CuO4 Units Research Articles

Asymmetric Cu-N1O3 Sites Coupling Atop-type and Bridge-type Adsorbed *C1 for Electrocatalytic CO2-to-C2 Conversion.

2D functional porous frameworks offer a platform for studying the structure-activity relationships during electrocatalytic CO2 reduction reaction (CO2RR). Yet challenges still exist to breakthrough key limitations on site configuration (typical M-O4 or M-N4 units) and product selectivity (common CO2-to-CO conversion). Herein, a novel 2D metal-organic framework (MOF) with planar asymmetric N/O mixed coordinated Cu-N1O3 unit is constructed, labeled as BIT-119. When applied to CO2RR, BIT-119 could reach a CO2-to-C2 conversion with C2 partial current density ranging from 36.9 to 165.0 mA cm-2 in flow cell. Compared to the typical symmetric Cu-O4 units, asymmetric Cu-N1O3 units lead to the re-distribution of local electron structure, regulating the adsorption strength of several key adsorbates and the following catalytic selectivity. From experimental and theoretical analyses, Cu-N1O3 sites could simultaneously couple the atop-type (on Cu site) and bridge-type (on Cu-N site) adsorption of *C1 species to reach the CO2-to-C2 conversion. This work broadens the feasible C-C coupling mechanism on 2D functional porous frameworks.

Low-dimensional magnetic properties of the ladder-like polynuclear complex Cu2(naphac)2(OH)2 (naphac = 3-(1-naphthyl)acrylate)

The polynuclear complex Cu2(naphac)2(OH)2 consists of isolated Cu ladders in which square planar CuO4 and square-pyramidal CuO5 units are linked alternately along the crystalline a direction through their corners, and the resultant two adjacent Cu alternating chains connect each other through edges of the CuO5 units to form a ladder. The temperature dependence of the magnetic susceptibility above 50 K is reproduced by the calculation of the spin-1/2 two-leg honeycomb spin ladder model with almost zero exchange coupling between two legs of ladder. This is explained by the Jahn-Teller elongation of square-pyramidal CuO5 units. The absence of lambda-shaped peak in the specific heat down to 1.9 K suggests the existence of large quantum fluctuations of the spin owing to low-dimensional antiferromagnetic interactions.

Eddavidite, Cu12Pb2O15Br2, a New Mineral Species, and Its Solid Solution with Murdochite, Cu12Pb2O15Cl2

Eddavidite is a new mineral species (IMA2018-010) with ideal formula, Cu12Pb2O15Br2, and cubic Fm3¯m symmetry: a = 9.2407(9) Å; V = 789.1(2) Å3; Z = 2. Eddavidite is the bromine analog of murdochite, Cu12Pb2O15Cl2, with which it forms a solid solution series. The type locality is the Southwest mine, Bisbee, Cochise County, Arizona, U.S.A. Eddavidite also occurs in the Ojuela mine, Mapimí, Durango, Mexico. Eddavidite occurs as domains within mixed murdochite–eddavidite crystals. The empirical formula, normalized to 12 Cu apfu, is Cu12(Pb1.92Fe0.06Si0.06)(O15.08F0.02)-(Br0.99Cl0.89☐0.12). Type locality samples contain up to 67% eddavidite component, while Ojuela mine samples contain up to 62%. Mixed eddavidite–murdochite crystals show forms {100} and {111}; the habit grades from cubic through cuboctahedral to octahedral. Mixed eddavidite–-murdochite crystals exhibit good cleavage on {111}. Eddavidite is black, opaque with submetallic luster, and visually indistinguishable from intergrown murdochite. Its Mohs hardness is 4; dmeas. = 6.33 g/cm3, dcalc. = 6.45 g/cm3. The crystal structure, refined to R = 0.0112, consists of corner-sharing square planar CuO4 units, arranged in Cu12O24 metal oxide clusters, which encapsulate Br atoms. PbO8 cubes share edges with Cu12O24 clusters in a continuous framework. Eddavidite incorporates bromine remaining after desiccation of paleo-seawater at its two known localities, which were both once situated along the Western Interior Seaway.

Conductive Metal-Organic Framework with Superior Redox Activity as a Stable High-Capacity Anode for High-Temperature K-Ion Batteries.

High-temperature rechargeable batteries are essential for energy storage in elevated-temperature situations. Due to the resource abundance of potassium, high-temperature K-ion batteries are drawing increasing research interest. However, raising the working temperature would aggravate the chemical and mechanical instability of the KIB anode, resulting in very fast capacity fading, especially when high capacity is pursued. Here, we demonstrated that a porous conductive metal-organic framework (MOF), which is constructed by N-rich aromatic molecules and CuO4 units via π-d conjugation, could provide multiple accessible redox-active sites and promised robust structure stability for efficient potassium storage at high temperatures. Even working at 60 °C, this MOF anode could deliver high initial capacity (455 mAh g-1), impressive rate, and extraordinary cyclability (96.7% capacity retention for 1600 cycles), which is much better than those of reported high-temperature KIB anodes. The mechanistic study revealed that C═N groups and CuO4 units contributed abundant redox-active sites; the synergistic effect of π-d conjugated character and reticular porous architecture facilitated the K+/e- transport and ensured an insoluble electrode with small volume deformation, thus achieving stable high-capacity potassium storage.

A Cu(II) Metal Organic Framework with a Tetranuclear Core: Structure, Magnetism, and Supercapacitor Activity

A Cu(II) coordinated metal–organic framework, {[Cu4(BTC)2(4-APy)2(μ3-OH)2]·[(CH3OH)0.5]2·(H2O)2}n (Cu-MOF), has been synthesized by the solvo-diffusion of Cu(NO3)2 to an alcoholic solution of 4-aminopyridine (4-APy) and 1,3,5-benzenetricarboxylic acid (H3BTC) in equimolar proportion. A single-crystal X-ray structure determination suggests that the four-Cu(II)-connected motif ([CuII]4) via edge sharing of two Cu3–O cores and bridging by six acetato functions of the BTC3– connector generates two five-coordinated distorted-square-pyramidal CuO5 units and two distorted-square-planar CuO4 units; the Cu(II) knot in the latter one (CuO4) is coordinated by pyridyl-N of 4-APy. The remaining donor centers of acetato-O of BTC3– bind adjacent [CuII]4 core to form an infinite 3D network structure. The coordination of CH3OH and H2O forms different hydrogen bonds to make a strong superstructure. A surface morphology determination shows a nanoflower pattern. The hybrid material Cu-MOF exhibits a very high specific capacitance, 547 F g–1, at a scan rate of 2 mV s–1 with excellent recycling stability (retains 97.4% after 5000 cycles). The χMT value for Cu-MOF at 300 K is 1.735 cm3 mol–1 K for four copper(II) ions, which is as expected for four isolated copper(II) ions with g = 2.15. The χMT values are almost constant until ca. 55 K, and then χMT decreases sharply, giving a minimum value of 0.753 cm3 K mol–1 at 2 K.

Applying Configurational Complexity to the 2D Ruddlesden–Popper Crystal Structure

The layered Ruddlesden-Popper crystal structure can host a broad range of functionally important behaviors. Here we establish extraordinary configurational disorder in a layered Ruddlesden-Popper (RP) structure using entropy stabilization assisted synthesis. A protype A2CuO4 RP cuprate oxide with five cations on the A-site sublattice is designed and fabricated into epitaxial single crystal films using pulsed laser deposition. When grown on a near lattice matched substrate, the (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 film features a T'-type RP structure with uniform A-site cation mixing and square-planar CuO4 units. These observations are made with a range of combined characterizations using X-ray diffraction, atomic-resolution scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption spectroscopy measurements. It is further found that heteroepitaxial strain plays an important role in crystal phase formation during synthesis. Compressive strain over ∼1.5% results in the formation of a non-RP cubic phase consistent with a CuX2O4 spinel structure. The ability to manipulate configurational complexity and move between 2D layered RP and 3D cubic crystal structures in cuprate and related materials promises to enable flexible design strategies for a range of functionalities, such as magnetoresistance, unconventional superconductivity, ferroelectricity, catalysis, and ion transport.

Highly dispersive magnons with spin-gap-like features in the frustrated ferromagneticS=12chain compoundCa2Y2Cu5O10detected by inelastic neutron scattering

We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out the full one magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio R=|J_{a2}/J_{a1}| of the FM NN and the AFM NNN couplings is found as ~0.23, close to the critical point Rc=1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas Rc>0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at ~11.5 and ~28 meV. The gap-like feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on DMRG simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO2 ones. It gives rise to non-equivalent CuO4 units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange integrals. The J's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J1=24 meV among FFESC cuprates can be explained by a non-universal Phi (not 90 deg.) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange K_{pd}~120 meV. Enhanced K_{pd} values are also needed to compensate a significant AFM J_{dd} > ~6 meV.

Synthesis, magnetic properties and electronic structure of the S = ½ uniform spin chain system InCuPO5

We have studied the structural and magnetic properties and electronic structure of the compound InCuPO5 synthesized by a solid state reaction method. The structure of InCuPO5 comprises S = ½ uniform spin chains formed by corner-shared CuO4 units. Magnetic susceptibility (χ(T)) data show a broad maximum at about 65 K, a characteristic feature of one-dimensional (1D) magnetism. The χ(T) data are fitted to the coupled S = ½ Heisenberg antiferromagnetic (HAFM) uniform chain model that gives the intra-chain coupling (J/kB) between nearest-neighbor Cu2+ ions as −100 K and the ratio of inter-chain to intra-chain coupling (J′/J) as about 0.07. The exchange couplings estimated from the magnetic data analysis are in good agreement with the values computed from the electronic structure calculations based on the density functional theory + Hubbard U (DFT + U) approach. The combination of theoretical and experimental analysis confirms that InCuPO5 is a candidate material for weakly coupled S = ½ uniform chains. A detailed theoretical analysis of the electronic structure further reveals that the system is insulating with a gap of 2.4 eV and a local moment of 0.70 µB/Cu.

Interplay of magnetic sublattices in langite Cu4(OH)6SO4 · 2H2O

Magnetic and crystallographic properties of the mineral langite Cu4(OH)6SOH2O are reported. Thermodynamic measurements combined with a microscopic analysis, based on density-functional bandstructure calculations, identify a quasi-two-dimensional (2D), partially frustrated spin-1/2 lattice resulting in the low Néel temperature of K. This spin lattice splits into two parts with predominant ferro- and antiferromagnetic (AFM) exchange couplings, respectively. The former, ferromagnetic (FM) part is prone to the long-range magnetic order and saturates around 12 T, where the magnetization reaches 0.5 /Cu. The latter, AFM part features a spin-ladder geometry and should evade long-range magnetic order. This representation is corroborated by the peculiar temperature dependence of the specific heat in the magnetically ordered state. We argue that this separation into ferro- and antiferromagnetic sublattices is generic for quantum magnets in Cu2+ oxides that combine different flavors of structural chains built of CuO4 units. To start from reliable structural data, the crystal structure of langite in the 100–280 K temperature range has been determined by single-crystal x-ray diffraction, and the hydrogen positions were refined computationally.

Visible light photo-oxidation of model pollutants using CaCu3Ti4O12: an experimental and theoretical study of optical properties, electronic structure, and selectivity.

Charge transfer between metal ions occupying distinct crystallographic sublattices in an ordered material is a strategy to confer visible light absorption on complex oxides to generate potentially catalytically active electron and hole charge carriers. CaCu3Ti4O12 has distinct octahedral Ti4+ and square planar Cu2+ sites and is thus a candidate material for this approach. The sol−gel synthesis of high surface area CaCu3Ti4O12 and investigation of its optical absorption and photocatalytic reactivity with model pollutants are reported. Two gaps of 2.21 and 1.39 eV are observed in the visible region. These absorptions are explained by LSDA+U electronic structure calculations, including electron correlation on the Cu sites, as arising from transitions from a Cu-hybridized O 2p-derived valence band to localized empty states on Cu (attributed to the isolation of CuO4 units within the structure of CaCu3Ti4O12) and to a Ti-based conduction band. The resulting charge carriers produce selective visible light photodegradation of 4-chlorophenol (monitored by mass spectrometry) by Pt-loaded CaCu3Ti4O12 which is attributed to the chemical nature of the photogenerated charge carriers and has a quantum yield comparable with commercial visible light photocatalysts.

Structural and Magnetic Properties of A-Site-Ordered Perovskites ACu3Sn4O12 with A = Ca2+, Sr2+, and Pb2+

A series of A-site-ordered perovskites ACu3Sn4O12 with A = Ca2+, Sr2+, and Pb2+ were prepared under high-temperature and high-pressure conditions. They have Cu2+ ions with S = 1/2 spins at the A site in the ABO3 perovskite structure and have nonmagnetic Sn4+ ions at the B sites. An increase in the size of the divalent A-site ions from Ca to Pb increases the cubic lattice constant by only 0.6%. The cubic lattice with rigid CuO4 units thus hardly expands and the different sizes of the A-site ions are accommodated by change of the SnO6 octahedra. The difference in the size of the A-site ions has little effect on the ferromagnetic transition temperatures, because the magnetic properties of these perovskites are determined primarily by the direct ferromagnetic interaction between Cu2+ ions at the A site.

Electronic structure and magnetic properties of Bi2CuO4

Bi2CuO4 is a spin 1/2 model compound with ferromagnetically (FM) ordered chains that are antiferromagnetically (AFM) arranged with respect to each other. To investigate the microscopic origin of this unusual magnetic structure, we performed DFT calculations to evaluate the relevant orbitals and couplings. Total energy calculations yield a magnetic ground state in agreement with the experimental data. Based on a tight-binding fit we estimated the leading exchange integrals. The main coupling arises between the chains, while the in-chain interaction is relatively small. The FM arrangement of chains is due to strong AFM exchange of neighbouring CuO4 units of the different chains.

Synthesis, Structure, and Magnetic Properties of Cs2-xRbxCu3P4O14 (0.0 ≤ x ≤ 0.8): A New Series of Copper(II) Phosphates Containing Periodic Arrays of Staggered Square-Planar CuO4 Trimers

In our continued exploratory synthesis of compounds containing transition-metal oxide magnetic nanostructures, a new copper(II) phosphate phase, Cs2Cu3P4O14 (1), was isolated employing the mixed CsCl/2CsI molten flux. The X-ray single-crystal structural analysis shows that the Cs2Cu3P4O(14) phase crystallizes in a monoclinic space group with a = 7.920(2) A, b = 10.795(2) A, c = 7.796(2) A, beta = 103.90(3) degrees , and V = 646.9(2) A(3); P2(1)/c (No. 14); Z = 2. The structure has been refined by the full-matrix least-squares method to a final solution with R1 = 0.0248, wR2 = 0.0553, and GOF = 1.02. The three-dimensional Cu-O-P framework exhibits pseudo-one-dimensional channels where the Cs+ cations reside. The framework consists of trimeric CuO4 square-planar units stacked in a staggered configuration. These CuO4 trimers are interlinked by the P2O7 units via vertex-sharing O atoms. The stacked CuO4 units are slanted with respect to the Cu...Cu...Cu vector, resulting in additional Cu-O long bonds, 2.71(1) A, and a possibly shortened Cu...Cu distance, 3.38(3) A. 1 shows limited cation substitution with smaller alkali-metal cations; in fact, only a relatively small concentration of Cs+ can be substituted by Rb+ to form Cs(2-x)RbxCu3P4O14 (0.0 </= x </= 0.8). The temperature-dependent magnetic susceptibility studies of 1 and its Rb-substituted analogues (x = 0, 0.33, 0.50, and 0.80) reveal a weak ferromagnetic transition at Tc = approximately 14 K, which evidently is independent of the variation of x. In this paper, we report the synthesis, structure, and properties of the title compounds, as well as its brief comparison with the previously discovered Li2Cu3Si4O12 phase, which exhibits fused square-planar CuO4 trimers.

Crystal structure, magnetic and electrical properties of new indium copper-oxycarbonates Ba2CuInx(CO3)1−xO2+2.5x+δ

A new indium copper oxycarbonate Ba2CuInx(CO3)1−xO2+2.5x+δ, existing for 0.0625≤x≤0.25 in the In2O3–BaO(CO2)–CuO pseudo-ternary system, has been identified and characterised. Rietveld refinement of powder X-ray diffraction data combined with electron microscope studies shows that this phase crystallises in the tetragonal system (space group P4/mmm) with unit cell (a=4.01333(1) Å, c=8.0572(1) Å for x=0.125) based on a doubling of the basic perovskite subcell in the c-direction. The refined crystal structure is characterised by a random distribution of copper atoms in the [Cu1−xInx–O] as well as the [(CO3)1−xCux–O] layers. The oxygen atoms from carbonate groups occupy all 14 possible structural positions around the carbon atoms. The Cu+2 ions with spin S=12 form a disordered sublattice of corner-sharing CuO4 units and isolated linear CuO2 dumbbells. All samples with δ=0 indicate non-superconductive properties in the investigated temperature range. The curves of the magnetisation versus magnetic field at 1.9 K, M(H), and magnetic susceptibility versus temperature, χs(T), do not indicate long range magnetic order, but the presence of low-dimensional magnetism with suppressed values of magnetic parameters due to zero-point spin fluctuations and covalency effects. The compound has a temperature dependence of the resistivity characteristic for disordered systems, satisfying Mott’s variable-range-hopping (VRH) law ρ=ρ0exp[T0/T]p with p=1/4 and T0≈3.107 K. In Ba2CuInx(CO3)1−xO2+2.5x compound the In sites in disordered [Cu1−xInx–O] layers may be the hopping centers, although estimated values for the density of localised states at the Fermi level N(EF), seem to be independent of the indium content x.

Crystal structure and magnetism of the linear-chain copper oxidesSr5Pb3−xBixCuO12

The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the compounds were found to comprise linear-chains at inter-chain distance of approximately 10 A. The parent chain compound (x = 0), however, shows less anisotropic magnetic behavior above 2 K, although it is of substantially antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain system. A magnetic cusp gradually appears at about 100 K in T vs chi with the Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold electrically insulating in the composition range.

Examination of the Anisotropic Spin Exchange Interactions of CuM2O6 (M=Sb, V, Nb) by Spin Dimer Analysis

The anisotropic spin exchange interactions of the magnetic solids CuM2O6 (M=Sb, V, Nb) were explained by analyzing their reported crystal structures and calculating the spin orbital interaction energies of their spin dimers. The magnetic orbital of each Cu2+ site in CuM2O6 is given by the “x2–y2” orbital so that the magnitude of an antiferromagnetic spin exchange interaction for a given spin dimer increases when the arrangement of the nearest-neighbor square-planar CuO4 units containing the magnetic orbitals provides a good sigma overlap between the adjacent magnetic orbitals. The one-dimensional magnetic chains of α-CuV2O6, β-CuNb2O6, and α-CuNb2O6 run along a direction different than their edge-sharing CuO4 chain directions. Our study predicts that the antiferromagnetic ordering in β-CuNb2O6 should make the magnetic unit cell double the chemical unit cell along the b-direction.

Synthesis and structural characterization of tricarbomethoxymethanate complexes of copper(II) and barium(II) and evaluation of their suitability for MOCVD applications

The reaction between Cu(OCH3)2 and HL [L = −C(CO2CH3)3] in THF gives a mixture of two products, CuL(OCH3) and CuL2(THF)2. CuL(OCH3) was characterized by elemental analysis, infrared spectroscopy and thermal decomposition studies, and its insolubility in THF, at room temperature, suggests that it may be polymeric. The solid state structure of CuL2(THF)2 was established ia a single-crystal X-ray diffraction analysis. This complex has a tetragonally distorted trans-disubstituted octahedral structure with L binding like a conventional bidentate β-diketonate ligand; the central CO2CH3 group of each L is not coordinated. CuL2(THF)2 readily loses the two THF molecules bound to the Cu(II) center upon drying in a stream of dinitrogen to produce THF-free CuL2. Alternatively, THF-free CuL2 can be prepared by the reaction of CuL(OCH3) with HL in refluxing toluene. X-ray crystallography shows that CuL2 is a polymeric solid composed of a planar Cu(η2-L)2 repeat unit in which the central CO2CH3 group of each L binds weakly to the Cu(II) center of a neighboring unit along a “stepped” (displaced) stack of CuO4 units. The reaction between elemental barium and HL in THF requires activation with NH3(g). The product is a white solid of empirical formula BaL2·0.36THF. It was characterized by elemental analysis, 1H NMR, 13C{1H} NMR, and infrared spectroscopies, and thermal decomposition studies. It is insoluble in common laboratory solvents but soluble in strong Lewis bases such as pyridine, dimethylsulfoxide, and hexamethylphosphoramide (HMPA). The product resulting from the depolymerization of BaL2 ·0.36THF with HMPA was characterized ia a single-crystal X-ray diffraction analysis. It is a dimer of empirical formula Ba2L4(HMPA)4. It consists of two BaL2(HMPA)2 fragments linked together, in a centrosymmetric fashion, by two μ2,η3-[−C(CO2CH3)3] ligands; this is made possible by the utilization of the donor power of the pendant C(O)OCH3 group not used in CuL2(THF)2. The remaining two −C(CO2CH3)3 ligands are also bidentate but are non-bridging, and the four HMPA molecules are bonded through oxygen, resulting in a coordination number of seven for each barium. CuL2 is volatile and sublimes upon heating the amorphous material obtained from spontaneous desolvation of CuL2(THF)2, or polymeric CuL2, or CuL(OCH3) under high vacuum. The barium complexes are not volatile. Metallic copper is obtained upon heating the Cu(II) complexes to 1000 °C in a stream of argon, and formation of CuO results when these complexes are decomposed in the presence of oxygen. Thermal decomposition of BaL2·0.36THF and Ba2L4(HMPA)4 has been carried out under argon and O2–Ar atmospheres; residues containing varying amounts of BaO, BaO2 and BaCO3 were obtained depending on the experimental conditions.

Magnetization jump in theXXZchain with next-nearest-neighbor exchange

We study the dependence of the magnetization M with magnetic field B at zero temperature in the spin-1/2 XXZ chain with nearest-neighbor (NN) J1 and next-NN J2 exchange interactions, with anisotropies Delta1 and Delta2 respectively. The region of parameters for which a jump in M(B) exists is studied using numerical diagonalization, and analytical results for two magnons on a ferromagnetic background in the thermodynamic limit. We find a line in the parameter space (J2/J1, Delta1/J1, Delta2/J2) (determined by two simple equations) at which the ground state is highly degenerate. M(B) has a jump near this line, and at or near the isotropic case with ferromagnetic J1 and antiferromagnetic J2, with |J2/J1| near 1/4. These results are relevant for some systems containing CuO chains with edge-sharing CuO4 units.

Ag2 Cu2 O3 : The First Silver Copper Oxide.

An efficient low-temperature route provides the first mixed oxide of silver and copper. Ag2 Cu2 O3 represents an important precedent in the search for silver-containing superconductors. It has an open structure with three-dimensional tunnels displaying square-planar CuO4 units, linerly coordinated silver ions, and vacant oxygen sites (see picture; Ag, Cu, and O are represented by white, large black, and small black spheres, respectively). The last feature allows for a rich solid-state redox chemistry.

The Synthesis, Crystal Structures and Magnetic Properties of Cu4(AsO4)2(O) and Ba2Cu7(AsO4)6

AbstractTwo new compounds Cu4(AsO4)2O (1) and Ba2Cu7As6O24 (2) were obtained from a mixture of CuO and As2O5 · xH2O heated to 1090°C for 72 h in a BaCO3 flux. Compound 1 was obtained as dark green crystals, belonging to the orthorhombic crystal system. Compound 2 was obtained as light gray to colorless crystals belonging to the triclinic crystal system. The structure of 1 contains two copper ions with distorted trigonal bipyramidal geometries and a third with a distorted square pyramidal geometry. One ‚oxide’︁ ion is surrounded by four copper ions in a distorted tetrahedral arrangement. Compounds 2 consists of two chains with alternating units of trigonal bipyramidal CuO5 and square planar CuO4 units, with the oxygen atoms derived from the AsO4 groups. Magnetic susceptibility measurements of 1 and 2 both show effective magnetic moments, μeff1.90–1.95 B.M./Cu at 25°C, which is consistent with Cu2+ ions having one unpaired electron. Significant antiferromagnetic coupling was revealed by variable temperature measurements. At very low temperatures (15–25 K) samples of both 1 and 2 undergo a transition to a weak ferromagnetic state.