X-ray photoelectron spectroscopic studies of the charged state of 3d metal ions in CuCr1?xVxS2 (x = 0–0.4)

The charged state of the 3d metal ions in layered cation-substituted disulfides CuCr_1−x V _x S₂ was studied by X-ray photoelectron spectroscopy. An analysis of the energy positions and structure of the Cu2p _3/2 and Cr2p _3/2 X-ray photoelectron lines showed that the corresponding polycrystalline samples of CuCr_1−x V _x S₂ contained mixed-valence chromium and copper ions. It was shown that the charged states of chromium and copper ions depended on the concentration of vanadium cations (x). The presence of mixed-valence Cu¹⁺ and Cu²⁺ ions in CuCr_1−x V _x S₂ may be correlated with the crystal structure of the corresponding layered disulfides. Original Russian Text Copyright ? 2009 by L. N. Mazalov, V. V. Sokolov, N. A. Kryuchkova, E. I. Vovk, I. Yu. Filatova, and G. M. Abramova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 461–467, May–June, 2009.     

UV/Vis Spectroscopy of Copper Formate Clusters: Insight into Metal-Ligand Photochemistry

The electronic structure and photochemistry of copper formate clusters, Cu^I₂(HCO₂)₃⁻ and Cu^II_n(HCO₂)_2n+1⁻, n≤8, are investigated in the gas phase by using UV/Vis spectroscopy in combination with quantum chemical calculations. A clear difference in the spectra of clusters with Cu^I and Cu^II copper ions is observed. For the Cu^I species, transitions between copper d and s/p orbitals are recorded. For stoichiometric Cu^II formate clusters, the spectra are dominated by copper d–d transitions and charge-transfer excitations from formate to the vacant copper d orbital. Calculations reveal the existence of several energetically low-lying isomers, and the energetic position of the electronic transitions depends strongly on the specific isomer. The oxidation state of the copper centers governs the photochemistry. In Cu^II(HCO₂)₃⁻, fast internal conversion into the electronic ground state is observed, leading to statistical dissociation; for charge-transfer excitations, specific excited-state reaction channels are observed in addition, such as formyloxyl radical loss. In Cu^I₂(HCO₂)₃⁻, the system relaxes to a local minimum on an excited-state potential-energy surface and might undergo fluorescence or reach a conical intersection to the ground state; in both cases, this provides substantial energy for statistical decomposition. Alternatively, a Cu^II(HCO₂)₃Cu⁰⁻ biradical structure is formed in the excited state, which gives rise to the photochemical loss of a neutral copper atom.     

Magnetic separation of heavy metal ions and evaluation based on surface‐enhanced Raman spectroscopy: Copper(II) ions as a case study

A new approach was developed for the magnetic separation of copper(II) ions with easy operation and high efficiency. p‐Mercaptobenzoic acid served as the modified tag of Fe₂O₃@Au nanoparticles both for the chelation ligand and Raman reporter. Through the chelation between the copper(II) ions and carboxyl groups on the gold shell, the Fe₂O₃@Au nanoparticles aggregated to form networks that were enriched and separated from the solution by a magnet. A significant decrease in the concentration of copper(II) ions in the supernatant solution was observed. An extremely sensitive method based on surface‐enhanced Raman spectroscopy was employed to detect free copper(II) ions that remained after the magnetic separation, and thus to evaluate the separation efficiency. The results indicated the intensities of the surface‐enhanced Raman spectroscopy bands from p‐mercaptobenzoic acid were dependent on the concentration of copper(II) ions, and the concentration was decreased by several orders of magnitude after the magnetic separation. The present protocol effectively decreased the total amount of heavy metal ions in the solution. This approach opens a potential application in the magnetic separation and highly sensitive detection of heavy metal ions.     

State of the copper ions in the catalysts for oxidation of carbon monoxide to carbon dioxide

The state of the copper ions in the catalysts for the oxidation of carbon monoxide to carbon dioxide, prepared by dissolving an activated copper-containing aluminum alloy in water followed by calcination (method A) and by impregnation of the support produced by dissolving activated aluminum in water with copper nitrate solution (method B), was investigated by diffuse reflection electronic spectroscopy. It was established that the catalysts contain Cu ²⁺ ions stabilized in fields of octahedral symmetry. The concentration of these ions depends on the method of synthesis of the catalyst, its copper content, and the pretreatment temperature. It is higher in the samples produced by impregnation than in the samples produced by fusion; increase in the amount of copper leads to a decrease while increase in the calcination temperature leads to an increase in the concentration of the above-mentioned ions. Treatment of the oxide systems with the reaction mixture does not affect the state and concentration of Cu ²⁺. The catalytic activity of the samples depends on the method of preparation and increases with decrease in the amount of Cu ²⁺ (O_h) and with increase in the content of the CuO phase in the system.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 786–790, April, 1992.     

Copper passivity and its breakdown in sodium bicarbonate solutions: A scanning electron microscopy and x-ray photoelectron and auger spectroscopy study

Effect of bicarbonate ions on the copper passivity and its local breakdown is studied by cyclic voltammetry, Auger spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. Comparing data for solutions with various sodium bicarbonate concentrations shows copper to undergo pitting in 0.02 M NaHCO₃, whereas it remains stably passive in 0.10 M NaHCO₃. Independent studies suggest that carbonates play a protective role in stabilization of the oxide-hydroxide passive film on copper.     

非水体系中苯并三唑在铜电极上吸附的电化学表面增强拉曼光谱研究

采用电化学现场表面增强拉曼光谱(SERS)研究了非水体系中苯并三唑(BTAH)在铜电极上的吸附及成膜行为, 结果表明非水体系中BTAH的吸附行为随电位变化而不同. 较负电位区间主要以中性分子形式吸附; 中间电位区间主要以BTA^－吸附并不可逆成膜; 而在氧化电位区间主要表现为铜的氧化. 随中性配体三苯基膦(pph₃)的加入, 在中间电位区间, 由于易溶的Cu(pph₃)_n⁺的生成而使铜的溶解速度加快, 最终该阳离子在溶液中和BTA^-作用而生成了多核铜的配合物. 采用直接电化学方法模拟电极表面过程合成了相应的吸附产物, 并对其组成进行了相关表征.     

Spectroscopic study of ternary copper(II) complexes on a silica surface

The formation of ternary surface complexes of copper(II) with one or two molecules of 2,2′-bipyridine (bpy) or α-picolinic acid (Hpic), which were obtained after adsorption on the silica surface in different ways, was studied by electronic and ESR spectroscopy. Coordination of the ligands, which were preliminarily adsorbed by copper ions, afforded only 1∶1 ternary surface complexes. In both cases, coordinatively more saturated ternary surface complexes were formed only when Cu(bpy)₂ ²⁺ and Cu(pic)₂ were adsorbed on the SiO₂ surface from solutions. The compositions and structures of the ternary surface complexes containing bipyridine ligands are temperature independent, whereas in the picolinate-containing ternary surface complexes, the coordination spheres of the adsorbed complexes are rearranged as the temperature changes. Presented at the First Moscow Workshop on Highly Organized Catalytic Systems (June 19, 1997). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1765–1771, October, 1997.     

Copper Complexes Stabilized by Chitosans: Peculiarities of the Structure,Redox, and Catalytic Properties

Peculiarities of the structure and physicochemical properties of copper–chitosan complexes prepared by different methods were studied by IR, UV-visible, ESR spectroscopy, and electron microscopy. The catalytic activity of redox copper centers stabilized by the chitosan matrix in the reactions of oxidation of o- and p-dihydroxybenzenes in an aqueous medium was determined. Quantitative ESR measurements provide evidence for the localization of virtually all copper ions introduced in the initial heterogeneous chitosan samples with copper contents below 1.5 wt % in the form of isolated Cu²⁺ ions in square planar coordination. The chitosan matrix was shown to strongly bind copper ions under conditions of redox transformations in the catalytic tests or upon prolonged heating in boiling water. Reoxidation of the samples with H₂O₂ results in quantitative restoration of the initial ESR signal of Cu(II). Heterogenized copper–chitosan samples exhibited high activity and stability in the catalytic oxidation of dihydroxybenzenes into quinones, whereas the homogeneous system was characterized by irreversible poisoning due to formation of copper–hydroquinone complexes. Preparation of the binary composite system with a thin heterogeneous copper–chitosan film supported on a macroporous silica allows one to dramatically enhance the specific catalytic activity and the efficiency of the active component. Such an approach may turn out to be useful in the synthesis of supported chitosan catalyst with a low noble metal content.     

Crystal Structure and Properties of Strontium Phosphate Apatite with Oxocuprate Ions in Hexagonal Channels

Strontium phosphate apatites containing different amounts of copper were prepared by a solid state reaction at 1100 °C or by arc melting above 1600 °C in air. The samples were characterized by X‐ray diffraction, ICP analysis, scanning electron microscopy, IR spectroscopy, MAS—¹H—NMR, diffuse reflectance spectroscopy, and SQUID magnetometry. X‐ray crystal structure determination was carried out for a single crystal obtained from the melt. The compound is formulated as Sr₅(PO₄)₃(CuO₂)_1/3 and has an apatite structure (space group P6₃/m, a = 9.7815(4)Å, c = 7.3018(4)Å, Z = 2) with linear CuO₂^3— ions occupying hexagonal channels. For solid state synthesized samples, Rietveld refinement of powder XRD patterns was performed. The samples obtained at 1100 °C acquire the composition Sr₅(PO₄)₃Cu_xOH_y, with x changing from 0.01 to 0.62 and y < 1—x. The copper content can be increased to x = 0.85 by annealing in argon at 950 °C. The compounds represent a hydroxyapatite in which part of the protons is substituted by Cu⁺ and Cu²⁺ ions. The ions form linear O—Cu—O units which are progressively condensed creating the Cu—O—Cu bridges on increasing copper content. IR and NMR data testify existence of OH groups, non‐disturbed and disturbed by neighboring Cu atoms. In the electron spectra, the samples exhibit absorption bands at 7800‐7900, 14200‐14500 and 17500‐17550 cm^—1, which were assigned to Cu²⁺ d‐electron transitions. By annealing the sample with x = 0.1 in oxygen at 800 °C copper is fully oxidized while retaining in channels in unusual for Cu²⁺ linear coordination.     

Synthesis,Crystal Structure and Spectroscopic Properties of [2,13‐Bis(1‐naphthalenylmethyl)‐5,16‐dimethyl‐2,6,13,17‐tetraazatricyclo(14,4,01.18,07.12)docosane]copper(II) Diperchlorate Acetonitrile Disolvate

The N‐functionalized macrocyclic ligand 2,13‐bis(1‐naphthalenylmethyl)‐5,16‐dimethyl‐2,6,13,17‐tetraazatricyclo(14,4,0^1.18,0^7.12)docosane (L³) and its copper(II) complex were prepared. The crystal structure of [Cu(L³)](ClO₄)₂·2CH₃CN was determined by single‐crystal X‐ray diffraction at 150 K. The copper atom, which lies on an inversion centre, has a square planar arrangement and the complex adopts a stable trans‐III configuration. The longer distance [2.081(2) Å] for Cu–N(tertiary) compared to 2.030(3) Å for Cu–N(secondary) may be due to the steric effect of the attached naphthalenylmethyl group on the tertiary nitrogen atom. Two perchlorate ions are weakly attached to copper in axial sites and are further connected to the ligand of the cation through NH ··· O hydrogen bonds [N ··· O 3.098 Å]. IR and UV/Vis spectroscopic properties are also described.     

Ubiquitin Associates with the N‐Terminal Domain of Nerve Growth Factor: The Role of Copper(II) Ions

Many biochemical pathways involving nerve growth factor (NGF), a neurotrophin with copper(II) binding abilities, are regulated by the ubiquitin (Ub) proteasome system. However, whether NGF binds Ub and the role played by copper(II) ions in modulating their interactions have not yet been investigated. Herein NMR spectroscopy, circular dichroism, ESI‐MS, and titration calorimetry are employed to characterize the interactions of NGF with Ub. NGF_1–14, which is a short model peptide encompassing the first 14 N‐terminal residues of NGF, binds the copper‐binding regions of Ub (K_D=8.6 10^?5 m ). Moreover, the peptide undergoes a random coil–polyproline type II helix structural conversion upon binding to Ub. Notably, copper(II) ions inhibit NGF_1–14/Ub interactions. Further experiments performed with the full‐length NGF confirmed the existence of a copper(II)‐dependent association between Ub and NGF and indicated that the N‐terminal domain of NGF was a valuable paradigm that recapitulated many traits of the full‐length protein.     

A Ferromagnetically Coupled (S=1) Peroxodicopper(II) Complex

Copper enzymes play important roles in the binding and activation of dioxygen in biological systems. Key copper/dioxygen intermediates have been identified and studied in synthetic analogues of the metalloprotein active sites, including the μ‐η²:η²‐peroxodicopper(II) motif relevant to type III dicopper proteins. Herein, we report the synthesis and characterization of a bioinspired dicopper system that forms a stable μ‐η¹:η¹‐peroxo complex whose Cu‐O‐O‐Cu torsion is constrained to around 90° by ligand design. This results in sizeable ferromagnetic coupling between the copper(II) ions, which is detected by magnetic measurements and HF‐EPR spectroscopy. The new dicopper peroxo system is the first with a triplet ground state, and it represents a snapshot of the initial stages of O₂ binding at type III dicopper sites.     

Copper–Carbene Intermediates in the Copper‐Catalyzed Functionalization of OH Bonds

Copper–carbene [Tp^xCu?C(Ph)(CO₂Et)] and copper–diazo adducts [Tp^xCu{η¹‐N₂C(Ph)(CO₂Et)}] have been detected and characterized in the context of the catalytic functionalization of O?H bonds through carbene insertion by using N₂?C(Ph)(CO₂Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N‐bound diazo adduct is a dormant species and is not en route to the formation of the copper–carbene intermediate.     

Infrared spectroscopy of cold trapped molecular ions using He‐tagging

This review summarizes experimental activities to study the structure of molecular ions via He tagging. The method is based on the attachment of a weakly bound helium atom to a cold ion followed by laser‐induced predissociation (LIP). Since my early involvements (it started in 1977 with a letter from Y.T. Lee), radio frequency (rf) ion traps and ion guides have been important elements in instruments dedicated to ion spectroscopy. Accumulating ions in a ring electrode trap (RET) and confining them together with the laser‐induced photofragments in a long octopole has been demonstrated in 1978 in Berkeley via photodissociation of metastable O₂⁺ ions. In the early stage of this instrument, as well as in various further developments, supersonic expansions have been used to create weakly bound complexes. An important step forward for ion spectroscopy was to push the conditions of cryogenic ion traps so far that, finally, He atoms could be attached to almost any mass‐selected ion of interest, including multiply charged ions and C₆₀⁺. Currently, modern ion storage instruments reach temperatures below 3 K and can be operated at helium densities above 10¹⁶ cm⁻³, opening up many avenues of application in spectroscopy, reaction dynamics, and analytical chemistry. In addition to a personal historical review, I discuss recent progress made with new cryogenic ion traps, especially in the field of He tagging. He‐M⁺ ions have been formed via ternary association for all kind of M⁺ ions ranging from atoms such as He⁺, N⁺, or Fe⁺ via molecules N₂⁺, VO⁺, and H₃⁺ to various polyatomic ions. The in situ synthesis of tagged ions made unique discoveries possible, such as determining the structure of doubly charged benzene, the first identification of a carrier of diffuse interstellar bands, or the characterization of the fundamental 4 electron 4 center system He–H₃⁺. In the conclusions, hints to additional applications will be given, emphasizing on the versatility of temperature‐variable ion traps.     

Comparative Analysis of a Solar Control Coating on Glass by AES, EPMA, SNMS and SIMS

 A solar control coating was analysed by different methods of surface analysis with respect to the layer sequence and the composition and thickness of each sublayer. The methods used for depth profiling were Auger electron spectroscopy, electron probe microanalysis, secondary neutral mass spectroscopy and secondary ion mass spectroscopy based on MCs⁺. The structure of the coating was unknown at first. All methods found a system of two metallic Ag layers, embedded between dielectric SnO_X layers. Additionally, thin Ni-Cr layers of 1–2 nm were detected on top of the Ag layers. Thus the detected layer sequence is SnO_X/Ni-Cr/Ag/SnO_X/Ni-Cr/Ag/SnO_X/glass. The Ni:Cr ratio in the nm-thin layers could be quantified by every method, the Cr fraction corresponding to less than one monolayer. We compare the capabilities and limitations of each method in routinely investigating this solar control coating. Importance was attached to an effective investigation. Nevertheless, by combining all methods, measuring artefacts could be uncovered and a comprehensive characterisation of the system was obtained.     

Physico‐Chemical Studies on Cu(II) Complexes of Acrylate Chelating Polymers

Abstract

Metal chelating polymers containing amide and carboxylic groups were prepared by gamma‐radiation polymerization of acrylic acid (AA) monomers in the presence of polyacrylamide (PAM). The resins obtained were loaded by copper ions and characterized by FT‐IR spectroscopy, electron spin resonance (ESR), thermogravimetric analysis (TGA), and differential scanning calorimetery (DSC). The IR spectra indicated a lower frequencies shift in the carbonyl bands due to copper ion chelation with carbonyl groups in the polymer resins. Also, the IR spectra reveal a splitting in the band at 3600–3200?cm^?1 that due to the coordination of the NH and OH groups with copper ions. The ESR spectrum was anisotropic with hyperfine structure having the following values 2.3808 and 2.07218 for g _∥ and g _⊥, respectively. These spectra for copper ions have square planar coordination with two nitrogen and two oxygen atoms. TGA and DSC studies show that radiation crosslinking and complexation with copper ion increase the thermal stability of PAM–AA resins. Meanwhile, resin complexes with copper ion showed a higher thermal stability than pure resin. The increase in thermal stability may be correlated with the metal ions coordination with NH and OH groups; this coordination prevents the splitting of ammonia and water molecules. Also, the metal ions providing a coordination crosslink between polymer chains could increase thermal stability.     

Synthesis and Structural Elucidation of N,N ’-Ditosyl-1,11-diaza-4,8,14,18-tetraselena-cycloicosane and its Copper and Platinum Complexes

The reaction of 1,2-diselenacyclopentane with N,O,O-tri-(toluene-p-sulphonate)-diethanolamine afforded a new seleno-azacrown ether, i.e. N,N′-ditosyl-1,11-diaza-4,8,14,18-tetraselena cycloicosane (1), in 19% yield, which was comprehensively characterized by elemental analysis, UV–Vis, ¹H NMR and mass spectroscopy. The reaction of 1 with copper(II) perchlorate (Cu(ClO₄)₂) and platinum(IV) tetrachloride (PtCl₄) gave its corresponding copper (2) and platinum complexes (3), respectively. The crystallographic investigations showed that the disparity of metal ion led not only to the distinct crystal system and space group, i.e. monoclinic system (C2/c) for 2 and triclinic system (P-1) for 3, but also the different coordination modes of copper and platinum ions with 1, i.e. normal coordination mode for 2 and ring-contracted coordination mode for 3. Moreover, the metal ions in the crystals 2 and 3 were found in Cu(I) and Pt(II) forms, respectively, although Cu(II) and Pt(IV) were used at the initial stage of coordination reaction.     

Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd,Y) Borate Single Crystals

Synthesized powders and grown single crystals of nominal compositions Li₆Ln(BO₃)₃:Yb³⁺ (Ln=Y, Gd) were investigated by means of powder and single‐crystal X‐ray diffraction (XRD), as well as optical near‐IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero‐phonon lines suggests the existence of two kinds of Yb³⁺ ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y³⁺. A strong temperature dependence of the intensity of Yb–Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb³⁺ is in good agreement with crystallographic ones: R=3.856 Å, R_cryst=3.849 Å.     

Copper(II) Complexes of a Hexadentate Mixed‐Donor N3S3 Macrobicyclic Cage: Facile Rearrangements and Interconversions

The potentially hexadentate mixed‐donor cage ligand 1‐methyl‐8‐amino‐3,13,16‐trithia‐6,10,19‐triazabicyclo[6.6.6]eicosane (AMME‐N₃S₃sar; sar=sarcophagine) displays variable coordination modes in a complex with copper(II). In the absence of coordinating anions, the ligand adopts a conventional hexadentate N₃S₃ binding mode in the complex [Cu(AMME‐N₃S₃sar)](ClO₄)₂ that is typical of cage ligands. This structure was determined by X‐ray crystallography and solution spectroscopy (EPR and NIR UV/Vis). However, in the presence of bromide ions in DMSO, clean conversion to a five‐coordinate bromido complex [Cu(AMME‐N₃S₃sar)Br]⁺ is observed that features a novel tetradentate (N₂S₂)‐coordinated form of the cage ligand. This copper(II) complex has also been characterized by X‐ray crystallography and solution spectroscopy. The mechanism of the reversible interconversion between the six‐ and five‐coordinated copper(II) complexes has been studied and the reaction has been resolved into two steps; the rate of the first is linearly dependent on bromide ion concentration and the second is bromide independent. Electrochemistry of both [Cu(AMME‐N₃S₃sar)]²⁺ and [Cu(AMME‐N₃S₃sar)Br]⁺ in DMSO shows that upon reduction to the monovalent state, they share a common five‐coordinated form in which the ligand is bound to copper in a tetradentate form exclusively, regardless of whether a six‐ or five‐coordinated copper(II) complex is the precursor.     

Networks based on chitosan and oxidized cyclodextrin—II. Structural and catalytic features of a copper (II)-loaded network

Chitosan is well known for its binding properties toward transition metal ions. We prepared a chemical hydrogel based on chitosan using as cross-linking agent a polyfunctionalized β-cyclodextrin and studied the structural and catalytic features of this hydrogel loaded with copper(II) ions in aqueous medium. Stability of the complex and its structural characteristics were determined by isothermal microcalorimetry and EPR spectroscopy, respectively. Kinetics of the oxidation of (d, l)-adrenaline and of l-adrenaline catalyzed by copper (II) bound to the matrix was monitored with a Clark-type O^-₂ sensitive electrode. The advantages of working with a heterogeneous system are coupled with the preservation of both structural and catalytic features of copper(II) site in the matrix with respect to copper(II) ions bound to chitosan derivatives in solution.