Axial Cu-O Bonds Research Articles

A new approach to study semi-coordination using two 2-methyl-5-nitroimidazole copper(ii) complexes of biological interest as a model system.

Two novel copper(ii) complexes [Cu(2mni)2(H2O)2](NO3)2·2H2O (1) and [Cu(2mni)2(NO3)2] (2), where 2mni is 2-methyl-5-nitroimidazole, were prepared and characterized in the solid state using single-crystal and powder X-ray diffraction analyses, EPR, electronic and vibrational spectroscopies (FTIR and Raman), and thermogravimetric methods. Both products present an elongated distorted octahedral geometry with axial Cu-O bond lengths of 2.606(14) and 2.593(15) Å, indicating semi-coordination. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ theory level were used to study the electronic properties of 1 and 2. The Independent Gradient Model (IGM) was employed to determine the Intrinsic Bond Strength Index (IBSI) of the semi-coordination and to plot δg isosurfaces for the electronic sharing between the metal center and ligands. A moderate to weak antibacterial activity against Escherichia coli cultures was found for 1 with a 50% growth inhibition (GI50) value of 0.25 mmol L-1. To the best of our knowledge, this is the first time that the semi-coordination analysis using IGM was carried out for a copper(ii) complex with axial elongation, finding a good correlation between the bond length and the IBSI, and the study was extended for a series of analogous complexes described in the literature.

Structural and Magnetic Characterization of Homo- and Heterometallic Trinuclear Ni(II) and Cu(II) Clusters with N2O6 Acyclic Polydentate Ligand

Homo- and heterometallic trinuclear complexes with an acyclic N2O6-type ligand, [Ni3(L)2(CH3COO)2]·H2O·MeOH (1) and [NiCu2(L)2(CH3COO)2]·3H2O (2) (H2L = N,N′-(hexane-1,6-diyl)bis(2-hydroxy-3-methoxybenzamide), were prepared, respectively, of which crystal structures as well as magnetic properties were characterized. The axial Cu-O bond lengths in complex 2 are 2.338–2.413 Å, unlike Ni-O, due to the axial bond elongation by the Jahn-Teller effect in Cu(II) complexes. Magnetic analyses revealed that both complexes showed intra-cluster ferromagnetic interactions with S = 3 for 1 and S = 2 for 2, respectively.

The first structural characterization of the proton-ated aza-cyclam ligand in catena-poly[[[(perchlorato)copper(II)]-μ-3-(3-carb-oxy-prop-yl)-1,5,8,12-tetra-aza-3-azonia-cyclo-tetra-deca-ne] bis-(per-chlorate)

The asymmetric unit of the title com-pound, catena-poly[[[(perchlorato-κO)copper(II)]-μ-3-(3-carb-oxy-prop-yl)-1,5,8,12-tetra-aza-3-azonia-cyclo-tetra-decane-κ4 N 1,N 5,N 8,N 12] bis-(per-chlorate)], {[Cu(C13H30N5O2)(ClO4)](ClO4)2} n , (I), consists of a macrocyclic cation, one coordinated per-chlorate anion and two per-chlorate ions as counter-anions. The metal ion is coordinated in a tetra-gonally distorted octa-hedral geometry by the four secondary N atoms of the macrocyclic ligand, the mutually trans O atoms of the per-chlorate anion and the carbonyl O atom of the protonated carb-oxy-lic acid group of a neighbouring cation. The average equatorial Cu-N bond lengths [2.01 (6) Å] are significantly shorter than the axial Cu-O bond lengths [2.379 (8) Å for carboxyl-ate and average 2.62 (7) Å for disordered per-chlorate]. The coordinated macrocyclic ligand in (I) adopts the most energetically favourable trans-III conformation with an equatorial orientation of the substituent at the protonated distal 3-position N atom in a six-membered chelate ring. The coordination of the carb-oxy-lic acid group of the cation to a neighbouring com-plex unit results in the formation of infinite chains running along the b-axis direction, which are cross-linked by N-H⋯O hydrogen bonds between the secondary amine groups of the macrocycle and O atoms of the per-chlorate counter-anions to form sheets lying parallel to the (001) plane. Additionally, the extended structure of (I) is consolidated by numerous intra- and interchain C-H⋯O contacts.

Crystal structures of trans-di-aqua-(3-R-1,3,5,8,12-penta-aza-cyclo-tetra-deca-ne)copper(II) isophthalate hydrates (R = benzyl or pyridin-3-ylmethyl).

The asymmetric units of the title compounds, trans-di-aqua-(3-benzyl-1,3,5,8,12-penta-aza-cyclo-tetra-decane-κ4 N 1,N 5,N 8,N 12)copper(II) isophthalate monohydrate, [Cu(C16H29N5)(H2O)2](C8H4O4)·H2O, (I), and trans-di-aqua-[3-(pyridin-3-ylmeth-yl)-1,3,5,8,12-penta-aza-cyclo-tetra-decane-κ4 N 1,N 5,N 8,N 12]copper(II) iso-phthalate 0.9-hydrate, [Cu(C15H28N6)(H2O)2](C8H4O4)·0.9H2O, (II) consist of one di-aqua macrocyclic cation, one di-carboxyl-ate anion and uncoordinated water mol-ecule(s). In each compound, the metal ion is coordinated by the four secondary N atoms of the macrocyclic ligand and the mutually trans O atoms of the water mol-ecules in a tetra-gonally distorted octa-hedral geometry. The average equatorial Cu-N bond lengths are significantly shorter than the average axial Cu-O bond lengths [2.020 (9) versus 2.495 (12) Å and 2.015 (4) versus 2.507 (7) Å for (I) and (II), respectively]. The coordinated macrocyclic ligand in the cations of both compounds adopts the most energetically favorable trans-III conformation. In the crystals, the complex cations and counter-anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles and the O-H groups of coordinated water mol-ecules as the proton donors and the O atoms of the carboxyl-ate as the proton acceptors. Additionally, as a result of O-H⋯O hydrogen bonding with the coordinated and water mol-ecules of crystallization, the isophthalate dianions form layers lying parallel to the (01) and (100) planes in (I) and (II), respectively.

Synthesis, structural characterization, EPR spectroscopy and Hirshfeld surface analysis of a novel Cu2+-doped 3,14-diethyl-2,13-diaza-6,17-diazoniatricyclo[16.4.0.07,12]docosane bis(perchlorate).

Cyclam derivatives and their metal complexes have been found to exhibit an anti-HIV effect and stimulate the activity of stem cells from bone marrow. The strength of their binding to the CXCR4 receptor correlates with anti-HIV and stem-cell activities. Knowledge of the conformation and crystal packing of various macrocyclic metal complexes has become important in developing new effective anti-HIV drugs. The synthesis and preparation of single crystals of a new Cu2+-doped macrocyclic compound, (3,14-diethyl-2,6,13,17-tetraazatricyclo[16.4.0.07,12]docosane)copper(II) bis(perchlorate)-3,14-diethyl-2,13-diaza-6,17-diazoniatricyclo[16.4.0.07,12]docosane bis(perchlorate) (0.69/0.31), {[Cu(C22H44N4)](ClO4)2}0.69·(C22H46N42+·2ClO4-)0.31, is reported. Characterization by X-ray diffraction analysis shows that the asymmetric unit contains half of a centrosymmetric molecule. The macrocyclic ligand in the compound adopts the most stable trans-III conformation. The Cu-N distances of 2.015 (3) and 2.047 (3) Å are normal, but the long axial Cu-O bond of 2.795 (3) Å may be due to a combination of the Jahn-Teller effect and the strong in-plane ligand field. The crystal structure is stabilized by hydrogen bonding between secondary N-H groups, the N atoms of the macrocycle and the O atoms of the perchlorate anions. Hirshfeld surface analysis with 2D (two-dimensional) fingerprint plots indicates that the main contributions to the crystal packing are from H...H (58.0%) and H...O/O...H (41.9%) interactions. Electron paramagnetic resonance (EPR) properties are also described.

Synthesis of Hetero- and Homo-multinuclear Complexes with a Tetracyanonickelate Anion: Structural Characterization [Cu(bcen)Ni(CN)4]2.

Two new complexes [Cu(bcen)Ni(CN)4]2 (1) and [Ni(bcen)Ni(CN)4] (2) where bcen is 4,7-diazadecanediamide, were synthesized by reaction of equimolar amounts of M(NO3)2 (M = Cu and Ni), bcen ligand and K2[Ni(CN)4]. Single-crystal X-ray diffraction analysis of compound 1, shows that the bcen ligand acts as a tridentate chelate, coordinating to the Cu(II) ion via the two nitrogen atoms of the amine groups and one oxygen atom of one amide group, and the other amide unit is left uncoordinated. The coordination geometry around the Cu(II) ions is five coordinate with a distorted square pyramid geometry, comprising two nitrogen atoms and one oxygen atom belonging to the bcen ligand and two nitrogen atoms of the cyano groups of two Ni(CN)4 2- units. The distance between the copper ion and the amide oxygen of the dangling arm of an adjacent tetranuclear species is within the expected range for an axial Cu-O bond, and hence suggests that the amide oxygen of an adjacent tetranuclear complex may weakly coordinate to the copper ion in an axial position. These contacts link the tetranuclear species into infinite chain polymers.

Crystal Growth of Cu6(Ge,Si)6O18·6H2O and Assignment of UV-VIS Spectra in Comparison to Dehydrated Dioptase and Selected Cu(II) Oxo-Compounds Including Cuprates

Low-dimensional quantum spin systems with the Cu2+ central ion are still in the focus of experimental and theoretical research. Here is reported on growth of mm-sized single-crystals of the low-dimensional S = 1/2 spin compound Cu6(Ge,Si)6O18·6H2O by a diffusion technique in aqueous solution. A route to form Si-rich crystals down to possible dioptase, the pure silicate, is discussed. Motivated by previously reported incorrect assignments of UV-VIS spectra, the assignment of dd excitations from such spectra of the hexahydrate and the fully dehydrated compound is proposed in comparison to dioptase and selected Cu(II) oxo-compounds using bond strength considerations. Non-doped cuprates as layer compounds show higher excitation energies than the title compound. However, when the antiferromagnetic interaction energy as Jz·ln(2) is taken into account for cuprates, a single linear relationship between the Dqe excitation energy and equatorial Cu(II)-O bond strength is confirmed for all compounds. A linear representation is also confirmed between 2A1g energies and a function of axial and equatorial Cu-O bond distances if auxiliary axial bonds are used for four-coordinated compounds. The quotient Dt/Ds of experimental orbital energies deviating from the general trend to smaller values indicates the existence of H2O respectively Cl− axial ligands in comparison to oxo-ligands, whereas larger Dt/Dqe values indicate missing axial bonds. The quotient of the excitation energy 2A1g by 2·2Eg-2B2g allows checking for correctness of the assignment and to distinguish between axial oxo-ligands and others like H2O or Cl−.

Crystal structure of trans-(1,8-dibutyl-1,3,6,8,10,13-hexa-aza-cyclo-tetra-decane-κ(4) N (3),N (6),N (10),N (13))bis-(perchlorato-κO)copper(II) from synchrotron data.

The structure of the title compound, [Cu(ClO4)2(C16H38N6)] has been determined from synchrotron data, λ = 0.62988 Å. The asymmetric unit comprises one half of the Cu(II) complex as the Cu(II) cation lies on an inversion center. It is coordinated by the four secondary N atoms of the macrocyclic ligand and the mutually trans O atoms of the two perchlorate ions in a tetra-gonally distorted octa-hedral geometry. The average equatorial Cu-N bond length is significantly shorter than the average axial Cu-O bond length [2.010 (4) and 2.569 (1) Å, respectively]. Intra-molecular N-H⋯O hydrogen bonds between the macrocyclic ligand and uncoordinating O atoms of the perchlorate ligand stabilize the mol-ecular structure. In the crystal structure, an extensive series of inter-molecular N-H⋯O and C-H⋯O hydrogen bonds generate a three-dimensional network.

Crystal structure of anhydrous poly[bis-(μ2-sarcosinato-κ(3) O,N:O')copper(II)

The title compound, [Cu(C3H6NO2)2] n , is a bis-complex of the anion of sarcosine (N-methyl-glycine). The asymmetric unit consists of a copper(II) ion, located on a center of inversion, and one mol-ecule of the uninegative sarcosinate anion. The copper(II) ion exhibits a typical Jahn-Teller distorted [4+2] coordination geometry. The four shorter equatorial bonds are to the nitro-gen and carboxyl-ate O atoms of two sarcosinate anions, and the longer axial bonds are to carboxyl-ate O atoms of neighboring complexes. The overall structure is made up from two chains formed by these longer axial Cu-O bonds, one extending parallel to [011] and the other parallel to [0-11]. Each one-dimensional array is connected by the equatorial bridging moieties to the chains on either side, creating an extended two-dimensional framework parallel to (100). There is a single inter-molecular hydrogen-bonding inter-action within the sheets between the amino NH group and an O atom of an adjacent mol-ecule.

Thermochromism, the Alexandrite Effect, and Dynamic Jahn–Teller Distortions in Ho2Cu(TeO3)2(SO4)2

A 3d-4f heterobimetallic material with mixed anions, Ho2Cu(TeO3)2(SO4)2, has been prepared under hydrothermal conditions. Ho2Cu(TeO3)2(SO4)2 exhibits both thermochromism and the Alexandrite effect. Variable temperature single crystal X-ray diffraction and UV-vis-NIR spectroscopy reveal that changes in the Cu(II) coordination geometry result in negative thermal expansion of axial Cu-O bonds that plays a role in the thermochromic transition of Ho2Cu(TeO3)2(SO4)2. Magnetic studies reveal an effective magnetic moment of 14.97 μB. which has a good agreement with the calculated value of 15.09 μB.

Copper(ii) complex of methionine conjugated bis-pyrazole based ligand promotes dual pathway for DNA cleavage

Three Cu(II) complexes of bis-pyrazole based ligands have been synthesized and structurally characterized by X-ray crystallography. One of the ligand (L2) contains a methionine ester conjugated to a bis-pyrazole carboxylate through an amide linkage. The binding constant for complexes 1-3 with CT DNA are of the order of 10(4) M(-1). The crystal structure suggests that the axial Cu-O bonds (ca. 2.31(4) Å) are relatively labile and hence during the redox cycle with ascorbic acid and oxygen one or both the axial Cu-O bonds might open to promote copper oxygen reaction and generate ROS. The chemical nuclease activity of complexes 1-3 in dark, show complete relaxation of supercoiled DNA at 100 μM concentration in presence of ascorbic acid (H2A). The mechanistic investigation suggests that the complexes 1 and 2 show involvement of peroxo species whereas 3 shows involvement of both singlet oxygen and peroxo species in DNA cleavage. The singlet oxygen formation in dark is otherwise unfavourable but the presence of methionine as pendant arm in L2 might activate the generation of singlet oxygen from the metal generated peroxo species. The results of DNA cleavage studies suggest that methionine based copper(II) complexes can promote dual pathway for DNA cleavage. Probing the cytotoxic activity of these complexes on MCF-7, human breast cancer cell line shows that 3 is the most effective one with an IC50 of 70(2) μM.

The effect of pressure on Cu-btc: framework compression vs. guest inclusion

Here we present detailed structural data on the effect of high pressure on Cu-btc. Application of pressure causes solvent to be squeezed into the pores until a phase transition occurs, driven by the sudden compression and expansion of equatorial and axial Cu-O bonds.

Metal‐Organic Niccolite: Synthesis, Structures, Phase Transition, and Magnetic Properties of [CH3NH2(CH2)2NH2CH3][M2(HCOO)6] (M=divalent Mn, Fe, Co, Ni, Cu and Zn)

We report the synthesis, crystal structures, thermal and magnetic characterizations of a family of metal-organic frameworks adopting the niccolite (NiAs) structure, [dmenH(2)(2+)][M(2)(HCOO)(6)(2-)] (dmen=N,N'-dimethylethylenediamine; M=divalent Mn, 1Mn; Fe, 2Fe; Co, 3Co; Ni, 4Ni; Cu, 5Cu; and Zn, 6Zn). The compounds could be synthesized by either a diffusion method or directly mixing reactants in methanol or methanol-water mixed solvents. The five members, 1Mn, 2Fe, 3Co, 4Ni, and 6Zn are isostructural and crystallize in the trigonal space group P31c, while 5Cu crystallizes in C2/c. In the structures, the octahedrally coordinated metal ions are connected by anti-anti formate bridges, thus forming the anionic NiAs-type frameworks of [M(2)(HCOO)(6)(2-)], with dmenH(2)(2+) located in the cavities of the frameworks. Owing to the Jahn-Teller effect of the Cu(2+) ion, the 3D framework of 5Cu consists of zigzag Cu-formate chains with Cu-OCHO-Cu connections through short basal Cu-O bonds, further linked by the long axial Cu-O bonds. 6Zn exhibits a phase transition probably as a result of the order-disorder transition of the dmenH(2)(2+) cation around 300 K, confirmed by differential scanning calorimetry and single crystal X-ray diffraction patterns under different temperatures. Magnetic investigation reveals that the four magnetic members, 1Mn, 2Fe, 3Co, and 4Ni, display spin-canted antiferromagnetism, with a Néel temperature of 8.6 K, 19.8 K, 16.4 K, and 33.7 K, respectively. The Mn, Fe, and Ni members show spin-flop transitions below 50 kOe. 2Fe possesses a large hysteresis loop with a large coercive field of 10.8 kOe. The Cu member, 5Cu, shows overall antiferromagnetism (both inter- and intra-chains) with low-dimensional characteristics.

Synthesis, properties, and molecular and crystal structure of hexaaquacopper(IV) bis(diaquacuprato-μ3-trihydroxyglutarato)germanate(IV) dihydrate [Cu(H2O)6][Ge(μ3-Thgl)2{Cu(H2O)2}2] · 2H2O

A procedure for the synthesis of the heteropolymetallic germanium(IV) and copper(II) complex with trihydroxyglutaric acid (H5Thgl) [Cu(H2O)6][Ge(μ3-Thgl)2{Cu(H2O)2}2] · 2H2O (I) was developed and the complex was isolated for the first time in the solid state. The product was characterized by elemental analysis, powder X-ray diffraction, thermogravimetry, and IR spectroscopy. Compound I was studied by X-ray crystallography. The crystals are monoclinic, a = 10.216(2)A, b = 12.272(3)A, c = 10.679(2)A, β = 93.13(3)°, V = 1336.9(5)A3, Z = 2, space group P21/n, R1 = 0.0261 for 3616 reflections with I > 2σ(I). Compound I is composed of bimetallic [Ge(μ3-Thgl)2{Cu(H2O)2}2]2− anions, [Cu(H2O)6]2+ cations, and water molecules of crystallization. In the centrosymmetric trinuclear complex anion, the Ge(1) atom is bound by two fully deprotonated bridging ligands to two Cu atoms. The Ge(1) atom is coordinated at distorted octahedron vertices by six hydroxyl oxygen atoms of two Thgl5− ligands (average Ge(1)-O distance is 1.8874(13)A). The Cu coordination polyhedron in the anion is an extended square pyramid (4 + 1) formed by the bridging hydroxyl oxygen atom (Cu(1)-O(3), 2.0039(12) A), two carboxyl oxygen atoms (average CU(1)-O distance is 1.9674(14)A) of two Thgl5− ligands, and two water oxygen atoms in equatorial and axial positions (Cu(1)-O, 1.9761(13) and 2.3643(14)A, respectively). In the centrosymmetric cation, the Cu coordination polyhedron is an extended square bipyramid (4 + 2). The equatorial Cu-O bond length is 1.9428(14) A (average), the axial Cu-O bond is elongated to 2.5151(14)A. The cations and anions are combined by H-bonds.

Metal–Organic Perovskites: Synthesis, Structures, and Magnetic Properties of [C(NH2)3][MII(HCOO)3] (M=Mn, Fe, Co, Ni, Cu, and Zn; C(NH2)3= Guanidinium)

We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal-organic perovskite ABX(3), [C(NH(2))(3)][M(II)(HCOO)(3)], in which A = C(NH(2))(3) is guanidinium, B = M is a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO(-). The compounds could be synthesized by either diffusion or hydrothermal methods from water or water-rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna2(1). In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti-anti formate bridges, thus forming the anionic NaCl-type [M(HCOO)(3)](-) frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn-Teller effect of Cu(2+) results in a distorted anionic Cu-formate framework that can be regarded as Cu-formate chains through short basal Cu-O bonds linked by the long axial Cu-O bonds. These materials show higher thermal stability than other metal-organic perovskite series of [AmineH][M(HCOO)(3)] templated by the organic monoammonium cations (AmineH(+)) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin-canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin-canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin-flop and a spin-flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics.

Crystal and molecular structure of four copper(II) ethylenediaminedisuccinates, [Cu2(RR,SS-Edds)] · 6H2O, Ba2[Cu(RR,SS-Edds)](ClO4)2 · 8H2O, Ba[Cu(SS-HEdds)]ClO4 · 2H2O, and Ba3[Cu2(RR,SS-Edds)2](ClO4)2 · 6H2O

Four Cu(II) complexes with the RR,SS-Edds4− and SS-HEdds3− anions are synthesized, and their crystal structures are studied. In the compounds [Cu2(RR,SS-Edds)] · 6H2O (I) and Ba2[Cu(RR,SS-Edds)](ClO4)2 · 8H2O (II), the ligand forms hexacoordinate chelate [Cu(Edds)]2− complexes with the N atoms and O atoms of the propionate groups in the equatorial positions and the O atoms of the acetate groups in the axial vertices. In the compounds Ba[Cu(SS-HEdds)]ClO4 · 2H2O (III) and Ba3[Cu2(RR,SS-Edds)2](ClO4)2 · 6H2O (IV), one of the propionate arms, the protonated arm in III and the deprotonated arm in IV, does not enter into the coordination sphere of the Cu atom. An acetate arm moves to its position in the equatorial plane, and the free axial vertex is occupied by an O atom of the perchlorate ion. In I–IV, the lengths of the equatorial Cu-N and Cu-O bonds fall in the ranges 1.970–2.014 and 1.921–1.970 A, respectively. The axial Cu-O bonds with the acetate groups and ClO4− anions are elongated to 2.293–2.500 and 2.727–2.992 A, respectively. In structure I, the second Cu atom acts as a counterion forming bonds with the O atoms of two water molecules and three O atoms of the Edds ligands. In II–IV, the Ba2+ cations are hydrated and bound to the O atoms of the anionic complexes and (except for one of the cations in IV) ClO4− anions. The coordination number of the Ba cations is nine. The structural units in I–IV are connected into layers. In I, an extended system of hydrogen bonds links the layers into a framework. In II and III, the layers are linked only by weak hydrogen bonds, one bond per structural unit. In IV, ClO4− anions are bound to the Ba and Cu atoms of neighboring layers, thus serving as bridges between the layers.

Bis{μ-6,6′-dimethoxy-2,2′-[propane-1,2-diylbis(iminomethylene)]diphenolato}bis[aquacopper(II)] dihydrate

In the title compound, [Cu(2)(C(19)H(24)N(2)O(4))(2)(H(2)O)(2)].2H(2)O, the asymmetric unit consists of one half of the bis{mu-6,6'-dimethoxy-2,2'-[propane-1,2-diylbis(iminomethylene)]diphenolato}bis[aquacopper(II)] complex and two water molecules. Two Cu(II) centres are bridged through a pair of phenolate groups, resulting in a complex with a centrosymmetric structure, with the centre of inversion at the middle of the Cu(2)O(2) plane. The Cu atoms are in a slightly distorted square-pyramidal coordination environment (tau = 0.07). The average equatorial Cu-O bond length and the axial Cu-O bond length are 1.928 (3) and 2.486 (3) A, respectively. The Cu-O(water) bond length is 2.865 (4) A, so the compound could be described as having a weakly coordinating water molecule at each Cu(II) ion and two solvent water molecules per dimetallic unit. The Cu...Cu distance and Cu-O-Cu angle are 3.0901 (10) A and 87.56 (10) degrees , respectively. The molecules are linked into a sheet by O-H...O and C-H...O hydrogen bonds parallel to the [001] plane.

In Situ Speciation Studies of Copper–Humic Substances in a Contaminated Soil during Electrokinetic Remediation

Speciation of copper-humic substances (HS) in the electrokinetic remediation (EKR) of a contaminated soil was studied by in situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies. The least-square fits of the XANES spectra suggested that the main Cu species in the contaminated soil were Cu-HS (50%), CuCO(3) (28%), Cu(2)O (11%), and CuO (11%). The Cu-HS in the contaminated soil possessed equatorial and axial Cu-O bond distances of 1.94 and 2.17 A with coordination numbers (CNs) of 3.6 and 1.4, respectively. In the EKR process, the axial Cu-O bond distance in the Cu-HS complexes was increased by 0.15 A, which might be due to a ligand exchange of the Cu-HS with H(2)O molecules in the electrolyte. After 180 min of EKR, about 50% of the Cu-HS complexes (or 24% of total Cu) in the soil were dissolved and formed [Cu(H(2)O)(6)](2+) in the electrolyte, 71% (or 17% of total Cu in the soil) of which were migrated to the cathode under the electric field (5 V/cm). This work exemplifies the use of in situ EXAFS and XANES spectroscopies for speciation studies of Cu chelated with HS in the contaminated soil during EKR.

Synthesis, Crystal and Molecular Structure of Mono- and Diaquadi(acetato-O)-Bis(2,4′-Bipyridyl) Copper(II)

The title compound has been synthesized and characterized by elemental analysis and conductivity studies. The crystal and molecular structure has been determined. There are two different types of molecules in the crystal: mono- and diaquadi(acetato-O)-bis(2,4'-bipyridyl) copper (II). Both copper atoms occupy special positions. The copper atoms show almost ideal square pyramidal (4 + 1) and square bipyramidal (4 + 2) coordination. Due to the Jahn-Teller effect, the axial Cu-O(water) bond distances are longer than respective equatorial Cu-O(acetate) bond distances. The bond valences of the copper were computed. An intramolecular strong hydrogen bond linking O(water) and O(acetate) atoms exists in the molecule. The differences of geometrical environment for copper in mono- and diaquadi(acetato-O)-bis(2,4'-bipyridyl) copper(II) are imposed by strong intermolecular hydrogen bonds creating a linear infinite chain structure along crystallographic x axis. Also weak intramolecular hydrogen bonds are present in the molecule.

Molecular scale characteristics of Cu(II) bonding in goethite–humate complexes

—Interactions between oxide minerals and natural organic matter affect metal adsorption properties of mineral surfaces, but the mechanisms of metal bonding are not well understood. Extended X-ray absorption fine structure (EXAFS) spectroscopy analyses were performed on aqueous pastes containing Cu(II) and goethite (α-FeOOH) with humic acid adsorbed at 0, 14, 28, 57, 88, 216, and 236 g kg −1 goethite, and with aqueous suspensions of humic acid only. Analyses were conducted at the Cu K edge with 40 mmol Cu(II) kg −1 goethite or 2 mmol Cu(II) kg −1 suspension for the humic acid system. Samples were equilibrated at pH 5.6 in a 0.1 M NaNO 3 background electrolyte. For all systems, analysis of EXAFS results suggests that Cu(II) is present in a distorted octahedral configuration containing four short equatorial (1.94–1.97 Å) and two longer axial bonds with oxygen. When the concentration of adsorbed humic acid on goethite was increased from 0 to 28 g kg −1, the axial Cu-O bond length decreased to 2.24 ± 0.03 Å, which was less than for individual humic acid (2.32 ± 0.02 Å) or goethite (2.29 ± 0.03 Å) samples. The apparent decrease in the axial Cu-O bond length was attributed to a decrease in the ligand field splitting energy. When humic acid ligands replace equatorial water molecules in the Cu(II) coordination sphere, a weaker ligand field strength occurs. For absorbed humic acid up to 88 g kg −1 goethite, second-shell iron neighbors were observed between 3.17 and 3.20 Å, suggesting that Cu(II) was bonded on average to both inorganic (goethite) and organic (humic acid) functional groups. In addition, derivative X-ray absorption near edge structure (XANES) spectra for Cu(II) on goethite–humate complexes (<88 g kg −1) were poorly fit by use of a linear combination of spectra for Cu(II) on goethite or humate alone. At humate concentrations between 216 and 236 g kg −1 goethite, second-shell iron neighbors could not be identified, and the Cu-O axial distance (2.32 ± 0.02 Å) and derivative XANES spectra strongly resembled that of Cu(II) adsorbed to humate only. Analysis of the XANES and EXAFS data suggested that Cu(II) was bonded on average to both inorganic and organic functional groups as a type A ternary complex at lower levels of adsorbed humate, and to organic groups as a type B complex at higher levels.