Copper Chains Research Articles

Chains of (4,4′-bipyridyl)copper(I) bridged by dimolybdate units

The crystal structure of the title compound, poly­[bis-[copper(I)-μ-(4,4′-bipyridyl)-N:N′]-μ-dimolybdato-O:O′],[Cu2(C10H8N2)2{Mo2O7}]n, consists of {Mo2O7}2− units (with the central O atom lying on twofold symmetry axes) and [Cu(4,4′-bipy)]nn+ chains (bipy = bipyridyl); the chains are generated by a c-glide-plane operation. The {Mo2O7}2− units are covalently bridged to two [Cu(4,4′-bipy)]nn+ chains, forming a complex with a bridged double-chain structure. The Cu—O and Cu—N distances are 2.191 (3) and 1.933 (3) Å, respectively.

Crystal and magnetic structure of ferromagnetic superconductingRuSr2GdCu2O8

The crystal and magnetic structure of a sample of ${\mathrm{RuSr}}_{2}^{160}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}$ which orders magnetically at 133 K and exhibits a superconducting transition at 35 K has been investigated by neutron powder diffraction. ${\mathrm{RuO}}_{6}$ octahedra, which substitute at the chain copper site in a ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$-type structure, are rotated by about 14\ifmmode^\circ\else\textdegree\fi{} around the c axis to accommodate physically reasonable Ru-O bond lengths in the plane. This results in a $\sqrt{2}{a}_{p}\ifmmode\times\else\texttimes\fi{}\sqrt{2}{a}_{p}\ifmmode\times\else\texttimes\fi{}c$ supercell. The ${\mathrm{RuO}}_{6}$ rotations are partially ordered to form competing domains that differ in the sense of rotation. We speculate that the degree of ordering depends on annealing conditions. Surprisingly, the only structural parameters that respond to the magnetic ordering at 133 K are the Cu-Cu distance, which defines the thickness of the ${\mathrm{CuO}}_{2}$ double layer, and the buckling angle of the ${\mathrm{CuO}}_{2}$ planes. Magnetic scattering consistent with the previously proposed ferromagnetic ordering of Ru moments perpendicular to the c axis is not observed. We do not rule out ordering of Ru moments parallel to the c axis or itinerant ferromagnetism.

63,65Cu nuclear quadrupole resonance study of Ni-doped YBa 2Cu 3O 7

We have prepared pure YBCO (YBa 2Cu 3O 7− δ ) and Ni-doped YBCO (YBa 2− x La x Cu 3− x Ni x O 7− δ , x=0.1) samples and performed 63,65Cu nuclear quadrupole resonance (NQR) measurements. La substitution introduced for charge compensation, as well as Ni doping, severely distorts the electric field gradient at the copper sites inducing extra 63,65Cu NQR peaks other than the main peaks, for both the plane and the chain sites. 63,65Cu NQR linewidths for the plane site increased significantly whereas those for the chain site remained similar. Furthermore, both the spin–lattice and the spin–spin relaxation times for the plane copper decreased whereas those for the chain copper increased. The Ni substitutional effects on linewidths and relaxation times confirm that Ni carrying a local moment substitutes for the plane copper.

Magnetic properties of chains in cuprate superconductors studied by the Luttinger-liquid model

Mapping the one-dimensional Hubbard model into the Luttinger-Tomonaga model, we have calculated the temperature dependencies of the chain copper nuclear magnetic spin-lattice relaxation rate and Knight shift for the normal state of the superconducting materials ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}.$ The dynamic spin susceptibility has been obtained by using a bosonization technique and results of the renormalization group analysis for one-dimensional quantum systems. A comparison of our results with experiment shows that the model is able to reproduce the main features of the spin dynamics in both materials.

Pseudogap effects on the c-axis charge dynamics in copper oxide materials

The c-axis charge dynamics of copper oxide materials in the underdoped and optimally doped regimes has been studied by considering the incoherent interlayer hopping. It is shown that the c-axis charge dynamics for the chain copper oxide materials is mainly governed by the scattering from the in-plane fluctuation, and the c-axis charge dynamics for the no-chain copper oxide materials is dominated by the scattering from the in-plane fluctuation incorporating with the interlayer disorder, which would be suppressed when the holon pseudogap opens at low temperatures and lower doping levels, leading to the crossovers to the semiconducting-like range in the c-axis resistivity and the temperature linear to the nonlinear range in the in-plane resistivity.

Synthesis, structure and spectroscopic properties of an o-phthalate-bridged copper(II) chain complex

An o-phthalate-bridged copper(II) chain complex of {[Cu(2,2′-bipyridine)(μ-phthalate)H2O]·3.5H2O}n has been prepared and characterized by X-ray crystallography and UV–vis spectroscopy measurements. It crystallizes in the monoclinic system, space group P21/c, with a=9.9585(5), b=14.8312(8), c=13.6875(7)Å, β=104.868(1)° and Z=4. The copper(II) center is in 4+1 surrounding that can be described as square-pyramid. Each Cu(II) atom links by o-phthalate to form a waving chain. A network structure is assembled by chains via π–π interactions and water molecules are clathrated in the cavities. The UV–vis absorption spectrum of the title complex is also reported and explained perfectly by the scaling radial theory which was proposed by us.

Alternating ferromagnetic and antiferromagnetic interactions in the azido-bridged copper(II) chain compound [Cu(phen)(N3)2] n

Single crystals of a copper(II) chain compound**, [Cu(phen)(N3)2]n (phen = 1,10-phenanthroline), were obtained and its crystal structure was determined by X-ray diffraction methods. The complex crystallizes in the space group P1¯ and is made up of neutral chains of copper(II) ions bridged by two azide groups exhibiting an asymmetrical tri-dentate μ(1,1,3) coordination mode. The copper atoms have a distorted CuN6 octahedral environment: the basal plane is built of two nitrogen atoms from a chelating phen molecule and two azide nitrogens from one bridging and one terminal azide, whereas two nitrogens from two bridging azides fill the axial positions. The intrachain copper(II)–copper(II) separation is 3.396(1) and 5.700(1) A. The magnetic behavior was investigated in the 5–300 K range. Weak intrachain alternating antiferromagnetic (J = −6.56 cm−1) and ferromagnetic (αJ = 12.76 cm−1) interactions were observed.

Syntheses and structures of novel heterobimetallic Cu(II)–Au(I) complexes Cu(cyclen)[Au(CN)2]2 and Cu(pyz)[Au(CN)2

Two novel cyano CuII–AuI bimetallic complexes, Cu(cyclen)[Au(CN)2]21 (cyclen = 1,4,7,10-tetraazacyclododecane) and Cu(pyz)[Au(CN)2]22 (pyz = pyrazine) were prepared; 1 has a dimeric structure arising from AuI⋯AuI interactions, while 2 consists of linear pyrazine-bridged copper chains intercalated to produce a 2-D pleated sheet structure.

A Neutron Powder Diffraction Study of the Ferromagnetic Superconductor RuSr2(Gd1.3Ce0.7)Cu2O10-σ

ABSTRACTThe temperature dependence of the crystal structure of the ferromagnetic superconductor RuSr2(160Gd1.3Ce0.7)Cu2O10-σ, which orders magnetically at TC ∼ 180 K and exhibits a Tc ∼ 30 K, has been investigated by time-of-flight neutron powder diffraction. In this system superconductivity is believed to occur in the CuO2 layers while the magnetic order is associated with the Ru moments. The tetragonal structure evolves from that of YBa2Cu3O7-σ by inserting a fluorite-type Gd1.3Ce0.7O2 layer instead of the Y ion and replacing the chain copper site with RuO6 octahedra. Rietveld analysis reveals that the basal oxygens of the RuO6 octahedra are displaced within the xy-plane to accommodate physically reasonable Ru-O in-plane bonds. These displacements are consistent with rotations of the octahedra by ∼ 15° around the c-axis. Data were collected at 40 K, 70 K, 100 K, 130 K, 150 K, 170 K 190 K and 230 K but no large structural response associated with the ferromagnetic transition is observed. A small level of oxygen deficiency within the (Gd/Ce)2O2−x, fluorite layer (x = 0.1) is detected leading to a refined stoichiometry of RuSr2(Gd1.3Ce0.7)Cu2O9.9.

An alternating copper(II) chain with bridging oxamidato and nitrito ligands: crystal structure and magnetic properties of [Cu(NO 2) 2CuL] n (L= N, N′-bis(2-methyl-2-aminopropyl) oxamide)

The reaction of the monomeric cis-oxamido copper complex CuL (L standing for N, N′-bis(2-methyl-2-aminopropyl) oxamide) with copper and nitrite ions yields a chain compound [Cu(NO 2) 2CuL] n resulting from the trans isomerization of the oxamide ligand. Within each chain, the Cu(II) ions are alternately bridged by one dideprotonated ligand (L) 2− and two (NO 2) − ions. In addition, there may be an interaction between each copper ion and a second nitrite oxygen. So, each NO 2 group acts simultaneously as a μ-1,1 bridging ligand and as a chelating ligand via two oxygen atoms. The structural data support a distorted 4+2 coordination mode for the copper ions. Analysis of the thermal variation of the magnetic susceptibility shows that the exchange interaction supported by the oxamidato bridge is antiferromagnetic and two orders of magnitude larger than the interaction occurring via the NO 2 groups, the sign of which is also antiferromagnetic.

Local Magnetic Structure of Layered Compounds Cu2(OD)3X with Exchangeable Acid Anion X Studied by Solid State High Resolution Deuterium NMR

The microscopic magnetic local structure of Botallackite-type layer structured compounds Cu2(OD)3X (X = NO3 − and HCOO−) exhibiting a nonequilateral planar triangular magnetic lattice was determined by the solid-state high resolution deuterium NMR of deuterated hydroxy groups in the high temperature region above 190 K. The magnetic interactions in a copper ion layer were probed by the paramagnetic NMR shifts of the two chemically distinct hydroxy groups. Isotropic NMR shift of each hydroxy group showed different temperature dependence, suggesting non-uniform magnetic interaction. The magnetic interaction in the copper layer could be decomposed into a sum of 1D-Heisenberg ferro- and antiferromagnetic chains in the high temperature region. Two distinct copper chains with ferro- and antiferromagnetic exchange interactions J= ± 19 ± 11 and − 21 ± 3 K were found for x = NO3− from the temperature dependence of the two distinct NMR signals, while J = ± 13 ± 7 and − 13 ± 5 K for x = HCOO−. The derived values of J almost reproduced the temperature behavior of the magnetic susceptibility χiA T vs. T.

Development of an energy barrier at the metal-chain–metallic-carbon-nanotube nanocontact

We perform ab initio pseudopotential calculations for a nanocontact between a metallic carbon nanotube and a copper chain. We find that the on-top position is the most stable geometry of the copper chain on the nanotube and a local energy gap of $\ensuremath{\lesssim}0.1 \mathrm{eV}$ opens as the mirror symmetry of the nanotube is broken by the presence of copper. A weak ionic bonding is formed between the tube and the copper chain and the charge density in the conducting channel around the Fermi level is reduced at the contact region. Therefore, the electronic transport across the contact occurs essentially through the tunneling process. Appearance of such a locally semiconducting property in the intrinsically metallic carbon nanotube may explain the unusual low-temperature current-voltage characteristics exhibiting a huge contact resistance or a quantum dot behavior.

Spin and charge dynamics in the Cu-O chains ofYBa2Cu4O8

We report an NQR-NMR study of the chain copper and apex oxygen in the high-temperature superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$. Above ${T}_{c},$ the temperature dependences of the Cu spin-lattice relaxation rate and the Knight shift are quantitatively described in the framework of the one-dimensional electron gas model, where the anisotropy and the correlation of the chain electron system are taken into account. Electric-field-gradient fluctuations due to charge carriers in the chains contribute partly to the chain Cu relaxation and dominate the apex oxygen relaxation. The different temperature dependences of the magnetic and quadrupolar relaxation rates of the chain Cu seem to confirm the separation of low-energy spin and charge excitations (spin-charge separation), expected in the framework of the one-dimensional electronic gas model. Finally, we present experimental evidence that below ${T}_{c}$ the Cu-O chains become superconducting through the proximity effect.

SYNTHESIS, CRYSTAL STRUCTURE AND MAGNETIC PROPERTIES OF A THIOCYANATE BRIDGED ONE-DIMENSIONAL CHAIN COPPER(II) COMPLEX: {[(232-tet)Cu(NCS)](C104)}n

A thiocyanate bridged one-dimensional chain copper(II) complex, {[(232-tet)Cu(NCS)]-(C104)} n , where 232-tet = N,N'-bis(2-aminoethyl)-l,3-propanediamine, has been synthesised and its crystal structure determined at room temperature. This complex crystallises in the orthorhombic system, space group Pca21, with a = 23.565(3), b = 9.011(2), c= 14.290(3)Å and Z = 4. Least-squares refinement of the structure leads to conventional R 1 and wR 2 factors of 0.052 and 0.142. The asymmetric unit consists of two [(232-tet)Cu(NCS)]+ units and two per-chlorate anions. The two symmetric independent [(232-tet)Cu(NCS)]+ units form two different chains in the crystal lattice. The intrachain copper(II)-copper(lI) separations are 7.282(5) [Cu(l)-Cu(l)a, a: 1.5 - x, y, 0.5+ z] and 7.334(5)Å [Cu(2)-Cu(2)b, b: 1-x,1-y,0.5 + z], respectively. The interchain copper(II)-copper(II) separation is 6.870(5) Å [Cu(l)-Cu(2)b, b: 1 — x, 1 —y, 0.5+ z]. The coordination environments of the two Cu(II) atoms are similar. Each Cu(II) atom is (4+ 1 +1′) coordinated in a distorted, elongated, tetragonal octahedron with four N atoms of the 232-tet ligand in the equatorial positions and one N atom of the thiocyanate and one S atom of the other thiocyanate in the axial positions. The ESR spectrum appeared to show axial symmetry with g⊺ = 2.05 and g‖ = 2.16. Variable temperature magnetic susceptibility shows that there is a weak antiferromagnetic interactions in intrachains.

Observations of spin gaps in the S = [formula omitted] quasi-one-dimensional magnet A 10Cu 17O 29 (A = Sr, Ca, Y, Bi)

Magnetic susceptibility and electron spin resonance measurements have been performed on the S = 1 2 quasi-one-dimensional compound A 10Cu 17O 29 (A = Sr, Ca, Y, Bi), in which copper ions are located in the isolated chains of the CuO squares and the two-leg ladder planes. The magnetic excitations in the copper chains are suggested to be the Wannier spin excitations. The spin gaps have shown to exist for both spin chains and two-leg spin ladders.

Influence of cobalt doping on superconducting transition in as-grown YBCO single crystals

The role of a charge buffer layer in the superconductivity of high- T c materials is best studied by cationic substitutions. In this work, the chain copper in YBCO single crystals is substituted by Co 3+ ion and consequent effect on superconducting transition temperature ( T c) studied. The T c is measured using non-resonant Microwave Absorption technique, which is a highly sensitive and contactless method. It is seen that T c of as-grown crystals is considerably enhanced by cobalt doping in low concentration regime. In contrast, higher T c is achieved in undoped crystals only after extended oxygen anneal. When dopant concentration increases beyond an optimal value, T c decreases and the system does not show superconductivity when cobalt content is high ( x>0.5 in YBa 2Cu 3− x Co x O 7± δ ). This behaviour consequent to cobalt substitution is discussed with reference to the apical oxygen model. Optimal cobalt doping can be thought of as an alternative to extended oxygen anneal in as-grown crystals of YBCO.

Ferromagnetic coupling through a carbonate bridge in the copper (II) chain [Cu(CO 3)(4-apy) 2] · H 2O (4-apy = 4-aminopyridine)

Atmospheric CO 2 fixation by aqueous solutions containing copper(II) bromide and 4-aminopyridine (4-apy) yields the first carbonatobridged copper(II) chain of formula [Cu(CO 3)(4-apy) 2] · H 2O that exhibits an intrachain ferromagnetic coupling.

Crystal structure and magnetic properties of the single-μ-chloro copper(II) chain [Cu(bipy)Cl 2] (bipy = 2,2′-bipyridine)

The crystal and molecular structure of the copper(II) chain [Cu(bipy)Cl 2] ( 1) (bipy = 2,2′-bipyridine) has been determined by X-ray diffraction methods. The crystal structure of 1 consists of neutral single chloro-bridged copper(II) chains with alternating short and long Cu–Cl distances through a screw axis parallel to a. The copper surrounding is best described as distorted square pyramidal, the equatorial plane being built by the two nitrogen atoms of the chelating bipy and two chlorine atoms (one terminal and the other bridging), whereas the apical position is filled by the bridging chlorine atom from the symmetry-related adjacent unit. The equatorial Cu–Cl bonds (2.291(3) and 2.259(3) Å) are shorter than the axial one (2.674(3) Å). The intrachain copper–copper separation is 4.010(3) Å whereas the shortest interchain copper–copper distance is 8.381(3) Å. The magnetic properties of 1 have been investigated in the temperature range 1.8–300 K. They reveal the occurrence of a weak intrachain antiferromagnetic coupling, J = −2.3 cm −1 (uniformly-spaced linear chain of local spin S = 1/2). This value is compared to those of related mono- and di-chloro-bridged copper(II) polymers and the available magneto-structural data are discussed in the framework of a simple orbital model.

Synthesis, crystal structure and property of a novel azide-bridged one-dimensional chain copper(II) complex with a dinucleating macrocyclic polyamine

An azide-bridged polymeric cationic chain complex, [LCu2(N3)2]n(ClO4)2n·n(H2O)**, where L=the dinucleating macrocyclic ligand bis-p-xylylBISDIEN, has been prepared and characterized by x-ray crystallography, u.v.-vis and i.r. spectra, and by magnetic measurements. The structure consists of cationic azide-bridged [LCu2(N3)2]2+ (unit) chains, non-coordinated perchlorate anions and crystallized water molecules. The azide anion is bound to two copper atoms in neighboring units with an end-to-end bridging mode. In each unit, the copper atoms have a different coordination geometry; Cu(1) is a four-coordinated, distorted square-planar geometry, whereas Cu(2) is a five-coordinated, distorted square-pyramid. The electronic spectra of the title complex differ in anhydrous and in aqueous MeCN solutions, indicating that dissociation and solvation occur in aqueous solutions. The characteristic i.r. absorptions of azides and perchlorates are described. Magnetic moments vary from 2.05 (B.M.) at 300K to␣2.01 (B.M.) at 80K, which suggests that very weak interactions exist between the metals.

Synthesis, crystal structure and magnetic properties of the first single azido-bridged copper(II) chain [Cu(bpym) (N32]n (bpym + 2,2′-bipyrimidine)

Single crystals of the copper(II) chain of formula [Cu(bpym) (N32]n (bpym = 2,2′-bipyrimidine) were prepared and characterized by X-ray diffraction methods. The structure consists of neutral chains of copper (II) ions bridged by a single azide group exhibiting the asymmetric end-to-end coordination mode. A terminally bound azide ligand and a didentate bpym group complete the square pyramidal geometry of the metal atom. The intrachain copper-copper separation is 5.063(1)Å. The magnetic behaviour was investigated in the temperature range 2.0–290 K. The susceptibility curve exhibits a maximum at .9 K showing the occurrence of a weak intrachain antiferromagnetic coupling. Analysis of the magnetic data using the Heisenberg uniform linear chain model (H^=−J∑S^i⋅S^i+1) leads to J = −3.8cm−1 and g = 2.12. The value of magnetic coupling of this compound is compared with that observed in the parent double end-to-end azido-bridged dinuclear copper(II) complexes.