2+} cation onto the Hf{sup 4+} sites in a HfNb(PO{sub 4}){sub 3} solid to realize high Mg{sup 2+} cation conductivity even at moderate temperatures. Due to the formation of well-ordered NASICON-type structure, both the high Mg{sup 2+} cation conductivity below 450 °C and the low activation energy for Mg{sup 2+} cation migration was successfully realized for the (Mg{sub 0.1}Hf{sub 0.9}){sub 4/3.8}Nb(PO{sub 4}){sub 3} solid. Pure Mg{sup 2+} cation conduction in the NASICON-type (Mg{sub 0.1}Hf{sub 0.9}){sub 4/3.8}Nb(PO{sub 4}){sub 3} solid was directly and quantitatively demonstrated by means of two kinds of dc electrolysis. - Graphical abstract: Image of the Mg{sup 2+} cation conduction in NASICON-type (Mg{sub 0.1}Hf{sub 0.9}){sub 4/3.8}Nb(PO{sub 4}){sub 3} and its Mg{sup 2+} conductivity. - Highlights: • We develop a three-dimensionally well-ordered NASICON-type Mg{sup 2+} cation conductor. • A high magnesium cation conductivity is realized even at moderate temperatures. • Divalent magnesium cation conduction is demonstrated directly and quantitatively.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Influence of montmorillonites exchange capacity on the basal spacing of cation–anion organo-montmorillonites
Graphical abstract: This picture shows the distribution of organic modifier (CTAB and SDS) in Mt interlayer and the basal spacing changes of Mt modified by CTAB and SDS. Organic modifier molecule in Mt interlayer is more and more orderly. The basal spacing of Mt is from 1.5 nm to 5 nm as modifier added. - Highlights: • The d{sub 001} of Ca-Mt, R-Na-Mt, Na-Mt modified by CTAB and SDS can reach 5 nm. • It is easier to get cation–anion OMt with greater d{sub 001} if CEC is lower. • The organic molecules distribution in cation–anion OMt was analyzed. • The influence mechanism of Ca-Mt CEC on the d{sub 001} was discussed. - Abstract: With cationic and anionic surfactants cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfonate (SDS) as modifiers, Ca-montmorillonites (Ca-Mt), artificial Na-montmorillonites (R-Na-Mt) and natural Na-montmorillonites (Na-Mt) with different cation exchange capacity (CEC) were modified by solution intercalation method, respectively. Then cation–anion organo-montmorillonites (OMt) were prepared. The influence of CEC on the basal spacing of cation–anion OMt and the influence mechanism were discussed by X-ray diffraction (XRD) and zeta potential testing. The results indicate that the basal spacing of cation–anion OMt is related to CEC. For the same type montmorillonites, the basal spacing of cation–anion OMt decreases with the increase of CEC and it is easier to get cation–anion OMt with greater basal spacing when CEC is lower. Moreover, the CEC of Na-Mt has the greatest influence on the basal spacing of cation–anion OMt.
36 MATERIALS SCIENCE↗
DFT-based investigation of solvation of Nd(III)/Yb(III) cations in room-temperature ionic-liquid
We report a DFT study on the solvation of bare rare-earth (RE) cations [Nd(III) and Yb(III)] in the room-temperature ionic-liquid (RTIL) based on 1,3-dimethyl-imidazolium + , PF 6 - , [MMI][PF 6 ]. In the present article, we aim to investigate whether the chosen RTIL can preferentially solvate any of the RE cations under study. First, the RTIL binding to the RE cation is studied in the gas phase, and then explored with continuum solvation model employing RTIL parameters. First, we considered the formation of the first solvation shell, where the PF 6 - anions directly bond with the Ln(III) cation. We then further surrounded the first solvation shell with [MMI]+ cations to form the second solvation shell. The stability of PF 6 - coordinated complexes is studied by calculating the binding energy values. The number of PF 6 - anions for both Ln(III) cations starts with three ligands and goes until the maximum binding energy in the RTIL medium is reached. The coordination number and binding modes of PF 6 - depend on the size of the RE cation. Comparing the binding energy values between the RE cations for the first solvation shell complexes, it is noticed that Yb-complexes have relatively greater binding energy than Nd-complexes. We have further performed a Boltzmann population analysis to find out the most dominant conformer among each category of PF 6 - coordinated complexes. A study using Natural Population Analysis shows that after complexation with PF 6 - the charge on the Yb-centers lower to a greater extent than Nd-centers, implying stronger bonding between Yb and PF 6 - , which is in harmony with the binding energy analysis. Overall, the computational investigation provides an in-depth understanding of the complexation phenomena of RE cations in RTIL, which can be useful for the practical separation of RE cations using RTIL.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cations Enhance Hydride Transfer to Noncatalytic Metals in Concentrated Alkaline Electrolytes
Alkali metal cations are known to influence the kinetics of the hydrogen evolution reaction (HER), acting as either promoters or inhibitors to the rate-determining step depending on the metal surface, local pH, and cation concentration. Despite the importance of concentrated electrolytes for commercial electrochemical cells, the impact of cations on the HER in concentrated alkaline environments (>1 M) and in mixed cation systems remains poorly understood. Here, this study quantifies the HER kinetics at polycrystalline metal surfaces (Pt, Au, Cu, and Fe) and the equilibrium solvation environment in pure and mixed alkali metal hydroxide electrolytes at concentrations up to 3.0 M. Kinetic analyses of Au, Cu, and Fe revealed a positive cation-concentration-effect that was primarily driven by changes to the charge transfer coefficient. Multinuclear NMR spectroscopy examined the solvation of H 2 O/OH – species and the alkali cations as a function of (mixed) alkali cation concentration(s), and demonstrated rapid exchange between solvent, hydroxide, and solvated cations. Together, these findings support models where HER kinetics on noncatalytic metal surfaces in strongly alkaline conditions are primarily governed by the average polarization and polarizability of the metal/solution interface and that increasing cation activity continues to increase the transfer coefficient at metal-hydroxide concentrations up to 3.0 M. Electrolytes and additives which can outcompete weakly hydrated cations and disrupt the interfacial water structure are expected to suppress parasitic HER at electrodes for energy storage and electroplating.
Cations↗