Cu-O Bond Length Research Articles

Unraveling the influence of oxygen vacancy with and without replacement on Cu<i>2</i>O: A DFT Study

This study delves into the structural and electronic effects of oxygen vacancies in Cu2O using density functional theory (DFT) enhanced with Hubbard U corrections (DFT+U). A 3x2x1 supercell of Cu2O was employed. The study meticulously investigates the removal of 1, 2, and 3 oxygen atoms, analyzing the ensuing changes in both structural stability and electronic properties, with particular emphasis on the band gap.The structural analysis revealed that oxygen vacancy formation induces significant modifications in Cu-O and Cu-Cu bond lengths, with elongations observed around the vacancy sites in which the Cu-Cu bond length decreased to 2.4035 Å, compared to 3.0066 Å in the pristine structure. The structural distortion followed the Jahn-Teller effect, leading to the formation of isolated units and transformation in bond angles. The introduction of oxygen vacancies without replacement (WOR) caused significant distortions in the Cu2O lattice, which were more pronounced with increasing vacancy concentration. The Cu-O bond length increased from 1.8492 Å in the pristine structure to 1.9840 Å in the single vacancy configuration. However, in the oxygen vacancies with replacement (WR) the Cu-Cu bond length increased slightly to 3.0218 Å, with the Cu-O bond length expanding to 1.8505 Å. The band structure analysis indicated a decrease in the band gap with increasing vacancy concentration. The pristine Cu2O exhibited a band gap of 1.67 eV as calculated, which was increased to 1.97 eV with a single vacancy and 1.16 eV with two vacancies, reflecting the significant impact of oxygen vacancies on the material’s optoelectronic properties. The findings underscore the critical role of oxygen vacancies in modulating the structural and electronic properties of Cu2O, providing insights that are pivotal for optimizing its performance in applications like photocatalysis and solar cells.

Copper-induced lattice distortion in Na4Fe3(PO4)2(P2O7) cathode enabling high power density Na-ion batteries with good cycling stability

Na4Fe3(PO4)2P2O7 (NFPP) has attracted attention due to its high theoretical capacity, low cost, and good structure stability for Na-ion batteries. However, its practical application is limited by the low intrinsic electronic conductivity and sluggish ion diffusion kinetics. To tackle those problems, lattice strain engineering by heteroatom doping is applied to tune the local molecular structure and optimize the electrochemical properties of electrode materials. Copper cation (+2) with a smaller ionic radius was chosen to dope at Fe-site in NFPP, and the doping amount was also optimized, illustrating the optimized sample of Na4Fe2.7Cu0.3(PO4)2P2O7 (NFPP-0.3Cu) delivered a high capacity of 119.01 mAh g-1 at 1C (1 C = 129 mA g-1) and a high capacity retention of 82.76% after 3000 cycles at 20 C. Notably, full cells with NFPP-0.3Cu as cathode and hard carbon as anode delivered a high energy density of 230 Wh kg-1 and a power density of 2280 W kg-1. The exceptional electrochemical performances are attributed to the modulated electronic structure and abundant lattice defects by Cu-doping. Furthermore, in-situ X-ray diffraction technique and theoretical calculation have jointly proved that the lattice distortions originated from Cu-doping have reduced the band gap of the NFPP-0.3Cu and altered the coordination environment of Fe, shortening the Fe-O and Cu-O bond lengths, significantly enhancing the intrinsic ionic conductivity and the diffusion kinetics of Na+. This work provides new point of views on lattice strain engineering and reaction kinetics of cathode materials in promoting high energy and power density sodium-ion batteries.

8-Hy-droxy-quinolinium tri-chlorido-(pyridine-2,6-di-carb-oxy-lic acid-κ3 O,N,O')copper(II) dihydrate.

The title compound, (C9H8NO)[CuCl3(C7H5NO4)]·2H2O, was prepared by reacting CuII acetate dihydrate, solid 8-hy-droxy-quinoline (8-HQ), and solid pyridine-2,6-di-carb-oxy-lic acid (H2pydc), in a 1:1:1 molar ratio, in an aqueous solution of dilute hydro-chloric acid. The CuII atom exhibits a distorted CuO2NCl3 octa-hedral geometry, coordinating two oxygen atoms and one nitro-gen atom from the tridentate H2pydc ligand and three chloride atoms; the nitro-gen atom and one chloride atom occupy the axial positions with Cu-N and Cu-Cl bond lengths of 2.011 (2) Å and 2.2067 (9) Å, respectively. In the equatorial plane, the oxygen and chloride atoms are arranged in a cis configuration, with Cu-O bond lengths of 2.366 (2) and 2.424 (2) Å, and Cu-Cl bond lengths of 2.4190 (10) and 2.3688 (11) Å. The asymmetric unit contains 8-HQ+ as a counter-ion and two uncoordinated water mol-ecules. The crystal structure features strong O-H⋯O and O-H⋯Cl hydrogen bonds as well as weak inter-actions including C-H⋯O, C-H⋯Cl, Cu-Cl⋯π, and π-π, which result in a three-dimensional network. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing involving the main residues are from H⋯Cl/Cl⋯H inter-actions, contributing 40.3% for the anion. Weak H⋯H contacts contribute 13.2% for the cation and 28.6% for the anion.

Catalytic Water Electrolysis by Co-Cu-W Mixed Metal Oxides: Insights from X-ray Absorption Spectroelectrochemistry.

Mixed metal oxides (MMOs) are a promising class of electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Despite their importance for sustainable energy schemes, our understanding of relevant reaction pathways, catalytically active sites, and synergistic effects is rather limited. Here, we applied synchrotron-based X-ray absorption spectroscopy (XAS) to explore the evolution of the amorphous Co-Cu-W MMO electrocatalyst, shown previously to be an efficient bifunctional OER and HER catalyst for water splitting. Ex situ XAS measurements provided structural environments and the oxidation state of the metals involved, revealing Co2+ (octahedral), Cu+/2+ (tetrahedral/square-planar), and W6+ (octahedral) centers. Operando XAS investigations, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), elucidated the dynamic structural transformations of Co, Cu, and W metal centers during the OER and HER. The experimental results indicate that Co3+ and Cu0 are the active catalytic sites involved in the OER and HER, respectively, while Cu2+ and W6+ play crucial roles as structure stabilizers, suggesting strong synergistic interactions within the Co-Cu-W MMO system. These results, combined with the Tafel slope analysis, revealed that the bottleneck intermediate during the OER is Co3+ hydroperoxide, whose formation is accompanied by changes in the Cu-O bond lengths, pointing to a possible synergistic effect between Co and Cu ions. Our study reveals important structural effects taking place during MMO-driven OER/HER electrocatalysis and provides essential experimental insights into the complex catalytic mechanism of emerging noble-metal-free MMO electrocatalysts for full water splitting.

Stabilizing lattice oxygen redox in layered sodium transition metal oxide through spin singlet state

Reversible lattice oxygen redox reactions offer the potential to enhance energy density and lower battery cathode costs. However, their widespread adoption faces obstacles like substantial voltage hysteresis and poor stability. The current research addresses these challenges by achieving a non-hysteresis, long-term stable oxygen redox reaction in the P3-type Na2/3Cu1/3Mn2/3O2. Here we show this is accomplished by forming spin singlet states during charge and discharge. Detailed analysis, including in-situ X-ray diffraction, shows highly reversible structural changes during cycling. In addition, local CuO6 Jahn-Teller distortions persist throughout, with dynamic Cu-O bond length variations. In-situ hard X-ray absorption and ex-situ soft X-ray absorption study, along with density function theory calculations, reveal two distinct charge compensation mechanisms at approximately 3.66 V and 3.99 V plateaus. Notably, we observe a Zhang-Rice-like singlet state during 3.99 V charging, offering an alternative charge compensation mechanism to stabilize the active oxygen redox reaction.

Enhanced cuprate superconductivity from elongated to compressed coordination

In 1986 Professor Müller and Bednorz discovered the historic superconductor of LaBaCuO (La214) that opens the prelude of unprecedented era for high Tc superconductivity research worldwide. The Jahn Teller effects combining with strong interlayer Coulomb interactions lead to the elongated copper oxygen coordination in La214, giving rise to the orbital order scenario that the Cu3dx2-y2 locates near Fermi surface while the 3dz2 is far below without contributions to the conductivity, hence single band model is favorite. We recently discovered a new type of cuprate superconductor Ba2CuO4-y (Ba214) synthesized at extreme high oxygen pressure that shares a similar crystal structure to the classical La214 but with notably a very rare compressive type octahedron. The compressed octahedron coordination results from the longer in plane CuO bond length than that for apical oxygen bond. The compressed octahedron will lead to a reversed orbital order, i.e. the 3dz2 will be lifted above 3dx2-y2,which is generally considered unfavorable to superconductivity based on the current theories of high Tc cuprates. Ba214 however exhibits bulk superconducting transition with Tc above 70 K at ambient pressure, a surprisingly 80 % enhancement from that for isostructural La214. Here we briefly introduce the unique structure features as well research progress for Ba214, indicating the paradigm shifts roles of 3dz2 orbital in (I) enhancing cuprate superconductivity, (II) favoring multiband scenario; (III) enabling the s wave pairing mechanism.

Negative magnetoresistance effect in Ba-doped layered double perovskite La2CuSnO6

The layered double perovskite La2-xBaxCuSnO6 (0.05 ≤ x ≤ 0.20) ceramics were synthesized successfully by solid-state reaction, and the crystal structure, transport and magnetic properties are investigated. It is found that the temperature-dependent resistivity ρ(T) shows a semiconductor behavior, which is related to magnetic ordering in two-dimensional CuO2 layers, and the MR effect exists in La2-xBaxCuSnO6. With decreasing the temperature, the MR effect changes from positive to negative, giving a positive maximum at Tmax (≈ TC) and showing a large negative MR effect at around 40 K with a value of about 20–30% under field H = ± 50 kOe. It is suggested that the negative MR effect in Ba-doped La2CuSnO6 is attributed to the field-induced suppression of in-plane spin-disorder scattering in CuO2 layers. A small amount of Ba doping can adjust the competition and synergy of the AFM and FM interactions through changing the tilt and distortion of CuO6 octahedrons, the in-plane Cu-O bond lengths, and the content of Jahn-Teller exciton Cu2+ ions, besides the stabilization of the La2CuSnO6 structure. The competition and synergy of the AFM and FM interactions CuO2 layers dominate the transport and magnetic properties of Ba-doped La2CuSnO6.

Study of Crystal Structure and Magnetics Properties in the Normal State of Electron-Doped Eu<sub>2-</sub><i><sub>x</sub></i>Ce<i><sub>x</sub></i>Cu<sub>0.97</sub>Zn<sub>0.03</sub>O<sub>4+</sub><i><sub>α-δ</sub></i> in Overdoped Regime

The normal state of high-Tc superconducting cuprates is crucial to understanding of the mechanism in superconductivity. There are two main ways to remove superconductivity so that the sample is in a normal state, that is by applying a large magnetic field or adding impurities such as Zn to the sample. To investigate the crystal structure and magnetic properties in the normal state of electron-doped high-Tc cuprates in overdoped regime, Eu2-xCexCu0.97Zn0.03O4+α-δ (ECCZO) with x = 0.16, 0.17, 0.18, and 0.19 has been synthesized by the solid-state reaction method. The crystal structure and magnetic properties of the samples were characterized by XRD and SQUID measurements. The results of XRD measurements shows all samples have T’-structure and the values of lattice parameters a, CuO bond length, and crystallite size increased with increasing x. On other hand, the value of lattice parameters c decreased with increasing x, causing the expansion of the tetragonal unit cell in the horizontal direction. From susceptibility measurements, in the normal state with 3% of Zn impurity all samples have the paramagnetic behaviour. The magnetic parameters of these samples analysed by the Curie law. With increasing of Ce concentration, the C and the are increased. The increase in the magnetic parameters since the increasing in magnetic ordering.

A new approach to study semi-coordination using two 2-methyl-5-nitroimidazole copper(ii) complexes of biological interest as a model system.

Two novel copper(ii) complexes [Cu(2mni)2(H2O)2](NO3)2·2H2O (1) and [Cu(2mni)2(NO3)2] (2), where 2mni is 2-methyl-5-nitroimidazole, were prepared and characterized in the solid state using single-crystal and powder X-ray diffraction analyses, EPR, electronic and vibrational spectroscopies (FTIR and Raman), and thermogravimetric methods. Both products present an elongated distorted octahedral geometry with axial Cu-O bond lengths of 2.606(14) and 2.593(15) Å, indicating semi-coordination. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ theory level were used to study the electronic properties of 1 and 2. The Independent Gradient Model (IGM) was employed to determine the Intrinsic Bond Strength Index (IBSI) of the semi-coordination and to plot δg isosurfaces for the electronic sharing between the metal center and ligands. A moderate to weak antibacterial activity against Escherichia coli cultures was found for 1 with a 50% growth inhibition (GI50) value of 0.25 mmol L-1. To the best of our knowledge, this is the first time that the semi-coordination analysis using IGM was carried out for a copper(ii) complex with axial elongation, finding a good correlation between the bond length and the IBSI, and the study was extended for a series of analogous complexes described in the literature.

Effect of Doping Different Cu Valence States in HfO2 on Resistive Switching Properties of RRAM

Metal dopants are important for HfO2-based resistive switching mechanisms in resistive random-access memory (RRAM) because they can improve the performance of RRAM devices. Although Cu ions have been widely explored as metal dopants, Cu dopants with different valence states have received little attention. Using the first principles method and the Vienna ab initio simulation package (VASP), the effect of electron gain or loss in different doped Cu states in hafnium oxide (HfO2) was investigated. The electron affinity, defect formation energy, and charge density difference suggest that Cu doping results in a loss of electrons, thereby stabilizing the system. The population, the isosurface of partial charge density, and the migration barrier of the Cu-doped systems with different ionic valence states (+2 and 0) were calculated. Furthermore, the impact of doping ions on the formation of conductive filaments and the stability of the system were investigated in this study. The results indicate that the average population of the Cu-doped (+2) system is smaller than that of the Cu (0) system, and the Cu-O bond length increases in the Cu-doped (+2) system. At the same isosurface level, the electronic local clusters in the Cu (+2) system are stable; however, by increasing the isosurface level, the conductive filament of the Cu (0) system breaks first. At the same starting and ending positions, the migration barrier of the Cu (+2) system was much lower. In the transition state of the Cu (+2) system, the number of atoms whose atomic structure changes by more than 0.1 Å is lower than that in the Cu (0) system, which has a relatively small displacement deviation. This study, which indicates that the Cu (+2) system helps to form conductive channels upon applying current or voltage, can provide theoretical guidance for preparing RRAM and improving its performance.

Changes in the Structural Parameters and Effective Magnetic Moment of Eu2−xCexCuO4+α−δ by Zn Substitution

The effect of nonmagnetic Zn impurities on the structural parameters and effective magnetic moment of electron-doped superconducting cuprates Eu2−xCexCu1−yZnyO4+α−δ (ECCZO) with x = 0.10 and 0.15 and y = 0 and 0.01 has been investigated using XRD and SQUID measurements. From XRD measurements, it is found that the lattice parameter of c and the Cu-O bond length increase with increasing y. The crystallite size of ECCZO samples was relatively smaller than the sample without impurities determined by the Debye–Scherrer equation and the W-H Plot method. Changes in the lattice parameters of c and Cu-O bond length can affect the appearance of superconductivity (Tc). The smaller the value of the lattice parameter of c and the Cu-O bond length causes the distance between the conducting layer and the charge reservoir to be close enough so that the charge transfer process becomes easier. From the magnetic susceptibility measurement, paramagnetic characteristics were observed for samples with x = 0.10. Meanwhile, for samples with x = 0.15, diamagnetic characteristics can be identified in sample with y = 0. The onset of Tc was observed around 11 K, as indicated by a change from paramagnetic to diamagnetic characteristics. The superconductivity phase disappears with y = 0.01. The effective magnetic moments in samples with y = 0 are smaller than those in samples with y = 0.01. The effective magnetic moment in ECCZO can be contributed by Cu2+. When the amount of Cu2+ decreases due to the addition of nonmagnetic Zn2+ atoms, the overall effective magnetic moment value also decreases. Another possibility that causes a decrease in the value of the magnetic moment of the ECCZO is the existence of stripe-pinning model, which results in suppressed superconductivity by Zn.

Structural Properties and Hopping Conduction in the Normal State of Electron-Doped Superconductor Cuprate Eu2-x Ce x CuO4+α-δ.

Electron-doped superconducting cuprate of Eu2–xCexCuO4+α–δ has been studied in the whole doping regime from x = 0.10–0.20 with reducing oxygen content to investigate the relation between the crystal structure and the hopping conduction in the normal state. Parameter of the crystal structure has been extracted from the X-ray diffraction (XRD) measurement while hopping conduction parameters have been obtained from resistivity measurements. The Eu–O bond length decreases with the increasing doping concentration, indicating the successful doping by the partial replacing of Eu3+ with Ce4+. The resistivity increases with decreasing temperature in all measured samples. This is an indication of bad metal-like behavior in the whole regime in the normal state of electron-doped superconducting cuprate of Eu2–xCexCuO4+α–δ. The temperature dependence of resistivity was analyzed by the Arrhenius law and the variable range hopping model. It is found that the hopping conduction mechanism more likely follows the variable range hopping rather than the Arrhenius law, indicating that the hopping mechanism occurs in three dimensions. The Cu–O bond length probably plays an important role in decreasing the activation energy. The decreasing value of the activation energy correlates with the increase in the localization radius.

Structural and Magnetic Characterization of Homo- and Heterometallic Trinuclear Ni(II) and Cu(II) Clusters with N2O6 Acyclic Polydentate Ligand

Homo- and heterometallic trinuclear complexes with an acyclic N2O6-type ligand, [Ni3(L)2(CH3COO)2]·H2O·MeOH (1) and [NiCu2(L)2(CH3COO)2]·3H2O (2) (H2L = N,N′-(hexane-1,6-diyl)bis(2-hydroxy-3-methoxybenzamide), were prepared, respectively, of which crystal structures as well as magnetic properties were characterized. The axial Cu-O bond lengths in complex 2 are 2.338–2.413 Å, unlike Ni-O, due to the axial bond elongation by the Jahn-Teller effect in Cu(II) complexes. Magnetic analyses revealed that both complexes showed intra-cluster ferromagnetic interactions with S = 3 for 1 and S = 2 for 2, respectively.

Two-band conduction and nesting instabilities in superconducting Ba2CuO3+δ : First-principles study

First principles investigations of the high temperature superconducting system Ba$_2$CuO$_{3+\delta}$, recently discovered at $\delta\approx0.2$ at $T_c=70$ K, are applied to demonstrate the effects of oxygen ordering on the electronic and magnetic properties. The observed `highly over-doped' superconducting phase displays stretched Cu-planar oxygen O$_{\rm P}$ distances and anomalously shortened Cu-apical O$_{\rm A}$ separations compared with other cuprates. The stoichiometric system $\delta=0$, with its strongly one-dimensional (1D) Cu-O$_{\rm P}$ chain structure, when nonmagnetic shows 1D Fermi surfaces that lead, within density functional theory, to antiferromagnetic Cu-O$_{\rm P}$ chains (a spin-Peierls instability). Accounting for 1D fluctuations and small interchain coupling according to the theory of Schulz indicates this system, like Sr$_2$CuO$_3$, is near the 1D Luttinger-liquid quantum critical phase. The unusual Cu-O bond lengths per se have limited effects on other properties for $\delta$=0. We find that a `doubled bilayer' structure of alternating Cu-O$_{\rm P}$ chains and wide rung Cu$_3$O$_4$ ladders is the energetically preferred one of three possibilities where the additional oxygen ions bridge Cu-O$_{\rm P}$ chains in the superconducting phase $\delta=1/4$. Nominal formal valences of the three Cu sites are discussed. The six-fold (octahedral) site is the most highly oxidized, accepting somewhat more holes in the $d_{z^2}$ orbital than in the $d_{x^2-y^2}$ orbital. The implication is that two-band physics is involved in the pairing mechanism and the superconducting carriers. The Fermi surfaces of this metallic bilayer structure show both 1D and 2D strong (incipient) nesting instabilities, possibly accounting for the lack of clean single-phase samples based on this structure and suggesting importance for the pairing mechanism.

Synthesis of Cu2O Nanostructures with Tunable Crystal Facets for Electrochemical CO2 Reduction to Alcohols.

Electrochemical CO2 reduction enables the conversion of intermittent renewable energy to value-added chemicals and fuel, presenting a promising strategy to relieve CO2 emission and achieve clean energy storage. In this work, we developed nanosized Cu2O catalysts using the hydrothermal method for electrochemical CO2 reduction to alcohols. Cu2O nanoparticles (NPs) of various morphologies that were enclosed with different crystal facets, named as Cu2O-c (cubic structure with (100) facets), Cu2O-o (octahedron structure with (111) facets), Cu2O-t (truncated octahedron structure with both (100) and (111) facets), and Cu2O-u (urchin-like structure with (100), (220), and (222) facets), were prepared by regulating the content of a polyvinyl pyrrolidone (PVP) template. The electrochemical CO2 reduction performance of the different Cu2O NPs was evaluated in the CO2-saturated 0.5 M KHCO3 electrolyte. The as-synthesized Cu2O nanostructures were capable of reducing CO2 to produce alcohols including methanol, ethanol, and isopropanol. The alcohol selectivity of the different Cu2O NPs followed the order of Cu2O-t < Cu2O-u < Cu2O-c < Cu2O-o (with the total Faradaic efficiencies of alcohol products of 10.7, 25.0, 26.2, and 35.4%). The facet-dependent effects were associated with the varied concentrations of oxygen-vacancy defects, different energy barriers of CO2 reduction, and distinct Cu-O bond lengths over the different crystal facets. The desired Cu2O-o catalyst exhibited good reduction activity with the highest partial current density of 0.51 mA/cm2 for alcohols. The Faradaic efficiencies of alcohol products were 4.9% for methanol, 17.9% for ethanol, and 12.6% for isopropanol. The good electrochemical CO2 reduction performance was also associated with the surface reconstruction of Cu2O, which endowed the catalyst with abundant Cu0 and Cu+ sites for promoted CO2 activation and stabilized CO* adsorption for enhanced C-C coupling. This work will provide a new route for enhancing the alcohol selectivity of nanostructured Cu2O catalysts by crystal facet engineering.

Effect of Co doping in tailoring the crystallite size, surface morphology and optical band gap of CuO thin films prepared via thermal spray pyrolysis

In this paper, we reported the nonmagnetic semiconductor to half metal transition behavior of Co doped CuO (CCO) thin films with p-to n-type characteristics for the first time. The thin films are prepared using a thermal spray pyrolysis technique with variations of Co doping concentration from 0 to 8 at.% in the steps of 2 at.%. Subsequently, the surface morphological, structural, optical, electrical properties and electronic band structures by density functional theory (DFT) have been studied intensively. The surface morphology of the CCO thin films is significantly influenced by Co doping concentrations and agglomerated spherical grains are formed, as indicated by field emission scanning electron microscopy (FESEM). The quantitative analysis is carried out by the energy dispersive X-ray (EDX) analysis that confirms the presence of Cu, O and Co atoms. X-ray diffraction (XRD) reveals all the deposited CCO thin films are belong to monoclinic structure with mixed phases, and average crystallite size shrinkages from 28.67 to 18.96 nm with Co doping concentrations. The optical transmittance and the band gap decrease noticeably from 85% to 58%, and 3.00 to 1.98 eV, respectively. Several significant optical parameters such as Urbach energy, steepness parameter, electron–phonon interaction, refractive index, dielectric constant and static dielectric constant is examined. Enhancement of Cu-O bond length is determined and found similarities between the Rietveld refinement and DFT studies. With the spin polarized density of state (DOS), polarized value lies between 0 and above 1 which confirms that semiconductor to half metal phase transition. Using the Hall Effect measurement, p- to n-type conductivity is determined, and finally a lower resistivity and mobility is found to be 07.83×10−3 Ω cm and 0.003 cm2V−1s−1, respectively at 8 at.% CCO thin film. Thus, the above results depict that 8 at.% of CCO thin films may have potential application in the field of spintronic and optoelectronic devices.

Equilibrium Cu isotope fractionation in copper minerals: a first-principles study

Copper is of importance in geosciences, biosciences, and industry. Its isotopes can be used to study planetary processes, trace Cu biogeochemical cycling, identify the type of Cu-bearing ore minerals, investigate the formation of ore deposits, and explore concealed ore-bodies. However, Cu isotope fractionation parameters of the majority of copper minerals remain poorly known, impeding the application of Cu isotopes as a geochemical tracer. In this study, the first-principles methods are used to compute Cu isotope fractionation parameters of chalcocite (Cu2S), covellite (CuS), villamaninite (CuS2), chalcopyrite (CuFeS2), cubanite (CuFe2S3), bornite (Cu5FeS4), cuprite (Cu2O), malachite (Cu2(CO3)(OH)2), azurite (Cu3(CO3)2(OH)2), antlerite (Cu3(SO4)(OH)4), brochantite (Cu4(SO4)(OH)6), liebauite (Ca3Cu5Si9O26), Cu-bearing enstatite (Mg31/16Cu1/16Si2O6), and native copper (Cu). The reduced partition function ratio of 65Cu/63Cu (103 ln β65−63) decreases in the order of Cu silicates > Cu carbonates > Cu sulfates > Cu oxide > native Cu > Cu sulfides. The103 ln β65−63values of these minerals display a weak correlation with oxidation state and Cu coordination number, while display a strong correlation with the average Cu-S bond lengths in Cu sulfides and the average Cu-O bond lengths in Cu oxysalt minerals with the same Cu coordination number. For Cu2S and Cu5FeS4 polymorphs, the extent of Cu isotope fractionation arising from polymorphic transformations is different. Our calculated results are useful for understanding the enrichment of Cu isotopes in nature. Cu isotope fractionation between sulfides and silicates may be a potential geothermometer.

Strain-induced local structural change and its effect on the superconducting properties of GdBa2Cu3O7-x /La0.7Sr0.3MnO3 heterostructure

The effect of ferromagnetic buffer layer on the superconducting properties of relatively thick, high temperature superconductors is investigated. Elaborately designed heterostructure films consisting of epitaxial GdBa2Cu3O7-x (GdBCO) on top of two types of La0.7Sr0.3MnO3 (LSMO) layer and particles, were fabricated by pulsed laser deposition. Unlike a typical superconducting/ferromagnetic system where the superconducting properties are degraded, the superconducting properties of our GdBCO/LSMO system are enhanced depending on the local structural details of the GdBCO and LSMO layers. The strain state of GdBCO characterized from the bond length of the Cu-O and the Mn-O bonds lengths is observed to vary depending on the formation of LSMO. The phase diagram of Tc for the GdBCO/LSMO system established by the micro-strain of the Cu-O bond-length shows that Tc reaches its maximum at the critical micro-strain. This result suggests the importance of strain state in improving the superconducting properties of thick-GdBCO/LSMO films.

3D domain swapping of azurin from Alcaligenes xylosoxidans.

Protein oligomers have gained interest, owing to their increased knowledge in cells and promising utilization for future materials. Various proteins have been shown to 3D domain swap, but there has been no domain swapping report on a blue copper protein. Here, we found that azurin from Alcaligenes xylosoxidans oligomerizes by the procedure of 2,2,2-trifluoroethanol addition to Cu(i)-azurin at pH 5.0, lyophilization, and dissolution at pH 7.0, whereas it slightly oligomerizes when using Cu(ii)-azurin. The amount of high order oligomers increased with the addition of Cu(ii) ions to the dissolution process of a similar procedure for apoazurin, indicating that Cu(ii) ions enhance azurin oligomerization. The ratio of the absorbance at 460 nm to that at ∼620 nm of the azurin dimer (Abs460/Abs618 = 0.113) was higher than that of the monomer (Abs460/Abs622 = 0.067) and the EPR A‖ value of the dimer (5.85 mT) was slightly smaller than that of the monomer (5.95 mT), indicating a slightly more rhombic copper coordination for the dimer. The redox potential of the azurin dimer was 342 ± 5 mV vs. NHE, which was 50 mV higher than that of the monomer. According to X-ray crystal analysis, the azurin dimer exhibited a domain-swapped structure, where the N-terminal region containing three β-strands was exchanged between protomers. The copper coordination structure was tetrahedrally distorted in the azurin dimer, similar to that in the monomer; however, the Cu-O(Gly45) bond length was longer for the dimer (monomer, 2.46-2.59 Å; dimer, 2.98-3.25 Å). These results open the door for designing oligomers of blue copper proteins by domain swapping.

The first structural characterization of the proton-ated aza-cyclam ligand in catena-poly[[[(perchlorato)copper(II)]-μ-3-(3-carb-oxy-prop-yl)-1,5,8,12-tetra-aza-3-azonia-cyclo-tetra-deca-ne] bis-(per-chlorate)

The asymmetric unit of the title com-pound, catena-poly[[[(perchlorato-κO)copper(II)]-μ-3-(3-carb-oxy-prop-yl)-1,5,8,12-tetra-aza-3-azonia-cyclo-tetra-decane-κ4 N 1,N 5,N 8,N 12] bis-(per-chlorate)], {[Cu(C13H30N5O2)(ClO4)](ClO4)2} n , (I), consists of a macrocyclic cation, one coordinated per-chlorate anion and two per-chlorate ions as counter-anions. The metal ion is coordinated in a tetra-gonally distorted octa-hedral geometry by the four secondary N atoms of the macrocyclic ligand, the mutually trans O atoms of the per-chlorate anion and the carbonyl O atom of the protonated carb-oxy-lic acid group of a neighbouring cation. The average equatorial Cu-N bond lengths [2.01 (6) Å] are significantly shorter than the axial Cu-O bond lengths [2.379 (8) Å for carboxyl-ate and average 2.62 (7) Å for disordered per-chlorate]. The coordinated macrocyclic ligand in (I) adopts the most energetically favourable trans-III conformation with an equatorial orientation of the substituent at the protonated distal 3-position N atom in a six-membered chelate ring. The coordination of the carb-oxy-lic acid group of the cation to a neighbouring com-plex unit results in the formation of infinite chains running along the b-axis direction, which are cross-linked by N-H⋯O hydrogen bonds between the secondary amine groups of the macrocycle and O atoms of the per-chlorate counter-anions to form sheets lying parallel to the (001) plane. Additionally, the extended structure of (I) is consolidated by numerous intra- and interchain C-H⋯O contacts.