Magnetic Interactions through Imidazolate‐Bridges: Synthesis,Spectroscopy, Crystal Structure and Magnetic Properties of μ‐Imidazolato‐Bridged Copper(II) Complexes

The synthesis, characterization and crystal structures of substituted imidazolate bridged binuclear copper(II) complexes, [Cu₂(dien)₂(L)](ClO₄)₃, where dien = diethylenetriamine, L = imidazolate (im^—) ( 1 ), 2‐methylimidazolate (mim^—) ( 2 ) and benzimidazolate (bim^—) ( 3 ), are reported. The copper(II) ions of 1 — 3 posses a square planar coordination environment with dien coordinating as a tridentate ligand and the fourth position being occupied by a nitrogen atom of the bridging μ‐imidazolato group. In all three compounds the tendency to form additional long apical bonds at the copper(II) ions to the oxygen atoms of the perchlorate anions is observed. Temperature depended susceptibility data of polycrystalline samples reveal an antiferromagnetic coupling of the copper(II) atoms in 1 — 3 with J = —63.8, —75.4 and —36.8 cm^—1, respectively. Significant changes for these coupling constants could not be observed for measurements on frozen aqueous solutions. ESR spectra for solids and frozen solutions are consistent with intramolecular antiferromagnetic exchange interaction between the metal ions. From the data reported it can be concluded that the predominate mechanism for transmitting exchange coupling through the imidazolate bridge is due to a σ exchange pathways.     

Etude des complexes sulfosalicylate de cuivre(III), nickel(II), cobalt(II) et uranyle(II) a l'aide d'une resine echangeuse de cations: Study of the sulphosalicylate complexes ofcopper(II), nickel(II), cobalt(II) and uranyl(II) by means of cation-exchange resins.

Study of the sulphosalicylate complexes of copper(II), nickel(II), cobalt(II) and uranyl(II) by means of cation-exchange resins.The conditional stability constants of the 1:1 complexes of the sulphosalicylate ions (L^3-) with copper(II), nickel(II), cobalt(II) and uranyl ions have been determined in a sodium perchlorate solution (0.1 M) and at various pH values by a cation-exchange method based on Schubert's procedure. The limits of application of the method are discussed. The variation with pH of the conditional stability constants can be explained by the existence of the complexes: CuH₂L, CuHL, CuL^-; NiH₂L⁺, NiHL, NiL^-; CoHL, CoL^-; UO₂H₂L⁺, UO₂HL, UO₂L^-, UO₂LOH^2-. The stability constants of these complexes are reported. Distribution diagrams of the various complexes of each element with pH and total concentration of sulphosalicylate parameters are given.     

Synthesis, structure and magnetic properties of the pillared perovskites La5Re3MO16(M=Mg, Fe, Co, Ni)

Four new compounds La₅Re₃MgO₁₆ La₅Re₃FeO₁₆ La₅Re₃CoO₁₆ La₅Re₃NiO₁₆ have been prepared by solid-state reaction and characterized by X-ray and neutron powder diffraction and SQUID magnetometry. Rietveld refinement revealed that the four compounds are isostructural with La₅Re₃MnO₁₆ and crystallize in space group with cell parameters a=7.9370(3), 7.9553(5), 7.9694(7), and 7.9383(4) Å; b=7.9998(3), 7.9960(6), 8.0071(8), and 7.9983(5) Å; c=10.1729(4), 10.1895(7), 10.182(1), and 10.1732(6) Å; α=90.190(3)°, 90.270(3)°, 90.248(4) °, 90.287(3)°; β=94.886(2)°, 95.082(3)°, 94.980(4)°, 94.864(3)°; γ=89.971(4)°, 90.001(5)°, 89.983(6)°, 89.968(4)° for Mg, Fe, Co, and Ni, respectively. The structures are related to a layered perovskite. The layers of corner-sharing octahedra Re⁵⁺M²⁺O₆ (M²⁺=Mg, Fe, Co, Ni) are pillared by diamagnetic edge-sharing octahedra dimers, Re₂O₁₀, involving a Re=Re double bond. Three crystallographically independent lanthanum atoms occupy the three-dimensional interstices. All compounds obey the Curie-Weiss law at sufficiently high temperatures with Curie constants or effective magnetic moments near the expected values for the combination of Re⁵⁺(S=1) and M²⁺(S=0, 2, 3/2, 1 for Mg, Fe, Co, and Ni, respectively). Weiss constants, θ_C, are negative (−575, −84, −71, and −217 K for Mg, Fe, Co, and Ni, respectively) indicating the predominance of antiferromagnetic exchange coupling. The phases for M=Fe, Co and Ni show long-range order at 155, 33, 36 and 14 K, respectively. Neutron diffraction discloses a magnetic structure for the Fe series member consisting of ferrimagnetic perovskite layers coupled antiparallel along the stacking c-axis, direction which is consistent with the magnetic structure found recently for La₅Re₃MnO₁₆.     

Crystal Growth and Structure Determination of LaMIn5 (M=Co, Rh, Ir)

The compounds CeMIn₅ (M=Co, Rh, Ir) have been shown to exhibit heavy fermion behavior. In order to better understand this effect and the nature of the observed superconductivity, we have synthesized and characterized the non-magnetic analogs, LaMIn₅ (M=Co, Rh, Ir). The structures of LaCoIn₅, LaRhIn₅, and LaIrIn₅ were determined by single-crystal X-ray diffraction. CeMIn₅ and LaMIn₅ compounds are isostructural and adopt a tetragonal structure with space group P4/mmm, Z=1. Lattice parameters are a=4.6399(4) and c=7.6151(6) Å for LaCoIn₅, a=4.6768(3) and c=7.5988(7) Å for LaRhIn₅, and a=4.6897(6) and c=7.5788(12) Å for LaIrIn₅. We compare these experimental data with band structure computations and examine structural trends that affect the magnetic and transport properties of these compounds.     

Silylmethyl and silylamino groups as ligands in tin(II), tin(IV), lead(II) and lead(IV) compounds—a multinuclear magnetic resonance study

We have studied tin(II), tin(IV), lead(II) and lead(IV) compounds of the type M[CH(SiMe₃)₂]₂ (5), M[N(SiMe₃)₂]₂ (6), M[N(SiMe₃)SiMe₂^tBu]₂ (7), Me₃MCH₂SiMe₃ (1), Me₃MCH(SiMe₃)₂ (3), Me₃MNHSiMe₂^tBu (2), Me₃MN(SiMe₃)₂ (4), Me₂M[N(SiMe₃)₂]₂, (8) and (Me₃M)₂NSiMe₂^tBu (9) by ¹³C, ¹⁵N, ²⁹Si, ¹¹⁹Sn and ²⁰⁷Pb NMR spectroscopy. In some cases, two-dimensional (2-D) ¹³C/¹H and ²⁹Si/¹H heteroscalar-correlated NMR spectra served for the comparison of the signs of the respective coupling constants [ⁿJ(M ¹³C), ²J(M²⁹Si) and ⁿJ(M¹H)]. The ¹³C and ¹⁵N NMR parameter of comparable compounds (replacement of the CH or CH₂ fragment by a nitrogen atom or the NH group, respectively), show analogous trends. In the monomeric M(II) compounds (5, 6, 7) the peculiar electronic situation at the metal is reflected by the extreme deshielding of the metal nuclei (e.g. δ²⁰⁷ Pb for 5b = +9110 ppm), by the strongly deshielded ¹³C (5) and ¹⁵N nuclei (6, 7), as well as by large negative contributions to the reduced nuclear spin—spin coupling constants ¹K(M¹³C) (5) and ¹K(M¹⁵N) (6). In the M(II) compounds 5 the ¹¹⁹Sn and, in particular, the ²⁰⁷Pb longitudinal and transverse nuclear relaxation is dominated by the chemical-shift-anisotropy mechanism. This is also true for 6 and 7, in which the transverse relaxation rate is further increased by scalar relaxation of the second kind owing to partially relaxed scalar coupling ¹J(M¹⁴N).     

Crystal chemistry of M[PO2(OH)2]2·2H2O compounds (M=Mg, Mn, Fe, Co, Ni, Zn, Cd): Structural investigation of the Ni, Zn and Cd salts

The compounds M[PO₂(OH)₂]₂·2H₂O (M=Mg, Mn, Fe, Co, Ni, Zn, Cd) were prepared from super-saturated aqueous solutions at room temperature. Single-crystal X-ray structure investigations of members with M=Ni, Zn, Cd were performed at 295 and 120 K. The space-group symmetry is P2₁/n, Z=2. The unit-cell parameters are at 295/120 K for M=Ni: a=7.240(2)/7.202(2), b=9.794(2)/9.799(2), c=5.313(1)/5.285(1) Å, β=94.81(1)/94.38(1)°, V=375.4/371.9 Å³; M=Zn: a=7.263(2)/7.221(2), b=9.893(2)/9.899(3), c=5.328(1)/5.296(2) Å, β=94.79(1)/94.31(2)°, V=381.5/377.5 Å³; M=Cd: a=7.356(2)/7.319(2), b=10.416(2)/10.423(3), c=5.407(1)/5.371(2) Å, β=93.85(1)/93.30(2)°, V=413.4/409.1 Å³. Layers of corner-shared MO₆ octahedra and phosphate tetrahedra are linked by three of the four crystallographically different hydrogen bonds. The fourth hydrogen bond (located within the layer) is worth mentioning because of the short O_h?O bond distance of 2.57-2.61 Å at room temperature (2.56-2.57 Å at 120 K); only for M=Mg it is increased to 2.65 Å. Any marked temperature-dependent variation of the unit-cell dimension is observed only vertical to the layers. The analysis of the infrared (IR) spectroscopy data evidences that the internal PO₄ vibrations are insensitive to the size and the electronic configuration of the M²⁺ ions. The slight strengthening of the intra-molecular P-O bonds in the Mg salt is caused by the more ionic character of the Mg-O bonds. All IR spectra exhibit the characteristic “ABC trio” for acidic salts: 2900-3180 cm⁻¹ (A band), 2000-2450 cm⁻¹ (B band) and 1550-1750 cm⁻¹ (C band). Both the frequency and the intensity of the A band provide an evidence that the PO₂(OH)₂ groups in M[PO₂(OH)₂]₂·2H₂O compounds form weaker hydrogen bonds as compared with other acidic salts with comparable O?O bond distances of about 2.60 Å. The observed shift of the O-H stretching vibrations of the water molecule in the order M=Mg>Mn≈Fe≈Co>Ni>Zn≈Cd has been discussed with respect to the influence of both the character and the strength of M↔H₂O interactions.     

Composition, stability, and structure of Cu(II), Ni(II), and Co(II) complexes with adipic acid dihydrazide in aqueous and aqueous-ethanol solutions

Solvation and complexation of Cu(II), Ni(II), and Co(II) with adipic acid dihydrazide (L) in aqueous and aqueous-ethanol solutions (ethanol mole fraction 0.07–0.68) were studied by spectrophotometry. The formation constants of the species M(LH)³⁺, ML²⁺, M₂L⁴⁺ (μ = Cu²⁺, Ni²⁺, Co²⁺), and also M₂L ₂ ⁴⁺ and ML ₂ ²⁺ (μ = Cu²⁺, Ni²⁺) were determined. With Cu(II), the complexes Cu(LH) ₂ ⁴⁺ , CuL(LH)³⁺, and Cu₂L(LH)⁵⁺ were also detected and characterized. Evidence is given for the hydrazide coordination mode: tridentate in ML²⁺, bidentate in M(LH)³⁺ and ML ₂ ²⁺ , and tetradentate in M₂L⁴⁺ and M₂L ₂ ⁴⁺ . The ligand exchange reactions involving CuL²⁺, Cu(LH)³⁺, Cu(LH) ₂ ⁴⁺ , CuL(LH)³⁺, CuL ₂ ²⁺ , and Cu₂L(LH)⁵⁺ in aqueous solutions of Cu(II) were revealed and kinetically characterized by nuclear magnetic relaxation. The heretofore unknown rate constants of formation of these complexes were calculated from the thermodynamic and kinetic parameters. Factors controlling the rate constants of the complex formation and chemical exchange are discussed.     

CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds

The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G₄ dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds α-cyclodextrin (α-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus α-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K_SV = 65(5) × 10⁴ M⁻¹; ACNB, K_SV = 19(2) × 10⁴ M⁻¹; and, MNP, K_SV = 33(1) × 10² M⁻¹. These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L⁻¹ for MNB and ACNB and about 0.1 mg L⁻¹ for MNP. No interferences or small interferences are observed for trinitrotoluene [K_SV = 10(2) × 10² × M⁻¹], 2,4-dinitrotoluene [K_SV = 20(3) × 10 M⁻¹], 2,6-dinitrotoluene [K_SV = 11(4) × 10 M⁻¹] and nitrobenzene [K_SV = 2(1) × 10³ × M⁻¹].     

Development of oxopyrrolidine-based anti-cancer compounds: DNA binding, in silico, cell line studies, drug-likeness and mechanism at supra-molecular level

Due to an increasing demand for effective anti-cancer drugs, an oxopyrrolidine-based ligand, sodium 1-(3-(2-aminoethylamino)propyl)-5-oxopyrrolidine-2-carboxylate, was synthesised by the sodium hydride-assisted coupling of pyroglutamic acid with 1,3-diiodopropane under a nitrogen atmosphere. The intermediate thus formed was allowed to react with ethylenediamine in acetonitrile. The ligand formed individual complexes with Cu(II) and Ni(II) metal ions, respectively. The complexes were relatively resistant to degradation in PBS at physiological pH. The DNA-binding constants (K _b) for the ligand, copper and nickel complexes were 2.09 × 104 M^-1, 2.37 × 104 M^-1 and 2.11 × 104 M^-1, respectively, revealing the strong binding of these complexes with DNA. Haemolysis assays indicated that the ligand and its complexes were less toxic to rabbit RBCs than doxorubicin. Lipinski’s parameters calculated for the reported compounds indicated their good oral bioavailability. All the compounds exhibited good activities towards MCF-7 (wild type) cancer cell lines. The results of in silico studies, DNA-binding and anti-cancer activities indicated that the reported compounds might be interacting with DNA as one of their possible mechanisms of action.     

Spectrophotometric and potentiometric study of the cobalt(II)-thiocyanate system in aqueous medium

The cobalt(II)—thiocyanate system was spectrophotometrically studied at 2.0 M ionic strength (NaClO₄) and 25°C. The following formation constants were obtained: β₁ = 6.9 M^?, β₂ = 28.9 M^?2, β₃ = 12.1 M^?3 and β₄ = 1.30 M^?4. Three wavelengths were considered, 515, 590 and 615 nm, and the molar absorptivities of each species were calculated. Linear relationships were obtained for $\text{ε}$ vs $\text{n}$ and α_i. There is strong evidence that the tetrahedral [Co(SCN)₄]^2? is virtually the only species absorbing at 590 and 615 nm. An indirect potentiometric method led to comparable equilibrium constants. The cadmium(II)—thiocyanate formation constants used in the indirect method, under the same conditions, were found to be β₁ = 21.51 ± 0.09 M^?1, β₂ = 123 ± 1 M^?2, β₃ = 130 ± 3 M^?3 and β₄ = 173 ± 1.2 M^?4, in good agreement with earlier literature data.     

Studies on the effects of doping cesium metal(III) halides of the type Cs3MIII2X9 (MIII = Sb or Bi, X = Cl or Br)

A series of compounds, Cs₃M^III₂X₉ (M^III = Sb and Bi, X = Cl or Br) are doped with impurity ions (Ba²⁺, Ca²⁺, Sn²⁺, Pb²⁺, Mg²⁺, Fe²⁺, Tl³⁺, In³⁺, Se⁴⁺). Lattices doped with Sn(II), Pb(II) and Se(IV) are colored. Sn-119m Mössbauer data are consistent with the donation of Sn-5s electron density from tin(II) to a conduction band to give a pseudo-tin(IV) electronic environment.     

The potentiometric determination of stability constants of sulfite and cobalt(II) in ionic strength 2.0 M (NaClO4). Use of the matrix method

Determination of the stability constants for the system Co(II)/SO₃²⁻, was made potentiometrically using SO₃²⁻/HSO₃⁻ as buffers. Computation and matrix methods lead to the following overall stepwise constants: β₁ = 4.3 x 10² M⁻¹, β₂ = 2.2 x 10⁴ M⁻² and β₃ = 3.0 x 10⁶ M⁻³. The partial constants (M⁻¹) obtained were: K₁ = 4.3 x 10², K₂ = 51 and K₃ = 1.4 x 10². The HSO₃⁻ competition was eliminated by using the extrapolation procedure.     

The effect of the Co-anion,SCN−, on macrocycle-facilitated selective transport of Cd (II) over Ag (I) in an emulsion membrane

Emulsion membrane systems consisting of (1) an aqueous source phase containing 0.001 M Cd (NO₃)₂ and/or 0.001 M AgNO₃ and varying concentrations of SCN⁻, (2) a toluene membrane containing dicyclohexano-18-crown-6 (DC18C6) (0.02 M) and the surfactant Span 80 (sorbitan monooleate) (3% v/v), and (3) an aqueous receiving phase containing MgS₂O₃ or Mg (NO₃)₂ were studied with respect to the disappearance of Cd (II) and/or Ag (I) from the source phase as a function of time. The transport rate of Cd (II) was highest when a maximum amount of the Cd(II) in the source phase was present as Cd(SCN)₂ ([SCN⁻] =0.4 M). Cadmium(II) was transported over Ag(I), which is present mainly as Ag(SCN)₄³⁻, by 5- and 55-fold in 5 minutes with 0.4 M SCN⁻ in the source phase and 0.3 M S₂O²⁻₃ and 0.3 M NO⁻₃, respectively, in the receiving phase. In these competitive experiments, the total percent of Cd (II) transported was 98 and 84, respectively. The results are explained using the various equilibrium constants for cation-DC18C6, cation-SCN⁻ and cation-S₂O²⁻₃ interactions. These results indicate that rapid transport occurs when a cation is present in the source phase as a neutral complex. Selectivity for neutral species can be designed into these membrane systems when other cations interact with the source-phase anion to form charged species. Emulsion systems like those above were studied with respect to the appearance of Li⁺ in the source phase as a measure of membrane breakage. Maximum membrane stability was obtained when the ionic strengths of the source and receiving phases were equal.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

Mixed oxides of sodium, antimony (5+) and divalent metals (Ni, Co, Zn or Mg)

A family of α-NaFeO₂-type oxides Na_xM_(1+x)/3Sb_(2−x)/3O₂ (M=Ni, Co, Zn, Mg; x≈0.8 or 0.9) has been prepared by solid state reactions and characterized by powder XRD. At x=1, ordering occurs with tripling the unit cells and formula units. The powder patterns for Na₃M₂SbO₆ (M=Ni, Co) comply with both trigonal P3₁12 cell and monoclinic C2/m cell. The Ni compound exhibits also a series of extremely weak reflections (I<0.3%) that need doubling of the c axis, and the final cell is C2/c, a=5.3048(3), b=9.1879(4), c=10.8356(7), β=99.390(5). These ambiguities are explained by stacking faults. The compounds absorb atmospheric moisture with c-axis expansion up to 29%. A delafossite-related superlattice Ag₃Co₂SbO₆ has been prepared by ion exchange and refined: P3₁12, a=5.3842(2), c=18.6613(10). Ionic conductivity of the Na_0.8Ni_0.6Sb_0.4O₂ ceramics, 0.4 S/m at 300 °C, is greater than reported previously, presumably owing to the grain orientation produced by hot pressing.     

Broken symmetry density functional study of a mixed‐valence unsymmetrical dinuclear iron complex

Density functional theory (DFT) calculations with different exchange‐correlation functionals were performed for a mixed valence Fe(II)/Fe(III) binuclear complex with μ‐methoxo and two μ‐carboxylate bridging ligands, (1) with geometry optimizations being performed for all possible spin multiplicities (M_S = 2, 4, 6, 8, and 10). Within the exchange‐correlation functionals studied, only the hybrid GGA functionals B3P and B3LYP and also the pure GGA functional RPBE, predicts the geometry with high spin (S = 9/2) to be more stable than the geometry with low spin state (S = 1/2) by 20 kcal/mol, in agreement with the experimental findings. These functionals also predict the same stability order for the different spin states, being M_S = 10>8>6>2>4. The meta‐GGA functionals TPSS and TPSSh and also the pure GGA functionals BLYP and BP86 predict different stability orders. The computed average EPR g‐tensor, g_av, of 2.03, at the B3LYP level, is in good agreement with the experimental findings. Heisenberg exchange coupling constants, J, were calculated within the broken‐symmetry formalism, at the B3LYP level, showing that the two iron centers are antiferromagnetic coupling, with a very weak coupling constant of about ?7 cm^?1, in good agreement with the experimental value. Additionally, the effect of using different multiplicities of the reference geometries on the computed J value is discussed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

DFT broken-symmetry exchange couplings calculation in a 1D chain of bridged iron basic carboxylates

DFT broken-symmetry calculations at the B3LYP level were carried out to evaluate the exchange coupling constants defined by the Heisenberg–Dirac–van Vleck spin Hamiltonian (HDvV), ? = ?2J?_a?_b, in a 1D chain of iron basic carboxylate cores [Fe₃O(Piv)₆(H₂O)] bridged by dicyanamide, and two related trinuclear Fe₃O moieties. The chain complex was modeled as two Fe₃O units that preserve all features of the repetitive unit in the infinite real system. All geometries were taken from the crystallographic data previously reported. The obtained calculated values for the J constants are in good agreement with experimental results. The weak anti-ferromagnetic inter-Fe₃O core interaction along the chain is also reasonably accounted by the calculations. This methodology appears as a useful tool in the theoretical evaluation of exchange coupling constants in 1D systems.     

Transition metal tetramolybdate dihydrates MMo4O13·2H2O (M=Co,Ni) having a novel pillared layer structure

Hydrothermal synthesis in the M/Mo/O (M=Co,Ni) system was investigated. Novel transition metal tetramolybdate dihydrates MMo₄O₁₃·2H₂O (M=Co,Ni), having an interesting pillared layer structure, were found. The molybdates crystallize in the triclinic system with space group P−1, Z=1 with unit cell parameters of a=5.525(3) Å, b=7.058(4) Å, c=7.551(5) Å, α=90.019(10)°, β=105.230(10)°, γ=90.286(10)° for CoMo₄O₁₃·2H₂O, and a=5.508(2) Å, b=7.017(3) Å, c=7.533(3) Å, α=90.152(6)°, β=105.216(6)°, γ=90.161(6)° for NiMo₄O₁₃·2H₂O The structure is composed of two-dimensional molybdenum-oxide (2D Mo-O) sheets pillared with CoO₆ octahedra. The 2D Mo-O sheet is made up of infinite straight ribbons built up by corner-sharing of four molybdenum octahedra (two MoO₆ and two MoO₅OH₂) sharing edges. These infinite ribbons are similar to the straight ones in triclinic-K₂Mo₄O₁₃ having 1D chain structure, but are linked one after another by corner-sharing to form a 2D sheet structure, like the twisted ribbons in BaMo₄O₁₃·2H₂O (or in orthorhombic-K₂Mo₄O₁₃) are.     

Decolorization of C.I. Reactive Red 2 by ozonation catalyzed by Fe(II) and UV

This work evaluated the effects of pH on decolorization of C.I. Reactive Red 2 by O₃, O₃/Fe(II), UV/O₃ and UV/O₃/Fe(II) systems. At pH 4, the decolorization rate constants of O₃, O₃/Fe(II), UV/O₃ and UV/O₃/Fe(II) systems were 1.78, 3.11, 2.04 and 3.18 hr⁻¹, respectively. The decolorization rates and effective energy consumption constants of all systems were higher under basic conditions than under acidic conditions.