Cu-Cu Bond Research Articles

Syntheses, characterization, crystal structure and magnetic properties of copper(II) α,β-unsaturated carboxylate complexes with trimethyl phosphate

Two ternary complexes Cu2A4[OP(OCH3)3]2 (A represents CH2=CH-COO− and CH2= C(CH3)-COO− have been synthesized, and elemental analyses, IR, ESR, electronic reflectance spectra and magnetic studies were carried out. The single crystal X-ray diffraction shows that Cu2[CH2=C(CH3)-COO]4[OP(OCH3)3]2 is triclinic, with space group P1, a = 1.05128(13), b = 1.7559(5), c = 1.94479(3) nm, α = 91.263(14)°, β = 102.559(6)°, γ= 106.339(13)°, Z = 4 and R = 0.0668. Two copper(II) atoms are bridged by four α-methacry late groups, and each copper(II) atom is coordinated with a trimethyl phosphate molecule in the axial position, forming a distorted square pyramidal configuration. The symmetric center is between the two copper(II) atoms, and the Cu-Cu bond distance is 0.26098(6) nm. The Cu-Cu distance and magnetic studies suggest that there exist anti-ferromagnetic interactions between the two copper(II) atoms.

Weak antiferromagnetism due to Dzyaloshinskii-Moriya interaction inBa3Cu2O4Cl2

The antiferromagnetic insulating cuprate ${\mathrm{Ba}}_{3}{\mathrm{Cu}}_{2}{\mathrm{O}}_{4}{\mathrm{Cl}}_{2}$ contains folded ${\mathrm{CuO}}_{2}$ chains with four magnetic copper ions $(S=1/2)$ per unit cell. An underlying multiorbital Hubbard model is formulated and the superexchange theory is developed to derive an effective spin Hamiltonian for this cuprate. The resulting spin Hamiltonian involves a Dzyaloshinskii-Moriya term and a more weak symmetric anisotropic exchange term besides the isotropic exchange interaction. The corresponding Dzyaloshinskii-Moriya vectors of each magnetic Cu-Cu bond in the chain reveal a well defined spatial order. Both, the superexchange theory and the complementary group theoretical consideration, lead to the same conclusion on the character of this order. The analysis of the ground-state magnetic properties of the derived model leads to the prediction of an additional noncollinear modulation of the antiferromagnetic structure. This weak antiferromagnetism is restricted to one of the Cu sublattices.

Synthesis, thermal decomposition and crystal structure of copper (II) α, β-unsaturated carboxylate with urea

A detailed synthesis is described for binuclear cage ternary complexes Cu2A4 [(NH2),CO]2, where A= CH2=CH-COO− and CH2=C(CH3)-COO−. Elemental analysis and thermal analysis have been investigated. The molecular structure of Cu2, (CH2, = CH-COO)4[(NH2)2CO]2 was determined by single crystal X-ray diffraction. The material forms blue crystal with tetragronal symmetry, space group P42,/n,a =b = 1.239 35(6) nm, c = 1.398 05 (16) nm, Z = 4. There exists a magnetic exchange interaction between the two paramagnetic Cu atoms. The Cu-Cu bond length is 0.260 94 nm.

Preparation and Spectroscopic Examination of new Mixed-Ligand 1,10-Phenantroline, Piienylhydrazine and Benzidike Complexes of Co(II), Ni(II), Cu(II) and Zn(II) Saccharinates

A series of new mixed-ligand saccharin complexes of Co, Ni, Cu and Zn with 1,10-phenantroline, phenylhydrazine and benzidine have bccn prepared and characterizcd by elemental analysis magnetic moments, spectral and themial analysis techniques. 1,10-Phenantroline and phenylhydrazine are coordinated to the metal ions as chelating ligands through their two N atoms, while benzidine acts a monodentate ligand. The metal ions usually have octahedral geometry with two saccharinate anions in the trans positions and the coordinating ligand in the cis positions. The complexes of Cu(II) saccharinates with phenylhydrazinc and benzidine exhibit bimetallic dimeric structures with Cu-Cu bonds.

Further Study of Very Close Nonbonded Cu(I)-Cu(I) Contacts. Molecular Structure of a New Compound and Density Functional Theory Calculations.

A new compound containing a Cu(I)-Cu(I) unit with a short internuclear distance, 2.453(1) Å, is reported. The question of whether such a short distance justifies the postulation of a metal-metal bond is addressed using density functional theory (DFT). The new compound is Cu(2)(hpp)(2), where hpp(-) (C(7)N(3)H(12)) is the anion derived from 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine. Cu(2)(hpp)(2) crystallizes in the monoclinic space group P2(1)/c with Z = 2 and cell dimensions a = 7.320(2) Å, b = 12.418(4) Å, c = 8.689(2) Å, and beta = 93.76(2) degrees. The density functional calculations show that the close approach of the copper atoms is predictable without involving any significant amount of covalent bonding. A DFT calculation on the Cu(3)[(p-tol)N(5)(p-tol)](3) molecule also foretells the observed short Cu-Cu separation (2.35 Å observed vs 2.38 Å calculated) but, again, does not imply the formation of Cu-Cu bonds. Very short Cu(I) to Cu(I) distances can be attributed to a combination of strong Cu-N bonding and very short (ca. 2.2 Å) bite distances for the ligands.

Synthesis and Characterization of New Mixed-Ligand bis(Hydrazine) and bis(Ethylenediamine) Complexes of Cobalt, Nickel and Copper Saccharinates

The mixed-ligand saccharin complexes of Co, Ni and Cu with hydrazine and ethylenediamine have been prepared and characterized by elemental analyses, magnetic susceptibility and spectral methods. Hydrazine and ethylenediamine act as bidentate ligands through their N atoms, as expected. The metal ions usually have octahedral geometry with two hydrazine or ethylenediamine molecules and two saccharinate anions in the trans positions. The Cu(II) saccharinate with hydrazine has a bimetallic dimeric structure with Cu-Cu bonds. The Co(III) saccharinate complex with ethylenediamine is also dinuclear, but its dimeric structure is achieved with hydroxo bridges. Referee I: E. H. Wong Referee II: J. G. Wardeska

XAFS Study of CuI-Y and CuII-Y Interacting with CO and NO

We report a study of the local copper environment in Cu I -Y prepared by gas phase reaction of H-Y with CuCI and in Cu II -Y prepared by conventional ion exchange with aqueous cupric salt For the Cu I -Y sample, the effect of the interaction with CO and NO will also been reported. XANES, UV-Vis and IR (NO dosed at 77 K) techniques prove that the copper species in the prepared samples have the desired oxidation state. Reduction of Cu I -Y with CO leads to the formation of small copper clusters well identified by EXAFS, XANES and UV-Vis spectroscopies, while interaction with NO partially oxydate Cu' to Cu II . For both as prepared Cu I -Y and Cu II -Y samples EXAFS does not observe first shell Cu-Cu bond lengths, so excluding the presence of so called Cu/dimers in zeolites prepared following our methods.

Local Structural Distortions in Quenched Au-Cu Alloys

Disordered alloys Au x Cu 1-x prepared by melt spinning method were analyzed by XAFS taken at 80 K. Local atomic structure around Au and Cu atoms was measured and strong deviations from perfect fcc structure were obtained resulting from the size disparity between Au and Cu atoms. A sharp asymmetry was found between the shorter (Cu-Cu) and the longer (Au-Au) nearest neighbor bond lengths. Average first nearest neighbor distance was found greater than obtained using linear interpolation of the pure components. Results on Debye-Waller factors showed strong concentration dependence for the Cu-Cu bond, suggesting the loosening of contact between these atoms when the concentration of Au increases.

Pyridineselenolate Complexes of Copper and Indium: Precursors to CuSe(x)() and In(2)Se(3).

The pyridineselenolate (2-Se-NC(5)H(4), (SePy)) and the 3-(trimethylsilyl)pyridineselenolate (3-Me(3)Si-2-Se-NC(5)H(4) (SePy)) ligands form air-stable homoleptic coordination compounds of Cu(I) { [Cu(SePy)](4) (1) and [Cu(SePy)](4) (2)} and In(III) {In(SePy)(3) (3) and In(SePy)(3) (4)}. Mass spectroscopic characterization of the Cu(I) compounds indicated a tetrametallic core, and this was confirmed with a single-crystal X-ray structural characterization of crystalline 1 and 2, which both contain a tetrametallic cluster of Cu(I) ions bound to two doubly bridging Se atoms and a pyridine nitrogen. The Cu coordination sphere is completed with two strong Cu-Cu bonds and one weaker Cu-Cu interaction. The indium compounds 3 and 4 are each distorted fac-octahedral molecules with chelating SePy ligands. These compounds are useful low-temperature precursors to the binary selenides. Both 3 and 4 sublime intact; 3 thermally decomposes to give In(2)Se(3). The Cu clusters do not sublime intact but still decompose to give metal selenide phases: 2 decomposes to give pure alpha-CuSe at low temperatures and increasing amounts of Cu(2)(-)(x)()Se at elevated temperatures, while 3 decomposes to give a mixture of CuSe phases at all temperatures. Crystal data (Mo Kalpha: 1, 153(5) K; 2-4, 293(2) K) are as follows: 1, monoclinic space group C2/c, a = 20.643(5) Å, b = 16.967(2) Å, c = 16.025(2) Å, beta = 114.16(2) degrees, Z = 8; 2, tetragonal space group I4(1)/a, a = 14.756(3) Å, c = 19.925(3) Å, Z = 4; 3, trigonal space group P&thremacr;c1, a = 13.352(2) Å, c = 13.526(2) Å, Z = 4; 4, monoclinic space group P2(1)/c, a = 9.793(1) Å, b = 20.828(6) Å, c = 16.505(1) Å, beta = 96.69(1) degrees, Z = 4.

The CuA center of cytochrome-c oxidase: electronic structure and spectra of models compared to the properties of CuA domains.

The electronic structure and spectrum of several models of the binuclear metal site in soluble CuA domains of cytochrome-c oxidase have been calculated by the use of an extended version of the complete neglect of differential overlap/spectroscopic method. The experimental spectra have two strong transitions of nearly equal intensity around 500 nm and a near-IR transition close to 800 nm. The model that best reproduces these features consists of a dimer of two blue (type 1) copper centers, in which each Cu atom replaces the missing imidazole on the other Cu atom. Thus, both Cu atoms have one cysteine sulfur atom and one imidazole nitrogen atom as ligands, and there are no bridging ligands but a direct Cu-Cu bond. According to the calculations, the two strong bands in the visible region originate from exciton coupling of the dipoles of the two copper monomers, and the near-IR band is a charge-transfer transition between the two Cu atoms. The known amino acid sequence has been used to construct a molecular model of the CuA site by the use of a template and energy minimization. In this model, the two ligand cysteine residues are in one turn of an alpha-helix, whereas one ligand histidine is in a loop following this helix and the other one is in a beta-strand.

Comparison of two sets of parameters for multi-band Hubbard models of high-Tc compounds using ferro-antiferro mixed phases in spin disordered configurations

We compare two sets of parameters proposed in the literature for the multi-band Hubbard model of high-Tc materials, one obtained by finite cluster analyses and other with band theory calculations. The comparison is done using a configuration mixing of ferro and antiferromagnetic Cu-Cu bonds in mean-field alloy theory. Both sets give qualitatively different results concerning the magnetic phases close to half-filling. A spin disordered phase is obtained upon doping with holes. Nevertheless, quantities like magnetic moments and charge transfers are rather different reflecting the difference of density of states close to the Fermi level in both cases.

Metal-metal bonding in biology: EXAFS evidence for a 2.5 A copper-copper bond in the CuA center of cytochrome oxidase.

Evidence for a direct Cu-Cu bond in the CuA center of cytochrome oxidase is reported. Simulation of the X-ray absorption spectrum of a recombinant CuA-binding domain of Bacillus subtilis cytochrome oxidase, and comparison with a structurally characterized directly-bonding Cu(1.5) ... Cu(1.5) inorganic complex, suggests that a Cu-Cu interaction of 2.5 +/- 0.1 A together with a short 2.2 A Cu-S interaction may be present in the CuA site. In light of these data, previous interpretations of the EXAFS of a number of cytochrome oxidase and nitrous oxide reductase enzymes which modeled the 2.6 A interaction as a long Cu-S(methionine) bond are possibly incorrect. A structural model based on the new data is presented which suggests that the CuA sites in cytochrome oxidase and N2O reductase are likely composed of a pair of modified type 1 copper centers with one histidine, one cysteine, and one weakly bound ligand (Met and/or Gln) joined by a Cu-Cu bond.

Cu6Br6(NPMe3)4, ein gemischt-valenter Kupfercluster / Cu6Br6(NPMe3)4, a Mixed-Valent Cluster of Copper

Abstract Cu6Br6(NPMe3)4 has been prepared as a by-product from the reaction of CuBr with Me3SiNPMe3 in a CH2Cl2 suspension. The dark red-violet crystals, which contain three molecules CH2Cl2 per unit cell, have been characterized by a crystal structure determination. Cu6Br6(NPMe3)4 · 3 CH2Cl2: Space group P1̅, Z = 2, lattice dimensions at -95 °C: a = 1165.2(4), b = 1168.9(4), c = 1842.9(6) pm, a = 75.61(3)°, β = 84.15(3)°, γ = 61.08(2)°, 6918 observed unique reflections, R = 0.066. In the cluster molecule Cu6Br6(NPMe3)4 the copper atoms form a nearly ideal octahedron with Cu-Cu bond lengths of 268.8 pm in average. Each of the Cu atoms is con­nected with a terminal bromine atom. Four planes of the octahedron are capped by μ3-nitrogen atoms of the (NPMe3)- groups.

SYNTHESIS AND STRUCTURE OF 1,2-BIS(DIPHENYLPHOSPHINO)ETHANE COMPLEXES OF COPPER(I) ACETATE. CATALYSTS FOR THE DECARBOXYLATION OF CARBOXYLIC ACIDS

Abstract Several dimeric complexes of copper(I) acetate with bidentate phosphine ligands have been synthesized. The solid-state structure of one of these derivatives, dppe(CuO2CCH3)2, where dppe = 1,2-bis(diphenylphosphino)ethane, has been determined. The complex is shown to exist in the solid-state as a polymeric chain of dimeric copper(I) units containing a dppe and two acetate ligands, with the dimers being linked together via weaker Cu-O interactions. The Cu-Cu bond length in the dimeric units is considerably longer, at 2.712(2) A, than that observed in copper(I) acetate of 2.556(2) A. The use of these derivatives as catalyst precursors for the catalytic decarboxylation of cyanoacetic acid to acetonitrile and carbon dioxide is discussed. Crystal data for dppe(CuO2CCH3)2: space group P2i/n,a = 14.976(6) A, b = 11.676(3) A, c = 16.999(6) A, β = 107.59(3)°, Z = 4, R = 7.33%

A study of the structure and stability of SrCuO2

Abstract We have investigated the structure and stability of SrCuO2 using both lattice statics and dynamics techniques as well as molecular dynamics. Short range interatomic pair potentials were obtained using Gordon-Kim1 techniques. Lattice dynamics indicates that the infinite layer, high Tc parent structure of Azuma et. al. 2 should not be stable for this material, with the largest instabilities appearing in the plane perpendicular to the Cu-Cu bonds (i.e. in the ab plane). The ground state structure and temperature variation of physical parameters obtained from molecular dynamics simulations will be discussed, as will the effects of varying ionicity.

A STUDY OF THE CHEMISORPTION OF CH3NO2 ON Cu(lll) SURFACE

The chemisorption of CH3NO2 on Cu(111) surface has been studied by the semiempirical quantum mechanical method (CNDO/2) of cluster models. The results indicate that the bridge site of Cu(111) is preferable for CH3NO2 adsorption, the orientation of CH3NO2 adsorption is that -NO2 points downward to the Cu surface, and the angle between the plane ONO and Cu-Cu bond is 60o. The orientation of adsorption and the density of states calculated by CNDO/2 calculation are in agreement with the experimental results. The analyses of atomic orbital percentages show that CH3NO2 adsorption is the result of interaction of 2p atomic orbitals of 0 for CH3NO2 with 3d atomic orbitals of Cu.

Molecular dynamic study of grain boundary embrittlement for [101] tilt copper bicrystals induced by bismuth segregation

The selective bismuth segregation and the microprocess of fracture for the three [101] tilt copper bicrystals Σ9(2̄1̄2) 38.94°, Σ11(3̄2̄3) 50.48°, and Σ33(5̄4̄5) 58.99° have been studied by a molecular dynamics technique. The results show that the Bi segregation and the fracture behavior of the Cu-Bi bicrystals are strongly dependent on the grain boundary (GB) structure. The Bi segregation is strongly related to the polyhedra constructing the GB cores and the stress fields of the GB dislocations (GBDs), and the GB embrittlement of copper induced by the Bi segregation is determined by the segregated concentration and the distribution of Bi atoms. With the increase of the relative number of pentagonal bipyramids and the localization of the stress fields of the GBDs in the GBs, the bicrystals Σ9, Σ11, and Σ33 show a decreasing propensity for the Bi segregation and subsequent different fracture behaviors. The severe intergranular brittle fracture that happens in the Σ9 bicrystal is mainly caused by the breaking of weakened Cu-Cu bonds, which is related to the highly concentrated Bi segregation at the GB core. In the case of the Σ11 bicrystal, the segregation of Bi atoms at the GB shows an inhomogeneous distribution characteristic, so that the fracture is intergranular but with a large amount of shear deformation. The transgranular fraction that appears in the Σ33 bicrystal is related to the low concentration of the Bi segregation and the dispersive distribution of the Bi atoms along the GB and in the grains.

MAGNETIC ORIGIN OF THE PHASE SEPARATION IN La2CuO4+δ

A model for the phenomenon of phase separation in La 2 CuO 4+δ is proposed. The model is studied by the Monte Carlo simulation. The phase separation is obtained and completely accounted for by magnetic effects. A hole induced by an excess-oxygen ion alternates ferromagnetic coupling between copper spins to ferromagnetic in a group of Cu-Cu bonds forming a defective nest. Clustering of the movable nests, which walk together with the excess oxygens, is energetically favorable, since it reduces frustration energy.

Large lattice-relaxation-induced electronic level shifts in random Cu1-xPdx alloys.

Mean-field theories of unrelaxed ${\mathrm{Cu}}_{0.75}$${\mathrm{Pd}}_{0.25}$ alloys exhibit a deep (${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{F}}$-5.5 eV) Pd bonding state at the bottom of the Cu d band that does not show up in photoemission experiments. We have applied the ``special quasirandom structures'' construct to ${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pd}}_{\mathit{x}}$ alloys in the context of local-density total-energy minimization, finding a distribution of Cu-Cu, Cu-Pd, and Pd-Pd bonds whose lengths deviate significantly from the single, unrelaxed value assumed in mean-field models. Such lattice distortions are found to induce a \ensuremath{\sim}1-eV shift in the Pd bonding state to lower binding energies, thus removing much of the discrepancy with experiment.

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.