Copper Chains Research Articles

Crystal structures and magnetic properties of uniform and alternating azido-bridged (2,2′-bipyridyl)copper(II) chains

Single crystals of four copper(II) complexes of formula [Cu(bipy)(N 3) 2] n ( 1,2), [Cu(bipy) 2(N 3)(ClO 4)] ( 3) and [Cubipy) 2(N 3)]ClO 4 ( 4) (bipy=2,2′-bipyridine) were obtained from aqueous solutions containing (2,2′-bipyridyl) copper(II) perchlorate and sodium azide, and their crystal structures were determined by X-ray diffraction methods. The structures of compounds 1 and 4 were already known, but the better accuracy of our structural determination of complex 1 led us to reconsider it here. The structures of compounds 1 and 2 are made up of neutral chains of copper(II) ions bridged by two azide groups exhibiting asymmetrical end-on ( 1) and alternating asymmetrical end-on and end-to-end bridging ( 2) modes. The copper atoms in 1 and 2 exhibit a distorted CuN 6 octahedral environment: two bipyridyl nitrogen atoms from a chelating bipy molecule and two azide nitrogens, either from two bridging azide ( 1) or from one bridging azide and a terminal one ( 2), occupy the equatorial positions whereas two azide nitrogens from the two neighbouring neutral [Cu(bipy)(N 3) 2] units fill the axial positions. The intrachain metal-metal separation is 3.516(1) and 3.497(1) Å in 1 and 3.434(1) and 5.378(1) Å in 2. The equatorial CuN bond lengths vary in the ranges 1.953(2)–2.029(2) ( 1) and 1.953(4)–2.029(3) Å ( 2). The axial bonds are significantly longer, 2.683(3) and 2.684(3) Å for 1 and 2.604(3) and 2.849(4) Å for 2. The structure of complex 3 consists of neutral [Cu(bipy) 2(N 3)(ClO 4)] units where the metal atom has a highly distorted CuN 5O octahedral environment: two chelating bipy in cis positions, a terminal azido group and a weakly coordinated percholrate form the coordination polyhedron. The basal plane is composed of four nitrogen atoms, three from two bipy molecules and one from the azido group (the metal to nitrogen bonds varying in the range 1.971(5)–2.030(5) Å, whereas the apical positions are occupied by a bipy nitrogen (2.218(5) Å) and a perchlorate oxygen (2.950(5) Å) atom. The magnetic properties of 1 and 2 have been investigated in the temperature range 2–300 K. Weak intrachain antiferro- ( 1) and alternating antiferro- and ferromagnetic ( 2) interactions have been observed and the efficiency of the out-of-plane exchange pathway through the azido bridge is analyzed and discussed in the light of the available magneto-structural parameters.

Synthesis of polynuclear copper(II) complexes by controlling the conformation ( cis or trans) of N, N′-bis(3-aminopropyl) oxamidate and the coordination mode of 2,2′-bipyrimidine

The synthesis, molecular structure and magnetic properties of three new polynuclear copper(II) complexes, [Cu( cis-oxpn)Cu(bpm)]- (ClO 4) 2·CH 3OH ( 1), [Cu 2( trans-oxpn) (bpm) 2](ClO 4) 2·2H 2O ( 2) and [Cu 2( trans-oxpn)( μ-bpm)](ClO 4) 2·2.5H 2O ( 3) are reported. The compounds were prepared by controlling the conformation ( cis or trans) of oxpn ( N, N′-bis(3-aminopropyl)oxamidate and the coordination mode (bi- or bisbidentate) of bpm (2,2′-bipyrimidine). Complex 1 is a dinuclear complex in which the copper(II) ions are bridged by a cis-oxamidate group and where bpm acts as a bidentate terminal ligand. 2 is a trans-oxamidate-bridged dinuclear copper(II) complex with two bidentate terminal bpm molecules. In 3, a bisbidentate bpm molecule connects the dinuclear Cu 2( trans-oxpn) units to generate an alternating oxamidate-bpm polynuclear copper(II) chain complex. Magnetic susceptibility measurements reveal the occurrence of strong antiferromagnetic exchange couplings for the three compouns with J values of −386.0 and −328.9 cm −1 for 1 and 2, respectively, and J = −340.0 cm −1, with an alternation parameter α = 0.24, for 3. Magnetic parameters are discussed on the basis of the structural results and compared with those of related complexes.

On the Electrochemically Grown Quasi-One-Dimensional KCu7-xS4 Series (0 ⩽ x ⩽ 0.34): Nonstoichiometry, Superlattice, and Unusual Phase Transitions

Whiskers of the quasi-one-dimensional copper(I) sulfide series were grown by employing electrochemical (E-Chem) methods via anodic dissolution of copper electrodes. The compound series can be prepared at 110 C in ethylenediamine solution of polysulfide K{sub 2}S{sub n} (n = 5,6) electrolytes and, in some cases, CuCl. Single-crystal structure analysis has reconfirmed the once ambiguous space group issue, and the study has also revealed that the KCu{sub 7}S{sub 4} phase reported by Ohtani et al. is nonstoichiometric. The present investigations on as-grown whiskers show that the previously observed unusual insulator-to-metal transition can be reproduced by the KCu{sub 6.86}S{sub 4} phase. Refined cell volumes increase linearly with increasing copper content. The extended framework resembles the (NH{sub 4})Cu{sub 7}S{sub 4} structure. It consists of quasi-one-dimensional Cu{sub 4}S{sub 4} columns interlinked by tetrahedral copper chains. New evidence shows that the title series exhibits complicated structure patterns with regard to the ordering of the Cu{sup +} cation along the tetrahedral chain. The nonstoichiometry and cation ordering are likely responsible for the anomalies observed in transport properties. A self-consistent model with respect to local ordering is discussed, and a recently proposed diffusive one-dimensional ordering model at the transitions is reiterated. The detailed synthesis and structure, alongmore » with preliminary electron diffraction studies and temperature-dependent magnetic susceptibility measurements, of the title series are presented.« less

NMR study of [formula omitted] resonance above Tc in fluorinated YBa 2Cu 3O x

The 19 F NMR spectra were obtained at 282.365 MHz, for a series of YBa 2Cu 3O x F y samples at a number of different temperatures, where y=0.1, 0.2 when x=7; y=0.10, 0.15, 0.29, 0.38 when x=6.7; and y=0.6, 0.98, 1.50 when x=6. These values of x span the fully oxygenated superconductor, the partially oxygenated superconductor, and the antiferromagnetic non-superconductor when the material is undoped. The spectra were obtained using a phase cycled echo. By measuring the echoes using a series of different times between pulses, we were able to resolve the spectra into two separate lines, representing two different F sites where the occupancy of one is much larger than the other, their ratio depending on the concentrations. The major site is attributed to the chain sites along a or b or both and the minor site is tentatively assigned to the apical position between the chain copper and the plain copper. The frequency shift of the major component is independent of both the oxygen and the fluorine concentration.

Extended Network via Axial Cu-Br Linkages of Zig-zag Coordination Chains of Copper(II) Ions Bridged Alternately by trans-Oxamidate and End-on Azide Groups

Abstract The zig-zag coordination chains [Cu2(trans-oxen)(N3)(Br)]n[H2oxen=N,N′-bis(2-aminoethyl)oxamide] with alternating bridges of trans-oxamidate and azide in bis-terdentate and end-on mode, respectively, are held together via axial Cu-Br linkage in a unique fashion to form an extended structure.

Étude par résonance quadrupolaire nucléaire de la rétention de carbone dans l'YBa2Cu3Oy≈7

We present a Nuclear Quadrupole Resonance (NQR) study of Cu(2) (planes) and Cu(1) (chains) sites in two YBa 2 Cu 3 O y ≈7 powder samples with carbon concentration equal to 500 ppm and 3000 ppm, and in a free-carbon sample. By comparison with standard spectra in YBa 2 Cu 3 O y , we show that a new NQR line appears at 30.90 MHz, the intensity of which is strongly correlated with the amount of carbon in the sample. Moreover, according to the spin-lattice relaxation rate 1/ T 1 measurements at different frequencies of the spectrum, we attribute this anomalous line to the formation of clusters in which the superconductivity is destroyed by the presence of carbonate groups, which substitute preferentially for copper chain site. Those results are in good agreement with those of Wang et al. [1], obtained by high resolution electron microscopy.

Syntheses, crystal structures and magnetic properties of one-, two- and three-dimensional 2,2′-bipyrimidine-containing copper(II) complexes

Three new copper(II) complexes of formula [Cu(bipym)(H2O)2][NO3]2·H2O 1, [Cu(bipym)(Cr2O7)] 2 and [Cu(bipym)(SO4)]·H2O 3 (bipym = 2,2′-bipyrimidine) have been synthesized and characterized by single-crystal X-ray diffraction. Compound 1 loses water very easily transforming into [Cu(bipym)][NO3]2 1′. The structure of 1 consists of zigzag chains of bipym-bridged copper(II) ions with unco-ordinated nitrate anions and co-ordinated and crystallization water molecules, whereas the structures of 2 and 3 are made up of bipym-bridged copper(II) chains which are connected through bis(monodentate)-dichromate (2) and -sulfate (3) groups to yield sheet-like (2) and three-dimensional (3) polymers. The copper atom in compounds 1–3 exhibits a distorted elongated-octahedral co-ordination. In 1, it is linked to two bis(chelating) bipym groups and two water molecules in cis positions. The equatorial positions of the octahedron are occupied by three bipym-nitrogen atoms and a water-oxygen, while the axial ones are filled by the remaining bipym-nitrogen and the second aqua ligand. The equatorial mean planes of two adjacent copper(II) ions within the chains are mutually perpendicular. In 2, two different bis(chelating) bipym groups alternate regularly within the chain. The four nitrogen atoms of one of them build the equatorial positions of two neighbouring octahedra and the two remaining equatorial sites around each metal atom are filled by an oxygen atom of the dichromate group and a nitrogen atom of the second bipym. The two trans axial positions are occupied by another nitrogen atom of the second bipym and an oxygen atom of the dichromate anion. The two adjacent equatorial copper(II) mean planes through this second bridging bipym in 2 are mutually parallel. Two adjacent crystallographically independent metal atoms alternate regularly within the bipym-bridged copper(II) chain in 3. Their equatorial plane is built by three nitrogen atoms from bipym and one oxygen atom from a sulfate anion, whereas the axial positions are filled by the remaining bipym nitrogen atom and an oxygen atom from another sulfate anion. The equatorial mean planes of adjacent copper(II) ions within the bipym-bridged chain of 3 are mutually perpendicular as in 1. The metal–metal separations across bridging bipym are 5.646(1) A in 1, 5.486(2) and 5.765(2) A in 2 and 5.648(1) and 5.715(1) A in 3, values which are close to that through bridging dichromate [5.774(1) A in 2] but shorter than those through bridging sulfate [6.464(2) and 6.417(2) A in 3]. Variable-temperature magnetic susceptibility measurements reveal that bridging bipym is able to mediate relatively strong (1′ and 2) and weak (1 and 3) antiferromagnetic couplings. The magnitude of the exchange coupling in this series is analyzed and discussed in the light of the complexes structural patterns.

Evaluation of the Structure Factor of Cuprite and Bonding Chracterisitcs

Cu2O is a semiconductor with a band gap of 2.17eV, and its crystal structure is simple cubic. Oxygen atoms form a bcc structure and each oxygen atom is tetrahedrally coordinated by copper atoms, which makes copper linearly coordinated by two oxygen atoms. The structure of cuprite is interesting because the charge state of Cu and oxygen. The most common charge states of Cu is 2+, however, in cuprite for each oxygen there are two Cu atoms which suggest a 1+ charge state of Cu. Charge density of Cu and oxygen are also interesting because of the high Tc superconductors based on copper and oxygen planes and chains. The superconductivity is believed due to the different charge states of copper and/or oxygen in the Cu-oxygen planes due to the doping or oxygen deficiency. by studying the naturally occurring charge states of Cu in Cu2O and CuO, a better understanding of the relationship between structure and bonding can be achieved for the important copper oxides.

Magnetic Interactions in the Copper Complex (L-Aspartato)(1,10-phenanthroline)copper(II) Hydrate. An Exchange-Coupled Extended System with Two Dissimilar Copper Ions.

We report EPR measurements in single-crystal samples at the microwave frequencies 9.8 and 34.3 GHz and magnetic susceptibility measurements in polycrystalline samples for the ternary complex of copper with aspartic acid and phenanthroline, (L-aspartato)(1,10-phenanthroline)copper(II) hydrate. The crystal lattice of this compound is composed of two dissimilar copper ions identified as Cu(A) and Cu(B), which are in two types of copper chains called A and B, respectively, running parallel to the b crystal axis. The copper ions in the A chains are connected by the aspartic acid molecule, and those in the B chains by a chemical path that involves a carboxylate bridge and a hydrogen bond. Both chains are held together by a complex network of hydrogen bonds and by hydrophobic interactions between aromatic amines. Magnetic susceptibility data indicate a Curie-Weiss behavior in the studied temperature range (2-300 K). The EPR spectra at 9.8 GHz display a single exchange collapsed resonance for any magnetic field orientation, in the so-called strong exchange regime. Those at 34.3 GHz are within the so-called weak exchange regime and display two resonances which belong to each type of copper ion chain. The decoupling of the spectra at 34.3 GHz using a theory based on Anderson's model for the case of two weakly exchange coupled spins S = (1)/(2) allows one to obtain the angular variation of the squares of the g-factor and the peak-to-peak line width of each resonance. This model also allows one to evaluate the exchange parameter |J(AB)/k| = 2.7(6) mK associated with the chemical path connecting dissimilar copper ions. The line width data obtained for each component of the spectra at 34.3 GHz are analyzed in terms of a model based on Kubo and Tomita's theory, to obtain the exchange parameters |J(A)/k| = 0.77(2) K and |J(B)/k| = 1.44(2) K associated with the chemical paths connecting the similar copper ions of types A and B, respectively.

Normal state properties of lithiated YBa2Cu3O7−x samples

Measurements of the resistivity in the normal state of lithiated YBa2Cu3O7−x are reported. At low xLi-values (<0.06), lithium substitutes copper of the CuO2 planes. The samples are metallic; a progressive localization of the charge carriers is observed. In the intermediate concentration range, lithium occupies both copper sites planes and chains which leads to a two-phased system; the slope dϱ/dT is nearly independent of temperature. In the concentrated range, lithium is in the chain site. The resistivity behaviour is well described by the simple relation $$\rho = \frac{{\rho _0 T_0 }}{T}$$ with ρ0T0=10Ω.cm.K, a result which is consistent with a single YBCO6-type phase.

Tunnelling barriers for high temperature superconductor devices

In this contribution we will discuss the requirements to be imposed on the barriers of HTS Josephson junctions as well as quasi particle injection devices. Factors that play a role are noise immunity, operating margins, injection efficiency etc., leading to the need for barriers in which the charge transport is dominated by direct tunnelling. So far, it is unclear if this has ever been observed in any practical device. We will demonstrate that localised states, that are probably ubiquitous in the materials used, are of prime importance in understanding device properties. In the model system we investigated, i.e. DyBCO/PrBCO/DyBCO, gallium-doping on the copper chain sites reduces the density of localised states appreciably without affecting the barrier height. Furthermore, it seems that due to an on-site Coulomb repulsion, pair transport proceeds via direct tunnelling, at least in the temperature region T< T c/2. Quasi particles, in contrast, tunnel resonantly via one or more localised states. At higher temperatures and bias voltages inelastic processes may dominate. These resonant tunnelling processes reduce the normal state resistance, and hence the I c R n-product. The consequences of these findings will be discussed and directions for future work set.

Structure and Magnetic Behavior of a New 1-D Compound with Simultaneous End-On Azido and Carboxylato Bridges. Unexpected Strong Ferromagnetic Coupling for a Cu-N-Cu Bond Angle of 111.9 degrees as a Consequence of Ligand HOMOs Countercomplementarity.

The X-ray structure of the &mgr;-carboxylate-&mgr;(1,1)-azido-bridged compound {[Cu(Hpht)(N(3))].H(2)O}(n)() has been determined (Hpht = hydrogen phthalate). Crystal data: formula C(8)H(7)CuN(3)O(5), monoclinic, P2(1)/m (No. 11), a = 7.383(3) Å, b = 6.568(4) Å, c = 10.659(4) Å, beta = 93.38(3) degrees, Z = 2. The compound is found to be a system formed by chains of copper atoms bridged simultaneously by syn-syn carboxylato and end-on azido bridges. The copper chains are linked by a second carboxylato bridge, giving a 2-D compound. Magnetic measurements indicate strong ferromagnetic coupling, which affords a good example of unexpected magnetic properties due to the countercomplementarity of the superexchange pathways of the two ligands.

Synthesis, structure, and magnetic properties of one-dimensional copper(II) coordination polymer, [Cu(pyrazine-2,3-dicarboxylate)(H2O)2]·2H 2O n

A title compound has been synthesized and characterized. The complex crystallizes in the monoclinic space group C2/ c with a = 12.768(1) A, b = 7.5159(8) A, c = 13.271(1) A, β = 123.591(4) °, V = 1060.8(2) A 3 and Z = 4. The complex consists of onedimensional chains of copper(II) ions bridged by pyrazine-2,3-dicarboxylate. Each copper ion has a distorted octahedral coordination with N 2O 4 chromophor. The magnetic susceptibility data over a range of 2–300 K were fitted by using an Heisenberg antiferromagnet, H=2 JΣ S i · S i+1 the parameters of J = −1.40 cm −1, g = 2.14 and ρ = 0.032.

ChemInform Abstract: A Novel Copper(I/II) Oxophosphate Chloride with a Quasi‐One‐ Dimensional μ4‐Oxo‐Bridged Copper(II) Chain. Crystal Structure and Magnetic Properties of (Na2CuII3(PO4)2)(CuIOCl).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Theorists Take Steps Toward Understanding Ladder Compounds

Whatever causes superconductivity above 40 K, it seems to involve the layers containing copper and oxygen atoms, which are common to all compounds exhibiting a high critical temperature, Tc. Hoping to gain insight into the mechanism for superconductivity in these complex structures, some theorists have looked at systems as simple as one‐dimensional chains of copper and oxygen atoms. More recently they have turned to copper oxide ladders—that is, pairs of copper oxide chains linked by additional oxygen atoms between the coppers. So far, the theorists have predicted a number of physical properties of such ladders, including the possibility that the ladders can go superconducting.

Oxidation of the pyrazine(pyz)-bridged polymeric copper(I) cation [Cu(cnge)(MeCN)(pyz)]+ by NOBF4 and formation of the corresponding copper(II) cation [Cu(MeCN)4(pyz)]2+(cnge = 2-cyanoguanidine)

The complex [Cu(cnge)(MeCN)(pyz)]BF4·0.5pyz 1(pyz = pyrazine, cnge = 2-cyanoguanidine) resulted from treatment of [Cu(MeCN)4]BF4 with mixtures of pyz and cnge in MeCN. Oxidation of compound 1 with NOBF4 in CH2Cl2 yielded Cu(pyz)(cnge)(BF4)22. Recrystallisation from MeCN resulted in loss of cnge and formation of [Cu(MeCN)4(pyz)][BF4]23. Reaction of 1 with NBut4NO2 in MeCN led to Cu(pyz)(cnge)(MeCN)(NO2)24. Single-crystal X-ray structural analysis has shown compound 1 to contain a one-dimensional zigzag cationic chain based on four-co-ordinate tetrahedral copper(I); each metal atom is ligated by two bridging pyz molecules and terminal MeCN and cnge molecules. The unco-ordinated pyz molecule, which is located at an inversion centre, connects parallel copper(I) chains via N ⋯ H–N bonds involving the amino moieties of ligating cnge molecules. The crystal structure of compound 3 contains a one-dimensional linear cationic chain based on six-co-ordinate copper(II), the tetragonally distorted octahedral co-ordination geometry of which comprises two bridging pyz molecules (equatorial) and four terminal MeCN molecules (two equatorial, two axial).

Synthesis and structures of copper(II) anion-bridged aggregates and chains: control over molecular shape

Di-2-pyridyl ketone (dpk) can complex metal ions in its activated [(NC5H4)2C(OR)(OH)] or non-activated form. In its activated form it displays a dinucleating behaviour as manifested by the compounds [{Cu2[(NC5H4)2C(OEt)O]Cl3(EtOH)}2] and [{Cu2[(NC5H4)2C(OMe)O]Cl3}∞](which also possess halide bridges). These compounds have been structurally characterised using single-crystal X-ray diffraction. In its non-activated form it acts as a simple bidentate chelate. The X-ray analysis of [{Cu(dpk)(NO3)2}∞] revealed an anion-bridged structure where bridging nitrato groups link the copper centres. The π-stacking arrangements of these compounds are also considered.

Implications of simultaneous doping at plane and chain copper sites in Y 1Ba 2Cu 3O 7−δ system for its superconducting properties

Recently we reported that codoping of Fe (chain dopant) and Zn (plane dopant) in Y 1Ba 2Cu 3O 7−δ leads to a giant Tc depression as compared to the cases of separate doping of either impurities at the same total concentration. In this work we have examined additional cases of codoping of Fe and Zn as well as Ga and Zn. Specifically, the dependence of Tc on the total concentration x in Y 1Ba 2Cu 3−xZn yM x−y (M = Fe or Ga, y = 0.1 fixed, x>0.1) is studied. Similarly, for a fixed concentration of 0.1 of Fe or Ga, the dependence of Tc on the increasing concentration of Zn is examined. The systematics reflect a correlation between Tc dependence and ortho/tetra structural transformation features.

Band structure of spin-Peierls cuprate CuGeO3

The spin-restricted and spin-polarized fully self-consistent linear muffin tin orbital band calculations for cuprate CuGeO3 are presented with Cu atoms in normal and displaced positions within the orthorhombic cells. This, computationally much cheaper, approach gives practically the same one-electron bands as recent linear augmented plane wave calculations, and the same qualitative explanation for the spin-Peierls transition observed at low temperatures in this compound. New self-consistent spin-polarized calculations of CuGeO3, for some supposed antiferromagnetic order in copper chains along the orthorhombic c axis, have given very small values for magnetic moments on Cu atoms. Again the dimerization of CuO2 chains can open a band gap at EF, if the Cu displacements in neighbouring chains are out of phase.

An Infrared Spectroscopic Study of Crystalline Copper (II) Propionate and Butyrate

Abstract Abstract: The vibrational spectra of crystalline anhydrous copper (II) propionate and butyrate were studied by FT-IR spectroscopy. A detailed assignment of the spectra of both compounds is presented and discussed. It is shown that the presence of two non-equivalent sets of carboxylate ligands within the crystals gives rise to several band splittings, which are particularly evident in those bands ascribable to normal modes involving predominantly the -CβH3 or -CβH2-fragments. In addition, the vibrational assignments made for the studied molecules are shown to be very useful to help understanding the much more complex spectra of long chain copper carboxylates.