Cu-Cu Bond Research Articles

Magnetic short-range order in CuO2 planes of high-Tc superconductors.

The electronic and magnetic structure at the ${\mathrm{CuO}}_{2}$ planes of high-${\mathit{T}}_{\mathit{c}}$ oxides as a function of hole doping is analyzed. The Emery model is solved in a mean-field approximation that includes spin correlations between copper atoms. It is found that the long-range antiferromagnetic order is destroyed with 0.025 extra holes per unit cell, while the magnetic moments of Cu are slightly reduced in the disordered phase. The antiferromagnetic long-range order is lost by the presence of ferromagnetic Cu-Cu bonds with the bridging oxygen atoms antiferromagnetically aligned with respect to them. For doping doses corresponding to the superconducting phase, the short-range antiferromagnetic correlations between Cu atoms are not completely lost, as is the case experimentally.

Crystal and molecular structure of the tetracyanato-bis(phenanthroline)copper(II) complex

At room temperature, the [Cu2(NCO)4(phen)2] complex possessed monoclinic symmetry, P21/n, with the unit cell parameters a = 0.7757(3) nm, b = 1.3563(5) nm, c = 1.1555(4) nm, β = 96.92(2)°, Z = 2. The central atom is involved in tetragonal pyramidal coordination comprising the CuN4Cu’ chromophor. The nitrogen atoms of the cyanate and phenanthroline ligands are in a square planar arrangement, from which the central copper atom is displaced in the axial direction. Through the Cu-Cu bond (0.320 nm), the [Cu(NCO)2(phen)] formula units are linked into centrosymmetric units, which in the crystal structure lie in parallel layers. The occurrence of the Cu-Cu bond can account for the fact that only one molecule of the heterocyclic ligand can be coordinated.

An in-situ surface EXAFS study of copper underpotential deposition on Pt (111): Part I. The observation of strong in-plane scattering at submonolayer coverage

The underpotential deposition of copper from a dilute (50 μM) aqueous solution of Cu 2+ on an iodine pretreated Pt (111) electrode has been studied using fluorescence detected surface EXAFS (extended X-ray absorption fine structure) with the plane of polarization of the X-ray beam parallel to the electrode surface. It was found that at coverages of copper of about 0.3 monolayer, the absorption fine structure at the Cu K edge was very pronounced, yielding a Cu-Cu bond length of about 0.288 ± 0.004 nm. The intensity of the EXAFS oscillations and near edge structure suggested a high number of copper backscatterers in the first coordination shell. The data are interpreted in terms of a model where clustering or nucleation occurs on certain regions of the electrode surface.

Modification of Cu-H bonding near a Ru(0001) surface

Surface linearized augmented plane wave (SLAPW) total energy calculations are used to study differences between Cu-H bonding on Cu(111) and on a pseudomorphic Cu monolayer on a Ru(0001) substrate. Bond lengths and vibration frequencies for H(1×1)/Cu(1×1)/Ru(0001) versus H(1×1)/Cu(111) roughly obey an “effective medium” picture: the H atoms prefer to reside at a particular clean-surface charge density (0.013-0.015 au), and vibrate along the surface normal with a frequency, ω ⊥, proportional to the local, clean-surface normal charge density gradient. This results in a predicted 20% reduction of ω ⊥ on Cu(1×1)/Ru(0001) surface relative to ω ⊥ for Cu(111). At the same time, the weakening of the Cu-Cu bond when a Cu(111) layer is strained to fit pseudomorphically on Ru(0001) is partially compensated by the fact that the Cu-Ru bonding is stronger than Cu-Cu. Thus the binding energy of a H monolayer on Cu(1×1)/Ru(0001) is calculated to be only 0.05 eV/H greater than on Cu(111).

Modification of Cu-H bonding near a Ru(0001) surface

Surface linearized augmented plane wave (SLAPW) total energy calculations are used to study differences between Cu-H bonding on Cu(111) and on a pseudomorphic Cu monolayer on a Ru(0001) substrate. Bond lengths and vibration frequencies for H(1 × 1)/ Cu(1 × 1) Ru(0001) versus H(1 × 1) Cu(111) roughly obey an “effective medium” picture: the H atoms prefer to reside at a particular clean-surface charge density (0.013–0.015 au), and vibrate along the surface normal with a frequency, ω ⊥, proportional to the local, clean-surface normal charge density gradient. This results in a predicted 20% reduction of ω ⊥ on Cu(1 × 1) Ru(0001) surface relative to ω ⊥ for Cu(111). At the same time, the weakening of the Cu-Cu bond when a Cu(111) layer is strained to fit pseudomorphically on Ru(0001) is partially compensated by the fact that the Cu-Ru bonding is stronger than Cu-Cu. Thus the binding energy of a H monolayer on Cu(1 × 1) Ru(0001) is calculated to be only 0.05 eV H greater than on Cu(111).

ChemInform Abstract: X‐RAY CRYSTAL STRUCTURES OF SOME ADDUCTS OF DIMERIC COPPER(II) ACETATE. NATURE OF THE COPPER‐COPPER INTERACTION

The crystal structures of the adducts of $CU_2(OCOCH_3)_4$ with methanol (l), acetic acid (2), dimethylformamide (3), and 1,4-diazabicyclo[2.2.2]octane (4) have been determined using single-crystal X-ray diffraction methods. The compounds are isostructural with that of $CU_2(OCOCH_3)_4.2H_2O$ with the water molecules in the axial positions being replaced by the respective ligands. The ligand 1,4-diazabicyclo[2.2.2]octane bridges two dimer units producing a chain structure, in which this ligand is disorderedm around the N-N axis. Crystal data : (I), monoclinic, space group $P2_1/n$, a = 8.129(2), b = 7.447(1), c = 13.332(1) \AA, \beta = 92.21$(1)^o$, and Z = 2 ; (2), space group, $P2_1/n$, a = 15.153(2), b = 7.772(1), c = 8.229(1) \AA, \beta = $103.08(1)^o$, and Z = 2; (3), triclinic, space group $P^-_1$, a = 8.002(1), b = 8.140(1), c = 9.394(2) \AA, \alpha = 105.85(2), \beta = 92.31 (2), \gamma = $113.84(1)^o$, and Z = 1; (4), monoclinic, space group A2/m, a = 7.709(7), b = 15.490(8), c = 8.1 72(3) \AA, \beta = $105.51 (5)^o$, and Z = 2. The structures have been solved by the heavy-atom method and refined to R values of 0.041 (l), 0.029 (2), 0.032 (3), and 0.065 (4) using, respectively, 1 787, 1 892, 1 600, and 594 diffractometer-measured intensities. The X-ray crystallographic results together with literature data have been utilised to examine a general relationship between the donor ability of the axial ligands and the length of the Cu-Cu bond and draw some conclusions regarding the nature of this bond.

The extended X-ray absorption fine structure in the reflectivity at the K edge of Cu

The reflectivity of a polycrystalline thin Cu film has been measured around the critical angle of total reflection and around the Cu K edge energy. The relation of the extended X-ray absorption fine structure (EXAFS) to the fine structure observed in the reflectivity above K edge energy is discussed in view of the evaluation of structural parameters of the surface near regions from the reflectivity spectra. The analysis of reflectivity fine structure spectra can be performed by techniques developed for the investigation of EXAFS spectra with additional phaseshift and amplitude functions entering the analysis of the reflectivity spectra. These quantities have been calculated from experiment and agree well with theory. The next-nearest Cu-Cu bond length in the surface region of Cu has been found to agree with the bulk value to within 0.01 AA.

アミノポリカルボン酸・金属錯体の電気分析化学

The increasing use of chelating reagent in analytical chemistry has created a demand for reliable values of equilibrium constants. Modern chelating ageants (TTHA: tetraethylentetraaminehexaacetic acid, TPHA : tetraethylenepentaamineheptaaceticacid) often contain a large number of coordination center, which means that in addition to normal chelates, they may form also mono- and diprotonated uni- nuclear and binuclear chelates. 1) pM and pH measurement (Stability constants) Ringbom's new method for the calculation of the stability constant of their chelate complexes by the measurement of pH and pM values has been reviewed. The method, which is based on a consistent use of side-reaction coefficient, is applicable to systems containing a large number of complexes. For example, the stability constants of mononuclear, binuclear and tinuclear silver complexes of TTHA are calculated. The constant KM, LMLL is given by eq. (1). log KM, LML=pM0.5+logαL(H)-logαML(H, OH)(1)The last term of eq. (1), log ML(H, OH), is zero if no acid or basic complex is formed by ML. The values of log KKM, L(ML)L are given in the forth column of Table 1 and plotted as a function of pH in Fig. 1.The formation of mixed complexes by metal ion and two competing ligand has been atracted interest in recent years. It was found that the 2: 1 HgTTHA chelate formed reacted with the buffer to form complexes of the type Hg2XA2hich X denotes the anion of TTHA and A-the secondary ligand (ammonia, irnidazole, urotropin). A method for the determination of the stability constants of mixed ligand complexes of metals is described. It is also interesting that the ion selective electrodes working as indicator electrode and lead (IV) acetate have been used in the TTHA titration. 2) Determination of a composition and structures of the chelates with TTHA or TPHA. On the basis of nuclear magnetic resonance (n.m.r.) spectroscopy, plausible solution structures are proposed. Resolution of structure of metal-chelates is the most important thing for analytical chemist. The preferable protonation sites determined in TPHA, TTHA, and metal-TPHA chelates by means of n.m.r. spectroscopy are summarized (Fig. 5 and 6). The possible instantaneous configurations (at various pH values) of the metal-TPHA complexes are also proposed (Fig. 7). For TTHAthe chemical shifts of the various proton are calculated by eq. (l4)-(2l). By the development in the esr theory for the determination of the distance between the copper ion in polynuclear species, two major structural possibilities presented by the binding sites of TTHA chelates are shown by the structures Fig. 8.a and 8.b (Cu-Cu bond length-5.5 A). An interesting series of synthetic chelating reagents that illustrated as the analogs of NTA and EDTA in the behaviour is listed in Table 7. Inspection of these stability data shows that the stabilities increase up to the point (DTPA for Ni (II), Cu (II), Zn (II)) and decrease slightly (TTHA and TPHA), according to the number of donor group and negative charges of the ligands increase. This behavior is characteristic of the increasing the number of coordinate bonds formed, which reaches a limit, when the number of donor groups matches the characteristic coordination number of the metal ion. Cu (II), has the lower coordination numbers (i.e., 6), while the coordination numbers of Th (IV) are believed to be much high (i.e., 8). The fact is indicated that the increasing number of donor groups of the ligand beyond 6 greatly increases the stabilities of the chelates formed. .The stability constant of the 1: 1 metal (II)-TPHA normal complex is lower than the corresponding constants of the EDTA, DTPA, TTHA chelates by 3-4 logarithmic units. The following reasons are proposed: