Soft Cations Research Articles

Suppression of Vanadium Oxide Dissolution via Cation Metathesis within a Coordination Supramolecular Network for Durable Aqueous Zn-V2 O5 Batteries.

Aqueous zinc metal batteries (ZMBs) are a promising sustainable technology for large-scale energy storage applications. However, the water is often associated with problematic parasitic reactions on both anode and cathode, leading to the low durability and reliability of ZMBs. Here, a multifunctional separator for the Zn-V2 O5 batteries by growing the coordination supramolecular network (CSN:Zn-MBA, MBA = 2-mercaptobenzoic acid) on the conventional non-woven fabrics (NWF) is developed. CSN tends to form a stronger coordination bond as a softer cation, enabling a thermodynamically preferred Zn2+ to VO2 + substitution in the network, leading to the formation of VO2 -MBA interface, that strongly obstructs the VO2 (OH)2 - penetration but simultaneously allows Zn2+ transfer. Moreover, Zn-MBA molecules can adsorb the OTF- and distribute the interfacial Zn2+ homogeneous, which facilitate a dendrite-free Zn deposition. The Zn-V2 O5 cells with Zn-MBA@NWF separator realize high capacity of 567 mAh g-1 at 0.2 A g-1 , and excellent cyclability over 2000 cycles with capacity retention of 82.2% at 5 A g-1 . This work combines the original advantages of the template and new function of metals via cation metathesis within a CSN, provides a new strategy for inhibiting vanadium oxide dissolution.

Arc magmatism and porphyry-type ore deposition are primarily controlled by chlorine from seawater

A better understanding of magmatism and ore metal deposition at convergent plate margins is essential to the safety and benefit of society. Despite their spatial and, to a certain extent, temporal association, a direct connection between these two geologic processes is enigmatic. A detailed evaluation of available data reveals that seawater is key to the connection between these processes as it is the source of the ubiquitous, hot aqueous fluid from the subducting slab that is central to the generation of primary arc magmas and transfer or recycling of crustal materials at convergent margins. Particularly regarding the transfer of fluid-mobile elements or the so-called subduction component from the slab to arc lavas, however, the slab-derived hydrothermal fluid is perceived as weak and, thus, other transfer agents are proposed. Most petrogenetic studies also do not connect the source and transfer of metals in the spatially associated ore deposits to the same fluid. Chlorine from seawater can provide the crucial link between the two processes. The presence of Cl makes the slab-derived fluid a potent solvent not only to transfer but also to solubilize both the subduction component and ore trace metals from the slab, mantle wedge and lower-middle arc crust to arc lavas and ore deposits, respectively. Moreover, the dissolution and mobility of many elements in the Cl-rich fluid are primarily dependent upon their respective ionic potential (i.p.) values. In general, elements with cations that have low (soft cations) and high (hard cations) i.p. are mobile whereas those with in-between (intermediate cations) values are immobile in the Cl-rich fluid. Subducted sediment provides the bulk of subduction component and ore metals. These results led to the creation of a unified conceptual model claiming that the mobility, or immobility, of almost all elements in hydrothermal fluids at or near the Earth's surface is primarily dependent upon the amount of Cl in the fluids.

N-Donor-Functionalized Acetylacetones for Heterobimetallic Coordination Polymers, the Next Episode: Trimethylpyrazoles

The ditopic molecule 3-(1,3,5-trimethyl-4-1H-pyrazolyl)acetylacetone (HacacMePz) combines an acetylacetone group suitable for deprotonation and O,O′ coordination to a Pearson hard cation with a softer N-donor site. Both binding modes were employed individually: the pyrazolyl moiety was coordinated to ZnII, HgII, and AgI, and with trivalent iron the tris-chelating O,O′ complex [Fe(acacMePz)3] was isolated. The CuII derivative shows shorter O,O′ chelation and N coordination in the more distant Jahn–Teller sites and exists in two alternative crystal forms: namely, as a tetranuclear discrete complex and as a chain polymer. The different Pearson hardnesses of the coordination sites of acacMePz– allow for the design of well-ordered mixed-metal solids. Selective complexation to a hard and soft cations was achieved in coordination polymers combining hard FeIII and softer HgII or AgI. Even slight differences in Pearson hardness based on different oxidation states of the same cation imply sufficient selectivity, as shown by the successful synthesis of a mixed-valence CuII/CuI chain polymer. A synopsis of all structurally characterized compounds confirms that HacacMePz represents a bridging ligand with restricted conformational freedom. No full rotation about the single bond between the pyrazolyl and acetylacetone fragments occurs, and dihedral angles between these moieties are limited to values of 90 ± 17°.

Dibenzoarsacrowns: an experimental and computational study on the coordination behaviors.

Dibenzoarsacrowns have been synthesized as a novel class of heteroatom-fused crown ethers. The dibenzoarsacrowns can size-selectively capture alkali metal cations, and the arsenic atoms chemoselectively coordinated to gold(i) chloride (AuCl) due to the soft Lewis acid-base interaction. It is notable that the AuCl complex of 21-dibenzoarsacrown-7 further encapsulated Na+ with the enhanced association constant from bare 21-dibenzoarsacrown-7. The positive allosteric effect was studied computationally.

Structural Deterioration of Well-Faceted MOFs upon H2S Exposure and Its Effect in the Adsorption Performance.

The structural deterioration of archetypical, well-faceted metal-organic frameworks (MOFs) has been evaluated upon exposure to an acidic environment (H2S). Experimental results show that the structural damage highly depends on the nature of the hybrid network (e.g., softness of the metal ions, hydrophilic properties, among others) and the crystallographic orientation of the exposed facets. Microscopy images show that HKUST-1 with well-defined octahedral (111) facets is completely deteriorated, ZIF-8 with preferentially exposed (110) facets exhibits a large external deterioration with the development of holes or cavities in the mesoporous range, whereas UiO-66-NH2 with (111) exposed facets, and PCN-250 with (100) facets does not reflect any sign of surface damage. Despite the selectivity in the external deterioration, X-ray diffraction and gas adsorption measurements confirm that indeed all MOFs suffer an important internal deterioration, these effects being more severe for MOFs based on softer cations (e.g., Cu-based HKUST-1 and Fe-based PCN-250). These structural changes have inevitable important effects in the final adsorption performance for CO2 and CH4 at low and high pressures.

3-(4-Methylthiophenyl)acetylacetone – ups and downs of flexibility in the synthesis of mixed metal–organic frameworks. Ditopic bridging of hard and soft cations and site-specific desolvation

Different Pearson-hardness of O and S donors leads to well-ordered mixed metal–organic frameworks.

Synthesis of the perovskite-type oxyfluoride AgTiO2F: an approach adopting the HSAB principle.

A synthetic approach for oxyfluorides involving the hard and soft acids and bases (HSAB) principle was examined. Using AgF composed of the Ag+ ion as a soft acid and F- as a hard base, we attempted to synthesize an oxyfluoride, AgTiO2F, that included the O2- ion as a softer base than the F- ion and the Ti4+ ion as a harder acid than the Ag+ ion. Consequently, a perovskite (Pv)-type oxyfluoride AgTiO2F was synthesized by a solid-state reaction under ambient pressure and under high pressure, and a heat treatment at 1000 °C for 30 min under a pressure of 4 GPa produced the Pv-type phase with minimal impurity phases. The lack of an optical second harmonic generation (SHG) response and the result of Rietveld refinement indicated that the compound is centro-symmetric and shows the anti-phase tilt of Ti(O, F)6 octahedra along the c-axis on the basis of the space group I4/mcm. O/F ordering on the anion site was not clarified. The phase stability of a Pv-type AgTiO2F is discussed in terms of the HSAB principle and the thermodynamics in the formation of the Pv-type phase by comparing KTiO2F and NaTiO2F. AgTiO2F has a light yellow color and a band gap energy of 2.8 eV in the visible region, which originates from the covalent bonding between the soft cation Ag+ and O2- as a softer anion than F-. We propose that the HSAB principle is useful for selecting a cation for the synthesis of oxyfluorides.

Distinctive Two-Step Intercalation of Sr2+ into a Coordination Polymer with Record High 90Sr Uptake Capabilities

Summary 90Sr2+ remediation from acidic nuclear waste solution and contaminated seawater attracts great public attention but is very challenging because the removal performance toward soft Sr2+ by traditional oxidic ion-exchange materials are greatly affected by hard cations including H+, Na+, and Ca2+. We report a layered oxidic coordination polymer [(CH3)2NH2][ZrCH2(PO3)2F] (SZ-4) showing a notable advance over existing ion-exchange materials in 90Sr removal efficiencies with elevated distribution coefficients and record-high uptake capacities under acidic conditions. Moreover, the removal of Sr2+ is not significantly affected by the presence of a large excess of hard cations, leading to the successful cleanup of 90Sr-contaminated seawater samples. Such superior capabilities are directly visualized by well-refined single-crystal structures during in situ Sr2+ sorption process, revealing a distinctive two-step intercalation mechanism and a unique soft cation uptake selectivity achieved through collaborative coordination by the host layer and the interlayer dimethylamine (DMA) as a soft N-donor ligand.

An alkali metal phosphate RbPbBi2(PO4)3 with three kinds of disorder: the effect of isolated soft cation units on the crystal structure

We have reported a new phosphate, RbPbBi2(PO4)3 with three kinds of disorder, and a concept of isolated soft units has been firstly put forward to study the origin of structural distortions and disorder.

Uncommon Optical Properties and Silver-Responsive Turn-Off/On Luminescence in a PtII Heteroleptic Dithiolene Complex.

Complex [Pt(iPr2 pipdt)(Quinoxdt)] (iPr2 pipdt=1,4-diisopropyl-piperazine-2,3-dithione; Quinoxdt=[1,4]dithiino[2,3-b]quinoxaline-2,3-dithiolate) exhibits a remarkable green emission at 570 nm (room temperature), which is above the lowest excited state. The complex is characterized by negative solvatochromism as well as a high second-order polarizability. Addition of AgI ions induces 1) hypsochromic shift of the lowest frequencies and 2) reversible quenching of luminescence. The corresponding Ni and Pd complexes have also been prepared and investigated to assist interpretation of optical properties within the triad. Computational studies based on DFT and time-dependent DFT highlight the electronic properties of [Pt(iPr2 pipdt)(Quinoxdt)]. The preferential site of interaction between the Pt complex and incoming AgI is evidenced by the shape of the Fukui functions, pointing to the thiolic sulfur and platinum atoms as the most reactive sites towards a soft cation. Calculated optical properties are in agreement with experimental findings. This study sheds light on the structure-property relationship for this class of compounds.

Convergent Use of Heptacoordination for Cation Selectivity by RNA and Protein Metalloregulators

The large yybP-ykoY family of bacterial riboswitches is broadly distributed phylogenetically. Previously, these gene-regulatory RNAs were proposed to respond to Mn2+. X-ray crystallography revealed a binuclear cation-binding pocket. This comprises one hexacoordinate site, with six oxygen ligands, which preorganizes the second, with five oxygen and one nitrogen ligands. The relatively soft nitrogen ligand was proposed to confer affinity for Mn2+, but how this excludes other soft cations remained enigmatic. By subjecting representative yybP-ykoY riboswitches to diverse cations invitro, we now find that these RNAs exhibit limited transition metal ion selectivity. Among the cations tested, Cd2+ and Mn2+ bindmost tightly, and comparison of three new Cd2+-bound crystal structures suggests that these riboswitches achieve selectivity by enforcing heptacoordination (favored by high-spin Cd2+ and Mn2+, but otherwise uncommon) in the softer site. Remarkably, the Cd2+- and Mn2+-selective bacterial transcription factor MntR also uses heptacoordination within a binuclear site to achieve selectivity.

Effect of soft cations on carbon steel corrosion in chloride media

Abstract The effect of soft cations (Na+, K+, NH4 +) on the corrosion behavior of carbon steel in chloride (Cl−) media was investigated using various electrochemical and nonelectrochemical techniques. Data revealed that the corrosion rate is higher in the case of ammonium chloride solution following the order NH4 +>K+>Na+. The polarization and electrochemical impedance spectroscopy (EIS) measurements indicated a significant influence of cations on both the corrosion rate and the mechanistic reaction pathway of carbon steel dissolution in Cl− media. The EIS measurement showed two time constants in all the cases. Electrical equivalent circuit was employed to model the EIS data. The surface morphology and the corrosion products were also analyzed. It was found that the hydration energy of cations and the initial pH of the solution play a critical role in describing the effect of cations present in Cl− media on carbon steel corrosion.

N Donor substituted acetylacetones – versatile ditopic ligands

Abstract Acetylacetone (2,4-pentanedione) derivatives with N donor substituents represent ditopic ligands with coordination sites of distinctly different Pearson hardness. Deprotonation of the acetylacetone (Hacac) moiety leads to O,O′ chelating monoanionic (acac) ligands suitable for coordination to hard cations. The softer N donor site(s) preferably act as nucleophiles towards softer partners. When the organic molecules are employed as linkers and coordinate via either site, they are often selective and allow to synthesize well-ordered heterometallic solids. This review addresses the derivatives of 17 pentanediones with nitrile, pyridyl and pyrazolyl moieties as N donor substituents, with an emphasis on structurally characterized compounds. Depending on the N donor substituents and the cations, O,O′ or N coordination will dominate. The nitrile-substituted compounds essentially behave as acetylacetones; they may easily O,O′ coordinate to a wide range of cations whereas N coordination is limited to AgI, CuI or, in the case of less soft cations, to longer and presumably weaker contacts, e.g. to the more distant sites in Jahn–Teller distorted CuII. In contrast, pyridyl-substituted pentanediones act as N donor ligands, regardless whether their (H)acac site is chelating a cation or not. The still scarcely explored pyrazolyl derivative shows the most complex coordination pattern: it may be deprotonated both at the acetylacetone and the pyrazol site, the latter affording N,N′ bridging ligands. In addition to N donor nucleophilicity, the distance between the alternative coordination sites and their mutual orientation are relevant for crystal engineering applications.

Evaluation of volatile iodine trapping in presence of contaminants: A periodic DFT study on cation exchanged-faujasite

Using periodic dispersion-corrected DFT calculations, the effect of potential inhibiting species (H2O, NO, CO, CH3Cl and Cl2) on the adsorption of iodine species (I2, CH3I) has been investigated over different monovalent (H, Li, Na, K, Rb, Cs, Cu and Ag) cation-exchanged faujasite. We have found out that van der Waals interactions play an important role and can contribute up to about 50% of the total adsorption energy for the alkaline series. Both computed adsorption energies at 0 K and adsorption enthalpies for temperatures ranging from 298 to 523 K highlight the following points: (i) CO and H2O have been identified as the most important inhibiting species; (ii) Hard cations such as H+ or Li+ are very sensitive to water whereas soft cations such as Cu+ and Ag+ can strongly adsorb I2 and CH3I. Therefore, Ag-FAU appears to be the most promising adsorbent in presence of all contaminants, except CO which can inhibit the adsorption of I2. These findings can help to improve the filtering devices used in nuclear plants to avoid the release of radioactive iodine in case of severe accident.

Synthesis of C 2-Symmetric Isoxazole-Fused BINOL: An Entry to Sterically Crowded Atropisomeric Systems

A fluorescence-active modified BINOL with heteroaromatic fused rings containing two different heteroatoms is synthesized in good yield. Its racemate form is well characterized by chiral HPLC analysis. The molecule bears sterically hindered geometry and has potential for stereochemical properties normally exhibited by BINOLs. The molecule has two ends with different ligating atoms in the form of hydroxy groups at one end and isoxazole ring heteroatoms on the other end. This feature may be useful for molecular recognition of both hard and soft cations.

Mercaptopropyl-grafted magadiite for lead and cadmium sorption and calorimetric determination

Sodium magadiite anchored with 3-mercaptopropyltrimethoxysilane was synthesized through direct functionalization. After this reaction, it was observed a decrease in crystallinity, with a slight increase in basal distance to 1.57 nm, when compared to the precursor value of 1.53 nm. This organofunctionalization was evidenced through infrared spectroscopy, indicating by the presence of C–H stretching vibration in the 2900–2800 cm−1 region and mainly from the appearance of T species at the 29Si NMR spectrum, centered at −65 and −55 ppm. The pendant chains covalently bonded to magadiite layers have the ability to sorb lead and cadmium cations, through a batchwise method at 298 ± 1 K, to give the maximum sorption capacity values of 1.54 and 2.72 mmol g−1, respectively. The energetic effects caused by both cation/sulfur basic center interactions at the solid/liquid interface were determined through calorimetric titration, to give the enthalpies −13.48 ± 0.05 and −0.83 ± 0.053 kJ mol−1 for lead and cadmium, respectively. The sulfur basic centers attached to the pendant chains reflect in spontaneous process with negative Gibbs energies of −26.8 ± 0.1 and −24.5 ± 0.1 kJ mol−1, resulting also in positive entropies of 44 ± 1 and 79 ± 1 J K−1 mol−1, respectively. This set of favorable thermodynamic data is more pronounced for the softer cation in interacting with the basic atom.

Revisiting H2O Nucleation around Au+ and Hg2+: The Peculiar "Pseudo-Soft" Character of the Gold Cation.

In this contribution, we propose a deeper understanding of the electronic effects affecting the nucleation of water around the Au+ and Hg2+ metal cations using quantum chemistry. To do so, and in order to go beyond usual energetical studies, we make extensive use of state of the art quantum interpretative techniques combining ELF/NCI/QTAIM/EDA computations to capture all ranges of interactions stabilizing the well characterized microhydrated structures. The Electron Localization Function (ELF) topological analysis reveals the peculiar role of the Au+ outer-shell core electrons (subvalence) that appear already spatially preorganized once the addition of the first water molecule occurs. Thus, despite the addition of other water molecules, the electronic structure of Au(H2O)+ appears frozen due to relativistic effects leading to a maximal acceptation of only two waters in gold’s first hydration shell. As the values of the QTAIM (Quantum Theory of Atoms in Molecules) cations’s charge is discussed, the Non Covalent Interactions (NCI) analysis showed that Au+ appears still able to interact through longer range van der Waals interaction with the third or fourth hydration shell water molecules. As these types of interaction are not characteristic of either a hard or soft metal cation, we introduced the concept of a “pseudo-soft” cation to define Au+ behavior. Then, extending the study, we performed the same computations replacing Au+ with Hg2+, an isoelectronic cation. If Hg2+ behaves like Au+ for small water clusters, a topological, geometrical, and energetical transition appears when the number of water molecules increases. Regarding the HSAB theory, this transition is characteristic of a shift of Hg2+ from a pseudosoft form to a soft ion and appears to be due to a competition between the relativistic and correlation effects. Indeed, if relativistic effects are predominant, then mercury will behave like gold and have a similar subvalence/geometry; otherwise when correlation effects are predominant, Hg2+ behaves like a soft cation.

Na1.5Ag1.5MO3F3 (M = Mo, W): An Ordered Oxyfluoride Derivative of the LiNbO3 Structure

Na(1.5)Ag(1.5)MoO(3)F(3) and Na(1.5)Ag(1.5)WO(3)F(3) have been synthesized by solid state reactions and structurally characterized using synchrotron X-ray and neutron powder diffraction. Unlike the vast majority of salts containing [MO(3)F(3)](3-) anions (M = Mo, W) the oxyfluoride groups in Na(1.5)Ag(1.5)MoO(3)F(3) and Na(1.5)Ag(1.5)WO(3)F(3) are orientationally ordered, so that the Na(+) ions are coordinated by fluorine and the Ag(+) ions by oxygen. The resulting structure type, which has not previously been reported, is related to the LiNbO(3) structure, but the combination of Na/Ag ordering and orientational ordering of the [MO(3)F(3)](3-) anions produces a supercell that doubles the c-axis and changes the space group symmetry from R3 to R3. The use of hard (Na(+)) and soft (Ag(+)) cations to direct the orientational ordering of polar oxyfluoride building units provides a new approach to the design of polar materials.

Synthesis and extraction abilities of mono-formylated calix[4]-1,3-aza-crown and its hydrazone derivatives

By formylation of calix[4]-1,3-aza-crown in hexamethylenetetramine/trifluoroacetic acid system, the first formylated calix[4]-aza-crown derivative 6 was synthesized in yield of 61%. Reacting compound 6 with salicyloyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarbazide afforded four novel calix[4]crown hydrazone derivatives 7a–d in yields of 70–90%. By condensating compound 6 with series of bifunctional reagents, the novel mono-bridged biscalix[4]-aza-crown hydrazone derivatives 8a–c were prepared in high yields. The extraction experiments showed that all new compounds were good receptors for metal cations, especially, for soft metal cations. The extraction results suggested that the hydrazone groups produced favorable influences for binding soft cations. The two calix[4]arene units in compounds 8a–c could bind metal cations concurrently.

Rubidium-Mediated Birch-Type Reduction of 1,2-Diphenylbenzene in Tetrahydrofuran

The reaction of 1,2-diphenylbenzene with rubidium metal in THF yields extremely sensitive and pyrophoric [η(5)-{1,2-diphenyl-2,5-cyclohexadienyl}rubidium](∞) (1). Compound 1 characterizes a possible intermediate in a Birch-type reaction and represents a very rare example of a fully characterized organorubidium complex as well as an open main-group metal pentadienide as part of a six-membered ring. In the solid state the rubidium atoms interact with the cyclohexadienyl moiety, whereas the coordination sphere of the soft cation is additionally stabilized exclusively by several metal π-arene interactions despite the presence of strongly coordinating donors. The bonding situation was elucidated by MP2/def2-TZVPP calculations including population analysis.