Coordination Sphere Of Cation Research Articles

Preventing Structural Rearrangements on Battery Cycling: A First-Principles Investigation of the Effect of Dopants on the Migration Barriers in Layered Li0.5MnO2

Layered LiMnO2 is a potential Li ion cathode material that is known to undergo a layered to spinel transformation upon delithiation, as a result of Mn migration. A common strategy to improve the structural stability of LiMnO2 has been to replace Mn with a range of metal dopants, although the mechanism by which each dopant stabilizes the structure is not well understood. In this work we characterize ion-migration barriers using hybrid eigenvector-following (EF) and density functional theory to study how trivalent dopants (Al3+, Cr3+, Fe3+, Ga3+, Sc3+, and In3+) affect Mn migration during the initial stage of the layered to spinel transformation in Li0.5MnO2. We demonstrate that dopants with small ionic radii, such as Al3+ and Cr3+, can increase the barrier for migration, but only when they are located in the first cation coordination sphere of Mn. We also demonstrate how the hybrid EF approach can be used to study the migration barriers of dopant species within the structure of Li0.5MnO2 efficiently. The t...

Functionalization of P4 in the coordination sphere of coinage metal cations.

Selective functionalization of white phosphorus is achieved by addition of ArLi to unique cationic coinage metal η(2)-P4 complexes. This novel approach allows controlled P-C bond formation using the bulky DmpLi (Dmp = 2,6-Mes2C6H3) and the unencumbered MesLi, giving sterically diverse doubly complexed RP4 butterfly derivatives in a single step.

Crystal Structure, Spectroscopic Studies and Thermal Behavior of a New Type Lanthanide Diphosphate HYbP2O7·5H2O

A new ytterbium diphosphate HYbP2O7·5H2O has been synthesized and characterized by single crystal X-ray diffraction. The compound belongs to the monoclinic P21/c space group, and its unit cell dimensions are: a = 6.845(1), b = 8.739(2), c = 17.342(4) A, β = 90.61(2)°, V = 1037.3(4) A3, Z = 4. The framework of this compound consists of layers, parallel to the ab plane, formed by HP2O7 groups and YbO7 polyhedra. They are interconnected by strong hydrogen bonds involving the acidic hydrogen and external oxygen atoms of adjacent diphosphate groups. This layer organization generates channels parallel to the a axis in which two crystallization water molecules are located. The remaining three water molecules complete the coordination sphere of the ytterbium cation. TG and DTA thermograms of the title compound show four decomposition steps, in the 298–1173 K temperature range, corresponding to the removal of the five crystallization water molecules and the acidic hydrogen. A mixture of monophosphate YbPO4 and ytterbium polyphosphate YbP3O9 is obtained at 1173 K. IR and Raman spectra of HYbP2O7·5H2O have also been investigated. Most of the IR bands are non-coincident with those observed in the Raman spectrum, as expected for a centrosymmetric crystal. The emission spectrum of 10 % Eu3+-doped HYbP2O7·5H2O was measured at room temperature and the Stark energy states of Eu3+ were calculated. The non-degenerate 5D0 → 7F0 transition confirms the unicity of the crystallographic site occupied by the lanthanide cation.

Mixed-ligand complexes of Zn(II), Cd(II) and Cu(II) with triethanolamine and p-nitrobenzoic acid: Syntheses and crystal structures

Three new mixed-ligand complexes of Zn, Cd and Cu with triethanolamine (TEA) and p-nitrobenzoic acid (NBA) have been synthesized and structurally characterized by single-crystal X-ray diffraction as compounds with the compositions [Cu2(NBA)2TEA](NBA)(5H2O), [Zn(NBA)2TEA] and [Cd(NBA)2TEA], respectively.The Zn complex crystallized in the monoclinic space group Cc. The coordination polyhedron around the zinc atom corresponds to a highly distorted octahedron of the ZnNO5 type. The TEA ligand is tetradentately coordinated to the cation, thus forming three five-membered chelate rings. In addition, two NBA anions are bonded to the Zn2+-cation in the monodentate mode.The Cd complex crystallized in the orthorhombic space group Pbca. The cadmium atom is seven-coordinated with one monodentate NBA and one bidentate NBA anion, and a TEA ligand in the tetradentate mode.The formation of a dinuclear Cu complex, crystallizing in triclinic space group, is unexpected. The copper(II) ions are five-coordinated, forming distorted tetragonal pyramids, and are O,O′ bridged by the carboxyl group of an NBA ligand and an alkoxide group of the TEA ligand. In addition, the deprotonated TEA ligand coordinates one Cu center in a tetradentate fashion; the coordination sphere of the other Cu cation is completed by a monodentate NBA and aqua ligands.Thus, the 3 divalent metal cations form complexes of very different structures and compositions with the same NBA and TEA ligands because size criteria and crystal field effects play a role.

Thermodynamics of nickel(II) and iron(III) complexation with nicotinamide in aqueous ethanol and aqueous dimethyl sulfoxide

The complexation of Ni(II) and Fe(III) with nicotinamide in aqueous ethanol and aqueous dimethyl sulfoxide was directly studied by calorimetry at T=298.15K and ionic strength value 0.25 (NaClO4). The results of thermochemical study were discussed using solvation-thermodynamic approach basing on the accounting of reagents solvation. The absence of contact ion pairing between Ni2+ and ClO4- was observed by IR-spectroscopy at ionic strength value 0.25. Nicotinamide was found to replace the water molecule within cation coordination sphere by means of UV–Vis spectroscopy.

XAS examination of glutathione–cobalt complexes in solution

In the present work, we have investigated the coordination modes of cobalt with glutathione (γ-l-glutamyl-l-cysteinyl-glycine, GSH). A systematic study of cobalt–GSH complexes at basic and neutral pH has been undertaken with a multi-spectroscopic approach combined with quantum chemistry calculations. XAS (x-ray absorption spectroscopy) has been performed at the cobalt K edge in order to shed light into the cation coordination sphere and formal oxidation states. XANES (x-ray absorption near edge structure) enabled to show that in basic and neutral media, cobalt oxidation state is equal to +III and +II respectively. EXAFS (extended x-ray absorption fine structure) provided indications on the donor atoms involved in the coordination with cobalt as well as the bond lengths. DFT (density functional theory)-based calculations and NMR experiments have been performed to assess the most stable structure of the cobalt–GSH complex in basic conditions.

Coordination modes of novel 4,5-dicyanoimidazolato ligand in alkali metal salts

As the use of lithium batteries became more and more wide-spread, the importance of the research on novel salts for batteries' electrolytes grew more and more important. The focus has been put on designing novel lithium and sodium salts which dissociate well in aprotic solvents and are electrochemically and thermally stable. Salts with heteroaromatic anions such as 2-trifluoromethane-4,5-dicyanoimidazolate (LiTDI) [1,2] are a promising alternative for the salts commonly used as charge carriers in lithium and sodium batteries. The class of new 4,5-dicyanoimidazolates ligands is based on N-heterocyclic five-membered ring substituted with nitrile group. Such a type of anions possesses four nitrogen donor centers able to coordinate cation, and is characterized by charge delocalization, both on imidazole ring and cyano substituents resulting in extended π electron system. In solid as well as liquid electrolytes one should expect the co-existence of a variety of ionic species, such as iosolated anions and cations solvated by solvent molecules, ionic pairs, for which the coordination sphere of cations is completed with solvent molecules, as well as dimers and aggregates with varied stoichiometry. The observed degree of aggregation depends mostly on the coordination properties of anions, their ability to form hydrogen bonds and their compatibility with the acidic properties of cations. The increase of the salt concentration should result in association process and the emergence of higher aggregates, up to polymeric systems, possessing structure of chains, ribbons, layers or networks. In order to define the coordination ability of the class of new ligands, we examined their organization modes in the alkali metal salts and have found a wide variety of mentioned motifs. Discovering and understanding the phenomena related to the organization of such systems in the solid state is crucial for the elaboration of novel electrolytes and should give information about cation and anion coordination in electrolytes. Our single-crystal diffraction studies have shown that new salts comprising 4,5-dicyano-2-(trifluoromethyl)imidazolato anion are interesting from the point of view of their crystalline structure, offering variety of possible coordination modes and are, therefore, worthy of examination.

Theory of ferromagnetism driven by superexchange in dilute magnetic semi-conductors

Magnetic properties of Ga$_{1-x}$Mn$_x$N are studied theoretically by employing a tight binding approach to determine exchange integrals $J_{ij}$ characterizing the coupling between Mn spin pairs located at distances $R_{ij}$ up to the 16th cation coordination sphere in zinc-blende GaN. It is shown that for a set of experimentally determined input parameters there are no itinerant carriers and the coupling between localized Mn$^{3+}$ spins in GaN proceeds via superexchange that is ferromagnetic for all explored $R_{ij}$ values. Extensive Monte Carlo simulations serve to evaluate the magnitudes of Curie temperature $T_\mathrm{C}$ by the cumulant crossing method. The theoretical values of $T_\mathrm{C}(x)$ are in quantitative agreement with the experimental data that are available for Ga$_{1-x}$Mn$_x$N with randomly distributed Mn$^{3+}$ ions with the concentrations $0.01 \leq x \leq 0.1$.

Dichlorido{8-[2-(dimethylamino)ethylamino]quinoline-κ3 N,N′,N′′}zinc

In the title complex, [ZnCl2(C13H17N3)], the coordination sphere of the zinc cation is distorted square pyramidal. The three N atoms of the N,N′,N′′-tridentate 8-[2-(di­methyl­amino)­ethyl­amino]­quinoline ligand and one chloride ion constitute a considerably distorted square base. The apical site is occupied by another chloride ion. The distortion from the ideal square-pyramidal geometry is manifested by the N—Zn—N angle of 133.25 (11)°. Like most square-pyramidal metal complexes, the zinc cation is displaced towards the apical chloride ion. In the crystal, mol­ecules are linked by N—H⋯Cl inter­actions. This leads to the formation of chains of mol­ecules parallel to the b-axis direction.

Comparative review of structural parameters of the nearest surrounding of monoatomic cations in water and methanol media

Literature data on structure of coordination sphere of selected monoatomic cations in aqueous and methanol solutions have been reviewed and compared. The following structural parameters have been considered: coordination number, interparticle distances, the second coordination sphere features, and ionic association type. It has been revealed that for doubly charged ions the parameters of the first coordination sphere are similar in the both solvents. The second coordination sphere of the same cation consists of fewer solvating molecules located farther from the ion in the case of methanol as compared to water.

Structure and Dynamics of Uranyl(VI) and Plutonyl(VI) Cations in Ionic Liquid/Water Mixtures via Molecular Dynamics Simulations

A fundamental understanding of the behavior of actinides in ionic liquids is required to develop advanced separation technologies. Spectroscopic measurements indicate a change in the coordination of uranyl in the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]) as water is added to the system. Molecular dynamics simulations of dilute uranyl (UO2(2+)) and plutonyl (PuO2(2+)) ) solutions in [EMIM][Tf2N]/water mixtures have been performed in order to examine the molecular-level coordination and dynamics of the actinyl cation (AnO2(2+)) ); An = U, Pu) as the amount of water in the system changes. The simulations show that the actinyl cation has a strong preference for a first solvation shell with five oxygen atoms, although a higher coordination number is possible in mixtures with little or no water. Water is a much stronger ligand for the actinyl cation than Tf2N, with even very small amounts of water displacing Tf2N from the first solvation shell. When enough water is present, the inner coordination sphere of each actinyl cation contains five water molecules without any Tf2N. Water also populates the second solvation shell, although it does not completely displace the Tf2N. At high water concentrations, a significant fraction of the water is found in the bulk ionic liquid, where it primarily coordinates with the Tf2N anion. Potential of mean force simulations show that the progressive addition of up to five water molecules to uranyl is very favorable, with ΔG ranging from −52.3 kJ/mol for the addition of the first water molecule to −37.6 kJ/mol for the addition of the fifth. Uranyl and plutonyl dimers formed via bridging Tf2N ligands are found in [EMIM][Tf2N] and in mixtures with very small amounts of water. Potential of mean force calculations confirm that the dimeric complexes are stable, with relative free energies of up to −9 kJ/mol in pure [EMIM][Tf2N]. We find that the self-diffusion coefficients for all the components in the mixture increase as the water content increases, with the largest increase for water and the smallest increase for the ionic liquid cation and anion. The velocity autocorrelation functions also indicate changes in structure and dynamics as the water content changes.

The effects of extreme pressures on single-crystal structures with distortions of the cation coordination sphere

The further development of single-crystal structure analysis from X-ray diffraction data to pressures well above 10 GPa is reviewed. In particular, it is shown on recent studies that new insights can be obtained into the effect of pressure on electronic and steric distortions of the cation coordination sphere from structural analyses up to 50 GPa.

Metal-dependent inhibition of HIV-1 integrase by 5CITEP inhibitor: A theoretical QM/MM approach

HIV-1 integrase (IN) is a potential target for developing drugs against AIDS. In this letter, QM/MM approach was used to study the inhibition of IN by 5CITEP inhibitor in presence of divalent cations (Mg2+ or Mn2+). In addition, the main interactions occurring in 5CITEP-IN complex and the influence of divalent cations (Mg2+ or Mn2+) in enzymatic inhibition were investigated using B3LYP/6-31+G(d,p)/MM. The results suggest that the Asp64, Asp116 and four crystal water molecules plays a crucial role in cation (Mg2+ or Mn2+) coordination sphere.

Interaction Between Group IIb Divalent Transition-Metal Cations and 3-Mercaptopropionic Acid: A Computational and Topological Perspective

Density functional theory was applied to study the interaction of group IIb transition-metal cations (Zn(2+), Cd(2+), and Hg(2+)) with one and two fully or partially deprotonated 3-mercaptopropionic acid ligands. In this investigation, we determined the geometries of all possible complexes resulting from the coordination of the metal ions with the ligands at different binding sites selected on each ligand. The relative energies of the complexes, metal-ion affinities, free energies, and entropies were also determined. The natures of the bonds were critically analyzed by natural bond orbital (NBO) analysis and clarified further using the atoms-in-molecules (AIM) approach. The substantial influence of the solvent (water) polarization on the energetics, geometries, and bonding of the molecular complexes was also investigated by the conductor-like screening solvation model (COSMO). In an attempt to simulate the complexes in an aqueous environment, water molecules were added explicitly to complete the coordination sphere of the metal cations, and the corresponding metal-ion affinities were calculated to study the effect of microhydration.

Nucleophilic addition of methanol and methanethiol to acetylene in the superbasic system KOH-DMSO: a quantum chemical model

Cluster-continuum models (KOH·nDMSO, n = 1, 5) were used to model the superbasic system “alkali metal hydroxide-dimethyl sulfoxide” within the framework of MP2/6-311++G**/ and B3LYP/6-31G* methods. The KOH molecule surrounded by five DMSO molecules exists as “solvate-loosened” ion pair with elongated K-O distance. It is proposed to consider the “solvate-loosened” ion pair of potassium cation with hydroxide anion in the surroundings of five solvent molecules as the catalytic coordination sphere of the superbasic system KOH-DMSO. Methanol and methanethiol molecules can be incorporated with ease into the first coordination sphere of potassium cation to form methoxide and methanethiolate ions. The possibility of nucleophilic attack of methoxide and methanethiolate ions on acetylene molecule in the first coordination sphere of potassium cation was studied. The model reaction system C2H2-CH3OK-H2O with one DMSO molecule included explicitly to maintain the “solvate-loosened” [CH3O]−...K+ ion pair and additional inclusion of solvent effects within the framework of the IEFPCM continuum model is the most preferable for serial calculations.

Temperature dependent resonant X-ray diffraction of single-crystalline Ge2Sb2Te5

The element distribution in the crystal structure of the stable phase of the well-known phase-change material Ge2Sb2Te5 was determined at temperatures up to 471 °C using single crystals synthesized by chemical transport reactions. Because of the similar electron count of Sb and Te, the scattering contrast was enhanced by resonant diffraction using synchrotron radiation (beamline ID11, ESRF). A simultaneous refinement on data measured at the K-absorption edges of Sb and Te as well as at additional wavelengths off the absorption edges yielded reliable occupancy factors of each element on each position (a = 4.2257(2) A, c = 17.2809(18) A, Pm1, R1 (overall) = 0.037). The dispersion correction terms Δf′ were refined and match experimental ones obtained from fluorescence spectra by the Kramers–Kronig transform. The structure contains distorted rocksalt-type blocks of nine alternating cation and anion layers, respectively, which are separated by van der Waals gaps between Te atom layers. Ge atoms prefer the cation positions near the center of the rocksalt-type block (occupancy factors Ge0.60(4)Sb0.36(2)), Sb atoms the one near the van der Waals gap (Ge0.33(7)Sb0.66(4)). Anti-site disorder is not significant. During heating up to 471 °C and subsequent cooling, a reversible structural distortion was observed. The refinements show that with increasing temperature the first pair of anion and cation layers next to the van der Waals gap becomes slightly detached from the block and increasingly resembles a GeTe-type layer. Thus, the difference between interatomic distances in the 3 + 3 cation coordination sphere of the mixed Ge–Sb position next to the gap becomes more pronounced. The element distribution, in contrast, neither changes during the heating experiment nor upon long-time annealing. Thus, the behavior of 9P-Ge2Sb2Te5 single crystals is predominantly under thermodynamic control.

Hydrogen Storage in Aromatic Carbon Ring Based Molecular Materials Decorated with Alkali or Alkali-Earth Metals

On the basis of first-principles calculations of molecular electron structure, we discuss the strategy of modifying the carbon-based materials in order to increase their capacity to bind with molecular hydrogen. In particular, we have studied hydrogen adsorption on molecular complexes having anionic aromatic carbon-based rings stabilized by cations of alkali (Li+, Na+, K+) or alkali-earth metals (Be2+, Mg2+, Ca2+). The adsorption depends more on the properties of the cation than on the ring itself. The interaction of the H2 molecule with an electrostatic field leads to the binding of the hydrogen molecule with the strongly polarized ionic molecular complex. The number of the adsorbed molecules is driven by two factors acting in opposite directions: the binding energy, which should be larger than a 4–5 kJ/mol threshold needed to keep hydrogen molecules attached, and the area around the cation (coordination sphere), which is determined by its radius. As a compromise between these factors, we propose several...

Bis[μ-(3-acetyl-2-hy-droxy-6-methyl-4H-pyran-4-one-κ(3)O:O',O'')]diaqua-tetra-kis-(pyridine-κN)dicopper(II) diperchlorate.

In the centrosymmetric binuclear cation of the title compound, [Cu(C8H7O4)(H2O)(C5H5N)2]2(ClO4)2, the CuII atoms are bridged by a pair of two dehydro­acetate anions in a bis-/monodentate mode. The distorted octa­hedral N2O4 coordination sphere of the metal cation is completed by two pyridine N atoms and one O atom of a water mol­ecule. The complex cations and the perchlorate counter anions are arranged in layers parallel to (100). O—H⋯O hydrogen bonds between the coordinating water mol­ecules and the perchlorate anions constitute ribbons parallel to [10-1]. C—H⋯O hydrogen bonds are also observed.

Microscopic Origin for Multistability in a Photomagnetic CoFe Prussian Blue Analogue

AbstractSwitchable compounds attract growing interest, as they offer promising perspectives for high‐density storage applications. Much effort has been invested in understanding the mechanisms involved in such properties, in order to prepare systems that are suitable for real applications. Compounds exhibiting an electronic transition that can be triggered by an external stimulus have been extensively studied. While most studies describe the switching properties of such systems in terms of a two‐state model, the existence of multistability in switchable systems remains a controversial topic. In thispaper, we compare the thermally populated CoIIFeIII and photoinduced (CoIIFeIII)* states of the Na2Co4[Fe(CN)6]3.3·14H2O Prussian blue analogue. The comparison of the infrared spectroscopic data for the two CoIIFeIII and (CoIIFeIII)* states shows differences at a microscopic scale that cannot be explained in terms of a two‐state model. These experimental data suggest a change in the coordination sphere of the sodium cation, which strongly supports a displacement of the sodium cation in the lattice between the two states. This direct evidence of several distinct CoFe states at an atomic level in this system highlights a new kind of multistability involving competitive metal‐to‐ligand interactions in a switchable compound.

Hydrates of the Alkali Trioxidomonosulfidomolybdates and -tungstates: K2[(Mo/W)O3S] · 1.5H2O and (Rb/Cs)2[(Mo/W)O3S] · H2O

Abstract The trioxidomonosulfidomolybdate and -tungstate anions [(Mo/W)O3S]2– are the first products formed when passing H2S gas through a solution of the oxidometalates. Their potassium, rubidium and cesium salt hydrates form as crystalline precipitates from these solutions depending on pH, the polarity of the solvent, educt concentrations and temperature. The structures of the sesqui- (K) and mono- (Rb, Cs) hydrates have been determined by means of X-ray single crystal diffraction data. The potassium sesquihydrates K2[(Mo/W)O3S] · 1.5H2O are isotypic and crystallize with a new structure type (monoäclinic, space group C2/c, M = Mo/W: a = 987.0(2)/993.13(11), b = 831.75(14)/831.10(11), c = 1868.9(4)/1865.2(2) pm, β = 99.34(2)/99.153(8)°, R1 = 0.0352/0.0390). In the crystal structure the [(Mo/W)O3S]2– anions are connected via hydrogen bonds to form columns along the c direction. Channels containing only water molecules run along the [101] direction. The dehydration process proceeds in a topotactic reaction between 60 to 95 °C and yields crystals of the anhydrous salts K2[(Mo/W)O3S]. The two different K+ cations exhibit a 5 + 3 and 5 + 2 O/S coordination. The heavier alkali metal cations form the four monohydrates (Rb/Cs)2[(Mo/W)O3S] · H2O (trigonal rhombohedral, space group R-3m) with lattice parameters for the Rb/Cs molybdates of a = 621.17(6)/624.62(10), c = 3377.9(4)/3388.6(8) pm (R1 = 0.0505/0.0734) and the tungstates of a = 642.80(3)/643.3(4), c = 3532.8(3)/3566(4) pm (R1 = 0.0348/0.0660). In the structures the 3m symmetrical tetrahedra are arranged to form double layers in such a way, that the O3 bases of the tetrahedra are pointing towards each other in a staggered conformation. These double layers are stacked in the c direction in a rhombohedral sequence. In these hydrates, there are no distinct hyrdogen bonds. Instead, partially disordered pairs of H2O molecules are situated in large cavities between the double layers. With a number of 10, the cation coordination sphere is increased compared to the K salts. The crystallographic results are confirmed by vibrational spectroscopy (Raman/IR) and thermal analytical studies of the new compounds.