A Self‐Binding,Melt‐Castable,Crystalline Organic Electrolyte for Sodium Ion Conduction

The preparation and characterization of the cocrystalline solid–organic sodium ion electrolyte NaClO₄(DMF)₃ (DMF=dimethylformamide) is described. The crystal structure of NaClO₄(DMF)₃ reveals parallel channels of Na⁺ and ClO₄^? ions. Pressed pellets of microcrystalline NaClO₄(DMF)₃ exhibit a conductivity of 3×10^?4 S cm^?1 at room temperature with a low activation barrier to conduction of 25 kJ mol^?1. SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55–65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO₄(DMF)₃, permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles.     

A Self‐Binding,Melt‐Castable,Crystalline Organic Electrolyte for Sodium Ion Conduction

The preparation and characterization of the cocrystalline solid–organic sodium ion electrolyte NaClO₄(DMF)₃ (DMF=dimethylformamide) is described. The crystal structure of NaClO₄(DMF)₃ reveals parallel channels of Na⁺ and ClO₄⁻ ions. Pressed pellets of microcrystalline NaClO₄(DMF)₃ exhibit a conductivity of 3×10⁻⁴ S cm⁻¹ at room temperature with a low activation barrier to conduction of 25 kJ mol⁻¹. SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55–65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO₄(DMF)₃, permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles.     

The inorganic cation-tailored “trapdoor” effect of silicoaluminophosphate zeolite for highly selective CO2 separation

Functional nanoporous materials are widely explored for CO₂ separation, in particular, small-pore aluminosilicate zeolites having a “trapdoor” effect. Such an effect allows the specific adsorbate to push away the sited cations inside the window followed by exclusive admission to the zeolite pores, which is more advantageous for highly selective CO₂ separation. Herein, we demonstrated that the protonated organic structure-directing agent in the small-pore silicoaluminophosphate (SAPO) RHO zeolite can be directly exchanged with Na⁺, K⁺, or Cs⁺ and that the Na⁺ form of SAPO-RHO exhibited unprecedented separation for CO₂/CH₄, superior to all of the nanoporous materials reported to date. Rietveld refinement revealed that Na⁺ is sited in the center of the single eight-membered ring (s8r), while K⁺ and Cs⁺ are sited in the center of the double 8-rings (d8rs). Theoretical calculations showed that the interaction between Na⁺ and the s8r in SAPO-RHO was stronger than that in aluminosilicate RHO, giving an enhanced “trapdoor” effect and record high selectivity for CO₂ with the separation factor of 2196 for CO₂/CH₄ (0.02/0.98 bar). The separation factor of Na-SAPO-RHO for CO₂/N₂ was 196, which was the top level among zeolitic materials. This work opens a new avenue for gas separation by using diverse silicoaluminophosphate zeolites in terms of the cation-tailored “trapdoor” effect.

The sodium form of silicoaluminophosphate RHO zeolite exhibits a pronounced cation-tailored “trapdoor” effect, showing an unprecedented selectivity adsorption separation performance for CO₂/CH₄ and CO₂/N₂.     

Rendering hydrophobic nanoclusters water-soluble and biocompatible

Hydrophobic and hydrophilic nanoclusters embody complementary superiorities. The means to amalgamate these superiorities, i.e., the atomic precision of hydrophobic clusters and the water dissolvability of hydrophilic clusters, remains challenging. This work presents a versatile strategy to render hydrophobic nanoclusters water-soluble—the micellization of nanoclusters in the presence of solvent-conjoined Na⁺ cations—which overcomes the above major challenge. Specifically, although [Ag₂₉(SSR)₁₂(PPh₃)₄]³⁻ nanoclusters are absolutely hydrophobic, they show good dissolvability in aqueous solution in the presence of solvent-conjoined Na⁺ cations (Na₁(NMP)₅ or Na₃(DMF)₁₂). Such cations act as both counterions of these nanoclusters and surface cosolvent of cluster-based micelles in the aqueous phase. A combination of DLS (dynamic light scattering) and aberration-corrected HAADF-STEM (high angle annular dark field detector scanning transmission electron microscopy) measurements unambiguously shows that the phase-transfer of hydrophobic Ag₂₉ into water is triggered by the micellization of nanoclusters. Owing to the excellent water solubility and stability of [Ag₂₉(SSR)₁₂(PPh₃)₄]³⁻[Na₁(NMP)₅]₃⁺ in H₂O, its performance in cell staining has been evaluated. Furthermore, the general applicability of the micellization strategy has been verified. Overall, this work presents a convenient and efficient approach for the preparation of cluster-based, biocompatible nanomaterials.

The presence of solvent-conjoined cations, [Na₁(NMP)₅]⁺ or [Na₃(DMF)₁₂]³⁺, induces the micellization of hydrophobic nanoclusters, rendering these nanoclusters water-soluble and biocompatible.     

Fluoro-containing coordination compounds of chromium(III). V. Preparation and crystal structure of the Racemic Cis-[Cr(en)2F2]ClO4 · NaClO4 · H2O

Cis-[Cr(en)₂F₂]ClO₄ · NaClO₄ · H₂O (en = 1,2-diaminoethane) was obtained as the red crystalline product from the saturated solutions of both NaClO₄ and cis-[Cr(en)₂F₂]ClO₄ in water. The compound crystallizes in the monoclinic P2₁/n (No.14) space group with a = 9.540(2), b = 11.840(2); c = 14.659(3) Å, β = 95.02(1)°, Z = 4. The unit cell of the racemic crystal contains cis-[Cr(en)₂F₂]⁺ in the Λλλ and Δδδ enantiometric forms, Na⁺, ClO₄^?, and lattice H₂O. Cr has octahedral coordination. Cr? F and Cr? N bonds are 1.868(4), 1.887(5) and from 2.067(2) to 2.100(8) Å. Mean Cl? O bond is 1.38 Å. Na⁺ ions are in the distorted octahedral environment. Infrared spectrum confirms the presence of the lattice H₂O and proves the cis structure of [Cr(en)₂F₂]⁺.     

Donor ligand, basal ligand and solvent effects on the equilibrium constants of triphenylphosphinecobalt(III) Schiff base complexes with phosphite ligands

The equilibrium constants and the thermodynamic parameters were spectrophotometrically measured for the 1:1 adduct formation of [Co(Salen)(PPh₃)]ClO₄.H₂O, and [Co(7,7′-Me₂Salen)(PPh₃)]ClO₄.H₂O as acceptors, with P(OR)₃ (R = methyl, ethyl, and i-propyl) as donors, in acetonitrile (CH₃CN) and dimethylformamide (DMF) as solvents at constant ionic strength (I = 0.1 M NaClO₄), and various temperatures (t = 10–50 °C). Our results revealed the following trends: stability of the cobalt(III) Schiff base complexes toward a given phosphite donor, [Co(7,7′-Me₂Salen)(PPh₃)]⁺ < [Co(Salen)(PPh₃)]⁺; binding of the donors (phosphites) toward a given cobalt(III) Schiff base complex, P(OEt)₃ > P(OMe)₃ > P(O-ⁱPr)₃; influence of solvent on the stability of a given cobalt(III) Schiff base complex toward a given phosphite donor, CH₃CN < DMF.     

Sterically controlled reductive oligomerisations of CO by activated magnesium(i) compounds: deltate vs. ethenediolate formation

An extremely bulky, symmetrical three-coordinate magnesium(i) complex, [{(^TCHPNacnac)Mg}₂] (^TCHPNacnac = [{(TCHP)NCMe}₂CH]⁻, TCHP = 2,4,6-tricyclohexylphenyl) has been prepared and shown to have an extremely long Mg–Mg bond (3.021(1) Å) for such a complex. It was shown not to react with either DMAP (4-dimethylaminopyridine) or CO. Three unsymmetrical 1 : 1 DMAP adducts of less bulky Mg–Mg bonded species have been prepared, viz. [(^ArNacnac)Mg–Mg(DMAP)(^ArNacnac)] (^ArNacnac = [(ArNCMe)₂CH]⁻ Ar = 2,6-xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), and their reactivity toward CO explored. Like the previously reported bulkier complex, [(^DipNacnac)Mg–Mg(DMAP)(^DipNacnac)] (Dip = 2,6-diisopropylphenyl), [(^DepNacnac)Mg–Mg(DMAP)(^DepNacnac)] reductively trimerises CO to give a rare example of a deltate complex, [{(^DepNacnac)Mg(μ-C₃O₃)Mg(DMAP)(^DepNacnac)}₂]. In contrast, the two smaller adduct complexes react with only two CO molecules, ultimately giving unusual ethenediolate complexes [{(^ArNacnac)Mg{μ-OC(H) C(DMAP^−H)O}Mg(^ArNacnac)}₂] (Ar = Xyl or Mes). DFT calculations show the latter reactions to proceed via reductive dimerizations of CO, and subsequent intramolecular C–H activation of Mg-ligated DMAP by “zig–zag” [C₂O₂]²⁻ fragments of reaction intermediates. Calculations also suggest that magnesium deltate complexes are kinetic products in these reactions, while the magnesium ethenediolates are thermodynamic products. This study shows that subtle changes to the bulk of the reacting 1 : 1 DMAP–magnesium(i) adduct complexes can lead to fine steric control over the products arising from their CO reductive oligomerisations. Furthermore, it is found that the more activated nature of the adduct complexes, relative to their symmetrical, three-coordinate counterparts, [{(^ArNacnac)Mg}₂], likely derives more from the polarisation of the Mg–Mg bonds of the former, than the elongated nature of those bonds.

Subtle changes to the bulk of 1 : 1 adducts of DMAP with magnesium(i) complexes leads to steric control over the products arising from their reductive oligomerisations of carbon monoxide.      

Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion

We report kinetically controlled chiral supramolecular polymerization based on ligand–metal complex with a 3 : 2 (L : Ag⁺) stoichiometry accompanying a helical inversion in water. A new family of bipyridine-based ligands (d-L1, l-L1, d-L2, and d-L3) possessing hydrazine and d- or l-alanine moieties at the alkyl chain groups has been designed and synthesized. Interestingly, upon addition of AgNO₃ (0.5–1.3 equiv.) to the d-L1 solution, it generated the aggregate I composed of the d-L1AgNO₃ complex (d-L1 : Ag⁺ = 1 : 1) as the kinetic product with a spherical structure. Then, aggregate I (nanoparticle) was transformed into the aggregate II (supramolecular polymer) based on the (d-L1)₃Ag₂(NO₃)₂ complex as the thermodynamic product with a fiber structure, which led to the helical inversion from the left-handed (M-type) to the right-handed (P-type) helicity accompanying CD amplification. In contrast, the spherical aggregate I (nanoparticle) composed of the d-L1AgNO₃ complex with the left-handed (M-type) helicity formed in the presence of 2.0 equiv. of AgNO₃ and was not additionally changed, which indicated that it was the thermodynamic product. The chiral supramolecular polymer based on (d-L1)₃Ag₂(NO₃)₂ was produced via a nucleation–elongation mechanism with a cooperative pathway. In thermodynamic study, the standard ΔG° and ΔH_e values for the aggregates I and II were calculated using the van''t Hoff plot. The enhanced ΔG° value of the aggregate II compared to that of the formation of aggregate I confirms that aggregate II was thermodynamically more stable. In the kinetic study, the influence of concentration of AgNO₃ confirmed the initial formation of the aggregate I (nanoparticle), which then evolved to the aggregate II (supramolecular polymer). Thus, the concentration of the (d-L1)₃Ag₂(NO₃)₂ complex in the initial state plays a critical role in generating aggregate II (supramolecular polymer). In particular, NO₃⁻ acts as a critical linker and accelerator in the transformation from the aggregate I to the aggregate II. This is the first example of a system for a kinetically controlled chiral supramolecular polymer that is formed via multiple steps with coordination structural change.

The nanoparticles were transformed into the supramolecular polymer as the thermodynamic product, involving a helical inversion from left-handed to right-handed helicity.     

FTIR study of ion solvation and ion-pair formation in alkaline and alkaline earth metal salt solutions in acetonitrile

The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO ₄ ^– ions in contact and solvent separated ion pairs. The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm^–1 is used for the calculation of cation solvation numbers for Li⁺(4), Na⁺(4), Mg²⁺(6), Ca²⁺(6), and Ba²⁺(6). No solvation is assumed for the contact ion pairs of LiClO₄, LiBr, NaClO₄, Mg(ClO₄)₂, Ca(ClO₄)₂, and Ba(ClO₄)₂. The association constants of the symmetrical electrolytes are compared to those obtained from other methods.     

Difluorination of α-(bromomethyl)styrenes via I(I)/I(III) catalysis: facile access to electrophilic linchpins for drug discovery

Simple α-(bromomethyl)styrenes can be processed to a variety of 1,1-difluorinated electrophilic building blocks via I(I)/I(III) catalysis. This inexpensive main group catalysis strategy employs p-TolI as an effective organocatalyst when combined with Selectfluor® and simple amine·HF complexes. Modulating Brønsted acidity enables simultaneous geminal and vicinal difluorination to occur, thereby providing a platform to generate multiply fluorinated scaffolds for further downstream derivatization. The method facilitates access to a tetrafluorinated API candidate for the treatment of amyotrophic lateral sclerosis. Preliminary validation of an enantioselective process is disclosed to access α-phenyl-β-difluoro-γ-bromo/chloro esters.

Simple α-(bromomethyl)styrenes can be processed to a variety of 1,1-difluorinated electrophilic building blocks via I(I)/I(III) catalysis.

Structural editing with fluorine enables geometric and electronic variation to be explored in functional small molecules whilst mitigating steric drawbacks.¹ This expansive approach to manipulate structure–function interplay continues to manifest itself in bio-organic and medicinal chemistry.² Of the plenum of fluorinated motifs commonly employed, the geminal difluoromethylene group³ has a venerable history.⁴ This is grounded in the structural as well as electronic ramifications of CH₂ → CF₂ substitution, as is evident from a comparison of propane and 2,2-difluoropropane (Fig. 1, upper). Salient features include localized charge inversion (C–H^δ+ to C–F^δ−) and a widening of the internal angle from 112° to 115.4°.⁵ Consequently, geminal difluoromethylene groups feature prominently in the drug discovery repertoire⁶ to mitigate oxidation and modulate physicochemical parameters. Catalysis-based routes to generate electrophilic linchpins that contain the geminal difluoromethylene unit have thus been intensively pursued, particularly in the realm of main group catalysis.^7–9 Motivated by the potential of this motif in contemporary medicinal chemistry, it was envisaged that an I(I)/I(III) catalysis platform could be leveraged to convert simple α-(bromomethyl)styrenes to gem-difluorinated linchpins: the primary C(sp³)–Br motif would facilitate downstream synthetic manipulations (Fig. 1, lower). To that end, p-TolI would function as a catalyst to generate p-TolIF₂in situ in the presence of an external oxidant¹⁰ and an amine·HF complex. Alkene activation (I) with subsequent bromonium ion formation (II)¹¹ would provide a pre-text for the first C–F bond forming process (III) with regeneration of the catalyst. A subsequent phenonium ion rearrangement¹²/fluorination sequence (III and IV) would furnish the geminal difluoromethylene group and liberate the desired electrophilic building block.Open in a separate windowFig. 1The geminal difluoromethylene group: bioisosterism, and catalysis-based access from α-(bromomethyl)styrenes via I(I)/I(III) catalysis.To validate this conceptual framework, a short process of reaction optimization (1a → 2a) was conducted to assess the influence of solvent, amine·HF ratio (Brønsted acidity)¹³ and catalyst loading (Table 1). Initial reactions were performed with p-TolI (20 mol%), Selectfluor® (1.5 equiv.) as an oxidant, and CHCl₃ as the reaction medium. Variation of the amine : HF ratio was conducted to explore the influence of Brønsted acidity on catalysis efficiency (entries 1–4). An optimal ratio of 1 : 6 was observed enabling the product 2a to be generated in >95% NMR-yield. Although reducing the catalyst loading to 10 and 5 mol% (entries 5 and 6, respectively) led to high levels of efficiency (79% yield with 5 mol%), the remainder of the study was performed with 20 mol% p-TolI. Notably, catalytic vicinal difluorination was not observed at any point during this optimization, in contrast with previous studies from our laboratory.^9d,i A solvent screen revealed the importance of chlorinated solvents (entries 7 and 8): in contrast, performing the reaction in ethyl trifluoroacetate (ETFA) and acetonitrile resulted in a reduction in yield (9 and 10). Finally, a control reaction in the absence of p-TolI confirmed that an I(I)/I(III) manifold was operational (entry 11). An expanded optimization table is provided in the ESI.^†Reaction optimization^a

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (R_gb). The colossal permittivities of ε′ ~ 0.7–1.4 × 10⁴ with slightly dependent on frequency in the frequency range of 10²–10⁶ Hz are obtained in the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased R_gb. The semiconducting grain resistance (R_g) of the Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics increases with increasing x, corresponding to the decrease in Cu⁺/Cu²⁺ ratio. The nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.     

Alloying a single and a double perovskite: a Cu+/2+ mixed-valence layered halide perovskite with strong optical absorption

Introducing heterovalent cations at the octahedral sites of halide perovskites can substantially change their optoelectronic properties. Yet, in most cases, only small amounts of such metals can be incorporated as impurities into the three-dimensional lattice. Here, we exploit the greater structural flexibility of the two-dimensional (2D) perovskite framework to place three distinct stoichiometric cations in the octahedral sites. The new layered perovskites A^I₄[Cu^II(Cu^IIn^III)_0.5Cl₈] (1, A = organic cation) may be derived from a Cu^I–In^III double perovskite by replacing half of the octahedral metal sites with Cu²⁺. Electron paramagnetic resonance and X-ray absorption spectroscopy confirm the presence of Cu²⁺ in 1. Crystallographic studies demonstrate that 1 represents an averaging of the Cu^I–In^III double perovskite and Cu^II single perovskite structures. However, whereas the highly insulating Cu^I–In^III and Cu^II perovskites are colorless and yellow, respectively, 1 is black, with substantially higher electronic conductivity than that of either endmember. We trace these emergent properties in 1 to intervalence charge transfer between the mixed-valence Cu centers. We further propose a tiling model to describe how the Cu⁺, Cu²⁺, and In³⁺ coordination spheres can pack most favorably into a 2D perovskite lattice, which explains the unusual 1 : 2 : 1 ratio of these cations found in 1. Magnetic susceptibility data of 1 further corroborate this packing model. The emergence of enhanced visible light absorption and electronic conductivity in 1 demonstrates the importance of devising strategies for increasing the compositional complexity of halide perovskites.

A novel 2D halide perovskite with stoichiometric quantities of Cu⁺, Cu²⁺, and In³⁺ in the inorganic slabs shows emergent properties not seen in Cu^II or Cu^I–In^III perovskites, including enhanced visible-light absorption and electronic conductivity.     

The underlying mechanism for reduction stability of organic electrolytes in lithium secondary batteries

Many organic solvents have very desirable solution properties, such as wide temperature range, high solubility of Li salts and nonflammability, and should be able but fail in reality to serve as electrolyte solvents for Li-ion or -metal batteries due to their reduction instability. The origin of this interfacial instability remains unsolved and disputed so far. Here, we reveal for the first time the origin of the reduction stability of organic carbonate electrolytes by combining ab initio molecular dynamics (AIMD) simulations, density functional theory (DFT) calculations and electrochemical stability experiments. It is found that with the increase of the molar ratio (MR) of salt to solvent, the anion progressively enters into the solvation shell of Li⁺ to form an anion-induced ion–solvent-coordinated (AI-ISC) structure, leading to a “V-shaped” change of the LUMO energy level of coordinated solvent molecules, whose interfacial stability first decreases and then increases with the increased MRs of salt to solvent. This mechanism perfectly explains the long-standing puzzle about the interfacial compatibility of organic electrolytes with Li or similar low potential anodes and provides a basic understanding and new insights into the rational design of the advanced electrolytes for next generation lithium secondary batteries.

By theoretical and experimental evidence, the underlying mechanism for the enhanced reduction stability of the HMRE is revealed, suggesting that the interfacial stability of the electrolyte can be adjusted through the modulation of the anion-induced ISC structure.

The state-of-the-art electrolytes in Li-ion batteries (LIBs) are mostly based on 1.0 mol L⁻¹ LiPF₆/ethylene carbonate (EC)-based carbonate due to the surface passivation of the graphite anode by forming a stable solid electrolyte interphase (SEI). However, these electrolytes cannot operate well for new electrode materials and battery systems that are expected to have higher voltage, better safety and wider temperature range than current commercial LIBs.^1–3 For example, EC-based carbonate electrolytes are easily oxidized on a high voltage cathode at or above 4.3 V, resulting in depletion of electrolytes, gas evolution and low coulombic efficiency, which reduce the cycle life and create safety hazards for LIBs.⁴ These problems of the conventional electrolyte significantly hinder the development of new generation lithium batteries and limit these batteries for high voltage and/or high capacity applications and operation in a wide temperature range.To overcome these problems, great efforts have been devoted in recent years to the development of new electrolytes, such as solid state electrolytes,⁵ ionic liquids,^6–8 highly-concentrated electrolytes (HCEs),⁹ electrolyte stabilizing additive,^10–13 and so on. Among them, the HCEs or high-molar-ratio electrolytes (HMREs) of salt to solvent have received particular attention, owing to their unusual electrochemical stability, nonflammability, and good compatibility with a wide range of anode and cathode materials.^14–17 These desirable properties are apparently attributed to the solution structure of HCEs, where there exist almost no free solvent molecules, and the parasitic side reactions of solvents are thereby greatly reduced. Due to the lack of solvent molecules in HCEs, anions have to enter into the solvation shell of Li⁺, in order to meet the Li⁺ coordination number of 4–6, to form an ion–solvent-coordinated (ISC) structure.¹⁸ Several studies have shown that the unique ISC structure of HCEs leads to the shift of the lowest unoccupied molecular orbital (LUMO) from solvent to salt, which makes anions preferentially reduced or decomposed to produce a robust anion-derived SEI.^14,19 In recent years, the anion-derived SEI structure has been regarded as the “holy grail” of electrolyte chemistry for understanding the interfacial stability and compatibility of HCEs. However, recent studies have showed that some HCEs containing non-film-forming salts and solvents can still achieve excellent reversible Li⁺ insertion reactions.²⁰ Therefore, an intrinsic origin for the interfacial stability of HCEs still remains unrevealed. In our previous studies on HCEs or HMREs, their interfacial stability was found to depend predominately on the molar ratio (MR) of salt to solvent rather than the molar concentration.^2,21,22 Thus, the HMREs instead of the HCEs in the following study could more clearly describe the nature of electrolyte stability.In this work, we reveal the correlation between the solvation microstructures and the LUMO energy levels of typical ISC structures in the electrolytes at various MRs with non-film-forming lithium salt (LiClO₄) and organic carbonate solvents (PC, DMC, EMC and DEC) by ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations. The choice of non-film-forming lithium salt and solvent in this study was aimed to exclude the contribution of the formation of the SEI film to the interfacial stability of the electrolytes. It is found from this study that the LUMO energy level of the ISC structure formed at a low MR is lower than that of pure solvent. With the increase of the MR, anions gradually enter into the first solvation shell of Li⁺ to form the anion-induced ISC (AI-ISC) structure, resulting in the increase of the LUMO energy level that enhances the reduction stability of the electrolyte. Also, it is revealed that the LUMO levels of ISC structures at different MRs are always situated at the coordinated solvent molecules, i.e., the strong reduction stability of HMREs is dominated by the modulation of solvent molecules rather than only the formation of the anion-derived SEI. Such a theoretical insight is further unequivocally evidenced by chemical compatibility experiments in this work. These findings reveal the origin of the greatly improved interfacial stability of HMREs and provide a mechanistic insight into the rational design of stable electrolytes for new generation alkali or alkaline metal based batteries.To investigate the specific ISC microstructures of the electrolytes with different MRs, AIMD simulations were first performed (see computational details in the ESI^†). Taking non-film-forming DEC solvent as an example, three types of electrolytes with MRs of LiClO₄ to DEC = 1 : 10, 1 : 5 and 1 : 2 are considered (Table S1^†). After long-time AIMD simulation, the representative images of the equilibrium structures are shown in Fig. 1a–c. To characterize the solution structures, the radial distribution function g(r) of the electrolyte with different MRs is analyzed (Fig. 1e–g), and the changes in the Li⁺ coordination number with the O atoms of solvents and anions are listed in Fig. 1d. In addition, it should be noted that the total coordination number of Li⁺ always remains around 4, which implies that the stable tetragonal solvation shell structure of Li⁺ does not change in the different MR electrolytes; meanwhile, both the coordination numbers of Li⁺ contributed by the solvent and anion change oppositely. This phenomenon can be corroborated experimentally through infrared spectroscopy (IR) because the C O bond of the carbonate group has a strong IR absorption in the carbonyl region (1650–1850 cm⁻¹) and its IR peak position shifts sensitively with its coordination environment. As shown in Fig. 1h, the IR band of carbonyl groups in pure DEC is located at ∼1741 cm⁻¹, which is shifted to ∼1710 cm⁻¹ in a LiClO₄/DEC (MR = 1 : 10) electrolyte due to the coordination of the O atom in C O with Li⁺. With the increase of the MR of Li⁺/DEC, its IR peak at ∼1741 cm⁻¹ gradually disappears, reflecting a gradual decrease in the number of free DEC molecules. In addition, the IR band of free ClO₄⁻ in a LiClO₄/DEC (MR = 1 : 10) electrolyte is located at ∼931 cm⁻¹, which is shifted to ∼942 cm⁻¹ in the 1 : 2 LiClO₄/DEC electrolyte due to the ionic association of Li⁺ and ClO₄⁻ (Fig. S1^†). Combining AIMD simulations and IR experiments, it can be concluded that with the increase of the MR of the electrolyte, the anions gradually enter into the solvation shell of Li⁺, which modulates the chemical stability of the electrolyte.Open in a separate windowFig. 1Snapshots of typical equilibrium trajectories from DFT-MD simulations: (a) 1 : 10 LiClO₄/DEC solution (2-LiClO₄/20-DEC), (b) 1 : 5 LiClO₄/DEC solution (3-LiClO₄/15-DEC) and (c) 1 : 2 LiClO₄/DEC solution (7-LiClO₄/14-DEC). (d) Typical ISC structure extracted from DFT-MD. (e–g) Radial distribution function of lithium–oxygen interaction (short dashed lines) and relationship between the coordination number and bond distances (full lines). (h) FTIR spectra of the carbonyl group in LiClO₄/DEC solution. Atom color: H, white; Li, purple; C, cyan; O, red; Cl, green.Coordination numbers (n(r)) of atom pairs of Li–O(DEC) and Li–O (ClO₄⁻) (cut-off length of r = 2.5 Å)

Copper(II) and nickel(II) complexes of mono-oxocyclam(5-oxo-1,4,8,11-tetraazacyclotetradecane). Synthetic and potentiometric studies

Summary The macrocyclic mono-oxotetraamine, 5-oxo-1,4,8,11-tetraazacyclotetradecane (mono-oxocyclam=LH) has been prepared by reaction of methyl acrylate with 2,3,2-tetra(1,9-diamino-3,7-diazanonane). The protonation constants of the ligand are log K₁=9.40, log K₂=6.65 and log K₃=2.87 at 25 °C (I=0.1 mol dm^–3 NaClO₄). Detailed potentiometric studies of the interaction of the base with copper(II) and nickel(II) have been carried out. In the pH range 2.5–7.0 two complexes, [CuLH]²⁺ and [CuL]⁺, form; the deprotonated complex being 100% abundant at pH 7. For nickel(II), only [NiL]⁺ forms (log _11–1 = 3.90), the yellow low spin nickel complex reaching its maximum concentration above pH 6. The [CuL][ClO₄] · H₂O and [NiL][ClO₄] 0.5 H₂O complexes have been characterised in the solid state. The nickel(II) complex is square planar with a d-d band at 22625 cm^–1.     

Magnesium–halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex

Complexes of the Lewis base-free cations (^MeBDI)Mg⁺ and (^tBuBDI)Mg⁺ with Ph–X ligands (X = F, Cl, Br, I) have been studied (^MeBDI = HC[C(Me)N-DIPP]₂ and ^tBuBDI = HC[C(tBu)N-DIPP]₂; DIPP = 2,6-diisopropylphenyl). For the smaller β-diketiminate ligand (^MeBDI) only complexes with PhF could be isolated. Heavier Ph–X ligands could not compete with bonding of Mg to the weakly coordinating anion B(C₆F₅)₄⁻. For the cations with the bulkier ^tBuBDI ligand, the full series of halobenzene complexes was structurally characterized. Crystal structures show that the Mg⋯X–Ph angle strongly decreases with the size of X: F 139.1°, Cl 101.4°, Br 97.7°, I 95.1°. This trend, which is supported by DFT calculations, can be explained with the σ-hole which increases from F to I. Charge calculation and Atoms-In-Molecules analyses show that Mg⋯F–Ph bonding originates from electrostatic attraction between Mg²⁺ and the very polar C^δ+–F^δ− bond. For the heavier halobenzenes, polarization of the halogen atom becomes increasingly important (Cl < Br < I). Complexation with Mg leads in all cases to significant Ph–X bond activation and elongation. This unusual coordination of halogenated species to early main group metals is therefore relevant to C–X bond breaking.

Complexes of a highly Lewis acidic Mg cation and the full series of Ph–X (X = F, Cl, Br, I) have been structurally characterized. The Mg⋯X–Ph angle decreases with halogen size on account of the growing halogen σ-hole.     

Nickel catalysis enables convergent paired electrolysis for direct arylation of benzylic C–H bonds

Convergent paired electrosynthesis is an energy-efficient approach in organic synthesis; however, it is limited by the difficulty to match the innate redox properties of reaction partners. Here we use nickel catalysis to cross-couple the two intermediates generated at the two opposite electrodes of an electrochemical cell, achieving direct arylation of benzylic C–H bonds. This method yields a diverse set of diarylmethanes, which are important structural motifs in medicinal and materials chemistry. Preliminary mechanistic study suggests oxidation of a benzylic C–H bond, Ni-catalyzed C–C coupling, and reduction of a Ni intermediate as key elements of the catalytic cycle.

A direct arylation of benzylic C–H bonds is achieved by integrating Ni-catalyzed benzyl–aryl coupling into convergent paired electrolysis.

Electrochemical organic synthesis has drawn much attention in recent years.¹ Compared to processes using stoichiometric redox agents, electrosynthesis can potentially be more selective and safe, generate less waste, and operate under milder conditions.^1b In the majority of examples, the reaction of interest occurs at one electrode (anode for oxidation or cathode for reduction), while a sacrificial reaction occurs at the counter electrode to fulfil electron neutrality.^1a,2 Paired electrolysis uses both anodic and cathodic reactions for the target synthesis, thereby maximizing energy efficiency.^1a,3 However, there are comparatively few examples of paired electrolysis for organic synthesis.^1a,3,4Paired electrolysis might be classified into three types: parallel, sequential, and convergent (Fig. 1).^1a,3a In parallel paired electrolysis (Fig. 1a), the two half reactions are simultaneous but non-interfering. In sequential paired electrolysis (Fig. 1b), a substrate is oxidized and reduced (or vice versa) sequentially. In convergent paired electrolysis (Fig. 1c), intermediates generated by the anodic and cathodic processes react with one another to yield the product.^1a,3a,4b,c,5 The activation mode of all three types of paired electrolysis is based on the innate redox reactivity of substrates. As a result, the types of reactions that could be conducted by paired electrolysis remain limited. We proposed a catalytic version of convergent paired electrolysis, where a catalyst is used to cross-couple the two intermediates generated at the two separated electrodes (Fig. 1d). Although mediators have been used in paired electrosynthesis,^3a,4c,6 catalytic coupling of anodic and cathodic intermediates remains largely undeveloped. This mode of action will leverage the power of cross-coupling to electrosynthesis, opening up a wide substrate and product space. Here we report the development of such a process, where cooperative nickel catalysis and paired electrolysis enable direct arylation of benzylic C–H bonds (Fig. 1e).Open in a separate windowFig. 1Different types of paired electrolysis: (a) parallel paired electrolysis, (b) sequential paired electrolysis, (c) convergent paired electrolysis, (d) catalytic convergent paired electrolysis and (e) this work.Our method can be used to synthesize diarylmethanes, which are important structural motifs in bioactive compounds,⁷ natural products⁸ and materials.⁹ Direct arylation of benzylic C–H bonds has been recognized as an efficient strategy to synthesize diarylmethanes, and methods using metal catalysis¹⁰ and in particular combined photoredox and transition-metal catalysis have been reported.¹¹ Electrosynthesis provides a complementary approach to these methods, with the potential advantages outlined above. The groups of Yoshida¹² and Waldvogel¹³ previously developed synthesis of diarylmethanes via a Friedel–Crafts-type reaction of a benzylic cation and a nucleophile. The benzylic cations were generated by anodic oxidation of benzylic C–H bonds.¹⁴ To avoid the overoxidation of products and to stabilize the very reactive benzylic cations, the reactions had to be conducted in two steps, where the benzylic cations generated in the anodic oxidation step had to be trapped by a reagent. We thought a Ni catalyst could be used to trap the benzyl radical to form an organonickel intermediate, which is then prone to a Ni-catalyzed C–C cross-coupling reaction. Although such a coupling scheme was unprecedented, Ni-catalyzed electrochemical reductive coupling of aryl halides was well established.¹⁵ We were also encouraged by a few recent reports of combined Ni catalysis and electrosynthesis for C–N,¹⁶ C–S,¹⁷ and C–P¹⁸ coupling reactions.We started our investigations using the reaction between 4-methylanisole 1a and 4-bromoacetophenone 2a as a test reaction (Table 1). Direct arylation of benzylic C–H bonds was challenging and was typically conducted using toluene derivatives in large excess, e.g., as a solvent.^{11a,b,11d–f} To improve the reaction efficiency, we decided to use only 3 equivalents of 4-methylanisole 1a relative to 2a. After some initial trials, we decided to conduct the reaction in an undivided cell using a constant current of 3 mA. These conditions are straightforward from a practical point of view. After screening various reaction parameters, we found that a combination of 4,4′-dimethoxy-2-2′-bipyridine (L1) and (DME)NiBr₂ as a catalyst, THF/CH₃CN (4 : 1) as a solvent, fluorine-doped tin oxide (FTO) coated glass as an anode and carbon fibre as a cathode gave a 50% GC yield of 1-(4-(4-methoxybenzyl)phenyl)ethanone 3a after 18 h (Table 1, entry 1). Extending the reaction time to 36 h improved the yield to 76% (isolated yield) (entry 2). The target products were formed in a diminished yield with other bipyridine type ligands (entries 3–5). Solvents commonly used in Ni-catalyzed cross-coupling reactions, such as DMA and DMF, were less effective (entries 7–8). Replacing carbon fibre by nickel foam or platinum foil as the cathode was detrimental to the coupling, but substantial yields were still obtained (entries 9–10). On the other hand, FTO could not be replaced as the anode. Using carbon fibre as the anode shut down the reaction (entry 11). Likewise, using Pt foil as the anode gave only a 7% GC yield (entry 12). The sensitivity of the reaction outcomes to the electrodes originates from the electrode-dependent redox properties of reaction components (see below). Additional data showing the influence of other reaction parameters such as nickel sources, current, concentration, and electrolytes are provided in the ESI (Table S1, ESI^†).Summary of the influence of key reaction parameters^a

Cation recognition on a fullerene-based macrocycle

Heterocyclic orifices in cage-opened fullerene derivatives are regarded as potential ligands toward metals or ions, being reminiscent of truncated fullerenes as a hypothetical class of macrocycles with spherical π-conjugation. Among a number of cage-opened examples reported thus far, the coordination ability and dynamic behavior in solution still remained unclear due to difficulties in structural determination with multiple coordination sites on the macrocycles. Herein, we present the detailed solution dynamics of a cage-opened C₆₀ derivative bearing a diketo bis(hemiketal) moiety in the presence of alkali metal ions. The NMR spectroscopy disclosed the coordination behavior which is identified as a two-step process with a 1 : 2 stoichiometry. Upon coordination to the Li⁺ ion, the macrocycle largely varies its properties, i.e., increased absorption coefficients in the visible region due to weakly-allowed charge transfer transitions as well as the inner potential field from neutral to positive by the charge delocalization along with the spherical π-surface. The Li⁺-complexes formed in situ underwent unprecedented selective dehydroxyhydrogenation under high-pressure conditions. These findings would facilitate further studies on fullerene-based macrocycles as metal sensors, bulky ligands in organic reactions, and ion carriers in batteries and biosystems.

A fullerene-based Lewis-basic macrocyclic ligand underwent complexation with alkali-metal ions in 1 : 1 and 1 : 2 fashions, resulting in considerable perturbation to absorption properties as well as the potential surface inside the cage.     

Synthesis,binding properties and electrochemistry of nickel(II) macrocyclic complexes containing crown ethers

Macrotetracyclic complexes of nickel(II) containing crown ethers as pendant arms, [Ni(B)](ClO₄)₂ and [Ni(C)](ClO₄)₂, were prepared and characterized. The binding constants of the complexes toward alkali metal ions are relatively small compared with those of free 15-crown-5 or 18-crown-6 and the reduction potentials of the [Ni(B)](ClO₄)₂ and [Ni(C)](ClO₄)₂ in the presence of alkali metal ions shift to the positive direction in the order Li⁺>Na⁺>K⁺ and K⁺>Na⁺>Li⁺, respectively.     

Infrared and permittivity studies on alkali perchlorates

The infrared spectroscopic studies and the dielectric constant measurements during the orthorhombic to cubic transformation of NaClO₄, KClO₄, RbClO₄, and CsClO₄ are reported here to investigate the possibility or not of rotation of ClO₄⁻ in the cubic form. The multiplicity of ν₃, the triply degenerate stretching frequency, change at T_t as it should go from a triplet to a singlet when the crystal structure changes from Cmcm to . The symmetric stretching frequency of ClO₄⁻ is active in Cmcm but symmetry forbidden in . At the respective transition temperature there is a sharp increase in the dielectric constants of these perchlorates proving the transition to be of order-disorder type with the possibility of rotation of ClO₄⁻ at least in NaClO₄ and KClO₄, but involves the discontinuity of properties characteristic of a first-order transition     

Sequential bond energies of water to sodium glycine cation

Absolute bond dissociation energies of water to sodium glycine cations and glycine to hydrated sodium cations are determined experimentally by competitive collision-induced dissociation (CID) of Na⁺Gly(H₂O)_x, x = 1–4, with xenon in a guided ion beam tandem mass spectrometer. The cross sections for CID are analyzed to account for unimolecular decay rates, internal energy of reactant ions, multiple ion–molecule collisions, and competition between reaction channels. Experimental results show that the binding energies of water and glycine to the complexes decrease monotonically with increasing number of water molecules. Ab initio calculations at four different levels show good agreement with the experimental bond energies of water to Na⁺Gly(H₂O)_x, x = 0–3, and glycine to Na⁺(H₂O), whereas the bond energies of glycine to Na⁺(H₂O)_x, x = 2–4, are systematically higher than the experimental values. These discrepancies may provide some evidence that these Na⁺Gly(H₂O)_x complexes are trapped in excited state conformers. Both experimental and theoretical results indicate that the sodiated glycine complexes are in their nonzwitterionic forms when solvated by up to four water molecules. The primary binding site for Na⁺ changes from chelation at the amino nitrogen and carbonyl oxygen of glycine for x = 0 and 1 to binding at the C terminus of glycine for x = 2–4. The present characterization of the structures upon sequential hydration indicates that the stability of the zwitterionic form of amino acids in solution is a consequence of being able to solvate all charge centers.