Coordination Bond Lengths Research Articles

Molecular structure of vapor-deposited amorphous selenium

The structure of amorphous selenium is clouded with much uncertainty and contradictory results regarding the dominance of polymeric chains versus monomer rings. The analysis of the diffraction radial distribution functions are inconclusive because of the similarities between the crystalline allotropes of selenium in terms of the coordination number, bond length, bond angle, and dihedral angle. Here, we took a much different approach and probed the molecular symmetry of the thermodynamically unstable amorphous state via analysis of structural phase transformations. We verified the structure of the converted metastable and stable crystalline structures using scanning transmission electron microscopy. In addition, given that no experimental technique can tell us the exact three-dimensional atomic arrangements in glassy semiconductors, we performed molecular-dynamic simulations using a well-established empirical three-body interatomic potential. We developed a true vapor-deposited process for the deposition of selenium molecules onto a substrate using empirical molecular vapor compositions and densities. We prepared both vapor-deposited and melt-quenched samples and showed that the simulated radial distribution functions match very well to experiment. The combination of our experimental and molecular-dynamic analyses shows that the structures of vapor- and melt-quenched glassy/amorphous selenium are quite different, based primarily on rings and chains, respectively, reflecting the predominant structure of the parent phase in its thermodynamic equilibrium.

X-Ray Spectroscopic Studies on the Electronic Structures of LiNiO2-Based Cathode Materials for Lithium-Ion Batteries

Introduction For development and popularization of electric vehicles, it is indispensable to improve the safety and the capacity of secondary batteries not only in a usual operating condition but also in harsh operating environments (e.g., at high temperature and in an overcharge condition). Basic knowledge regarding the electronic and bonding states of functional 3d transition metal (TM) elements is necessary to design and develop cathode materials of lithium-ion batteries in this direction. Core-level X-ray spectroscopies provide the element-selected information about electronic states of constituent elements. In this study, we applied X-ray spectroscopies to LiNiO2-based cathode materials to investigate the electronic and bonding states of Ni in different states of charge. Experimental All the samples for X-ray spectroscopies were prepared by using a two-electrode cell comprised of LiNi0.80Co0.15Al0.05O2 as an active material of a working electrode, Li metal as a counter electrode, and mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate containing 1.0 mol dm− 3 LiPF6. The cell was charged at a current density of 1 mA cm−2 (ca. 1 C rate) at room temperature. X-ray absorption spectroscopy (XAS) was performed at the Ni and Co K-edges at the BL33XU (the Toyota beamline) and at the Ni and Co L 2,3-edges and at the O K-edge at the BL27SU of SPring-8, Japan. X-ray emission spectroscopy was also carried out at the Ni K-edge at the BL39XU and the BL33XU of SPring-8. Local structural analysis based on extended X-ray absorption fine structure (EXAFS) was done by using ATHENA and ARTEMIS with the scattering phase shift and the effective scattering amplitudes calculated by FEFF9.05. Results The oxidation state of Ni is often estimated by using an empirical index of absorption energy, at which normalized absorbance is 0.5. This empirical method was applied to the present system, and revealed that the absorption energy at the Ni K-edge monotonically increased as the state of charge approached from 0 to 100 and slightly decreased as the cell was more overcharged. In general, the change in the electronic state of Ni involves that in local structure around Ni, which suggests that structural parameters such as coordination numbers and bond length for the first coordination Ni–O should be alternate indicators of the oxidation state of Ni. Actually, it was found that these structural parameters could be good indicators of average Ni valence. The structural parameters monotonically increased even in the overcharge region as the cell was charged, differently from the above-mentioned empirical absorption energy. The difference in the changing trend of the oxidation-state indicator and the electronic structure of Ni was further investigated by using 3d TM L 2,3-edge and O K-edge XAS and X-ray emission spectroscopy, which will be discussed in the conference. Acknowledgement X-ray spectroscopic studies were performed at the BL27SU, the BL33XU, and BL39XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) with the proposal numbers of 2014B1582, 2014B7008, and 2014B1574.

Observation of Sb2S3-type post-post-perovskite in NaFeF3. Implications for ABX3 and A2X3 systems at ultrahigh pressure

AbstractWe describe the structures and transformations that lead to the crystallization of a post-post-perovskite of Sb2S3 type in a GdFeO3-type fluoroperovskite system at high-pressure conditions, through use of large-volume powder and single-crystal x-ray diffraction techniques. The results of this analysis gives unique access to the relative crystallographic orientations of all the polymorphs encountered (GdFeO3 type, CaIrO3 type and Sb2S3 type). We use this information to extend this description to include other calculated and observed forms that are competitive in ABX3 and A2X3 stoichiometries (e.g. α-Gd2S3 and Be3N2 types) and provide substantial information on inter-relationships between these structures. Such information is critical to the interpretation of transition mechanisms, predicting transition sequences and to the expression of directional properties in those transformed structures. The transformation from CaIrO3 type to Sb2S3 type is group-subgroup, from Cmcm with fc2a, to Pnma c5, with no observable volume change, but considerable change to the morphology of the lattice. There is a concomitant increase in coordination and average bond length compared to the post-perovskite form of NaFeF3.

Complexation of Trivalent Metal Cations to Mannuronate Type Alginate Models from a Density Functional Study.

Complexation of alginate models, built of β-d-mannuronic units (M) linked by a 1-4 glycosidic bridge, to Al(3+), Sc(3+), Cr(3+), Fe(3+), Ga(3+), and La(3+) cations was studied by applying the quantum chemical density functional theory (DFT) based method. The binding modes and energies were obtained for complexes with one, two, and three truncated alginate chain(s). In all the hydrated structures a monodentate binding mode is established to be the energetically most favored with shorter M(3+)···O(COO(-)) bonds than M(3+)···O(OH) bonds. Coordination bond lengths are found to be specific to each cation and to depend very little on the water in the coordination sphere and on the number of saccharide units used to model an alginate chain. The binding energy tendency Fe(3+) ≈ Cr(3+) > Al(3+) ≈ Ga(3+) ≫ Sc(3+) ≥ La(3+) is not affected by the alginate models, the coordination to water molecules, and the number of chains. A significant covalent contribution that arises predominantly from a charge donation from the carboxylate oxygen to the metal cation was established from the orbital population analysis. An exothermic chain-chain association is predicted by the computed enthalpy variations. A comparison between the structural features of alginate complexation to trivalent and divalent cations is provided and discussed.

Extraction of local coordination structure in a low-concentration uranyl system by XANES.

Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoretical L3-edge X-ray absorption near-edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE1 = 168.3/R(U-Oax)(2) - 38.5 (for the axial plane) and ΔE2 = 428.4/R(U-Oeq)(2) - 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the U L3-edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X-ray absorption fine-structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl-ligand complexes, such as the uranyl-carbonate complex. Most importantly, the XANES research method could be extended to low-concentration uranyl systems, as indicated by the results of the uranyl-amidoximate complex (∼40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides.

Synthesis and magnetic properties of a dinuclear manganese(II) complex with two manganese(II) ions of C2-twisted octahedral geometry

A dinuclar manganese(II) complex [Mn2(sym-hcp)2](BPh4)2·2acetone·2H2O (1) was synthesized with a new dinucleating ligand, 4-chloro-2,6-bis[(2-hydroxyethyl)methylaminomethyl]phenol [H(sym-hcp)], for the purpose of studying the magnetic properties. The single-crystal X-ray analysis revealed a bis-μ-phenolato-dimanganese(II) core structure containing two distorted octahedral manganese(II) ions of C2 symmetry. The order of the coordination bond lengths is Mn–O(phenolato)<Mn–O(hydroxy)<Mn–N. Magnetic susceptibility data for 1 was fitted well with the parameters 2J=−0.93cm−1 and g=2.03, indicating weak antiferromagnetic interaction.

Crystal structure of [bis-(2-amino-ethyl-κN)(2-{[4-(tri-fluoro-meth-yl)benzyl-idene]amino}-eth-yl)amine-κN]di-chlorido-copper(II).

The Cu(II) atom in the title compound, [CuCl2(C14H21F3N4)], adopts a coordination geometry that is between distorted square-based pyramidal and very Jahn-Teller-elongated octa-hedral. It is coordinated by three N atoms from the bis-(2-amino-eth-yl)(2-{[4-(tri-fluoro-meth-yl)benzyl-idene]amino}-eth-yl)amine and two chloride ligands. The two crystallographically unique copper complexes present in the asymmetric unit exhibit noticeable differences in the coordination bond lengths. Considering the Cu(II) atoms as having square-pyramidal geometry, the basal Cu-Cl bond lengths are typical [2.2701 (12) and 2.2777 (12) Å], while the apical distances are considerably elongated [2.8505 (12) and 2.9415 (12) Å]. For each mol-ecule, a Cu(II) atom from inversion-related mol-ecules are in nearby proximity to the remaining axial Cu(II) sites, but the Cu⋯Cl distances are very long [3.4056 (12) and 3.1645 (12) Å], attributable to van der Waals contacts. Nonetheless, these contacts appear to have some structure-directing properties, leading to association into dimers. These dimers associate via stacking of the aromatic rings to form extended zigzag chains.

Molecular and dissociative adsorption of a diethylsulfide molecule on (010) and (001) faces of a TiO2 anatase nanoparticle

Adsorption of aliphatic sulfide on the faces of a 1.4×1.4×2.1 nm anatase nanoparticle of the stoichiometry Ti114O228 with ideal (001) and (100) faces are considered in this work. Molecular adsorption on the (001) face proceeds with the enthalpy varying from –6 kcal/mol to –38 kcal/mol by coordinating the sulfide sulfur atom to titanium and oxygen atoms, with the most exothermic adsorption occurring on atoms of the edges between (001) and (010) or (100) faces. Molecular adsorption on the (100) face proceeds with the enthalpy varying from –18 kcal/mol to –30 kcal/mol by coordinating the sulfur atom to oxygen atoms or simultaneously to oxygen and titanium atoms. In molecular adsorption complexes the S-Ti coordination bond length is 2.56-2.69 A and the S-O bond length is 2.35-2.57 A. Dissociative adsorption is observed on the (100) face and proceeds with the enthalpy up to –23 kcal/mol by coordinating the thiyl group to titanium and oxygen atoms and the ethyl group to surface oxygen atoms.

Importance of coordination number and bond length in titanium revealed by electronic structure investigations (Phys. Status Solidi B 9/2015)

Importance of coordination number and bond length in titanium revealed by electronic structure investigations (Phys. Status Solidi B 9/2015)

Role of Sacrificial Protein-Metal Bond Exchange in Mussel Byssal Thread Self-Healing.

Marine mussels tether to seashore surfaces with byssal threads, proteinaceous fibers that effectively dissipate energy from crashing waves. Protein-metal coordination bonds have been proposed to contribute to the characteristic mechanical and self-healing properties of byssal threads; however, very little is understood about how these cross-links function at the molecular level. In the present study, combined Raman and X-ray absorption spectroscopy (XAS) measurements were employed to confirm the presence of protein-Zn(2+) coordination bonds in the mussel byssus and to monitor transitions in the coordination structure during thread deformation and self-healing. Results indicate that Zn(2+) coordination bonds, primarily mediated via histidine, are ruptured during thread yield and reformed immediately following thread relaxation. Mechanical healing, on the other hand, is correlated with the transition toward shorter coordination bond lengths. Calculation of the healing activation energy suggests that protein-Zn bond exchange provides a primary rate-limiting step during healing.

Importance of coordination number and bond length in titanium revealed by electronic structure investigations

AbstractWe study the influence of coordination number and bond length on the phase stability and orbital occupation in Ti using density functional theory. In particular, Ti under a wide range of conditions (equilibrium state, hydrostatic pressure, anisotropic strain, and phase transformations) is systematically investigated allowing us to derive generic energetic and electronic trends. Our analysis of the correlations between electronic structure and the atomic geometry reveals that the most suitable descriptors of the system are an effective coordination number and an effective bond length. Utilizing these descriptors, we show that (i) the phase stability of Ti increases with coordination number, because of the increased number of interatomic bonds; (ii) the occupation number of the d (s and p) orbital decreases (increases) with increasing the bond length, because of the localized (delocalized) character of the d (p and s) orbital. These dependencies are particularly evident after applying a simple harmonic strain correction to the energy and an electron‐transfer correction within the phase. The physical picture derived from pure Ti is used to explain the phase stability and orbital occupation of Ti–Nb and Ti–Zr alloys, which reveals the underlying mechanisms for various experimental phenomena in Ti alloys.

Preparation and crystal structure of [Ru2(μ-Cl)3(P(CH2OH)3)6]Cl

A new water-soluble phosphine Ru complex, [Ru2(μ-Cl)3(P(CH2OH)3)6]Cl, has been prepared from [Ru(PPh3)3Cl2] and P(CH2OH)3 in methanol. The complex was characterized by X-ray analysis. The crystal system is triclinic, space group $P\bar 1$ , a = 9.3659(1) A, b = 13.0976(2) A, c = 16.791(3) A, α = 105.620(5)°, β = 91.114(6)°, γ = 110.193(3)°, V = 1847.3(5) A3, Z = 2. It contains [Ru2(μ-Cl)3(P(CH2OH)3)6]+ and Cl− ions, bound together by hydrogen bonds. Ru has octahedral coordination, with Ru-Cl and Ru-P bond lengths of 2.4815(17)–2.5034(15) and 2.2738(18)–2.2772(18) A, respectively. The RuiRu distance is nonbonding, 3.350(2) A, which is atypical of Ru(II) complexes.

Probing the Limits of Conventional Extended X-ray Absorption Fine Structure Analysis Using Thiolated Gold Nanoparticles.

We present a method for quantifying the accuracy of extended X-ray absorption fine structure (EXAFS) fitting models. As a test system, we consider the structure of bare Au147 nanoparticles as well as particles bound with thiol ligands, which are used to systematically vary disorder in the atomic structure of the nanoparticles. The accuracy of the fitting model is determined by comparing two distributions of bond lengths: (1) a direct average over a molecular dynamics (MD) trajectory using forces and energies from density functional theory (DFT) and (2) a fit to the theoretical EXAFS spectra generated from that same trajectory. Both harmonic and quasi-harmonic EXAFS fitting models are used to characterize the first-shell Au-Au bond length distribution. The harmonic model is found to significantly underestimate the coordination number, disorder, and bond length. The quasi-harmonic model, which includes the third cumulant of the first-shell bond length distribution, yields accurate bond lengths, but incorrectly predicts a decrease in particle size and little change in the disorder with increasing thiol ligands. A direct analysis of the MD data shows that the particle surfaces become much more disordered with ligand binding, and the high disorder is incorrectly interpreted by the EXAFS fitting models. Our DFT calculations compare well with experimental EXAFS measurements of Au nanoparticles, synthesized using a dendrimer encapsulation technique, showing that systematic errors in EXAFS fitting models apply to nanoparticles 1-2 nm in size. Finally we show that a combination of experimental EXAFS analysis with candidate models from DFT is a promising strategy for a more accurate determination of nanoparticle structures.

Crystal structure of tetra-aqua-[2-(pyridin-2-yl)-1H-imidazole-κ(2) N (2),N (3)]iron(II) sulfate.

In the title compound, [Fe(C8H7N3)(H2O)4]SO4, the central Fe(II) ion is octa-hedrally coordinated by two N atoms from the bidentate 2-(pyridin-2-yl)-1H-imidazole ligand and by four O atoms of the aqua ligands. The largest deviation from the ideal octa-hedral geometry is reflected by the small N-Fe-N bite angle of 76.0 (1)°. The Fe-N coordination bonds have markedly different lengths [2.1361 (17) and 2.243 (2) Å], with the shorter one to the pyrimidine N atom. The four Fe-O coordination bond lengths vary from 2.1191 (18) to 2.1340 (17) Å. In the crystal, the cations and anions are arranged by means of medium-strength O-H⋯O hydrogen bonds into layers parallel to the ab plane. Neighbouring layers further inter-connect by N-H⋯O hydrogen bonds involving the imidazole fragment as donor group to one sulfate O atom as an acceptor. The resulting three-dimensional network is consolidated by C-H⋯O, C-H⋯π and π-π inter-actions.

Oxidation and Deprotonation of a Ruthenium(II) Complex with Quinoline-2-carbaldehyde (Pyridine-2-carbonyl)hydrazone and Formation of Hydrazonato-Bridged Heterodimetallic Complexes

Abstract Reactions of a ruthenium(II) complex containing quinoline-2-carbaldehyde (pyridine-2-carbonyl)hydrazone (HL), trans(P,P)-[RuCl2(PPh3)2(HL)] (1), and 3d-metal(II) chlorides resulted in heterodimetallic complexes, [RuCl2(PPh3)2(µ-L)MCl2] (2M, M = Mn, Fe, Co, Ni, Cu, and Zn), in which the deprotonated hydrazonate (L−) bridged two metal ions in the µ-1(Ru)κ2N,O:2(M)κ3N′,N′′,N′′′ mode. The coordination bond lengths around the Ru and M centers suggested that the oxidation states in the complexes 2M could be assigned as RuIII and MII; this was also supported by magnetic, electrochemical, and spectroscopic measurements. In addition, oxidation of complex 1 by (NH4)2[Ce(NO3)6] gave the corresponding mononuclear RuIII complex with the deprotonated hydrazonate, trans(P,P)-[RuCl2(PPh3)2(L)] (3). It is suggested that oxidation of the Ru center lead to the concerted deprotonation from the hydrazone ligand. Addition of excess HClO4 to complex 3 gave a doubly protonated RuIII complex, 4(ClO4)2; in this complex the hydrazonate moiety was not protonated, but both the quinolyl and pyridyl N atoms were protonated. Complexes 3 and 42+ could be interconverted by the addition of acid or base without changing the oxidation state of the Ru center.

Self-assembly and chemical reactivity of alkenes on platinum nanoparticles.

Stable platinum nanoparticles were synthesized by the self-assembly of alkene derivatives onto the platinum surface, possibly forming platinum-vinylidene (Pt═C═CH-) or -acetylide (Pt-C≡) interfacial bonds as a result of dehydrogenation and transformation of the olefin moieties catalyzed by platinum. Transmission electron microscopic measurements showed that the nanoparticles were well-dispersed without apparent agglomeration, indicating effective passivation of the nanoparticles by the ligands, and the average core was estimated to be 1.34 ± 0.39 nm. FTIR measurements showed the emergence of a new vibrational band at 2023 cm(-1), which was ascribed to the formation of Pt-H and C≡C from the dehydrogenation of alkene ligands on platinum surfaces. Consistent behaviors were observed in photoluminescence measurements, where the emission profiles were similar to those of alkyne-functionalized Pt nanoparticles that arose from intraparticle charge delocalization between the particle-bound acetylene moieties. Selective reactivity with imine derivatives further confirmed the formation of Pt═C═CH- or Pt-C≡ interfacial linkages, as manifested in NMR and electrochemical measurements. Further structural insights were obtained by X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure analysis, where the coordinate numbers and bond lengths of the Pt-Pt and Pt-C linkages suggested that the metal-ligand interfacial bonds were in the intermediate between those of Pt-C≡ and Pt-Csp(2).

Ultrathin two-dimensional inorganic materials: new opportunities for solid state nanochemistry.

CONSPECTUS: The ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called "nanochemistry" for short, primarily studies the microstructures and macroscopic properties of a nanomaterial's aggregation states. Due to abundant microstructures in the aggregation states, it is only possible to build a simple but imprecise correlation between the microscopic morphology and the macroscopic properties of the nanostructures. Notably, atomically thin two-dimensional inorganic materials provide an ideal platform to establish clear structure-property relationships in the field of solid state nanochemistry, thanks to their homogeneous dispersion without the assistance of a capping ligand. In addition, their atomic structures including coordination number, bond length, and disorder degree of the examined atoms can be clearly disclosed by X-ray absorption fine structure spectroscopy. Also, their more exposed interior atoms would inevitably induce the formation of various defects, which would have a non-negligible effect on their physicochemical properties. Based on the obtained atomic and defect structural characteristics, density-functional calculations are performed to study their electronic structures. Then, after the properties of the individual ultrathin two-dimensional materials or their assembled highly oriented thin film-based nanodevices are measured, the explicit relationship between atomic, defect, and electronic structure and intrinsic properties could be established. In this Account, we focus on our recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations. In addition, we summarize the close correlation between atomic, defect, and electronic structure variations and the optoelectronic, electrical, magnetic, and thermal properties of ultrathin two-dimensional materials. Finally, we also propose the major challenges and opportunities that face solid state nanochemistry. We believe that all the past achievements in ultrathin two-dimensional materials could bring new opportunities for solid state nanochemistry.

Crystal structure of tetra-aqua-(5,5'-dimethyl-2,2'-bipyridyl-κ(2) N,N')iron(II) sulfate.

In the title compound, [Fe(C12H12N2)(H2O)4]SO4, the central Fe(II) ion is coordinated by two N atoms from the 5,5'-dimethyl-2,2'-bi-pyridine ligand and four water O atoms in a distorted octa-hedral geometry. The Fe-O coordination bond lengths vary from 2.080 (3) to 2.110 (3) Å, while the two Fe-N coordination bonds have practically identical lengths [2.175 (3) and 2.177 (3) Å]. The chelating N-Fe-N angle of 75.6 (1)° shows the largest deviation from an ideal octa-hedral geometry; the other coordination angles deviate from ideal values by 0.1 (1) to 9.1 (1)°. O-H⋯O hydrogen bonding between the four aqua ligands of the cationic complex and four O-atom acceptors of the anion leads to the formation of layers parallel to the ab plane. Neighbouring layers further inter-act by means of C-H⋯O and π-π inter-actions involving the laterally positioned bi-pyridine rings. The perpen-dicular distance between π-π inter-acting rings is 3.365 (2) Å, with a centroid-centroid distance of 3.702 (3) Å.

Supramolecular Polymers Self‐Assembled from trans‐Bis(pyridine) Dichloropalladium(II) and Platinum(II) Complexes

Two structurally similar trans-bis(pyridine) dichloropalladium(II)- and platinum(II)-type complexes were synthesized and characterized. They both self-assemble in n-hexane to form viscous fluids at lower concentrations, but form metallogels at sufficient concentrations. The viscous solutions were studied by capillary viscosity measurements and UV/Vis absorption spectra monitored during the disassembly process indicated that a metallophilic interaction was involved in the supramolecular polymerization process. For the two supramolecular assemblies, uncommon continuous porous networks were observed by using SEM and TEM revealed that they were built from nanofibers that fused and crosslinked with the increase of concentration. The xerogels of the palladium and platinum complexes were carefully studied by using synchrotron radiation WAXD and EXAFS. The WAXD data show close stacking distances driven by π-π and metal-metal interactions and an evident dimer structure for the platinum complex was found. The coordination bond lengths were extracted from fitting of the EXAFS data. Moreover, close Pt(II) -Pt(II) (Pd(II) -Pd(II) ) and PtCl (PdCl) interactions proposed from DFT calculations in the reported oligo(phenylene ethynylene) (OPE)-based palladium(II) pyridyl supramolecular polymers were also confirmed by using EXAFS. The Pt(II) -Pt(II) interaction is more feasible for supramolecular interaction than the Pd(II) -Pd(II) interaction in our simple case.

XAFS study of the local structure of (Yb0.03Sc0.97−xYx)2O3 transparent ceramics

Abstract (Yb 0.03 Sc 0.97− x Y x ) 2 O 3 ( x = 0.10, 0.39, and 0.485) transparent ceramics were prepared by solid-state reaction and sintered in H 2 atmosphere. The X-ray absorption fine structure (XAFS) spectroscopy was used to probe the local structure around Yb. The results show that the trivalent Yb ions are positioned at sites in cubic lattice with octahedral coordination. The local structure around Yb in our samples is quite different from that in the pure Yb 2 O 3 , and also different when Y 2 O 3 content increases. The incorporation of Y 2 O 3 leaded to more drastic distortion in Yb-cation network than that in the first shell Yb–O. The fitting parameters show that the coordination number, bond length and degree of structural disorder in the first shell Yb–O increase with the growing Y 2 O 3 content.