Oxygen Bond Distances Research Articles

Itinerant Spins and Bond Lengths in Oxide Electrocatalysts for Oxygen Evolution and Reduction Reactions

Thorough analyses of structural factors in catalysis are interesting because they allow the massive prescreening of potential optimum compositions. Overall, this article shows how the orbital physics of magnetic compositions relates with spin–lattice interactions and then band gaps and bond lengths together become relevant descriptors in catalytic oxygen technologies. Active electrocatalysts for the oxygen evolution reaction (OER) include magnetic oxides with metals at relatively high oxidation states, so chemisorbed molecular O2 is not very stable. On the other hand, ideal compositions for the oxygen reduction reaction (ORR) have metals in a comparatively lower oxidation state, which can supply electrons to activate O2 molecules toward electron-richer oxygen atoms. Spin–lattice interactions in these strongly correlated oxides relate the orbital configurations and oxidation state with distinctive metal–oxygen bond distances, indicating localized or itinerant electronic behavior and selectivity in oxygen e...

Atomic-level insight into super-efficient electrocatalytic oxygen evolution on iron and vanadium co-doped nickel (oxy)hydroxide

It is of great importance to understand the origin of high oxygen-evolving activity of state-of-the-art multimetal oxides/(oxy)hydroxides at atomic level. Herein we report an evident improvement of oxygen evolution reaction activity via incorporating iron and vanadium into nickel hydroxide lattices. X-ray photoelectron/absorption spectroscopies reveal the synergistic interaction between iron/vanadium dopants and nickel in the host matrix, which subtly modulates local coordination environments and electronic structures of the iron/vanadium/nickel cations. Further, in-situ X-ray absorption spectroscopic analyses manifest contraction of metal–oxygen bond lengths in the activated catalyst, with a short vanadium–oxygen bond distance. Density functional theory calculations indicate that the vanadium site of the iron/vanadium co-doped nickel (oxy)hydroxide gives near-optimal binding energies of oxygen evolution reaction intermediates and has lower overpotential compared with nickel and iron sites. These findings suggest that the doped vanadium with distorted geometric and disturbed electronic structures makes crucial contribution to high activity of the trimetallic catalyst.

A Brief Review of the Effects of Pressure on Wolframite-Type Oxides

In this article, we review the advances that have been made on the understanding of the high-pressure (HP) structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but also tantalates and niobates, with an isomorphic ambient-pressure wolframite structure, have been included in this review. Apart from estimating the bulk moduli of all known wolframites, the cation–oxygen bond distances and their change with pressure have been correlated with their compressibility. The composition variations of all wolframites have been employed to understand their different structural phase transitions to post-wolframite structures as a response to high pressure. The number of Raman modes and the changes in the band-gap energy have also been analyzed in the basis of these compositional differences. The reviewed results are relevant for both fundamental science and for the development of wolframites as scintillating detectors. The possible next research avenues of wolframites under compression have also been evaluated.

Phase transition and proton ordering at 50 K in 3-(pyridin-4-yl)pentane-2,4-dione

Single-crystal neutron diffraction experiments at 100 and 2.5 K have been performed to determine the structure of 3-(pyridin-4-yl)pentane-2,4-dione (HacacPy) with respect to its protonation pattern and to monitor a low-temperature phase transition. Solid HacacPy exists as the enol tautomer with a short intramolecular hydrogen bond. At 100 K, its donor···acceptor distance is 2.450 (8) Å and the compound adopts space group C2/c, with the N and para-C atoms of the pyridyl ring and the central C of the acetylacetone substituent on the twofold crystallographic axis. As a consequence of the axial symmetry, the bridging hydrogen is disordered over two symmetrically equivalent positions, and the carbon–oxygen bond distances adopt intermediate values between single and double bonds. Upon cooling, a structural phase transition to the t 2 subgroup P\bar 1 occurs; the resulting twins show an ordered acetylacetone moiety. The phase transition is fully reversible but associated with an appreciable hysteresis in the large single crystal under study: transition to the low-temperature phase requires several hours at 2.5 K and heating to 80 K is required to revert the transformation. No significant hysteresis is observed in a powder sample, in agreement with the second-order nature of the phase transition.

Domain Structures of Ni and NiFe (Oxy)Hydroxide Oxygen-Evolution Catalysts from X-ray Pair Distribution Function Analysis

Ni–Fe (oxy)hydroxides, Ni(1–z)FezOxHy, are among the fastest-known water oxidation catalysts in alkaline media on a per-cation basis. At current densities relevant for electrolysis (e.g., >0.5 A/cm–2), mass and electron transport through catalyst films with high mass loading are critical and depend substantially on the extended and intermediate catalyst architecture. Here we use X-ray pair distribution function (PDF) analysis to determine the intermediate nanostructures of electrodeposited Ni(1–z)FezOxHy films. We report the effects of electrodeposition technique (pulsed versus continuous), electrochemical cycling, and Fe content on the structure of the catalyst film. The PDF patterns for Ni(1–z)FezOxHy films are best simulated by model structures consisting of brucite-like β-Ni(OH)2 fragments 1 to 3 layers in thickness. Only the oxidation state of the film significantly affects the intralayer scattering behavior (i.e., metal–oxygen bond distance). The interlayer interactions, however, are affected by Fe ...

Synthesis and Characterization of an Isomorphous Lanthanide-Thiophenemonocarboxylate Series (Ln = La–Lu, except Pm) Amenable to Color Tuning

A series of 14 lanthanide compounds bearing 2-thiophenecarboxylate (TC) have been prepared under aqueous conditions and structurally characterized. Single crystal X-ray diffraction studies reveal a full isomorphous series across the 4f block of the general formula [(Ln(TC)3(H2O)2)·(HPy·TC)]n, (Ln = La (La-1) – Lu (Lu-1), excluding Pm), with observable contraction of the cell volume and average metal–oxygen bond distances occurring when moving from lanthanum to lutetium. The 8-coordinate Ln metal centers are bound to two water molecules as well as six oxygen atoms from one bidentate and four bridging TC units that link LnO8 structural units into 1D chains. One lattice stabilizing pyridinium and one outer coordination sphere TC anion are present per formula unit. Reaction optimization provided moderate to high yields of the title products; a lanthanum byproduct [La(TC)3(HTC)2]n (La-2) was formed by performing the reaction at reduced temperature, or alternatively, successive grinding of La-1 in ethanol resul...

Influence of Boron Substitution on the Crystal and Electronic Properties of LiCrO2 Battery Cathode

Boron-substituted LiCrO2 battery cathode material samples were investigated by X-ray-based techniques to probe the influence of boron on their crystal and electronic structure properties. Studies were carried on a series of Li-ion battery cathode materials with the general formula LiCr1−x B x O2. Up to 10 pct boron substitution amounts, light boron atoms were determined to sit in Cr coordinations. However, for more substitutions (>10 pct), higher electronegativity of boron was determined to govern the crystal structure by obtaining isolated boron-centered domains and built Li2BO4 structures. Electronic structure studies and further crystal structure analysis were carried by X-ray absorption fine structure technique. In the studied samples, increasing boron concentration in the samples (i.e., >10 pct substitution) were determined to cause a decrease in oxygen bond distances as a result of boron sitting in some chromium locations. As a result of this study, 10 pct boron substitution was determined as a threshold to protect the LiCrO2 crystal structure.

Probing the accuracy of reactive and non-reactive force fields to describe physical and chemical properties of graphene-oxide

Graphene-oxide (GO) has been shown to be a promising material for numerous technological applications. Extensive computational work has been devoted to elucidate the structure, stability and properties of different GO species. As some applications require large GO sizes, classical molecular dynamics simulations are necessary to fully investigate GO properties and behavior. There are few classical force fields parameterized to examine oxidized hydrocarbon compounds, and not all of them are able to simulate GO structures. Here, we present the first comparative study of some GO properties between three classical force fields: Reactive Empirical Bond Order for carbon, hydrogen and oxygen (REBO-CHO), third generation of the Charge Optimized Many Body (COMB3) and Chemistry at HARvard Macromolecular Mechanics (CHARMM) force field. The chemical and physical properties tested include key binding energies, carbon–oxygen bond distances and elastic modulus. When compared to density functional theory calculations or experimental data, the COMB3 reactive force field is shown to provide the best overall results, while REBO-CHO and CHARMM provide good results for certain properties of most GO-systems.

Structural relaxation around Cr3+ at the Na(Al1-x Cr x )P2O7 octahedral site: an XRPD and EAS study

Abstract The isovalent substitution of chromium for aluminium at octahedral site along the Na(Al1-x Cr x )P2O7 pyrophosphate solid solution has been investigated by means of the combined application of X-ray powder diffraction (XRPD) and electronic absorption spectroscopy (EAS). In agreement with the structural refinements, deconvolution of the optical spectra revealed a progressive decreasing of the crystal field strength parameter 10Dq moving toward the NaCrP2O7 end-member, meaning that the local chromium–oxygen bond distance increased along the join with the amount of chromium. The calculated structural relaxation coefficient around the substituent ion Cr3+ was ε=0.97 (i.e., very close to that predicted by the Hard Spheres model). A detailed comparison with compact crystal structures (i.e., perovskite, garnet, spinel, clinopyroxene, and corundum) as well as with other pyrophosphate compounds with II-NaMP2O7 structure-type (with M=Al, Cr, Fe, V, Ti, Mo and In) highlighted that compounds belonging to the Na(Al1-x Cr x )P2O7 solid solution – characterized by a network connectivity which is basically a framework topology – undergo a structural relaxation that is confined within the first shell (i.e., occurs at the octahedral site), while P2O7 dimers act as rigid units.

IR absorption spectroscopic study of mixed cobalt substituted lithium ferrites

The IR spectra of Li0.5−(x/2)CoxFe2.5−(x/2)O4 ferrite samples (0≤x≤0.6) prepared by solution combustion method have been reported. The influence of Co substitution is verified. XRD studies confirm the spinel phase formation of ferrites. Lattice constant varies linearly from 8.31Å (x=0) to 8.35Å (x=0.6) with composition. Evidence of two absorption bands in the IR spectra (below 800cm−1) reveals the characteristic feature of spinel ferrite. The IR spectra featured additional three absorption bands around 550, 670 and 705cm−1 for the samples x=0.1 and x=0.6. Absence of bands splitting specifies that Fe ions do not exist in excess form. It is found that high frequency band (ν1), due to tetrahedral (A) group, lies at around 600cm−1 and low frequency band (ν2), due to octahedral (B) group, around 450cm−1. The positions of bands are found to be composition dependent. The IR bands due to tetrahedral complexes shift slightly towards high frequency side with composition upto x=0.4 where as that due to octahedral complexes shift towards lower frequency side with x. Based on the data of absorption bands, force constants (kt, ko) and bond lengths (RA, RB) were estimated. Compositional dependence of force constants is explained on the basis of cation–oxygen bond distances of respective sites and cation distribution.

Origin of podiform chromitite, a new model based on the Luobusa ophiolite, Tibet

Podiform chromitites have been interpreted as the result of melt–rock reaction and related melt mixing in upper mantle sections of ophiolites. However, the discovery of ultrahigh-pressure (UHP) minerals, especially diamond and coesite, in many podiform chromitites and host peridotites, raises fundamental questions about the validity of this model. Chromitites in the Luobusa ophiolite of Tibet range from massive, to nodular to disseminated. Chromite grains in both the chromitites and peridotites have variable but relatively high MgO and are classified as magnesiochromite. Many magnesiochromite grains in the massive chromitites contain inclusions of forsterite and pyroxene, as well as diamonds and other unusual minerals. Forsterite inclusions have Fo numbers of 97–99 and NiO contents of 1.11–1.29wt.%. Mg#s (=100∗Mg/(Mg+Fe)) of clinopyroxene inclusions are 96–98 and those of orthopyroxene are 96–97. X-ray studies show that the olivine inclusions have very small unit cells and short cation–oxygen bond distances, suggesting crystallization at high pressure. In contrast, magnesiochromite grains in nodular and disseminated chromitites lack pyroxene inclusions and their olivine inclusions have lower Fo numbers of 94–96 and lower NiO contents of 0.35–0.58wt.%. In addition, magnesiochromite in massive ores has higher Fe3+/Fetotal (0.42) than that in nodular and disseminated ores, which have ratios of 0.22. Disseminated chromitites also show systematic changes in olivine and magnesiochromite compositions from the dunite envelope to the massive ore, indicating melt–rock reaction. These observations suggest that the formation of podiform chromitites is a multi-stage process. Magnesiochromite grains and perhaps small bodies of chromitite crystallize deep in the mantle under low ambient ƒO2 from partial melts of peridotite. UHP minerals and highly magnesian olivine and pyroxene inclusions are trapped in these magnesiochromite grains. When oceanic crustal slabs are trapped in suprasubduction zones (SSZ), they are modified by island arc tholeiitic and boninitic magmas, which change the magnesiochromite compositions and deposit chromitite ores in melt channels.

Tuning luminescent properties through solid-solution in (Ba1−xSrx)9Sc2Si6O24:Ce3+,Li+

A solid-solution of cerium-substituted alkaline earth scandium silicate phosphors, (Ba1−xSrx)9Sc2Si6O24:Ce3+,Li+ (x = 0, 0.25, 0.50, 0.75, 1), have been prepared by solid-state reaction. The structures, characterized using synchrotron X-ray powder diffraction, show the solid-solution closely follows Vegard's law. The substitution of Sr for Ba results in a decrease of the alkaline earth–oxygen bond distances by more than 0.1 Å at all three crystallographic sites, leading to changes in optical properties. The room temperature photoluminescent measurements show the structure has three excitation peaks corresponding to Ce3+ occupying the three independent alkaline earth sites. The emission of (Ba1−xSrx)9Sc2Si6O24:Ce3+,Li+ is red-shifted from the near-UV (λmax = 384 nm) for x = 0 to blue (λmax = 402 nm) for x = 1. The red-shifted photoluminescent quantum yield also increases when Sr is substituted for Ba in these compounds.

Local structural relaxation around Co2+ along the hardystonite–Co-åkermanite melilite solid solution

Six pure compounds belonging to the hardystonite (Ca2ZnSi2O7)–Co-akermanite (Ca2CoSi2O7) solid solution were investigated by the combined application of X-ray powder diffraction and electronic absorption spectroscopy. Structural refinements of the XRPD data revealed a negative excess volume of mixing due to the single isovalent substitution of Co for Zn in the tetrahedral site. In agreement with the diffraction data, deconvolution of the optical spectra showed a progressive decreasing of the crystal field strength parameter 10Dq moving toward the Co-akermanite end-member, meaning that the local cobalt–oxygen bond distance, \( \langle {\text{Co}}{-}{\text{O}}\rangle^{\text{local}} \), increased along the join with the amount of cobalt. The calculated structural relaxation coefficient around the fourfold coordinated Co2+ in the Ca2(Zn1−x Co x )Si2O7 join was e = 0.69, very far from the one predicted by the Vegard’s law (e = 0) and at variance with e = 0.47 previously found for tetrahedrally coordinated Co2+ in gahnite–Co-aluminate spinel solid solution. This difference is consistent with the largest constraints existing on the spinel structure, based on cubic closest packing, compared to the more flexible layered melilite structure.

A3V2(PO4)3 (A = Na or Li) probed by in situ X-ray absorption spectroscopy

Two stable modifications of A3V2(PO4)3 (A = Na or Li) were synthesized by citric acid assisted modified sol–gel synthesis. The obtained samples were phase pure Li3V2(PO4)3 and Na3V2(PO4)3 materials embedded in a carbon matrix. The samples were tested as half cells against lithium or sodium metal. Both samples delivered about 90 mAh g−1 at a C/10 cycling rate. The change of vanadium oxidation state and changes in the local environment of redox center for both materials were probed by in-situ X-ray absorption spectroscopy. Oxidation state of vanadium was determined by energy shift of the absorption edge. The reversible change of valence from trivalent to tetravalent oxidation state was determined in the potential window used in our experiments. Small reversible changes in the interatomic distances due to the relaxation of the structure in the process of alkali metal extraction and insertion were observed. Local environment (vanadium–oxygen bond distances) after 1st cycle were found to be the same as in the starting material. Both structures have been found very rigid without significant changes during alkali metal extraction.

Modulation of catalyst particle structure upon support hydroxylation: Ab initio insights into Pd 13 and Pt 13/γ-Al 2O 3

An atomic picture of highly dispersed palladium and platinum catalysts supported on gamma-alumina is provided. Understanding the structure–reactivity relationship in the field of catalysis by metals requires the rationalization of the role of the metal-support interaction on the morphology and electronic properties of nanometer size metallic particles. Thus, the interaction energies and the structures of Pd 13 and Pt 13 clusters deposited on two relevant gamma-alumina surfaces are systematically investigated by density functional theory calculations. The hydroxylation of the support weakens the metal adhesion and influences the cluster morphologies. Flat lying bi-planar clusters with strong interaction energies are stabilized on the dehydrated (1 0 0) surface, whereas clusters with a three-dimensional morphology are favored by the hydroxyl groups of the (1 1 0) surface. A consistent comparison of Pt and Pd is achieved. The shortest metal–oxygen (M–O) bond distances calculated by DFT agree well with EXAFS M–O distances. Moreover, the presence of metal–aluminum bond distances close to 2.61–2.64 Å may explain experimental features. The present work also provides structural and electronic clues for the understanding of the reactivity of highly dispersed Pd and Pt catalysts.

ChemInform Abstract: Substitution Studies of Second- and Third-Row Transition Metal Oxo Complexes

Publisher Summary This chapter discusses substitution studies of second- and third-row transition metal OxO complexes and proton, oxygen, and cyanide exchange. The relative dynamics of the different exchange processes taking place on the selected second- and third-row transition metal Oxo complexes. The kinetic behavior is especially an important aspect determining the preparation, uptake, and clearance of such radiopharmaceutical agents. This distortion results in changes in the overlap of the ligandmetal orbitals and variations in the corresponding bond strengths and has definite effects on the proton, water, and cyanide exchange processes. Some aspects related to the reactivity of the Tc(V) and Re(V) complexes, where the former is widely applied as an imaging nuclide in the radiopharmaceutical industry, are also discussed in the chapter. An interesting point comes from the comparison of the in vivo data with the other ligand substitution results in general. A correlation is obtained with rhenium–oxygen bond distances as determined from crystallographic studies.

Supramolecular networks of polymethylphosphonic acid groups bonded to aromatic platforms: biphenyldiyl-2,2′-bis(methylphosphonic acid) and benzenetriyl-1,3,5-tris(methylphosphonic acid)

Biphenyldiyl-2,2'-bis(methylphosphonic acid) (BBMP) and benzenetriyl-1,3,5-tris(methylphosphonic acid) (BTMP) as ligands have been synthesized from diphenic acid and trimesic acid, respectively. Cu, Mn and Co complexes of BBMP have been prepared but similar complexes of BTMP did not crystallize. However, a copper compound with added 4,4'-bipyridyl was obtained. This copper complex is dimeric in which the dimers are linked into a supramolecular compound through the bipyridyl groups. Interestingly, the structure was solved in P1 with an unusual correlation between the ligand oxygen bond distances and the copper bond distances to water molecules. The Mn and Co BBMP complexes are isostructural in which the BBMP ligands phenyl groups rotate around each other to bridge the metal atoms forming 1:1 linear chains. There are four water molecules bonded to Co that can be removed reversibly. In the case of the Cu compound, one Cu is square planar bonded to four phosphonate oxygen atoms from two BBMP molecules. The second copper is six coordinate adding two water molecules in the axial positions. The two copper ions alternate forming a one dimensional chain but with ligands bonding the chain on both sides. The four coordinate copper atoms are chelated by two BBMP ligands utilizing one oxygen atom from the two phosphonate groups of each ligand and a second oxygen atom from these groups that bridge across the Cu atoms to bond to the six coordinate copper ion. A detailed synthetic procedure for each of the two ligands is supplied as ESI.

Actinide incorporation in a zirconia based pyrochlore (Nd 1.8An0.2)Zr 2O 7+x ( An=Th, U, Np, Pu, Am)

Actinides (thorium, uranium, neptunium, plutonium, and americium) were infiltrated into a porous Nd 1.8Zr 2O 6.7 matrix, prepared by gel-supported precipitation. (Nd 1.8 An 0.2)Zr 2O 7+ x pyrochlores were formed after sintering in Ar/H 2 and the pyrochlore structure remains during oxidation at 800 °C in air. X-ray diffraction reveals a linear relationship between the pyrochlore lattice parameter and the ionic radii of the actinides. EXAFS measurements on actinide L 3-edge show a split shell of nearest neighbour oxygen atoms similar to that surrounding of Nd. The actinide–oxygen bond distances decrease with the actinide ionic radii, which verifies that these actinides adopt the Nd site in the (Nd 1.8 An 0.2)Zr 2O 7+ x pyrochlore. The oxidation susceptibility of Np is related to the availability of oxygen vacancies and in contrast to stabilised zirconia Np(V) can be obtained in zirconia based pyrochlore.

Unusual Physical and Chemical Properties of Cu in Ce1‐xCuxO2 Oxides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enthalpies of formation and lattice enthalpies of alkaline metal acetates

The standard ( p° = 0.1 MPa) molar enthalpies of formation in the crystalline state of the alkaline metal acetates CH 3COOM (M = Li, Na, K, Rb, Cs), at T = 298.15 K, were determined by reaction-solution calorimetry as: Δ f H m ° ( C H 3 COOLi , cr ) = − ( 741.40 ± 0.95 ) kJ mol −1, Δ f H m ° ( C H 3 COONa , cr ) = − ( 711.01 ± 0.51 ) kJ mol −1, Δ f H m ° ( C H 3 COOK , cr ) = − ( 722.36 ± 0.49 ) kJ mol −1, Δ f H m ° ( C H 3 COORb , cr ) = − ( 722.31 ± 1.09 ) kJ mol −1, Δ f H m ° ( C H 3 COOCs , cr ) = − ( 726.10 ± 1.07 ) kJ mol −1. These results, taken together with the enthalpies of formation of the haloacetates XCH 2COOM (M = Li, Na; X = Cl, Br, I) and chloropropionates ClCH(CH 3)COOM (M = Li, Na) re-evaluated from literature data were used to derive a consistent set of lattice energies, and discuss some general trends of the structure–energetics relationship for the CH 3COOM, XCH 2COOM, and ClCH(CH 3)COOM compounds, based on the Kapustinskii approximation. It was found that the lattice energies of the haloacetates are essentially independent of the halogen and ca. 17–25 kJ mol −1 smaller than those of the corresponding acetates. In addition, no significant difference between the lattice enthalpy values of the haloacetates and chloropropionates was observed. Finally, linear correlations of very similar slope were obtained by plotting the M O bond distances derived from the Kapustinskii equation against the published experimental M O bond distances for alkaline metal acetates and alkoxides. The analysis of these relations suggests that the metal–oxygen bond distances for the lithium, potassium, and rubidium acetates, whose molecular structures in the solid state have not been determined, can be estimated as 214, 288, and 304 pm, respectively.