Change In Coordination Environment Research Articles

Structural Phase Transition, Optical and Electrical Property Evolutions of Thiospinel AgIn5S8 under High Pressure.

Thiospinel AgIn5S8 as a visible-light-active semiconductor has been frequently used as a photoabsorber in solar cells, optoelectronics devices, and photoelectrochemical cells. Similar to temperature, pressure is an efficient external stimulus for both crystalline structural and electronic modulations to improve properties. Herein, we present the pressure tuning effect on AgIn5S8 up to 40 GPa. A pressure-driven phase transition from the ambient cubic spinel structure to an orthorhombic structure is observed around 10 GPa as evidenced from the in situ high pressure synchrotron X-ray diffraction results. The high pressure phase of AgIn5S8 adopts the defective LiVO2-type structure with all the Ag+/In3+ cations sitting in the octahedrally coordinated environments. Both the electric transport and photocurrent measurements show dramatic changes along with the phase transition around 10 GPa, and the high pressure phase of AgIn5S8 exhibits greatly improved conductivity but decreased responses to visible light illumination. Surprisingly, the in situ UV-vis measurements reveal the onset pressure point of bandgap evolution around 7.5 GPa, far below the structural phase transition pressure around 10 GPa, which indicates the early initiated local structural change in the pressure range 7.5-10 GPa. An in situ Raman technique is used to confirm the coordination environment changes of AgIn5S8 under compression, the results of which reveal the coexistence of both the ambient and the high pressure structure features of AgIn5S8 in the pressure range 7.5-10 GPa. This work provides a demonstration on how external pressure affects the crystal structure, electronic structure, and optical properties of chalcogenide semiconductors and sheds light on the structure design of better optoelectrical materials under ambient conditions.

Cover Feature: Solvent and Counter‐Ion Induced Coordination Environment Changes Towards AgI Coordination Polymers (Eur. J. Inorg. Chem. 33/2019)

Cover Feature: Solvent and Counter‐Ion Induced Coordination Environment Changes Towards Ag^I Coordination Polymers (Eur. J. Inorg. Chem. 33/2019)

Co-aromatization of methane with propane over Zn/HZSM-5: The methane reaction pathway and the effect of Zn distribution

The co-aromatization of methane with propane is investigated using Zn/HZSM-5 as the catalyst at 400 °C. The presence of methane has a pronounced effect on the product distribution in terms of improved formation of phenyl rings and substitution groups of aromatic species. Isotopic labeling and solid-state NMR spectroscopy studies reveal that the favored site for methane incorporation varies at different stages along the co-aromatization reaction, from the benzylic sites at the initial stage to the phenyl rings and then substitution groups as the reaction proceeds. SIMS spectroscopy of the involved reaction intermediates suggests the formation of C4 species over the Zn sites that are bonding to the oxygen atoms of the zeolite framework, which is supported by theoretical calculations. The interaction between Zn species and the zeolite framework is also confirmed by XAS and changes in coordination environments are identified through XANES and solid-state NMR spectroscopy. The redistribution of Zn during the reaction is observed on the surface of the zeolite support. Scanning transmission X-ray microscopy images show that Zn is rich in the inner pores compared with the external surface of the catalyst particles in the pristine catalysts. XANES and XPS spectra demonstrate that the Zn concentration increases on the external surface after the reaction, a conclusion that is further supported by the theoretical study. The Zn redistribution might be among the reasons for methane participation pathway alternation during the co-aromatization, since the Zn species located within the inner pores and on the external surface might prefer to catalyze the methane incorporation to the phenyl rings and substitution groups of the formed aromatics, respectively.

Coordination environment changes of the vanadium in vanadium-dependent haloperoxidase enzymes

Vanadium-dependent haloperoxidases are a class of enzymes that catalyze oxidation reactions with halides to form halogenated organic products and water. These enzymes include chloroperoxidase and bromoperoxidase, which have very different protein sequences and sizes, but regardless the coordination environment of the active sites is surprisingly constant. In this manuscript, the comparison of the coordination chemistry of V-containing-haloperoxidases of the trigonal bipyramidal geometry was done by data mining. The catalytic cycle imposes changes in the coordination geometry of the vanadium to accommodate the peroxidovanadium(V) intermediate in an environment we describe as a distorted square pyramidal geometry. During the catalytic cycle, this intermediate converts to a trigonal bipyramidal intermediate before losing the halogen and forming a tetrahedral vanadium-protein intermediate. Importantly, the catalysis is facilitated by a proton-relay system supplied by the second sphere coordination environment and the changes in the coordination environment of the vanadium(V) making this process unique among protein catalyzed processes. The analysis of the coordination chemistry shows that the active site is very tightly regulated with only minor changes in the coordination geometry. The coordination geometry in the protein structures deviates from that found for both small molecules crystalized in the absence of protein and the reported functional small molecule model compounds. At this time there are no examples reported of a structurally similar small molecule with the geometry observed for the peroxidovanadium(V) in the active site of the vanadium-containing haloperoxidases.

Morphological Development and Coordination Change in the Course of Cd2+ Hydrolysis

Abstract Morphological development from nanowire to hexagonal platelet was observed for hydrolysis products of Cd(NO3)2 aqueous solution. 113Cd cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy and X-ray diffraction revealed that the morphological development corresponds to the change of coordination environment around Cd2+ from double salts containing nitrate ions to β-Cd(OH)2.

A family of related Co(II) terpyridine compounds exhibiting field induced single-molecule magnet properties

We describe the syntheses, crystal structures and magnetic properties of several Co(II) complexes containing 4′-pyrrolidine-2,2′:6′,2″-terpyridine (pyrtpy) or 4′-triflouromethylsulfonate-2,2′:6′,2″-terpyridine (OTftpy) ligands: [(OTftpy)CoCl2] (1), [Co(pyrtpy)2](BPh4)2 (2b), and [(OTftpy)Co(κ2-O2NO)2] (3). The compounds display different coordination numbers, where 1, 2b and 3 are distorted square pyramidal (pentacoordinate), octahedral (hexacoordinate) and pentagonal bipyramidal (heptacoordinate) about the cobalt center, respectively. Field-induced slow magnetic relaxation properties are observed for all compounds; however, compounds 1 and 3 display two relaxation events, whereas 2b shows only one relaxation event. The origin of the varied dynamic magnetic properties for these complexes arises from the change in coordination environment as well as dipolar interactions between neighboring complexes. These experimental results are supported by computational investigations for each species, implicating lower-lying excited states for complex 2b, which increase the impact of spin–orbit coupling, in turn leading to a larger axial anisotropy value.

Complexation Enhancement Drives Water-to-Oil Ion Transport: A Simulation Study.

We address the structures and energetics of ion solvation in aqueous and organic solutions to understand liquid-liquid ion transport. Atomistic molecular dynamics (MD) simulations with polarizable force field are performed to study the coordination transformations driving lanthanide (LnIII ) and nitrate ion transport between aqueous and an alkylamide-oil solution. An enhancement of the coordination behavior in the organic phase is achieved in contrast with the aqueous solution. In particular, the coordination number of Ce3+ increases from 8.9 in the aqueous to 9.9 in the organic solutions (from 8 in the aqueous to 8.8 in the organic systems for Yb3+ ). Moreover, the local coordination environment changes dramatically. Potential of mean force calculations show that the LnIII -ligand coordination interaction strengths follow the order of LnIII -nitrate>LnIII -water>LnIII -DMDBTDMA. They increase 2-fold in the lipophilic environment in comparison to the aqueous phase, and we attribute this to the shedding of the outer solvation shell. Our findings highlight the importance of outer sphere interactions on the competitive solvation energetics that cause ions to migrate between immiscible phases; an essential ingredient for advancing important applications such as rare earth metal separations. Some open questions in simulating the coordination behavior of heavy metals are also addressed.

Metal-ion exchange induced structural transformation as a way of forming novel Ni(II)− and Cu(II)−salicylaldimine structures

A Zn(II)−salicylaldimine complex [Zn(Lsalpyca)(H2O)]n (1, where H2Lsalpyca=4-hydroxy-3-(((pyridin-2-yl)methylimino)methyl)benzoic acid), with a one-dimensional (1D) chain structure, has been successfully converted to a discrete Ni(II)−salicylaldimine complex [Ni(Lsalpyca)(H2O)3] (2) and an infinite Cu(II)−salicylaldimine complex {[Cu(Lsalpyca)]·3H2O}n (3) through a metal-ion exchange induced structural transformation process. However, such processes do not worked by Mn(II) and Co(II) ions. Solid-state structure analyses reveal that complexes 1–3 form comparable coordinative or supramolecular zigzag chains running along the crystallographic [201] direction. In addition, replacing Zn(II) ion by Ni(II) and Cu(II) ions caused changes in coordination environment and sphere of metal centers, from a 5-coordinate intermediate geometry of square pyramidal and trigonal bipyramidal in 1 to a 6-coordinate octahedral geometry in 2, and to a 4-coordiante square planar geometry in 3. This study shows that metal-ion exchange serves as a very efficient way of forming new coordination complexes that may not be obtained through direct synthesis.

First principles study of oxygen diffusion in a α-alumina twin grain boundary

We have investigated atomistic scale behaviour of oxygen diffusion along the twin grain boundary in α-Al2O3 (alumina) using molecular dynamics simulation and first principles total energy calculations. Based on the GB structure model which is verified by atomic-scale STEM observations on the bicrystal sample, quantitative evaluation of migration energies for dominant migration paths were performed by atomistic calculations. The preset calculation results confirmed fast oxygen diffusion behaviour along the GB. Our analysis shows that the dominant migration path or difference in the migration energies can be well correlated with the geometry of local atomic coordination around the migrating oxygen; lower migration energies are generally expected for paths with less change in coordination environment on migration. This trend holds both among gain boundary paths and bulk paths in α-alumina examined in the present study.

Incorporation of Cr, Mn and Ni into goethite (α-FeOOH): mechanism from extended X-ray absorption fine structure spectroscopy

The crystal-chemical mechanisms by which transition metals are associated with goethite are fundamental to our understanding of the solubility and bioavailability of micronutrients and heavy metals in soils, and in the formation of laterite ore deposits. Transition metals such as Cr, Mn and Ni may sorb onto goethite by forming surface precipitates, surface complexes or by replacing Fe3+ in the goethite structure. In the work reported here, we investigated the local coordination environment of Cr, Mn and Ni in synthetic goethite using EXAFS spectroscopy. We demonstrate the isomorphous substitution for Fe3+ by Cr3+ (up to 8 mol.%), Mn3+ (up to 15 mol.%) and Ni2+ (up to 5 mol.%). We find, however, that the next-nearest-neighbour coordination environment changes with composition. The perturbations are likely to be responsible for limiting the accommodation of Cr3+, Mn3+ or Ni2+ in the FeOOH structure.

Watching Iron Nanoparticles Rust: An in Situ X-ray Absorption Spectroscopic Study

Iron nanoparticles and iron oxide nanoparticles are among the most commonly studied nanomaterials because of their applications in fields ranging from catalysis to ferrofluids. However, many synthetic methods give iron nanoparticles with large size distributions, and it is difficult to follow the kinetics of iron nanoparticle oxidation reactions and the relative speciation of iron oxidation states in real time. Herein, we introduce a simple approach of controlling the sizes of Fe@FexOy nanoparticles and a novel method for following Fe@FexOy nanoparticle oxidation in situ in liquid solutions by Fe K- and L-edge X-ray absorption near-edge structure (XANES) spectroscopy. XANES results show that these Fe@FexOy nanoparticles have similar XANES spectra before exposure to air. In situ XANES measurements allow for quantitative oxidation kinetics of different nanoparticle sizes to be followed; results show that the rate of Fe(0) oxidation increases with a decrease in average nanoparticle size. However, the rate of Fe core size depletion was found to be ca. 0.02 nm/min for all the nanoparticle systems studied. This suggests similar oxidation mechanisms are at work for all the particle sizes studied. This work shows that in situ liquid cell XANES can be used to follow oxidation state and coordination environment changes in Fe NP dispersions.

Redox modulation of Low-Volume (100 µL) Solutions for XAFS measurements

A key to the understanding of transition metal catalysis is a detailed knowledge of the changes in coordination environment that accompany a change in redox state. The capacity of a given metal complex to support the high rates of electron transfer needed for effective catalysis is strongly dependent on the magnitude of structural reorganization coupled to the redox step. The ability of the ligand to control the dynamics of electron transfer is beautifully illustrated by copper redox proteins such as plastocyanin.[1] The polypeptide-imposed constraints on the environment at the coordination site of the metal minimize the structural change attendant on interconversion between the CuI and CuII redox states of the metal, facilitating fast electron transfer. Further, unravelling the molecular details of enzyme catalysis often hinges on knowledge of the structural changes attendant on oxidation or reduction. XAFS can provide the key structural information for reactive or unstable redox states of biological and abiological molecules. Our research has mostly centred on the use of a combination of spectroscopic and computational techniques to reveal the chemistry associated with dihydrogen activation in diiron compounds related to [FeFe]-hydrogenases [2], where a combination of XAFS, IR spectroscopy and theory can provide reliable structural information. Sampling of such species can provide a comparable challenge to spectral analysis – an issue made more difficult in cases where the quantity of sample is limited. We have developed low-volume electrosynthesis cells suitable for the study of electrogenerated species where the total volume of solution required for XAS data collection is of order 100 µL [3]. The design and operation of cells designed to allow freeze quenching and tow-temperature spectral collection or RT on-line measurement will be described.

Two-Dimensional Coordination Polymers Comprising Mixed Tripodal Ligands for Selective Colorimetric Detection of Water and Iodine Capture

Two ternary coordination polymers (CPs) {[Co3(BTC)2(TIB)2(H2O)4]·(H2O)4}n (1) and {[Cu3(BTC)2(TIB)2(H2O)2]·(H2O)6}n (2) comprising tripodal linkers 1,3,5-benzenetricarboxylate (BTC) and 1,3,5-tris(imidazol-1-ylmethyl)benzene (TIB) are synthesized and characterized by single crystal X-ray diffraction and other physicochemical techniques. Adsorption experiments show that the materials can uptake molecular iodine in the vapor phase and can endure the adsorbed guest at ambient conditions. 27.92 and 28.62 wt % iodine uptake was observed for 1 and 2 respectively, which corresponds to the 1.88 and 1.96 molecules of iodine per formula units of 1 and 2 respectively. The adsorbed iodine can be slowly released in organic solvents. An interesting chromism phenomenon was also observed in the case of 1 which shows intense pink color in its pristine (hydrated) form and dark blue color in dehydrated forms which also may be attributed to the change in coordination environment around Co(II) centers. Interestingly, reversib...

In Situ Observation of Gating Phenomena in the Flexible Porous Coordination Polymer Zn2(BPnDC)2(bpy) (SNU-9) in a Combined Diffraction and Gas Adsorption Experiment

The intrinsic structural dynamic during the adsorption of CO2 at 195 K and N2 at 77 K on flexible porous coordination polymer Zn2(BPnDC)2(bpy) (SNU-9) was studied in situ by powder XRD. The crystal structures of as made and solvent free (activated) phases were determined by single crystal X-ray diffraction. During the structural transformation caused by activation, the rearrangement of Zn-O bonds occurs that leads to changes in coordination environment of Zn atoms. Such changes lead to the contraction of the unit cell and to decreasing unit cell volume of nearly 28% in comparison to the pristine as made structure. The solvent accessible volume of the unit cell decreases from 40.8% to 12.8%. The adsorption of CO2 and N2 on SNU-9 proceeds in a different way: the formation of intermediate phase during the CO2 adsorption could be postulated, while the transformation from narrow pore form to the open structure occurs in quasi-one-step in the case of N2 adsorption (the intermediate phase is formed only in very narrow pressure region). The transformation of the structure is guest dependent and the differences in the structures of CO2@SNU-9 at 195 K and N2@SNU-9 at 77 K were proven by Pawley and Rietveld refinements of powder XRD patterns. The structure of N2@SNU-9 is identical to this of as synthesized phase, while the structure of CO2@SNU-9 differs slightly.

Raman spectroscopic determination of the length, energy, Debye temperature, and compressibility of the C–C bond in carbon allotropes

Raman phonon relaxation dynamics in carbon allotropes including graphene, carbon nanotube, C60, carbon nanobud, graphite, and diamond has been formulated in terms of the bond order–length–strength (BOLS) correlation. The length and energy responses of the representative bond to the change of coordination environment, pressure, and temperature determine intrinsically the Raman shifts. Reproduction of the measured results in quantitative information of the bond length, bond energy, mode cohesive energy, binding energy density, Debye temperature, and the compressibility of the C–C bond in each phase without needing involvement of the phonon scattering resonant processes or the mode Grüneisen constants.

Dipyridylamide isomer influenced dimensionality in luminescent cadmium phthalate coordination polymers with similar tetranuclear clusters and ribbon motifs

Hydrothermal reaction of cadmium nitrate, potassium hydrogen phthalate (KHphth), and either 4-pyridylnicotinamide (4-pna) or 3-pyridylisonicotinamide (3-pina) afforded two new luminescent coordination polymers with similar structural components but different dimensionality. {[Cd2(phth)2(4-pna)(H2O)]·0.25H2O}n (1, phth=phthalate) manifests [Cd4(phth)4(H2O)2] ribbons based on tetranuclear clusters, connected to two others by pairs of tethering 4-pna ligands to afford 4-connected 2D (4,4) layers. [Cd2(phth)2(3-pina)(H2O)]n (2) has similar tetranuclear clusters and [Cd4(phth)4(H2O)2] ribbons, which are linked to four others by 3-pina tethers to construct a 6-connected 3D 41263pcu network. Subtle differences in phth binding and bridging mode, along with changes in coordination environment, serve to influence the dimensionality of the resulting coordination polymer. Thermal decomposition behavior is also discussed.

Synthesis and Characterization of Fe(II) β-Diketonato Complexes with Relevance to Acetylacetone Dioxygenase: Insights into the Electronic Properties of the 3-Histidine Facial Triad

A series of high-spin iron(II) β-diketonato complexes have been prepared and characterized with the intent of modeling the substrate-bound form of the enzyme acetylacetone dioxygenase (Dke1). The Dke1 active site features an Fe(II) center coordinated by three histidine residues in a facial geometry--a departure from the standard 2-histidine-1-carboxylate (2H1C) facial triad dominant among nonheme monoiron enzymes. The deprotonated β-diketone substrate binds to the Fe center in a bidentate fashion. To better understand the implications of subtle changes in coordination environment for the electronic structures of nonheme Fe active sites, synthetic models were prepared with three different supporting ligands (L(N3)): the anionic (Me2)Tp and (Ph2)Tp ligands ((R2)Tp = hydrotris(pyrazol-1-yl)borate substituted with R-groups at the 3- and 5-pyrazole positions) and the neutral (Ph)TIP ligand ((Ph)TIP = tris(2-phenylimidazol-4-yl)phosphine). The resulting [(L(N3))Fe(acac(X))](0/+) complexes (acac(X) = substituted β-diketonates) were analyzed with a combination of experimental and computational methods, namely, X-ray crystallography, cyclic voltammetry, spectroscopic techniques (UV-vis absorption and (1)H NMR), and density functional theory (DFT). X-ray diffraction results for complexes with the (Me2)Tp ligand revealed six-coordinate Fe(II) centers with a bound MeCN molecule, while structures of the (Ph2)Tp and (Ph)TIP complexes generally exhibited five-coordinate geometries. Each [(L(N3))Fe(acac(X))](0/+) complex displays two broad absorption features in the visible region that arise from Fe(II)→acac(X) charge transfer and acac(X)-based transitions, consistent with UV-vis data reported for Dke1. These absorption bands, along with the Fe redox potentials, are highly sensitive to the identity of L(N3) and substitution of the β-diketonates. By interpreting the experimental results in conjunction with DFT calculations, detailed electronic-structure descriptions of the complexes have been obtained, with implications for our understanding of the Dke1 active site.

ChemInform Abstract: Keys for Unlocking Photolabile Metal‐Containing Cages.

AbstractReview: 100 refs.

Keys for Unlocking Photolabile Metal‐Containing Cages

Photolabile metal-containing cages are metal complexes that undergo a change in coordination environment upon exposure to light of an appropriate wavelength. The light-responsive functionality can either be a component of the encapsulating ligand or a property of the metal complex itself. The altered coordination properties of light-responsive complexes can result in release of the coordinated metal ion into its surroundings, a differential reactivity of the metal center, or the liberation of a reactive molecule that had been passivated by binding to the metal center. These triggerable agents can be useful tools for manipulating the bioavailability of metals or their coordinating ligands in order to study biological pathways or for potential therapeutic purposes.

X-ray Absorption Spectroscopic Investigation of Molybdenum Multinuclear Sorption Mechanism at the Goethite−Water Interface

Understanding in situ metalloid surface speciation on mineral surfaces is critical to predicting the bioavailability in surface and subsurface environments. In this study, Mo K-edge X-ray absorption spectroscopy (XAS) was used to elucidate Mo(VI) surface speciation at the goethite-water interface. Effects of pH and loading levels were investigated. X-ray absorption near edge structure (XANES) analysis indicated that the Mo(VI) coordination environment changes from tetrahedral to octahedral with decreasing pH. At near neutral pH, Mo(VI) predominantly remains as tetrahedral molecules, forming inner-sphere surface species via corner- and edge-sharing attachment with iron octahedral structures (interatomic distance of Mo-Fe (R(Mo-Fe)) at ∼2.8 and ∼3.4 Å, respectively). In contrast, a mixture of surface species comprising tetrahedrally and octahedrally coordinated Mo(VI) exists at pH ∼3-4. While the same Mo(VI) tetrahedral surface species are present at acidic pH, there was an additional MoO(6) polymer attachment on iron octahedral structures, resulting in a R(Mo-Fe) at 3.53 Å. The coordination number (CN) of a Mo-Mo backscatterer gradually increased with increasing loading level, suggesting the formation of surface polymerization. Overall, there seems to be a transition from Mo(VI) tetrahedral to octahedral coordination environment with decreasing pH. The XAS findings further support a Mo(VI) inner-sphere adsorption mechanism that was previously suggested in the pressure-jump relaxation study by Zhang and Sparks (Soil Sci. Soc. Am. J. 1989, 53 (4), 1028-1034). pH-Dependent multinuclear Mo(VI) surface speciation may be important in predicting Mo(VI) transport process in the soil-water environment.