π Coordination de diazoalcanes sur le dicyclopentadienylvanadium (II)

The X-ray crystal and molecular structure of η⁵-cyclopentadienyl-η¹-2,4-diphenylcyclobut-1-en-3-oneiron dicarbonyl (I) was determined (monoclinic crystals, a 9.2371(9), b 26.4502(9), c 8.2450(7) Å, β 115.502(6)°, Z = 4, space group P2₁ /c, 1902 unique reflections, R = 0.068). Molecule I contains the η¹-cyclobut-1-en-3-one ligand with three sp² and one sp³ carbon atoms in a four-membered cycle, σ-bonded to the CpFe(CO)₂ fragment (bond distance FeC 1.935(6) Å).     

A coumarin based highly selective fluorescent chemosensor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a new coumarin based fluorescent chemosensor 1, in which tren and quinolone are introduced as receptors for sequential recognition of Cu²⁺ and PPi. The structure of chemosensor 1 was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. Sensor 1 showed an obvious “on-off” fluorescence quenching response toward Cu²⁺, and the quenching efficiency reached a maximum of 99.6% with the addition of 20 equiv. of Cu²⁺. The 1-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions, especially HPO₄^2? and H₂PO₄^?. The detection limit of sensor 1 was 1.9?×?10^?6?M to Cu²⁺ and 5.96?×?10^?8?M to PPi. In addition, sensor 1 showed a 1:1 binding stoichiometry to Cu²⁺ and sensor 1-Cu²⁺ showed a 2: 1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.4). The stable pH range of sensor 1 to Cu²⁺ and 1-Cu²⁺ to PPi was from 4 to 8.     

Charge dynamics of 57Fe probe atoms in La2Li0.5Cu0.5O4

The objective of this study is to characterize the electronic state and local surrounding of ⁵⁷Fe Mössbauer probe atoms within iron-doped layered perovskite La₂Li_0.5Cu_0.5O₄ containing transition metal in unusual formal oxidation states “+3”. An approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that a large amount of charge is transferred via Cu-O bonds from the O: 2p bands to the Cu: 3d orbitals and the ground state is dominated by the d⁹L configuration (“Cu²⁺-O^-” state). The dominant d⁹L ground state for the (CuO₆) sublattice induces in the environment of the ⁵⁷Fe probe cations a charge transfer Fe³⁺ + O⁻(L) → Fe⁴⁺ + O²⁻, which transforms “Fe³⁺” into “Fe⁴⁺” state. The experimental spectra in the entire temperature range 77–300 K were described with the use of the stochastic two-level model based on the assumption of dynamic equilibrium between two Fe³⁺↔Fe⁴⁺ valence states related to the iron atom in the [Fe(1)O₄]^4- center. The relaxation frequencies and activation energies of the corresponding charge fluctuations were estimated based on Mössbauer data. The results are discussed assuming a temperature-induced change in the electronic state of the [CuO₄]^5- clusters in the layered perovskite.     

Crystal structure and magnetic properties of [{Cu(cyclam)}3{Fe(CN)6}2] · 6H2O,a cyano-bridged assembly with a rope-ladder chain structure

The synthesis, crystal structure and magnetic properties of the cyano-bridged complex [{Cu(cyclam)}₃{Fe(CN)₆}₂] · 6H₂O are reported. Its structure is made up of centrosymmetric S-shaped pentanuclear [{Cu(cyclam}₃{Fe(CN)₆)}₂] units, in which three [Cu(cyclam)]²⁺ units are alternatively bridged by two trans-CN groups of [Fe(CN)₆]³⁻ anions and water molecules. The pentanuclear Fe₂Cu₃ units are held together by two complementary and very weak Fe–CN?Cu1 bonds, forming a rope-ladder chain along the c axis. The compound exhibits a ferromagnetic interaction between the Cu(II) and Fe(III) ions as a consequence of the orthogonality of their magnetic orbitals of σ and π nature, respectively. The magnetic data were fitted to the calculated magnetic susceptibility equation for a pentanuclear model, leading to the following magnetic parameters: J₁ = 9.0(3) cm⁻¹, J₂ = 3.8(4) cm⁻¹, g = 2.2, θ = −1.2 K. These results show that the interactions through the long Cu–N axial bonds are not so weak as is usually assumed.     

A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

A new azoimine receptor, R₁, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F^? and also toward Cu²⁺ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F^? followed by Cu²⁺ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R₁ + F^? operated as an “OFF–ON” fluorescent sensor for Cu²⁺ ions. Considering emission intensity and absorption wavelength for F^? and Cu²⁺ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R₁ behaved as a molecular security keypad lock with F^? and Cu²⁺ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460?nm.     

Two new cyano-bridged Cu(II)-Fe(II) complexes: Synthesis and crystal structures

Two new cyano-bridged Cu(II)-Fe(II) binuclear complexes, [Cu(L¹)Fe(CN)₅(NO)] (I) [L¹ = 1,3,6,8,11,14-hexaazatricyclo[12.2.1.1^8,11]octadecane and [Cu(L²)Fe(CN)₅(NO)] · 2H₂O (II) L² = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane, have been assembled and structurally characterized by spectroscopy and X-ray crystallography. Complex I crystallizes in the monoclinic crystalline system of space group P2₁/c, while complex II crystallizes in the monoclinic crystalline system of space group P2₁/n. These two complexes assume a binuclear structure in which the Fe²⁺ ion is in an octahedron environment and the Cu²⁺ ion is in a square-prism geometry environment.     

Cyanonitrosylferrate und Cyanocarbonylnitrosylferrate niedriger Oxydationsstufen

Cyanonitrosylferrates and Cyanocarbonylnitrosylferrates of Low Oxidation States By the reduction of sodium nitroprusside with alkali metals in liquid ammonia the cyanonitrosylferrates [Fe[CN]₅, NO]^3?, [Fe(CN)₄, NO]^2?, [Fe(CN)₄N0]^3? and [Fe(CN)₃N0]^4? are formed. Preparation and properties of these reduction products (Table 1) and of the cyanocarbonylnitrosylferrates still missing within the series [Fe(CN)_n(CO)_3?nNO]^(n+l)? (n = 1 and 2) are described. Structure and bonding of these complexes are discussed with respect to their magnetic properties and their i.r. spectra.     

Correlation between thermal electron transfer in solution and photoelectron emission

The activation free energy for electron transfer in solution or at electrodes is correlated to the corresponding Franck—Condon determined reorganization free energy R_m for photoelectron emission. Excellent to fair agreement is obtained between the activation free energies predicted from R_m and experimental values. Data are given for V²⁺, Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, and Fe(CN)^4?₆ in aqueous solution.     

Electrochemical studies of nitroprusside in the presence of copper(II): formation of Cu(I) reduced nitroprusside species

Cu²⁺ is reduced in the presence of nitroprusside to form two Cu(I) reduced nitroprusside species at about +0.050 V (pH 7.6). These species are reduced further at about −0.60 V. The two species are formed by an EC mechanism, and the species are believed to be [Cu^IFe(CN)₄NO]⁻, which predominates in acidic solution, and [Cu^IFe(CN)₅NO]²⁻, which predominates in alkaline solution. These conclusions are supported by cyclic voltammetric and bulk electrolysis/coulometric experiments.     

Sur de nouveaux ferrites oxyfluorés d'yttrium ou de gadolinium à structure grenat

The oxyfluoride garnets of formula Y₃Fe_5?xM_xO_12?xF_x and Gd₃Fe_5?xM_xO_12?xF_x (M = 3d transition element) result from partial substitution of O^2? by F^? in Y₃Fe₅O₁₂ and Gd₃Fe₅O₁₂ oxides. The cationic charge compensation is obtained by replacing the Fe³⁺ ions by divalent ions as Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ or Zn²⁺ ions. The site occupied by some of these ions (Mn²⁺, Ni²⁺, Zn²⁺) is determined by magnetic or Mössbauer measurements.     

The electrochemical Peltier effect observed with electrode reactions of Fe(II)/Fe(III) redox couples at a gold electrode

The electrochemical Peltier effect was studied at a gold electrode in solutions containing some Fe(II)/Fe(III) redox couples by measuring the local temperature change in the electrode/solution interphase under controlled-potential and controlled-current polarization. Relative values of the electrochemical Peltier coefficient for the cathodic process at equilibrium potential, which is denoted by (Π_c)_I=0, were determined by analyzing the observed temperature change as a function of current. The values of (Π_c)_I=0 were found to be positive for the Fe(H₂O)₆²⁺/Fe(H₂O)₆³⁺ systems in HClO₄ (1 M), HNO₃ (1 M), H₂SO₄ (0.5 M), and HCl (1 M), their magnitudes being very similar in the first three acid solutions, but smaller in the HCl solution. On the other hand, a negative value of (Π_c)_I=0 was obtained in the case of a Fe(CN)₆^4?/Fe(CN)₆^3? couple in a H₂SO₄ (0.5 M) solution. Such a difference in the Peltier coefficient is considered to be due to the difference in the ionic species of iron involved in the electrode reaction.     

Electrodes of Conductive Metallic Oxides : Part B. S. Trasatti (Editor). Studies in Physical and Theoretical Chemistry,Vol. 11. Elsevier,Amsterdam, 1981, xvi + 366 pp. $72.25, Dfl.170.00.

Chronoamperometry, chronocoulometry and chronopotentiometry were applied to measure apparent diffusion coefficients, D_app, for Mo(CN)₈^4?, W(CN)₈^4?, Fe(CN)₆^3? and Fe(CN)₆^4? bound electrostatically within coatings of protonated poly(4-vinylpyridine) on graphite electrodes. The relative advantages of the three experimental techniques are discussed. Values of D_app for the incorporated anions showed a strong decrease as the anion concentration within the coating increased until a steady value was reached at anion concentrations near 1 M. Some of the factors that may contribute to this behavior are discussed.     

Electron-transfer rate constants for redox systems of Fe(III)/Fe(II) complexes with 2,2′-bipyridine and/or cyanide ion as measured by the galvanostatic double pulse method

The formal standard rate constants for the redox systems, Fe(bipy)₃³⁺/Fe(bipy)₃²⁺,Fe(bipy)₂(CN)₂^?/Fe(bipy)₂(CN)₂, Fe(bipy)(CN)₄^?/Fe(bipy)(CN)₄^2? and Fe(CN)₆^3?/Fe(CN)₆^4? (bipy=2,2′-bipyridine), in aqueous solution and N,N-dimethylformamide solution are measured with the aid of the galvanostatic double pulse method. The standard rate constant decreases as the number of the coordinated 2,2′-bipyridine decreases. It is in accordance with the trend in the homogeneous rate constants for these systems and is interpreted on the basis of the extension of ligand π-orbitals. This finding may be evidence for the mechanistic similarity of the electrochemical electron-transfer reaction of a redox system to the corresponding homonuclear electron-exchange reaction occurring in solution phase. An empirical relation between rate constants for both kinds of reactions is discussed. It is noted that the maximum electrochemical rate constant is limited at a value much smaller than the one theoretically allowed.     

Synthesis and applications of cyano‐vinylene‐based polymers containing cyclopentadithiophene and dithienosilole units for photovoltaic cells

Two β‐cyano‐thiophenevinylene‐based polymers containing cyclopentadithiophene ( CPDT‐CN ) and dithienosilole ( DTS‐CN ) units were synthesized via Stille coupling reaction with Pd(PPh₃)₄ as a catalyst. The effects of the bridged atoms (C and Si) and cyano‐vinylene groups on their thermal, optical, electrochemical, charge transporting, and photovoltaic properties were investigated. Both polymers possessed the highest occupied molecular orbital (HOMO) levels of about ?5.30 eV and the lowest unoccupied molecular orbital (LUMO) levels of about ?3.60 eV, and covered broad absorption ranges with narrow optical band gaps (ca. 1.6 eV). The bulk heterojunction polymer solar cell (PSC) devices containing an active layer of electron‐donor polymers ( CPDT‐CN and DTS‐CN ) blended with an electron‐acceptor, that is, [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM), in different weight ratios were explored under 100 mW/cm² of AM 1.5 white‐light illumination. The PSC device based on DTS‐CN: PC₇₁BM (1:2 w/w) exhibited a best power conversion efficiency (PCE) value of 2.25% with V_oc = 0.74 V, J_sc = 8.39 mA/cm², and FF = 0.36. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Anhydrous tin and lead hexacyanoferrates (II).: Part I. Synthesis and crystal structure.

The crystal structure of Pb₂Fe(CN)₆ and Sn₂Fe(CN)₆ has been first determined and refined using the Rietveld method with combined CuKα₁ X-ray and constant-wavelength neutron powder diffraction data in space group P-3 (147, Z=1). The unit cell constants are a=7.1346(1) and 7.1805(1) Å, c=5.4531(2) and 5.3639(1) Å, respectively. The compounds are layered, groups of three nearest [Fe(CN)₆]⁴⁻-complexes are joined to layers by means of Pb or Sn atoms. The same Pb or Sn atoms (c.n.=3+3) joint three nearest complexes from the next layer. The jointing goes through ‘nitrogenlead(tin)nitrogen’ bonds.     

Reactions between YBa2Cu3O7−δ and La2O3 and SrCO3

Solid state reactions at 925°C between the high-T _c ceramic superconductor YBa₂Cu₃O_7?δ and La₂O₃ and SrCO₃, respectively, mixed in various molar ratiosr=MeO_n/YBa₂Cu₃O_7?δ, were studied using X-ray powder diffraction and scanning electron microscopy. The reaction between YBa₂Cu₃O_7?δ and La₂O₃ yielded (La_1?xBa_x)₂CuO_4?δ, withx≈0.075?0.10. La_2?xBa_1+xCu₂O_6?δ, withx≈0.2?0.25 and La-doped (Y_1?xLa_x)₂BaCuO₅, withx≈0.10?0.15. Forr=3.0, Y-doped La₂BaCuO₅ resulted also. The reaction between YBa₂Cu₃O_7?δ and SrCO₃ yielded (Sr_1?zBa_z)₂CuO₃, withz≈0.1, Y₂(Ba_1?zSr_z)CuO₅, withz=0.1?0.15, and a nonsuperconducting compound with an approximate composition of Y(Ba_0.5Sr_0.5)₅Cu_3.5O_10±δ. At values ofr≤2.0, unsubstituted YBa₂Cu₃O_7?delta was found in the reaction products.     

Cyanide-bridged complexes based on dinuclear Cu(II)-M(II) [M = Pb and Cu] building blocks: Synthesis, crystal structures and magnetic properties

Four cyanide-bridged heterometallic complexes {[CuPb(L 1 )][Fe III (bpb)(CN) 2 ]} 2 ·(ClO 4 ) 2 ·2H 2 O·2CH 3 CN (1), {[CuPb(L 1 )] 2 [Fe II (CN) 6 ](H 2 O) 2 }·10H 2 O (2), {[Cu 2 (L 2 )][Fe III (bpb)(CN) 2 ] 2 }·2H 2 O·2CH 3 OH (3) and {[Cu 2 (L 2 )] 3 [Fe III (CN) 6 ] 2 (H 2 O) 2 }·10H 2 O (4) have been synthesized by treating K[Fe III (bpb)(CN) 2 ] [bpb 2-=1,2-bis(pyridine-2-carboxamido)benzenate] and K 3 [Fe III (CN)] 6 with dinuclear compartmental macrocyclic Schiff-base complexes [CuPb(L 1 )] (ClO 4 ) 2 or [Cu 2 (L 2 )]·(ClO 4 ) 2 , in which H 2 L 1 was derived from 2,6-diformyl-4-methyl-phenol, ethylenediamine, and diethylenetriamine in the molar ratio of 2:1:1 and H 2 L 2 from 2,6-diformyl-4-methyl-phenol and propylenediamine in the molar ratio of 1:1. Single crystal X-ray diffraction analysis reveals that compound 1 displays a cyclic hexanuclear heterotrimetallic molecular structure with alternating [FeⅢ (bpb)(CN) 2 ]- and [CuPb(L 1 )] 2+ units. Complex 2 is of a neutral dumb-bell-type pentanuclear molecular configuration consisting of one [Fe(CN)6] 4- anion sandwiched in two [CuPu(L 1 )] 2+ cations, and the pentanuclear moieties are further connected by the hydrogen bonding to give a 2D supramolecular framework. Heterobimetallic complex 3 is a tetranuclear molecule composed of a centrosymmetric [Cu 2 (L2)] 2+ segment and two terminal cyanide-containing blocks [FeⅢ (bpb)(CN)2 ]- . Octanuclear compound 4 is built from two [Fe(CN)6]3- anions sandwiched in the three [Cu 2 L 2 ] 2+ cations. Investigation of their magnetic properties reveals the overall antiferromagnetic behavior in the series of complexes except 2.     

Electronic structures,chemical bonding,and defect formation in mixed cyanoferrates M<Subscript>2</Subscript>Cu[Fe(CN)<Subscript>6</Subscript>] (M = Na,K, Rb,and Cs)

The effect of the alkali metal nature on the electronic structures and chemical bonding in mixed cyanoferrates M₂Cu[Fe(CN)₆] (M = Na, K, Rb, and Cs) was studied by ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method (in the spin-polarized implementation) and the extended Hückel molecular orbital (EHMO) method. It was found that the X-ray photoelectron spectra of the ferrimagnetic compounds Na₂Cu[Fe(CN)₆] (I), K₂Cu[Fe(CN)₆] (II), Rb₂Cu[Fe(CN)₆] (III), and Cs₂Cu[Fe(CN)₆] (IV) are similar. The magnetic moments on Cu²⁺ and iron ions remain virtually constant in compounds I–IV (μ(Cu) = 0.9 μ_B, μ(Fe) < ?0.06 μ_B). Analyses of the electron density maps and the bond overlap populations showed that the cubic frameworks of cyanoferrates are built from stable fragments ?-Fe-C≡N-Cu-?. The bond strength in these fragments decreases substantially in the order C-N → Fe-C → Cu-N and only slight in the order IV → III → II → I. The calculated total energies of the cyanoferrates Cs_2?x Cu[Fe(CN)₆], CsHCu[Fe(CN)₆], and NaHCu[Fe(CN)₆] for different concentrations and configurations of defects (cesium vacanices and hydrogen substitution defects) suggest mutual repulsion of defects. This repulsion is responsible for the experimentally observed lowering of the ionic conductivity with an increase in the defect concentration in the mixed cyanoferrates.     

Two modifications of bis(μ2-chloro)tetrachlorodicuprate(II) bis[(18-crown-6)potassium]: Synthesis and crystal structure

Two crystal modifications of a novel complex bis(μ₂-chloro)tetrachlorodicuprate(II) bis[(18-crown-6)potassium, [K{(18-crown-6)}₂Cu₂Cl₆] were synthesized and studied by X-ray diffraction. The structures of two monoclinic modifications—Iα (space group P2₁/n, a = 9.053, b = 33.815, c = 13.469 Å, β = 101.29°, Z = 4) and Iβ (space group P2₁/c, a = 10.991, b = 8.187, c = 22.542 Å, β = 98.15°, Z = 2) were solved by the direct method and refined by the full-matrix least-squares method in anisotropic approximation to R = 0.073 (Iα) and 0.068 (Iβ) for 4883 (Iα) and 3525 (Iβ) independent reflections (CAD-4 automated diffractometer, λMoK _α). The molecules of Iα and Iβ consist of the central binuclear complex anion [Cu₂Cl₆]^2? and two peripheral host-guest cationic fragments [K(18-crown-6)]⁺, each linked with the [Cu₂Cl₆]^2? anions through the K-Cl bonds. The molecule of Iα and centrosymmetric Iβ molecule have different structures, since they have different orientation of the [K(18-crown-6)]⁺ fragments relative to the central [Cu₂Cl₆]^2? anion. The coordination polyhedron of the Cu²⁺ cation in the latter anion in Iα and Iβ is intermediate between flattened tetrahedron and square. In the [K(18-crown-6)]⁺ ions of Iα and Iβ, the K⁺ cation has the distorted hexagonal pyramidal coordination polyhedron with six O atoms of the 18-crown-6 ligand in a base and bifurcate vertex at two Cl atoms of the [Cu₂Cl₆]^2? anion. The 18-crown-6 ligands of Iα and Iβ have standard crown conformation.     

Novel coumarin-based containing denrons selective fluorescent chemosesor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a novel coumarin-based dendrons derivative CD and its chemical structure was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor CD showed an obvious “on-off” fluorescence quenching response toward Cu²⁺ with a maximum quenching efficiency of 99.8%. The CD-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions. The detection limit of the sensor CD was 0.29?×?10^?6?M to Cu²⁺ and 2.39?×?10^?9?M to PPi. In addition, the sensor CD showed a 1:1 binding stoichiometry to Cu²⁺ and the sensor CD-Cu²⁺ showed a 2:1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.2). The stable pH range of sensor CD to Cu²⁺ and CD-Cu²⁺ to PPi was from 3 to 8.