Inclusion Of Solvent Molecules Research Articles

Conversion of Isolated Voids into Channel Spaces by Modulating the Stacking Manner of Hydrogen-Bonded Ladders.

1,2,3,4-Tetrakis(carboxyphenyl)benzene (CPB) forms a predictable ladder-shaped porous motif through intermolecular hydrogen-bonding of the carboxy groups. The stacking manner of the ladder motif, on the other hand, cannot be controlled, yielding a crystal structure with discrete inclusion spaces. To modulate the stacking manner, its derivative CPB(OMe) with methoxy substituent groups at 5,6-positions was synthesized and crystallized to yield a crystalline hydrogen-bonded organic framework (HOF), in which the ladder motifs are stacking with a different manner to form 1D inclusion channels, instead of discrete voids. Because of the channel structure, removal of the included solvent molecules can be easily conducted, and the resultant activated HOF CPB(OMe)-a exhibited micropores with BET surface area of 199 m2 g-1, which is larger than that of the other HOF CPB-a.

Two-dimensional Cu2N–A high-performance anode material for ion batteries with excellent electrical conductivity and electrolyte wettability

Determining suitable anode materials is crucial in the advancement of lithium-ion and sodium-ion battery technologies. We propose that the two-dimensional (2D) material Cu2N holds promise as a viable anode candidate. The Cu2N monolayer exhibits a stable checkerboard lattice crystal structure, ensuring structural integrity. Its excellent metallic electronic structure facilitates efficient conductivity during battery operation. We have observed that Li/Na ions can chemically bond to Cu2N substrates via specific charge exchange mechanisms. Moreover, the Cu2N monolayer demonstrates favorable wettability and compatibility with common electrolytes used in lithium-ion and sodium-ion batteries, including solvent molecules and metal salts. Our findings indicate that the Li/Na storage capacity of the Cu2N monolayer reaches approximately 760/760 mAh/g, surpassing that of graphite anodes significantly. Notably, the Li/Na diffusion barrier on the Cu2N monolayer is merely 5/13 meV, lower than that of most other 2D anode materials. Our results underscore the potential of the Cu2N monolayer as an outstanding electrode material, offering high storage capacity, rapid charge/discharge rates, and favorable wettability with electrolytes.

Supramolecular hydrogen-bonded networks formed from copper(II) carboxylate dimers.

The well-known copper carboxylate dimer, with four carboxylate ligands extending outwards towards the corners of a square, has been employed to generate a series of crystalline compounds. In particular, this work centres on the use of the 4-hydroxybenzoate anion (Hhba-) and its deprotonated phenolate form 4-oxidobenzoate (hba2-) to obtain complexes with the general formula [Cu2(Hhba)4-x(hba)xL2-y]x-, where L is an axial coligand (including solvent molecules), x = 0, 1 or 2, and y = 0 or 1. In some cases, short hydrogen bonds result in complexes which may be represented as [Cu2(Hhba)2(H0.5hba)2L2]-. The main focus of the investigation is on the formation of a variety of extended networks through hydrogen bonding and, in some crystals, coordinate bonds when bridging coligands (L) are employed. Crystals of [Cu2(Hhba)4(dioxane)2]·4(dioxane) consist of the expected Cu dimer with the Hhba- anions forming hydrogen bonds to 1,4-dioxane molecules which block network formation. In the case of crystals of composition [Et4N][Cu2(Hhba)2(H0.5hba)2(CH3OH)(H2O)]·2(dioxane), Li[Cu2(Hhba)2(H0.5hba)2(H2O)2]·3(dioxane)·4H2O and [Cu2(Hhba)2(H0.5hba)2(H0.5DABCO)2]·3CH3OH (DABCO is 1,4-diazabicyclo[2.2.2]octane), square-grid hydrogen-bonded networks are generated in which the complex serves as one type of 4-connecting node, whilst a second 4-connecting node is a hydrogen-bonding motif assembled from four phenol/phenolate groups. Another two-dimensional (2D) network based upon a related square-grid structure is formed in the case of [Et4N]2[Cu2(Hhba)2(hba)2(dioxane)2][Cu2(Hhba)4(dioxane)(H2O)]·CH3OH. In [Cu2(Hhba)4(H2O)2]·2(Et4NNO3), a square-grid structure is again apparent, but, in this case, a pair of nitrate anions, along with four phenolic groups and a pair of water molecules, combine to form a second type of 4-connecting node. When 1,8-bis(dimethylamino)naphthalene (bdn, `proton sponge') is used as a base, another square-grid network is generated, i.e. [Hbdn]2[Cu2(Hhba)2(hba)2(H2O)2]·3(dioxane)·H2O, but with only the copper dimer complex serving as a 4-connecting node. Complex three-dimensional networks are formed in [Cu2(Hhba)4(O-bipy)]·H2O and [Cu2(Hhba)4(O-bipy)2]·2(dioxane), where the potentially bridging 4,4'-bipyridine N,N'-dioxide (O-bipy) ligand is employed. Rare cases of mixed carboxylate copper dimer complexes were obtained in the cases of [Cu2(Hhba)3(OAc)(dioxane)]·3.5(dioxane) and [Cu2(Hhba)2(OAc)2(DABCO)2]·10(dioxane), with each structure possessing a 2D network structure. The final compound reported is a simple hydrogen-bonded chain of composition (H0.5DABCO)(H1.5hba), formed from the reaction of H2hba and DABCO.

Solvent-controlled solid-state phase transitions of a heterospin Cu(II) complex with imidazolyl-substituted nitronyl nitroxide.

Spontaneous solvent-controlled solid-state transformations were observed for a series of polymeric chain solvates [Cu(hfac)2LPr]·0.5Solv (Solv = (CH3)2CO, THF, CH2Cl2, CH2Br2, CHCl3) with 2-(1-propyl-1H-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LPr) under ambient conditions. The conversion of powdered polymeric chain [Cu(hfac)2LPr]·0.5THF and [Cu(hfac)2LPr]·0.5(CH3)2CO complexes, accompanied by the loss of solvent molecules, occurs completely to binuclear [Cu(hfac)2LPr]2 within a day. On the other hand, in the case of [Cu(hfac)2LPr]·0.5Solv (Solv = CH2Cl2, CH2Br2, CHCl3), the partial transformation into a desolvated 1D polymer [Cu(hfac)2LPr] or its mixture with [Cu(hfac)2LPr]2 takes much longer time. The magnetic behavior of the isostructural solvates is highly sensitive to the included solvent molecules. The complexes with THF, CH2Cl2, CH2Br2, and CHCl3 undergo a transition to a magnetically ordered state below 4 K, a phenomenon reported for the first time for the polymeric chain Cu(II) complexes with a "head-to-tail" motif. [Cu(hfac)2LPr]·0.5THF and [Cu(hfac)2LPr]·0.5(CH3)2CO undergo a spin transition at 190 K, which is induced by the transformation of the Cu atom environment. In the case of the THF solvate, the increase in the distances between the Cu and oxygen atoms leads to enhanced ferromagnetic exchange interactions, while in the acetone solvate, the nitroxide coordination type changes from axial to equatorial at certain coordination sites, resulting in the emergence of strong antiferromagnetic exchange.

Polymorphism in S(+)Clopidogrel-Picrate: Insights from X-ray Diffraction, Vibrational Spectroscopy, Thermal Analysis, and Quantum Chemistry

The crystal structures of two pseudopolymorphic forms of S(+)clopidogrel–picrate are reported. Form 1 crystallizes in the monoclinic space group P21 with an ionic couple S(+)ClopH+·Pic− and a molecule of solvent ethanol in the asymmetric unit, while Form 2 crystallizes in the monoclinic space group C2 with two ionic couples in the asymmetric unit. The configurations and conformations of the ionic couples, held together by ionized +N-H···O hydrogen bonds, are nearly identical in the structures. The self-assembly properties are compared with reported clopidogrel salts, including those used in pharmaceutical formulations. The hydrogen bonds are discussed in reference to the general corresponding behavior of the N-bases picrates and the properties of the acid-base coformers. The preparations of the pseudopolymorphs were optimized toward two different methods: solvent evaporation and mechanochemical treatment. Reproducibility to generate the single crystalline phases was confirmed by thermal and vibrational spectroscopic properties. Periodic third-order density-functional tight binding (DFTB3) calculations predict rather small energy difference between the two pure phases of polymorphs 1 and 2. However, the included solvent molecules in Form 1 decrease the lattice energy for ~10.5 kcal mol−1, which leads to a lower ΔElatt. lattice energy in comparison to Form 2 (by ~7.3 kcal mol−1). All predicted trends are in line with the experimentally observed formation of Form 1 instead of its simulated non-solvated Form 1.

Simulating Assembly Landscapes for Comprehensive Understanding of Supramolecular Polymer-Solvent Systems.

Complexity in supramolecular polymer systems arises from interactions between different components, including solvent molecules. By varying their concentration or temperature in such multicomponent systems, complex phenomena can occur such as thermally bisignate and dilution-induced assembly of supramolecular polymers. Herein, we demonstrate that both these phenomena emerge from the same underlying interaction mechanism between the components. As a model system, amide-decorated supramolecular polymers of porphyrins were investigated in combination with aliphatic alcohols as hydrogen-bond scavengers, and thermodynamic mass-balance models were applied to map the three-dimensional assembly landscapes. These studies unveiled that the interaction between hydrogen-bond scavengers and monomers is temperature-dependent and becomes dominant at high monomer concentrations. With these insights, we could exploit competitive monomer-alcohol interactions to prompt the dilution-induced assembly of various common monomers as well as bisignate assembly events. Moreover, kinetic insights were obtained by navigating through the assembly landscape. Similar to phase diagrams of covalent polymers, these assembly landscapes provide a comprehensive picture of supramolecular polymerizations, which helps to precisely regulate the system properties. The generality of this approach using assembly landscapes makes it relevant for any supramolecular system, and this enhanced control will open the door to build complex and functional supramolecular polymer systems.

Gating ion and fluid transport with chiral solvent.

The development of modern membranes for ionic separations and energy-storage devices such as supercapacitors depends on the description of ions at solid interfaces, as is often provided by the electrical double layer (EDL) model. The classical EDL model ignores, however, important factors such as possible spatial organization of solvent at the interface and the influence of the solvent on the spatial dependence of the electrochemical potential; these effects in turn govern electrokinetic phenomena. Here we provide a molecular-level understanding of how solvent structure can dictate ionic distributions at interfaces using a model system of a polar, aprotic solvent, propylene carbonate, in its enantiomerically pure and racemic forms, at a silica interface. We link the interfacial structure to the tuning of ionic and fluid transport by the chirality of the solvent and the salt concentration. The results of nonlinear spectroscopic experiments and electrochemical measurements suggest that the solvent exhibits lipid-bilayer-like interfacial organization, with a structure that is dependent on the solvent chirality. The racemic form creates highly ordered layered structure that dictates local ionic concentrations, such that the effective surface potential becomes positive in a wide range of electrolyte concentrations. The enantiomerically pure form exhibits weaker ordering at the silica surface, which leads to a lower effective surface charge induced by ions partitioning into the layered structure. The surface charge in silicon nitride and polymer pores is probed through the direction of electroosmosis that the surface charges induce. Our findings add a new dimension to the nascent field of chiral electrochemistry, and emphasize the importance of including solvent molecules in descriptions of solid-liquid interfaces.

Thermal tuning of protein hydration in a hyperthermophilic enzyme.

Water at the protein surface is an active biological molecule that plays a critical role in many functional processes. Using NMR-restrained MD simulations, we here addressed how protein hydration is tuned at high biological temperatures by analysing homologous acylphosphatase enzymes (AcP) possessing similar structure and dynamics under very different thermal conditions. We found that the hyperthermophilic Sso AcP at 80°C interacts with a lower number of structured waters in the first hydration shell than its human homologous mt AcP at 37°C. Overall, the structural and dynamical properties of waters at the surface of the two enzymes resulted similar in the first hydration shell, including solvent molecules residing in the active site. By contrast the dynamical content of water molecules in the second hydration shell was found to diverge, with higher mobility observed in Sso AcP at 80°C. Taken together the results delineate the subtle differences in the hydration properties of mt AcP and Sso AcP, and indicate that the concept of corresponding states with equivalent dynamics in homologous mesophilic and hyperthermophylic proteins should be extended to the first hydration shell.

The electrical‐double layer revisited

AbstractThe electrical‐double layer (EDL) model is fundamental to our understanding of interactions in ionic solutions, and is widely used in chemical, biological, and technological contexts, particularly in the description of aqueous electrolyte solutions. However, recent experiments have raised questions regarding the validity of this model in polar, aprotic solvents; some observations, such as a surface potential that changes sign with increasing salt concentration, are not consistent with the EDL picture. We demonstrate in a model system, acetonitrile at a silica interface, that solvent organization dictates the ionic distributions. Ion‐transport measurements in nanopores, surface‐selective spectroscopy, and molecular dynamics simulations reveal that the distribution of ions in acetonitrile at a silica interface is determined by the lipid‐bilayer‐like organization that the interface imposes upon the liquid, which accounts for the change in sign of the potential. Our findings emphasize the importance of including solvent molecules and ions explicitly in descriptions of solid/liquid interfaces.Key Points In a range of acetonitrile‐based electrolyte solutions in contact with silica, the effective surface potential is negative at low salt concentrations and positive at high salt concentrations. The long‐range, lipid‐bilayer‐like organization of acetonitrile at this interface dictates the preferred locations for cations and anions. Due to this organizational effect, the classical electrical double‐layer modal is not applicable to the acetonitrile/silica system, as likely also does not hold for other systems involving polar, aprotic liquids.

Transformation of π-conjugated macrocycles: from furanophanes to napthalenophanes.

Applying sequential Diels-Alder cycloaddition and deoxygenation to small π-conjugated furan macrocycles fully converts them to 1,4-naphthalophanes with either ethylene or acetylene spacers, depending on the reaction conditions. 1,4-Napthalenophane tetraene exhibits a 1,3-alternating conformation in the solid state, inclusion of solvent molecules within the macrocycle, and low reduction potentials.

Beyond Continuum Solvent Models in Computational Homogeneous Catalysis

In homogeneous catalysis solvent is an inherent part of the catalytic system. As such, it must be considered in the computational modeling. The most common approach to include solvent effects in quantum mechanical calculations is by means of continuum solvent models. When they are properly used, average solvent effects are efficiently captured, mainly those related with solvent polarity. However, neglecting atomistic description of solvent molecules has its limitations, and continuum solvent models all alone cannot be applied to whatever situation. In many cases, inclusion of explicit solvent molecules in the quantum mechanical description of the system is mandatory. The purpose of this article is to highlight through selected examples what are the reasons that urge to go beyond the continuum models to the employment of micro-solvated (cluster-continuum) of fully explicit solvent models, in this way setting the limits of continuum solvent models in computational homogeneous catalysis. These examples showcase that inclusion of solvent molecules in the calculation not only can improve the description of already known mechanisms but can yield new mechanistic views of a reaction. With the aim of systematizing the use of explicit solvent models, after discussing the success and limitations of continuum solvent models, issues related with solvent coordination and solvent dynamics, solvent effects in reactions involving small, charged species, as well as reactions in protic solvents and the role of solvent as reagent itself are successively considered.

Homo- and heterometallic oxalate-based complexes obtained using [Cr(C2O4)3]3− building block – Two polymorphs of a solvate

Two heterometallic complex salts, as polymorphs of a solvate, consisting of three different mononuclear units, [CuCl(phen)2][Cu(H2O)(phen)2][Cr(C2O4)3]·nH2O [n = 5 (1) and n = 8 (2); phen = 1,10-phenanthroline] were obtained in reactions in which [Cr(C2O4)3]3− was used as a building unit. The polymorphs of a solvate are obtained in crystalline forms that differ in type or stoichiometry of included solvent molecules, mostly obtained under different conditions. In this [CuIICrIII] system, the used solvents and crystallization method influence the final product, i.e., the formation of a specific solvatomorph. From the reaction of an aqueous solution of K3[Cr(C2O4)3]·3H2O and acetonitrile solutions containing phen and CuCl2·2H2O, compound 1 was formed when the layering technique is used; and compound 2 can be obtained from the mixture of these reactants, but using methanol instead of acetonitrile. Based on the index parameter for the degree of trigonality, τ, the geometry of copper(II) atoms of the [Cu(H2O)(phen)2]2+ cations in 1 and 2 are distorted from square pyramidal toward trigonal bipyramidal conformation, while those of [CuCl(phen)2]+ have a trigonal bipyramidal geometry. Interestingly, in the presence of [NBu4]+ cations, and applying slow liquid diffusion, partial decomposition of the building block [Cr(C2O4)3]3− occurred and the homobinuclear oxalate-bridged complex [{Cu(bpy)Cl}2(µ-C2O4)]·CH3OH (3; bpy = 2,2′-bipyridine) was formed. Consequently, the oxalate ligand released from the coordination sphere of CrIII was coordinated to CuII ions during the crystallization process. The obtained oxalate-based compounds 1–3 were characterized by IR spectroscopy and single-crystal X-ray diffraction.

Thermodynamic and MD studies of anion complexation by cyclopentaleucine in acetonitrile and dimethyl sulfoxide

Complexation affinity of cyclic pentaleucine for halogen anions, thiocyanate and oxoanions was studied in acetonitrile and dimethyl sulfoxide. Equilibrium constants and derived Gibbs energies, as well as enthalpies and entropies of the corresponding reactions were determined by means of microcalorimetric and 1H NMR titrations. To get more detailed insight into the binding of anions by the cyclopeptide, classical molecular dynamics simulations were carried out. The preorganization of cyclopentaleucine binding site by inclusion of solvent molecules was observed in acetonitrile by these simulations. The investigated receptor showed larger affinity for all anions in acetonitrile than in dimethyl sulfoxide. The results of 1H NMR studies and those of molecular dynamics simulations indicated that the bound anions were coordinated by the amide groups of cyclopeptide. The stoichiometry of most of the complexes was 1:1 (receptor:anion), with the exception of dihydrogen phosphate and hydrogen sulfate complexes, where higher stoichiometries (1:2 and 2:1, respectively) were also observed. In the case of complexes with H2PO4– anion, in both acetonitrile and dimethyl sulfoxide the binding of dihydrogen phosphate dimer was observed, whereas the species in which two ligands coordinate one HSO4– ion was observed in acetonitrile. The obtained thermodynamic reaction parameters and the observed rather strong solvent effect on the studied equilibria were discussed regarding anions and receptor structural properties as well as solvation abilities of the solvents used.

Environmental Control of Single-Molecule Junction Evolution and Conductance: A Case Study of Expanded Pyridinium Wiring.

Environmental control of single‐molecule junction evolution and conductance was demonstrated for expanded pyridinium molecules by scanning tunneling microscopy break junction method and interpreted by quantum transport calculations including solvent molecules explicitly. Fully extended and highly conducting molecular junctions prevail in water environment as opposed to short and less conducting junctions formed in non‐solvating mesitylene. A theoretical approach correctly models single‐molecule conductance values considering the experimental junction length. Most pronounced difference in the molecular junction formation and conductance was identified for a molecule with the highest stabilization energy on the gold substrate confirming the importance of molecule–electrode interactions. Presented concept of tuning conductance through molecule–electrode interactions in the solvent‐driven junctions can be used in the development of new molecular electronic devices.

Environmental Control of Single‐Molecule Junction Evolution and Conductance: A Case Study of Expanded Pyridinium Wiring

AbstractEnvironmental control of single‐molecule junction evolution and conductance was demonstrated for expanded pyridinium molecules by scanning tunneling microscopy break junction method and interpreted by quantum transport calculations including solvent molecules explicitly. Fully extended and highly conducting molecular junctions prevail in water environment as opposed to short and less conducting junctions formed in non‐solvating mesitylene. A theoretical approach correctly models single‐molecule conductance values considering the experimental junction length. Most pronounced difference in the molecular junction formation and conductance was identified for a molecule with the highest stabilization energy on the gold substrate confirming the importance of molecule–electrode interactions. Presented concept of tuning conductance through molecule–electrode interactions in the solvent‐driven junctions can be used in the development of new molecular electronic devices.

Role of Explicitly Included Solvents on Ultrafast Electron Injection and Recombination Dynamics at TiO2/Dye Interfaces.

Solvent effects are important for photovoltaic systems like dye-sensitized solar cells (DSCs) but remain largely unexplored, partly due to the complexity of explicitly including solvent molecules in atomistic simulations. To address these issues, we have systematically investigated the solvent effects in practical solar cells using ab initio excited state dynamics simulations. In this computational protocol and the extended model system, we considered giving a novel perspective on the excited state changes in response to solvation and finite temperature at the heterointerface of DSCs. By directly comparing the geometric stability of interface bonding, photoabsorption, interfacial electronic structure, and dynamics of vacuum and solvent systems, we obtain useful insights into how solvents influence the key factors that determine the efficiency of DSCs. Solvents significantly enhance the intensity of visible light absorption of chromophores (∼2 times) through two effects: (a) by inducing changes to the dye molecule structure due to intermolecular dye-solvent interactions, and (b) by the dielectric screening of the solvent. Furthermore, by adsorbing onto the TiO2 surface, solvent molecules adjust the interfacial band alignment to a favorable level and screen out the attraction force between injected electrons in the semiconductor substrate and holes left on the chromophore to a large extent, dramatically slowing down the recombination process (>8 times). Our findings provide a comprehensive picture of the explicit solvent effects on individual energy conversion steps in DSCs at the microscopic scale and lead to more accurate prediction of the performance of nanodevices in practical environments, contributing to the optimization of realistic renewable energy devices.

THERMOGRAVIMETRIC STUDIES OF POLYSTYRENE OF MODIFIED COBALT 5-METHYL-5-HEXEN-2,4-DIONATE

Thermogravimetry was used to study polystyrene samples modified with cobalt 5-methyl-5-hexene-2,4-dionate (MHD-Co) in two ways. The first method consists in copolymerizing styrene with the metal monomer MHD-Co, which simultaneously acts as an initiator and an inhibitor in this process, namely it exhibits a multifunctional effect in radical copolymerization with vinyl monomers. The polystyrene obtained in this way contains ≤ 0,5% cobalt in the form of β-diketonate groups covalently linked to the macromolecule, which are located both at the ends and in the middle of the polymer chain. Such polymers can be macroinitiators and graft side chains already at the stage of their synthesis; therefore, they have a branched structure of macrochains. The second modification method consists in the preliminary preparation of a styrene copolymer with unsaturated β-diketone followed by the complexation reaction of the obtained macroligand with a metal salt. In this case, when using the Co (III) salt, polymer chelates are formed as a result of the interaction of several polymer chains, and in the case of the Co (II) salt, two β-diketone groups inside the same macromolecule form a chelate structure. Moreover, for coordination saturation, metal complexes include solvent molecules. Thus, depending on the production method, polystyrene samples containing cobalt β-diketonate have a different structure, which affects the destruction mechanism, which will be different in each method. However, regardless of the modification method, all the studied samples have increased resistance to thermal oxidative degradation compared to the sample obtained using the traditional initiator benzoyl peroxide. The paper discusses the reasons for increasing the thermal stability of polystyrene containing an organometallic modifier.

High-resolution structure of a Y27W mutant of the Dishevelled2 DIX domain.

Dishevelled (Dvl) is a positive regulator of the canonical Wnt pathway that downregulates the phosphorylation of β-catenin and its subsequent degradation. Dvl contains an N-terminal DIX domain, which is involved in its homooligomerization and interactions with regulators of the Wnt pathway. The crystal structure of a Y27W mutant of the Dishevelled2 DIX domain (DIX-Y27W) has been determined at 1.64 Å resolution. DIX-Y27W has a compact ubiquitin-like fold and self-associates with neighbouring molecules through β-bridges, resulting in a head-to-tail helical molecular arrangement similar to previously reported structures of DIX domains. Glu23 of DIX-Y27W forms a hydrogen bond to the side chain of Trp27, corresponding to the Glu762...Trp766 hydrogen bond of the rat Axin DIX domain, whereas Glu23 in the Y27D mutant of the Dishevelled2 DIX domain forms a salt bridge to Lys68 of the adjacent molecule. The high-resolution DIX-Y27W structure provides details of the head-to-tail interaction, including solvent molecules, and also the plausibly wild-type-like structure of the self-association surface compared with previously published Dvl DIX-domain mutants.

Homoleptic Silver Complexes of the Cages P4Se3 and As4S3

By reacting P4Se3 and As4S3 with Ag[Al(ORF)4] {–RF = –C(CF3)3 or –hfip [= –C(H)(CF3)2]} in suitable solvents, Ag(P4Se3)[Al(Ohfip)4] (1), Ag(P4Se3)2[Al(ORF)4] (2), Ag(P4Se3)3[Al(ORF)4] (3), Ag2(As4S3)3[Al(ORF)4]2 (4) and Ag(As4S3)2[Al(ORF)4] (5) were synthesized and characterized by SC‐XRD, Mass spectrometry, Raman spectroscopy as well as solution NMR spectroscopy. When using stronger coordinating anions, only P4Se3 forms an isolable complex yielding 1 featuring a [Ag2(P4Se3)2]2+ core capped by anions acting as the first example of P4Se3 coordinating through selenium atoms. Upon using the weakly coordinating anion [Al{OC(CF3)3}4]–, the dimeric complexes 2 and 4 are accessible in dichloromethane or ortho‐difluorobenzene (o‐dfb), respectively. Complex 2 shows isolated [Ag2(P4Se3)4(CH2Cl2)2]2+ dications with a [Ag2(P4Se3)2]2+ core similar to 1. Complex 4 shows isolated [Ag2(As4S3)3]2+ dications featuring a weak argentophilic contact. All of these complexes include solvent molecules or anions in the coordination sphere of the metal. When switching to the polar yet non‐coordinating solvent SO2, the coordination spheres are filled with additional ligands and compounds 3 and 5 form. Complex 3 shows condensed [Ag(P4Se3)3]+ units yielding a one dimensional chain and represents the first homoleptic metal(P4Se3) complex. Complex 5 shows a similar paddle wheel structure as in 4 with interconnecting As4S3 ligands and is the first known example of a homoleptic metal(As4S3) complex.

Evaluation of HNa[Cu2(Ac)6] As a Cathode Material for Li-Ion Batteries

Cathode materials in currently commercialized rechargeable Li-ion batteries (LIBs) use transition metal ions such as Mn, Fe, Co, and Ni as the redox centres. Such electrode materials include LiMn2O4, LiFePO4, LiNi0.8Co0.15O2, and LiCoO2.1 As the market for LIBs has expanded exponentially, the needs for such species have increased significantly despite their continuously dwindling natural reserves, leading to the cost increases for the electrode materials. Therefore, the search for alternative cathode materials using earth-abundant and nontoxic Cu ions has been going on for decades albeit with limited success possibly mainly due to two reasons. First, Cu2+/Cu+ tend to get reduced to metallic Cu, resulting in the framework collapses and cycling instability. Second, many Cu2+/Cu+-based inorganic frameworks tend to have their electrochemical potentials in the anode ranges. Few successful exceptions include Cu(2,7-AQDC) (AQDC = Anthraquinone -dicarboxylate)2 and a core-shell structure with K0.1Cu[Fe(CN)6]0.7·3.8H2O as the core.3 However, the previous case uses a large ligand with a large molecular mass, leading to a lower theoretical capacity and the inclusion of solvent molecules into the framework and slow Li-ion diffusion in cycling. The latter uses toxic CN- ligand and the core needs to be stabilized by the K0.1Ni[Fe(CN)6]0.7·4.1H2O shell. The Cu2+/ Cu+ in these two cases are coordinated by four O atoms and five N atoms, respectively. Here we report the evaluation of a metal-organic framework, namely HNa[Cu2 (Ac)6] (HAc = Acetic acid) as a nontoxic cathode material for LIBs. A hydrothermal reaction between Cu(Ac)2 and NaAc at 105 ºC for 24 h gave deep blue single crystals of HNa[Cu2(Ac)6] that were selected for single crystal structural analysis. HNa[Cu2(Ac)6] contains discrete binuclear paddle-wheel [Cu2(Ac)6]2- anions (Fig. 1a). In each [Cu2(Ac)6]2-, four acetate (i.e. Ac-) groups connect two Cu2+ as paddles with two additional Ac- groups to occupy the two axial sites of Cu2+. Such paddlewheel exists in Cu(2,7-AQDC) as [Cu2(COO)4] that uses the COO- groups to connect to each other via organic groups. Here each Cu2+ is five- coordinated with a distorted square pyramidal {O5} donor set in which each of the five O atoms is from the five Ac- groups. Packings of the [Cu2(Ac)6]2- anions (Fig. 1b–c) show they are separated and charge-balanced by Na+ and H+ ions. Each Na+ is weakly coordinated by six O atoms from six Ac- groups with a distorted octahedral coordination polyhedron. Powder X-ray powder diffraction (PXRD) analysis confirms the product is pure (Fig. 1d). In the first discharge, HNa[Cu2(Ac)6] delivers more than 90 mAh/g at the 1.85 V plateau and a total of 150 mAh/g (Fig. 2a). Its discharge capacity being higher than its theoretical capacity (106 mAh/g; Mw = 505.34) based on reversible Cu2+/+ redox pair suggests at least partial reduction of Cu2+ to metallic Cu. To understand the mechanism, ex-situ PXRD analysis (Fig. 2b) was used to track the electrode during cycling. When it was discharged to 1.85 V, all the main PXRD peaks from HNa[Cu2(Ac)6] remained with the relative intensities of some peaks changed, possibly mainly due to the insertion of Li+ into the framework and the accompanied structural rearrangement. There were no apparent new phases coming from the decomposition, indicating the metallic copper may be amorphous or leave the electrodes. Similar partial reduction to form metallic Cu during the initial insertion of Li+ into the framework is also observed in Cu3(PO4)2.4 When HNa[Cu2(Ac)6] was further discharged to 1.5 V, all the PXRD peaks related to the framework disappeared and the electrode material was amorphous. Interestingly, when HNa[Cu2(Ac)6] was charged to 3.5 V, ca. 60% of the framework was recrystallized back judging from the relative intensity of the (110) peak at 8.34°. Thereafter, the discharge and charge capacities during the second cycle were 78 and 91 mAh/g. During the fifth cycling, the capacities were 35 mAh/g and its PXRD pattern indicates the absence of crystalline phase and the complete decomposition of the framework. Investigations on correlating the framework structures and the coordination environments of Cu2+ with their electrochemical performances toward Li+ insertion-removal are ongoing. References Blomgren, G. E. J. Electrochem. Soc. 2017, 164, A5019–A5025.Zhang, Z. Y.; Yoshikawa, H.; Awaga, K. J. Am. Chem. Soc. 2014, 136, 16112–16115.Asakura, D.; Li, C. H.; Mizuno, Y.; Okubo, M.; Zhou, H. S.; Talham, D. R. J. Am. Chem. Soc. 2013, 135, 2793–2799.Zhong G. M.; Bai, J. Y.; Duchesne, P. N.; McDonald, M. J.; Li, Q. et al. Mater., 2015, 27, 5736–5744. Figure 1