Guest Water Molecules Research Articles

A sustainable route from spent hydrogenation catalysts to lamellar spherical vanadium oxide hydrates for superior low-cost aqueous Zn-ion batteries

Vanadium oxides are the promising cathode candidate for zinc ions batteries due to their fascinating structure with adjustable tunnels. Whereas, the expensive reagent-grade vanadium raw materials impede their economically-feasible production for scale-up battery applications. Herein, based on the selective recycling of vanadium and facile hydrothermal treatment, the hierarchical hydrated vanadium oxides (HVO) derived from spent hydrogenation catalysts were successfully fabricated as superior cathode materials of ZIBs. The regulating role of guest water molecules on morphology and electrochemical performance of vanadium oxides was elucidated. The lamellar spherical V10O22.8·12H2O achieved a specific discharge capacity of 287 mA h g − 1 at 0.2 A g − 1 and the discharge specific capacity of 238 mA h g − 1 at 1 A g − 1. Meanwhile, it exhibited a high energy density of 106 Wh kg−1 at a power density of 3324 W kg−1 and excellent capacity retention of 82% after 3000 cycles at a high density of 10 A g − 1. The storage mechanism of zinc ions were disclosed by ex situ Raman and XRD tests. This waste-to-wealth strategy may provide a promising route for the efficient utilization of hazardous spent catalysts and sustainable development of high performance vanadium-based cathode materials.

Synthesis, structure and luminescent properties of Zn(II) metal–organic frameworks constructed by flexible and rigid ligands

The synthesis of new coordination polymers based on flexible ligands is a challenging task. The use of two types of ligands is a possible approach to obtain crystalline compounds. The combination of flexibility and rigidity can lead to unusual topologies and properties. We are managed to obtain two new metal–organic frameworks (MOFs) based on flexible 1,3-bis(2-methylimidazolyl)propane and rigid isophtalic (1,3-benzenedicarboxylic) acid: [Zn2(iph)2(bmip)2] (1) and [Zn4(iph)4(bmip)3]·2DMF·3.5H2O (2). Structure of both compounds were determined by single-crystal X-ray analysis. Compound 1 is 3-fold interpenetrating 3D framework with dmp topology. Compound 2 is 2-fold interconnecting 3D framework with rare topology, described as (4,6)-c net. Compound 2 contains guest DMF and water molecules. Interestingly, compound 2 easily loses guest molecules in air and undergoes to another crystalline compound 2a. The photoluminescence at room temperature of the compounds 1 and 2a were investigated in the solid state. Quantum yields (QY) of luminescence for 1 and 2a are 30.5% and 39.8%, respectively. The short decay times are allowed to attribute the emission to fluorescence characteristic for intraligand transitions.

Molecular Inclusion of Small Aging Products into the Hexanitrohexaazaisowurtzitane (CL‐20) Lattice: Part II, Polymorph Dependence

AbstractIn Part I of this two‐part series, we conducted accelerated aging studies of β CL‐20 thin films deposited on glass surfaces in different environments (N2, air, air/water) and analyzed the samples with attenuated total reflectance infrared (ATR‐IR) spectroscopy. We observed a polymorph transformation to α CL‐20, accompanied by lattice incorporation of water and other small guest molecules when samples were aged in air/water. Comparison to simulated IR spectra identified NO2 (possibly interacting with a carbon species), HNCO, N2O, and CO2 as potential molecular inclusions. For these molecules, we assessed the thermodynamic feasibility of lattice incorporation into α, β, and ϵ CL‐20 and the accompanying local stress due to lattice expansion in Part II, reported here. We found that the insertion of guest molecules (with the exception of water), into β and ϵ CL‐20 is thermodynamically and kinetically unfavorable, explaining the absence of ATR‐IR features corresponding to molecular inclusions in β CL‐20 prior to polymorph conversion. We hypothesize that water facilitates the transformation to α CL‐20, which allows the insertion of small degradation products into the CL‐20 lattice. We predict a larger stability of ϵ CL‐20 compared to β CL‐20 towards polymorph transformation to α CL‐20, including in the presence of water.

CO2-CH4 Exchange Process in Structure I Clathrate Hydrates: Calculations of the Thermodynamic Functions Using a Flexible 2D Lattice-Gas Model and Monte Carlo Simulations.

A two-dimensional lattice-gas model, supplemented by Monte Carlo simulations in the grand canonical ensemble, is applied to study the CO2/CH4 exchange process in sI clathrate hydrates. The coverage dependence of the Helmholtz free energy, chemical potential, entropy, and degree of deformation of the sI structure is given. Two different situations are considered according to the value of the intra- and inter-species' interactions. First, lateral interactions between the guest species and water molecules are introduced by following the well-known Lorentz-Berthelot mixing rules. Second, the study is restricted to an ideal clathrate hydrate, where the lateral interactions are neglected and entropy governs the exchange of CH4 by CO2. In the case of real clathrate hydrates (non-zero lateral interactions), the displacement phenomenon is clearly observed from the behavior of the chemical potential and Helmholtz free energy as functions of coverage. The guest species CO2 has an occupation of more than 80% of the cavities, and therefore displaces the CH4 species. Only 13 to 15% of CH4 remains stagnant in the sI structure. With respect to the degree of deformation, a direct relationship between cell distortion and cell occupancy is observed. Finally, the detailed analysis carried out for the ideal clathrate hydrate allows us to interpret the physical mechanism underlying the exchange process: it is entropy, not energy, that drives the displacement of CH4 by CO2 in sI clathrate hydrates.

Effect of hydrogen-bonding networks in water on the proton conductivity properties of metal–organic frameworks

We study the proton conductivity properties of MOF-801. We find that MOF-801 possesses intrinsic proton carrier sites, μ3-OH groups, in clusters yielding the generation of hydrogen-bonding networks with guest water molecules at high relative humidity (RH), facilitating proton transport. Remarkably, this material has a high proton conductivity of 1.82 × 10−3 S cm−1 under 98% RH at 90 °C and maintains its performance over an extended time. Our investigations reveal that the increase in proton conductivity is correlated to numerous hydrogen bonds within the MOF structure. The activation energy of this process is low (Ea = 0.21 eV), showing that the protons hop through the membrane by the Grotthus mechanism. Interestingly, density functional theory (DFT) calculations combined with molecular dynamics (MD) simulations show that a water cluster mechanism dominates the proton conductivity in this material via the large number of hydrogen bonds formed at different temperatures and relative humilities.

A two-dimensional manganese coordination polymer: Crystal structure, proton conductivity and catalytic property

Herein, we report a new Manganese coordination polymer, Mn3L2(H2O)4·2H2O (1), based on the 4′-(1-H-tetrazol-5-yl)-[1,1′-biphenyl]-3,5-dicarboxylic acid (H3L) ligand under solvothermal condition. 1 shows a two-dimensional layer structure and has strong interaction with the guest water molecules by the Hydrogen-bond network. Moreover, 1 exhibits good proton conductivity with a value of 1.59 × 10−5 S cm−1 under 98% RH at 75 °C. The proton conduction mechanism can be viewed as vehicle mechanism due to the lattice water in the structure of 1. In addition, after removed the water molecules, the open metal sites at the metal nodes of 1 can be used as Lewis acidic active sites and used as heterogeneous catalyst for the cyanosilylation reaction with good reactivity. We anticipate this work can encourage the investigation of the properties of the coordination polymers assembled by tetrazole derivative ligands.

Four Cu(II) coordination polymers with biocompatible isonicotinamide and picolinate ligands in interplay with anionic and neutral linkers

Four Cu(II)-based neutral coordination polymers, 1D {[Cu(isonia)2(adi)(dmf)].0.5H2adi}n (1), 2D {[Cu(isonia)2(adi)](H2O.H2adi)}n (2), 1D {[Cu(pic)(CH3COO)(bpe)].H2O}n (3), and 2D [Cu2(pic)2(CH3COO)2(bpy)]n (4) with biocompatible molecules: isonicotinamide (isonia), pyridine-2-carboxylic (picolinic, Hpic) and adipic (H2adi) acids and 1,2-bis(4-pyridyl)-ethane (bpe) and 4,4′-bipyridine (bpy) as neutral linkers are reported. The polymer extension in 1 and 2 is reached via bidentate bridging adi anions with isonia ligands as single (1) and double (2) pillars. 1D and 2D coordination arrays are associated in elegant 3D H-bonded networks via interplay of robust amide(isonia)…amide(isonia) homosynthon and NH…O(COO–) side interactions. In 3 the pic residue coordinates in a chelate mode and forms the five-membered [Cu(pic)] corner fragment. The structure expansion occurs via bidentate-bridging bpe neutral linker registered in a coordination wire as different conformers thus providing long (Cu-bpe)6 crystallographically unique chain fragment. Oppositely, in 4 the pic residue acts in a bidentate chelate bridging mode and gives rise to the 2D coordination array. The bpy trapping between each two Cu(II) atoms, does not participate in further structure extension. The decisive impact of amido-group of isonia ligand in structure rigidification and retention of protic H2adi and water guest molecules is demonstrated. The gradual decrease of guest’s capacity correlates with an increased liphophilicity of 3 and 4 comparing with 1 and 2.

Self‐Assembly of a Purely Covalent Cage with Homochirality by Imine Formation in Water

AbstractSelf‐assembly of host molecules in aqueous media via metal–ligand coordination is well developed. However, the preparation of purely covalent counterparts in water has remained a formidable task. An anionic tetrahedron cage was successfully self‐assembled in a [4+4] manner by condensing a trisamine and a trisformyl in water. Even although each individual imine bond is rather labile and apt to hydrolyze in water, the tetrahedron is remarkably stable or inert due to multivalence. The tetrahedral cages, as well as its neutral counterparts dissolved in organic solvent, have homochirality, namely that their four propeller‐shaped trisformyl residues adopt the same rotational conformation. The cage is able to take advantage of hydrophobic effect to accommodate a variety of guest molecules in water. When a chiral guest was recognized, the formation of one enantiomer of the cage became more favored relative to the other. As a consequence, the cage could be produced in an enantioselective manner. The tetrahedron is able to maintain its chirality after removal of the chiral guest—probably on account of the cooperative occurrence of intramolecular forces that restrict the intramolecular flipping of phenyl units in the cage framework.

Self-Assembly of a Purely Covalent Cage with Homochirality by Imine Formation in Water.

Self-assembly of host molecules in aqueous media via metal-ligand coordination is well developed. However, the preparation of purely covalent counterparts in water has remained a formidable task. An anionic tetrahedron cage was successfully self-assembled in a [4+4] manner by condensing a trisamine and a trisformyl in water. Even although each individual imine bond is rather labile and apt to hydrolyze in water, the tetrahedron is remarkably stable or inert due to multivalence. The tetrahedral cages, as well as its neutral counterparts dissolved in organic solvent, have homochirality, namely that their four propeller-shaped trisformyl residues adopt the same rotational conformation. The cage is able to take advantage of hydrophobic effect to accommodate a variety of guest molecules in water. When a chiral guest was recognized, the formation of one enantiomer of the cage became more favored relative to the other. As a consequence, the cage could be produced in an enantioselective manner. The tetrahedron is able to maintain its chirality after removal of the chiral guest-probably on account of the cooperative occurrence of intramolecular forces that restrict the intramolecular flipping of phenyl units in the cage framework.

Phase Diagrams for sII Clathrate Hydrates of CO2 from First-Principles Thermodynamics.

Clathrate hydrates are crystalline solid compounds consisting of a water caged framework and guest molecules such as CH4, C2H6, and CO2. Understanding the phase equilibrium conditions of hydrates is significantly important for the industrial exploitation and experimental synthesis of hydrates. Based on the correct description of the intermolecular noncovalent interactions of clathrate hydrates with vdW-DF2, we studied the crystal structures and the chemical potential phase diagrams of sII hydrates encapsulated with CO2 molecules to provide a deep understanding of the stability mechanism of hydrates. Under the given p-T conditions, the partially occupied hydrates (136H2O·1CO2 and 136H2O·16CO2) and fully occupied hydrates (136H2O·24CO2) are thermodynamically stable, and the equilibrium temperature decreases as the relative CO2 chemical potential increases at the same pressure. We expect that the present study may provide vital information on the stability conditions of CO2 hydrates and trigger new experiments to establish an effective replacement strategy for CO2/CH4.

Synthesis, spectroscopic, thermal, crystal structure properties and characterization of new Hofmann-type-like clathrates with 4-aminopyridine and water.

In this study, synthesis of two new heteronuclear tetracyanonickelate(II) clathrates based on 4-aminopyridine (4AP) and guest water (H2O) molecule and investigation of their structural properties were reported. These clathrates were characterized by using vibration spectroscopy, elemental, thermal analysis and single crystal X-ray diffraction (SC-XRD) techniques. Examining the elemental and spectral data of these clathrates, it was observed that the formulas [Zn(II)(4AP)2Ni(µ-CN)2(CN)2]·6H2O and [Cu(II)(4AP)4Ni(µ-CN)2(CN)2]·H2O were defined their structures. General information about the structural properties of these clathrates in single crystal form has been obtained by considering the changes in the characteristic peaks of the cyanide group and the 4AP that formed them. The thermal behaviors of these clathrates were obtained by examining the temperature-dependent changes of their masses. The magnetic susceptibilities of these clathrates in single crystal form were measured with a Gouy balance. According to the data obtained using SC-XRD technique, the heterometallic [Zn(II)(4AP)2Ni(µ-CN)2(CN)2]·6H2O compound has Cmcm and the heterometallic [Cu(II)(4AP)4Ni(µ-CN)2(CN)2]·H2O compound has crystal structures in the C2 / c space group.

Reversible Water Ad-/Desorption Behavior of a 3D Polycatenation Network, [Zn(bpp)(BDC)]·1.5(H2O), Constructed by 2D Undulated Layered MOF

A three-dimensional (3D) polycatenation supramolecular network with chemical formulas, [Zn(bpp)(BDC)]·1.5H2O (1), (bpp = 1,3-bis(4-pyridyl)propane, BDC2− = dianion of terephthalic acid), was synthesized and structurally determined. In compound 1, the coordination geometry of Zn(II) ion is distorted tetrahedral, where its 2D undulated layered framework is constructed via the bridges of Zn(II) ions with bpp and BDC2− ligands. Adjacent 2D layers are arranged in a combined parallel and interpenetrated manner to complete its 3D polycatenation supramolecular architecture. Compound 1 shows a one-step dehydration process with the weight losses of 6.1%, approximately equal to the weight percentage of losing 1.5 guest water molecules. The cyclic thermogravimetric analysis reveals that compound 1 shows reversible, sponge-like water de-/adsorption behavior during de-/rehydration processes. Compound 1 also exhibits significant water vapor hysteresis isotherm.

Enhancing Hydrogen Cluster Storage in Clathrate Hydrates via Defect-Mediated Lattice Engineering

Can we create even more “plenty of room at the bottom” of the confined nanospaces in clathrate hydrates by tuning the complex interactions between the host water frameworks and guest molecules? Because the lattice of the clathrate hydrate is stabilized by van der Waals forces between the host and guest, irradiating the lattice of the clathrate hydrate with energetic particles is anticipated to introduce artificial defects on the host water molecules, resulting in creating a better occupation of guest molecules. Here, we explored the effects of proton irradiation on the intermolecular hydrogen and intramolecular polar covalent bonds in the host frameworks of THF hydrates. The distinct roles of the secondary guest molecules in the lattice elongation of the proton irradiated THF hydrates were examined experimentally. Conclusively, multiple occupations of H2 in small cages was observed at moderate pressure and temperature conditions following H2 reloading of the lattice elongated THF hydrate.

Recognition of hydrophilic molecules in deep cavitand hosts with water-mediated hydrogen bonds.

We describe new container host molecules - deep cavitands with benzimidazole walls and ionic feet - to recognize highly hydrophilic guest molecules in water. The aromatic surfaces of the cavity recognize hydrophobic portions of the guest while bound water molecules mediate hydrogen bonding in the complex. Spectroscopic (NMR) evidence indicates slow in/out exchange on the chemical shift timescale and thermodynamic (ITC) methods show large association constants (Ka up to 6 × 104 M-1) for complexation of small, water-soluble molecules such as THF and dioxane. Quantum chemical calculations are employed to optimize the host-guest geometries and elucidate the hydrogen bonding patterns responsible for the binding.

Energetically significant anti-parallel π-stacking and unconventional anion-π interactions in phenanthroline based Ni(II) and Cu(II) coordination compounds: Antiproliferative evaluation and theoretical studies

Two new coordination compounds of Ni(II) and Cu(II), viz. [Ni(phen)2Cl(H2O)] 4-NO2bz·3H2O (1) and [Cu(phen)2Cl]Cl·5H2O (2) (phen = 1,10-phenanthroline, 4-NO2bz = 4-nitrobenzoate) have been synthesized and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, electronic spectroscopy, TGA and EPR. The detailed crystal structure analysis of the Werner Type Clathrate 1 reveals the self-assembled unconventional enclathration of 4-NO2bz moieties in supramolecular Ni(II) hosts. In addition to the conventional discrete (H2O)n clusters in the crystal structure of 2, the layered architecture involves enclathration of single guest water molecules in the Cu(II) supramolecular hosts. We have theoretically analysed the biologically relevant anti-parallel π-stacking interactions in compound 1 and two types of anion–π interactions involving coordinated and uncoordinated chloride ions in compound 2. MEP surface analysis and DFT calculations reveal that the anti-parallel π-stacking interaction in 1 is energetically significant and enhanced upon complexation of the ligands to the Ni(II) centre. Remarkably, studies also reveal that in addition to the conventional anion⋯π interaction involving the chloride anion in the lattice, the unusual Cl(chlorido)⋯π interaction observed in the crystal assembly of 2 is also energetically significant. The antiproliferative potential of the compounds 1 and 2 have been studied in Dalton’s Lymphoma (DL) malignant cancer cell lines considering MTT cell viability and apoptosis assays. The compounds 1 and 2 exhibited significant concentration dependent increase in cell cytotoxicity and apoptosis in DL cells with negligible cytotoxicity in normal (PBMC) cells.

Insights into the local structures of water in 1-butyl-3-methylimidazolium iodide

Recently, the presence of cavities in ionic liquids (ILs), which affects the solubility of solute molecules such as CO2, has been demonstrated. With the aim of gaining more insight into the interactions between the IL and guest water molecules, the changes experienced upon addition of water molecules to an IL have been monitored by Raman spectroscopy. This study focuses on how the difference in the nanoheterogeneous structures of two ILs, 1-butyl-3-methylimidazolium iodide (abbreviated as [bmim][I]) and 1-butyl-3-methylimidazolium tetrafluoroborate (abbreviated as [bmim][BF4]) influences the local structure of water embedded in the ILs. The evolution of local water clusters formed in the ILs is compared. Then, the connections between microscopic and macroscopic properties were reviewed.

Proton conducting behavior of a microporous metal-organic framework assisted by ligand isomerization

A microporous Tm-MOF {[Tm2L2(ox)(H2O)2]·4H2O}n (Tm-MOF, L ​= ​2-(pyridin-4-yl)-2H-imidazole-4, 5-dicarboxylate dianion; ox ​= ​oxalate dianion) with hydrogen bonds between the guest water molecules and host framework has been obtained. The CV and AC impendence studies suggested there was remarkable proton conducting behavior within Tm-MOF crystals, which was influenced by external voltage. The proton conducting mechanism was explored through dynamic simulation calculation. It was suggested that proton transferred between L ligand and water molecules through hydrogen bonds. And L ligand can isomerize to excited state stimulated by external voltage, which was essential and ensured the continuity of proton transfer. This simulated proton conduction process was verified by the fact that the low proton conductivity at 0 ​V vs. Ag-AgCl increased dramatically while open-circuit voltage increased to 1.6 ​V vs. Ag-AgCl. The UV absorption peak red shifting under higher voltage and the Ea value of 0.22eV lower than 0.4eV also confirmed the result of dynamic simulation.

Acetylene/Ethylene Separation and Solid-State Structural Transformation via [2 + 2] Cycloaddition Reactions in 3D Microporous ZnII Metal-Organic Frameworks.

Purification of ethylene by removing acetylene from an ethylene/acetylene (99/1 v/v) mixture is a challenging task in the petrochemical industry. Our effort toward finding new porous materials that can selectively uptake acetylene resulted in two 3D metal-organic frameworks. Compound 1, {[Zn(p-pda)(bpee)]} (p-pda = p-phenylenediacetate and bpee = 1,2-bis(4-pyridyl)ethylene) turned out to be a nonporous structure due to the presence of a bulky and rigid aromatic ring in the p-pda ligand. Interestingly, replacement of p-pda with succinic acid yields the microporous framework {[Zn2(μ3-OH)(suc)1.5(bpee)]·CH3OH·2H2O} (2; suc = succinate), which offers a 1D channel along the a direction occupied by guest methanol and water molecules. Remarkably, the desolvated framework of 2 shows selective uptake of C2H2 over other gas molecules such as C2H4, C2H6, CO2 and CH4 at 293 K. An ideal absorbed solution theory (IAST) study predicts a high selectivity value for acetylene adsorption over the other gas molecules mentioned above. The efficiency of removal of acetylene from ethylene/acetylene mixtures containing 1% acetylene was established through a column breakthrough experiment performed at room temperature. The performance of our material in the purification of ethylene by removing acetylene is comparable with those reported in the literature. In the frameworks of both 1 and 2, the ethylenic double bonds of adjacent bpee linkers are aligned parallel and readily undergo [2 + 2] cycloaddition reactions upon UV-light irradiation to yield {[Zn2(p-pda)2(rctt-tpcb)]} (1IR) and {[Zn4(μ3-OH)2(suc)3(rctt-tpcb)]·2CH3OH·4H2O} (2IR), respectively (rctt-tpcb = regio-cis,trans,trans-tetrakis(4-pyridyl)cyclobutane). Photochemical structural transformations of 100% were observed in single-crystal to single-crystal fashions, which were also supported by 1H NMR spectroscopy. The structures of both 2 and 2IR underwent temperature-dependent reversible structural transformations, which was confirmed by SCXRD and DSC analysis. Selective C2H2 uptake of the dehydrated framework of 2IR was also examined, which demonstrates results similar to those of 2.

In Situ Formation of NiAl-Layered Double Hydroxide with a Tunable Interlayer Spacing in a Confined Impinging Jet Microreactor

This work reports for the first time an in situ synthesis of a NiAl-layered double hydroxide (NiAl-LDH) with a tunable interlayer spacing using a confined impinging jet microreactor (CIJ). It is found that CIJ allows simultaneous guest (water molecules and carbonate) intercalation and in situ growth of NiAl-LDH by imposing a proper micromixing scale in a space-confined mixing chamber. The final interlayer spacing of NiAl-LDH can be easily regulated from 0.9 to 3.6 nm by tuning the Reynolds number flow range from 4.8 × 103 to 6.7 × 102. The supercapacitor has been chosen as a model reaction to investigate the electrochemical activity of NiAl-LDHs. Results demonstrate that a higher interlayer space increases the electrochemical activity and enhances supercapacitor performances due to improvement in space accessibility of NiAl-LDHs during the faradaic redox reaction. NiAl-LDH with an interlayer space up to 3.6 nm presents fairly good performance as a supercapacitor electrode material in terms of specific capacitance (1285.2 F·g–1 at 1 A·g–1) and stability (capacitance retention rates over 80% after 5000 cycles). This work develops a rapid and continuous flow methodology for a one-pot, in situ formation of NiAl-LDH with the controlled interlayer spacing via microreactor technology.

Gas hydrates porosity and effective volume under multiphase flow conditions

Gas hydrate is a severe flow assurance problem in oil and gas production. Hydrate formation is a phase transition of systems containing small guest molecules and water molecules. Traditionally the industry handles hydrate challenges by keeping the systems out of the hydrate forming region. Due to the high costs, the industry is turning to hydrate slurry management, which does not prevent hydrate formation but focus on dispersing hydrate as solid particles and generating a transportable slurry. The hydrate slurry management requires a good prediction of the hydrate slurry transportability to manage the risks associated with the presence of solids, including its potential accumulation along the flowline. Hydrate slurry is a multiphase flow system with solids. On the macroscale, the porosity and effective volume of hydrate matrix are important variables to predict the overall system transportability. Despite their importance, they have not been widely discussed in the open literature. In this article, we report the hydrate formation results of different multiphase flow systems to highlight the importance of hydrate porosity and effective volume. Our results show that water, oil, and gas can all be trapped into the hydrate matrix, resulting a highly porous structure without and with additives, such as anti-agglomerants. The effective solid volume in our study was 3–10 times as large as the calculated pure hydrate volume. Our results suggest that the porosity is necessary in the multiphase models to better capture the physical characteristics and characterize the flow assurance risks.