A pyrazole-based orthogonal ferromagnetically coupled [2 × 2] homoleptic square Cu4 grid: Magnetostructural correlations

The synthesis and structure of a pyrazole-based orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid complex [Cu₄(PzOAPyz)₄(ClO₄)₂](ClO₄)₂ · 6H₂O (1), formed by the reaction between the ditopic ligand PzOAPyz and Cu(ClO₄)₂ · 6H₂O, are described. The ligand contains terminal pyrazole and pyrazine residues bound to a central flexible diazine subunit (N–N) as well as one potentially bridging alkoxo group. The two adjacent metal centers are linked by an alkoxo oxygen forming essentially a square Cu₄(μ-O₄) cluster. In the Cu₄(μ-O₄) core, out of the four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by one of the oxygen atoms of a coordinated perchlorate ion. Complex 1 has been characterized structurally and magnetically. Although the large Cu–O–Cu bridge angles (137–138°) and short Cu–Cu distances (3.964–3.970 Å) are suitable for the transmission of the expected antiferromagnetic coupling, the square-based Cu₄(μ-O₄) cluster exhibits an intramolecular ferromagnetic exchange (J = 7.47 cm⁻¹) between the metal centers with an S = 2 magnetic ground state associated with the quasi orthogonal arrangement of the magnetic orbitals (d_x2-y2${\text{d}}_{x^2-y^2}$). The exchange pathway parameters have been evaluated from density functional calculations.     

Surface tension of dimethyl ether + propane from 243 to 333 K

The surface tension of the binary refrigerant mixture dimethyl ether (RE170)(1) + propane (R290)(2) at three mass fraction of w₁=0.3007,0.4975 ??and ??0.6949$w_1=\mathrm{0.3007,0.4975}\text{\hspace{0.17em}??}\text{and}\text{\hspace{0.17em}??}0.6949$ was measured in the temperature range from 243 to 333 K with a differential capillary rise method. The uncertainties of the measurement of the temperature and the surface tension were estimated to be within ±10 mK and ±0.2 mN m⁻¹, respectively. A correlation for the surface tension of the binary refrigerant mixture RE170 + R290 was developed as a function of the composition.     

Ternary (liquid + liquid) equilibria of the azeotrope (ethyl acetate + 2-propanol) with different ionic liquids at T = 298.15 K

Experimental (liquid + liquid) equilibria involving ionic liquids {1,3-dimethylimidazolium methyl sulfate (MMIM MeSO₄)}, {2-propanol + ethyl acetate + 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF₆)} and {2-propanol + ethyl acetate + 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF₆)} were carried out to separate the azeotropic mixture ethyl acetate and 2-propanol. Selectivity and distribution ratio values, derived from the tie-lines data, were presented in order to analyze the best separation solvent in a liquid extraction process. Experimental (liquid + liquid) equilibria data were compared with the correlated values obtained by means of the NRTL, Othmer-Tobias and Hand equations. These equations were verified to accurately correlate the experimental data.     

The role of ancillary ligands and of electron poor alkenes and alkynes in stabilizing Pd(0) derivatives: A comparative study

The peculiar characteristics of the ligand neocuproine (2,9-dimethylphenanthroline) allow a number of exchange equilibrium studies between the low valence complex [Pd(η²-nq)(Neocup)] (nq = naphthoquinone; Neocup = neocuproine) and several alkenes and alkynes. A new order of stability which compares differently unsaturated molecules was established. An overview of the factors governing the stability of palladium(0) alkene and alkyne derivatives as a function of the steric and electronic characteristics of both the unsaturated molecule and the ligand becomes accessible and a comparison with the previously determined order was therefore feasible. Such a comparison enlightens the importance of the substituent methyl groups in ortho position of the hetero-aromatic ring which represents the molecular fragment common to all the ligands considered. Taking advantage of the steric requirements of the alkene tmetc (tmetc = tetramethylethylenetetracarboxylate) a kinetic investigation of the reaction between the olefin itself and the complexes [Pd(η²-dmfu)(L-L′)] (dmfu = dimethylfumarate; L-L′ = 8-diphenylphosphanyl-2-methyl-quinoline, neocuproine, phenanthroline) was carried out. The structures of the complexes [Pd(η²-dmfu)(DPPQ)] and [Pd(η²-deta)(Neocup)] (deta = but-2-ynedioc acid diethyl ester) were also reported in the present paper. The structure of the latter represents the first example of a palladium(0) complex in which the N₂C₂ donor set around the metal centre is supported by a chelating η²-alkyne.     

(Liquid + liquid) equilibria of the (water + acetic acid + dibasic esters mixture) system

(Liquid + liquid) equilibrium (LLE) data for the {water + acetic acid + dibasic esters mixture (dimethyl adipate + dimethyl glutarate + dimethyl succinate)} system have been determined experimentally at T = (298.2, 308.2, and 318.2) K. Complete phase diagrams were obtained by determining solubility curve and tie-line data. The reliability of the experimental tie-line data was confirmed by using the Othmer-Tobias correlation. The UNIFAC model was used to predict the phase equilibrium in the system using the interaction parameters determined from experimental data between CH₂, CH₃COO, CH₃, COOH, and H₂O functional groups. Distribution coefficients and separation factors were compared with previous studies.     

Density-functional study for the NOx (x = 1, 2) dissociation mechanism on the Cu(1 1 1) surface

Spin-polarized density functional theory calculation is employed to study the adsorption and dissociation of NO₂ molecule on Cu(1 1 1) surface. It is shown that the most favorable adsorption structure is the NO₂ (T,T-O-,O′-nitrito) configuration which has an adsorption energy of −1.49 eV. The barriers for step-wise NO₂ dissociation reaction, NO_2(g) → N_(a) + 2O_(a), are 1.05 (for O–N–O bond activation), and 2.08 eV (for N–O bond activation), respectively, and the entire process is 0.6 eV exothermic. The energetics of single N–O dissociation with and without the presence of N atom or O atom on the surface are also calculated. The results indicate that in the presence of O atom on Cu(1 1 1) surface would raise the N–O dissociation barrier, whereas in the presence of N atom decrease it. The interaction nature between adsorbates and substrate is analyzed by the local density of states (LDOS) calculation.     

Reactivity of [CpRh(η-C6H3NH2-2,6-i-Pr2)](OTf)2 toward phosphines and alkynes

The cationic aniline complex [Cp^∗Rh(η⁶-2,6-(Me₂CH)₂C₆H₃NH₂)](OTf)₂ (1) was prepared from either [Cp^∗Rh(η²-NO₃)(η¹-OTf)] or [Cp^∗Rh(OH₂)₃](OTf)₂ and 2,6-diisopropylaniline. Complex 1 underwent substitution with phosphines or phosphites, indicating the labile character of the η⁶-aniline ligand. Complex 1 mediated cycloaddition reactions of several alkynes in refluxing ethanol: the [2 + 2] dimerization for PhCCPh and the [2 + 2 + 1] trimerization for PhCCH and CH₃C₆H₄CCH. The unexpected cyclobutadiene complex [Cp^∗Rh(η⁴-C₄(C(O)CH₃)₂H(SiMe₃))] was obtained from complex 1 and Me₃SiCCCCSiMe₃ and structurally characterized by X-ray diffraction.     

Theoretical study of the thermochemistry and the kinetics of the SFxCl (x = 0-5) series

A systematic thermodynamic and kinetic study of the entire SF_xCl (x = 0-5) series has been carried out. High-level quantum chemical composite methods have been employed to derive enthalpy of formation values from calculated atomization and isodesmic energies. The resulting values for the SCl, SFCl, SF₂Cl(C₁), SF₃Cl(C_s), SF₄Cl(C_s) and SF₅Cl molecules are 28.0, −36.0, −64.2, −134.3, −158.2 and −237.1 kcal mol⁻¹. A comparison with previous experimental and theoretical values is presented. Statistical adiabatic channel model/classical trajectory, SACM/CT, calculations of selected complex-forming and recombination reactions of F and Cl atoms with radicals of the series have been performed between 200 and 500 K. The reported rate coefficients span over the normal range of about 6 × 10⁻¹² and 5 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ expected for this type of barrierless reactions.     

H2O + Fe(NO3)3 + Ni(NO3)2 ternary system isotherms at 0 °C and 30 °C

H₂O + Ni(NO₃)₂ binary system were investigated in the temperature range from −25 °C to 55 °C. The solid-liquid equilibria of the ternary system H₂O + Fe(NO₃)₃ + Ni(NO₃)₂ were studied using a synthetic method based on conductivity measurements. Tow isotherms were established at 0 °C and 30 °C, and the appearing stable solid phases are iron nitrate nonahydrate (Fe(NO₃)₃·9H₂O), iron nitrate hexahydrate (Fe(NO₃)₃·6H₂O), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and nickel nitrate tetrahydrate (Ni(NO₃)₂·4H₂O).     

Selective electronalysis of peracetic acid in the presence of a large excess of H2O2 at Au(1 1 1)-like gold electrode

Peracetic acid (PAA) has been selectively electroanalyzed in the presence of a large excess of hydrogen peroxide (H₂O₂), about 500 fold that of PAA, using Au (1 1 1)-like gold electrode in acetate buffer solutions of pH 5.4. Au(1 1 1)-like gold electrode was prepared by a controlled reductive desorption of a previously assembled thiol, typically cysteine, monolayer onto the polycrystalline gold (poly-Au) electrode. Cysteine molecules were selectively removed from the Au(1 1 1) facets of the poly-Au electrode, keeping the other two facets (i.e., Au(1 1 0) and Au(1 0 0)) under the protection of the adsorbed cysteine. It has been found that Au(1 1 1)-like gold electrode positively shifts the reduction peak of PAA, while, fortunately, shifts the reduction peak of H₂O₂ negatively, achieving a large potential separation (around 750 mV) between the two reduction peaks as compared with that (around 450 mV) obtained at the poly-Au electrode. This large potential separation between the two reduction peaks enabled the analysis of PAA in the presence of a large excess of H₂O₂. In addition, the positive shift of the reduction peak of PAA gives the present method a high immunity against the interference of the dissolved oxygen.     

A many-body theory of the Ti M2,3-VV Auger-photoelectron coincidence spectroscopy (APECS) spectrum of TiO2(1 1 0)

We calculated the Ti M_2,3-VV Auger-photoelectron coincidence spectroscopy spectrum of TiO₂(1 1 0) by a many-body theory. The spectral main line is governed by the DOS of the two O 2p holes living longer than the Ti ∣cd²L²〉 → ∣L²〉 super Coster-Kronig (sCK) decay. The two O 2p holes are created by the charge transfer core-hole screening at the Ti atomic site. Here c and L are the Ti 3p hole and the ligand O 2p hole, respectively. Analysis of the spectrum shows that the two (or three) CT O 2p holes in the π bonding states are localized, whereas those in the σ bonding states are delocalized. The three localized CT O 2p (π) holes in ∣cd³L³〉 in Ti M_2,3 main line (or satellite) of TiO₂(1 1 0) live longer than the Ti ∣cd³L³〉 → ∣d¹L³〉 sCK decay so that the Coulomb repulsion from the surrounding Ti ions gives the O⁺ ion desorption from the surface.     

(p, ρ, T) properties, and apparent molar volumes V? of ZnBr2 in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa

The (p, ρ, T) properties of pure methanol, the (p, ρ, T) properties and apparent molar volumes V_? of ZnBr₂ in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa are reported, and apparent molar volumes have been evaluated. The experimental (p, ρ, T, m) values were described by an equation of state. For the solutions the experiments were carried out at molalities m = (0.05772, 0.37852, 0.71585 and 1.95061) mol · kg⁻¹ of zinc bromide.     

Vapour pressure and excess Gibbs free energy of binary mixtures of hydrogen sulphide with ethane, propane, and n-butane at temperature of 182.33 K

The vapour pressure of binary mixtures of hydrogen sulphide with ethane, propane, and n-butane was measured at T = 182.33 K covering most of the composition range. The excess Gibbs free energy of these mixtures has been derived from the measurements made. For the equimolar mixtures for (H₂S + C₂H₆), (820.1 ± 2.4) J · mol⁻¹ for (H₂S + C₃H₈), and (818.6 ± 0.9) J · mol⁻¹ for (H₂S + n-C₄H₁₀). The binary mixtures of H₂S with ethane and with propane exhibit azeotropes, but that with n-butane does not.     

Surface tension of pentafluoroethane + 1,1-difluoroethane from (243 to 328) K

The surface tension of the binary refrigerant mixture pentafluoroethane (HFC-125) + 1,1-difluoroethane (HFC-152a) was measured in the temperature range from (243 to 328) K with a differential capillary rise method, for three compositions around the composition of the optimum refrigeration performance (HFC-125 + HFC152a, 15%/85%). The uncertainties of the measurement of the temperature and the surface tension were estimated to be within ±10 mK and ±0.2 mN m⁻¹, respectively. A correlation for the surface tension of the binary refrigerant mixture HFC-152a + HFC-125 was developed as a function of the composition.     

Synthesis, characterization and crystal structures of a new 2-ferrocenylnaphthoxazole and its mercurated derivatives

A new ferrocenylnaphthoxazole [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)C(O)N(C₁₀H₆)}] (1) was synthesized under mild conditions. Two mercurated derivatives: ortho-mercurated product [HgCl{(η⁵-C₅H₅)Fe[(η⁵-C₅H₃)C(O)N(C₁₀H₆)]}] (2) and the product mercurated on the unsubstituted Cp ring [HgCl{(η⁵-C₅H₄)Fe[(η⁵-C₅H₄)C(O)N(C₁₀H₆)]}] (3) were obtained by the reaction of 1 with mercuric acetate. All the new compounds 1, 2 and 3 were characterized by elemental analyses, IR, NMR, MS spectra and X-ray crystal structure analysis. The crystal structure of 1 extended into a 2D supramolecular network through the intermolecular π-π stacking interaction between the Cp ring and naphthoxazole ring. In the crystal of 2, there exist bridged Cl-Hg bonds, CH(Cp) ? Cl and CH? Hg hydrogen bonds, π-π stacking interactions, which facilitate construction of this complex into a 3D supramolecular structure.     

One-electron redox reactions involving chromium(0) and molybdenum(0) bis-1,3,5-trimethylbenzene derivatives

The reaction of M(η⁶-1,3,5-Me₃C₆H₃)₂, M = Cr, Mo, with the tetrahalides of Groups 4 and 5 elements proceeds with the monoelectronic oxidation of the metal bis-arene to the [M(η⁶-Me₃C₆H₃)₂]⁺ cation. In the case of MX₄, M = Ti, X = Cl, Br, M = V, X = Cl, and of Nb₂Cl₁₀ the reduction products are the titanium(III), vanadium(III) halides and the niobium(IV) chloride, isolated as the solvate anions [MCl₄(THF)₂]⁻ and [NbCl₄(CH₃CN)]⁻. The reaction of the tetrachloro complexes MCl₄(THF)₂, M = Zr, Hf, with Cr(η⁶-1,3,5-Me₃C₆H₃)₂ in THF produces the ionic [Cr(η⁶-1,3,5-Me₃C₆H₃)₂][MCl₅(THF)], which has been characterized by single-crystal X-ray diffraction in the case of hafnium.     

The photochemistry of (η-2-R-C3H4)Fe(CO)(NO)(X) (R = H or Cl; X = CO or PPh3) in room temperature solution or frozen gas matrixes

A photochemical study of allyl iron complexes of the type, (η³-2-R-C₃H₄)Fe(CO)(NO)(X) (R = H or Cl; X = CO or PPh₃) is presented. These compounds were studied in solid matrixes at 20 K, and at room temperature, by a combination of laser flash at 355 nm and steady-state photolysis. The predominant photochemical process for these compounds is loss of a CO ligand. In addition, exhaustive irradiation of (η³-2-R-C₃H₄)Fe(CO)(NO)(PPh₃) with λ_exc > 300 nm provided evidence for a haptotropic shift of the allyl group from η³ to η¹ coordination.     

Experimental (solid + liquid) phase equilibria of (alkan-1-ol + benzonitrile), (amine + benzonitrile) binary mixtures,and (decan-1-ol + decylamine + benzonitrile) ternary mixtures

(Solid + liquid) phase diagrams, SLE have been determined for (octan-1-ol, or nonan-1-ol, or decan-1-ol, or undecan-1-ol + benzonitrile) and for (hexylamine, or octylamine, or decylamine, or 1,3-diaminopropane + benzonitrile) using a cryometric dynamic method at atmospheric pressure. Simple eutectic systems with complete immiscibility in the solid phase and complete miscibility on the liquid phase have been observed. The solubility decreases with an increase of the number of carbon atoms in the alkan-1-ol, or amine chain. The temperature of the eutectic points increases and shifts to lower alkan-1-ol, or amine mole fractions as the alkyl chain length of the alkan-1-ol, or amine increases. The higher intermolecular interaction was observed for the (alkan-1-ol + benzonitrile) systems.     

Vapour pressure and excess Gibbs free energy of the ternary system {x1CH3F + x2HCl + x3N2O} at temperature of 182.33 K

The equilibrium pressure of ternary mixtures of {x₁CH₃F + x₂HCl + x₃N₂O} covering the entire composition range has been measured at temperature of 182.33 K by the static method. The system exhibits a minimum pressure for the binary {x₁CH₃F + x₂HCl}. The molar excess Gibbs free energy has been calculated from the experimental equilibrium pressure. For the equimolar mixture . The (p, x, y) surface for the ternary system and the corresponding curves for the three constituent binary mixtures obtained from the Peng-Robinson equation of state are in agreement with the experimental data.     

On the influence of the heterocyclic ring substituents on the structure of dimethylthallium pyrimidine-2-thionato complexes. Crystal structure of dimethyl-(4-trifluoromethylpyrimidine-2-thionate)thallium(III): a compound with intermolecular C-H ? π interactions

The complex [Me₂Tl(4-CF₃pymS)] has been prepared by reacting 4-trifluoromethylpyrimidine-2-thione (4-CF₃pymSH) with dimethylthallium(III) hydroxide in methanol. The resulting compound has a polymeric chain structure, with the thallium atom coordinated by two nitrogen and two sulfur atoms from two different ligands, which act as bridges between two metal atoms, as well as by two carbon atoms of the methyl groups. An intermolecular C-H ? π interaction is observed between an H atom of each methyl group and one of the pyrimidine rings of the neighbouring chain. The structure of the complex is discussed in terms of the IR absorptions, the ¹H, ¹³C and ²⁰⁵Tl NMR spectra and FAB data.