Numerical Interchain Mean-Field Theory for the Specific Heat of the Bimetallic Ferromagnetically Coupled Chain Compound MnNi(NO2)4(en)2 (en = Ethylenediamine)

We present a detailed study of the field-dependent specific heat of the bimetallic ferromagnetically coupled chain compound MnNi(NO2)4(en)2, en = ethylenediamine. For this material, which in zero field orders antiferromagnetically below TN=2.45 K, small fields suppress magnetic order. Instead, in such fields, a double-peak-like structure in the temperature dependence of the specific heat is observed. We attribute this behavior to the existence of an acoustic and an optical mode in the spin-wave dispersion as a result of the existence of two different spins per unit cell. We compare our experimental data to numerical results for the specific heat obtained by exact diagonalization and Quantum Monte Carlo simulations for the alternating spin-chain model, using parameters that have been derived from the high-temperature behavior of the magnetic susceptibility. The interchain coupling is included in the numerical treatment at the mean-field level. We observe remarkable agreement between experiment and theory, including the ordering transition, using previously determined parameters. Furthermore, the observed strong effect of an applied magnetic field on the ordered state of MnNi(NO2)4(en)2 promises interesting magnetocaloric properties.     

Volumetric properties of (an organic compound + di-n-butyl ether) atT = 298.15 K

Excess molar volumes V_m^Eof {di- n -butyl ether (DBE)  +  a monofunctional organic compound} have been determined atT =  298.15 K over the whole composition range by means of a vibrating-tube densimeter. TheV_m^E values were either positive (propylamine, or butylamine, or acetone, or tetrahydrofuran  +  DBE) or negative (methanol, or butanol, or diethyl ether, or cyclopentanone, or acetonitrile  +  DBE). Markedly asymmetric V_m^Ecurves were displayed by (DBE  +  methanol) and (DBE  +  acetonitrile). Partial molar volumes __ V_m^oat infinite dilution in DBE, both from this work and the literature, were analysed in terms of an additivity scheme, and the group contributions thus obtained were discussed and compared with analogous results in water. DBE revealed a greater capability of distinguishing between polar and non-polar solutes, as well as in discriminating differently shaped molecules (unbranched, branched, cyclic). The limiting slopes of apparent excess molar volumes are evaluated and briefly discussed in terms of solute–solute and solute–solvent interactions.     

Magnetic properties and DMRG modeling of the 1D bimetallic thiocyanate bridged compound {(CuL1)[Co(NCS)4]} (L1 = N-rac-5,12-Me2-[14]-4,11-dieneN4)

The magnetic properties of the bimetallic compound {(CuL₁)[Co(NCS)₄]}, where L₁ = N-rac-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene have been numerically analysed on the basis of the anisotropic Heisenberg spin-chain model. In the model the single-ion anisotropy of the Co(II) ions is taken into account and the interchain interactions are neglected. The thermodynamic properties are calculated using the DMRG technique adapted to the molecular-based chains for the first time which is reliable in the entire temperature region. The high accuracy results of our simulations have been successfully fitted to the corresponding experimental susceptibility and magnetization data measured for the powder sample and the model parameters (the exchange coupling J, the absolute value of the anisotropy constant D, the anisotropic g factors) have been estimated. The quantum model parameters are consistent with the previous findings, although the ferromagnetic interactions between Cu(II) and Co(II) ions through the thiocyanate bridge are somewhat weaker (J/k_B = 1.0 ± 0.1) than found before.     

(Solid + liquid) isothermal evaporation phase equilibria in the aqueous ternary system (Li2SO4 + MgSO4 + H2O) at T = 308.15 K

The solubility and the density in the aqueous ternary system (Li₂SO₄ + MgSO₄ + H₂O) at T = 308.15 K were determined by the isothermal evaporation. Our experimental results permitted the construction of the phase diagram and the plot of density against composition. It was found that there is one eutectic point for (Li₂SO₄ · H₂O + MgSO₄ · 7H₂O), two univariant curves, and two crystallization regions corresponding to lithium sulphate monohydrate (Li₂SO₄ · H₂O) and epsomite (MgSO₄ · 7H₂O). The system belongs to a simple co-saturated type, and neither double salts nor solid solution was found. Based on the Pitzer ion-interaction model and its extended HW models of aqueous electrolyte solution, the solubility of the ternary system at T = 308.15 K has been calculated. The predicted solubility agrees well with the experimental values.     

Excess molar enthalpies and excess molar volumes of (an alkanol + a nitrile compound) atT = 298.15 K andp = 0.1 MPa

Excess molar enthalpies and excess molar volumes at T =  298.15 K andp =  0.1 MPa are reported for (methanol, or ethanol, or 1-propanol  +  1,4-dicyanobutane, or butanenitrile, or benzonitrile). For all the mixtures investigated in this work the excess molar enthalpy is large and positive. The excess molar enthalpy decreases as the carbon chain number of the alkanol species increases from methanol to propanol. The excess molar volumes are both positive and negative. The Extended Real Associated Solution and the Flory–Benson–Treszczanowicz models were used to represent the data. Both these models describe better the excess molar enthalpy than the excess molar volumes of (an alkanol  +  a nitrile compound).     

(Solid + liquid) metastable equilibria in quaternary system (Li2SO4 + K2SO4 + Li2B4O7 + K2B4O7 + H2O) at T = 288 K

Metastable equilibrium solubilities and properties such as densities, conductivity, pH, refractive index, and viscosity of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagram was plotted. In the phase diagram, there are three invariant points, seven univariant curves, five fields of crystallization: Li₂SO₄ · H₂O, K₂SO₄, Li₂B₄O₇ · 3H₂O, K₂B₄O₇ · 4H₂O, and K₂SO₄ · Li₂SO₄. The double salt K₂SO₄ · Li₂SO₄ was found in the quaternary system metastable equilibria. Lithium sulfate (Li₂SO₄) has the highest concentration and strong salting-out effects on other salts.Also, the relationship diagram between the properties and the ion concentration of solution was constructed. It can be seen from the relationship diagram that the equilibrium solution density values, viscosity values, and refractive index values are increased apparently with the rise of sulfate ion concentration, reaching the maximum values at eutonic point F3. Electrical conductivity values and pH values, however, fall down with the rise of ion concentration on the whole.     

Pressure effects on a dimetallic ferrimagnet [Mn(en)]3[Cr(CN)6]2 · 4H2O

We have investigated pressure effects on a dimetallic ferrimagnet [Mn(en)]₃[Cr(CN)₆]₂ · 4H₂O (en; ethylenediamine) through the magnetic measurements using a diamond anvil cell in the pressure region up to P = 4.7 GPa. This ferrimagnetic compound has an eminent high transition temperature (Tc) of 69 K at ambient pressure in the structurally characterized molecule-based magnet system. Under hydrostatic pressure, Tc linearly increases against pressure, and exceeds 130 K at P = 4.7 GPa. The amount of the saturated moment hardly changes in the considered pressure region. This pressure experiment might become a prototype of artificial material control for the high-Tc molecule-based magnet.     

Synthesis and characterization of the bimetallic polymers [MS4Ag2(Hmimt)2]n (where M = Mo or W,Hmimt = 1-methylimidazoline-2(3H)-thione): crystal structures of [WS4Ag2(Hmimt)2]n and [Ag2I2(Hmimt)]n

The title compounds were synthesized by the reactions of [NH₄]₂[MS₄] (M = Mo, W), AgI and Hmimt in acetone and characterized by IR, ¹H NMR and UV–Vis spectroscopy. The polymeric structure of [WS₄Ag₂(Hmimt)₂]_n was determined by X-ray crystallography. In this compound, there are two distinctly different coordination modes for the silver atoms. One Ag atom has a pseudo-tetrahedral geometry with one terminal monodentate-S Hmimt, two μ₂-S bridging Hmimt and one S atom of a monodentate WS₄ unit. The other is surrounded by four sulfur atoms belonging in pairs to two WS₄ fragments; the coordination geometry is distorted tetrahedral. The [WS₄Ag₂(Hmimt)₂]_n polymer represents the first example of tetrathiometalate anions [MS₄]²⁻ (M = Mo, W, or V) coordinated to another metal atom in a monodentate fashion. In both crystal structures determined the Hmimt ligands are present in the thione form, with coordination taking place via the sulfur atom only.     

Thermodynamic study of (m1Cs2SeO4 + m2NiSeO4)(aq)wheremdenotes molality atT = 298.15 K

The isopiestic method has been used to determine the osmotic coefficients of the binary solutions Cs₂SeO₄(aq) at T =  298.15 K from (1.090 to 4.591)mol · kg ^− 1. The molalities m of (m₁Cs₂SeO₄ + m₂NiSeO₄)(aq) have been investigated by physicochemical analysis. The crystallization of a new double salt Cs₂SeO₄· NiSeO₄· 6H₂O has been established. The Pitzer ion-interaction model has been used for thermodynamic analysis of the results obtained. The thermodynamic data needed (binary and ternary parameters of ionic interaction, thermodynamic solubility products) have been calculated and the theoretical solubility isotherm has been plotted. The experimentally obtained and the calculated solubilities are in very good agreement. The standard molar Gibbs energy of the synthesis reaction Δ_rG_m^oof the double salt Cs₂SeO₄· NiSeO₄· 6H₂O from the corresponding simple salts Cs₂SeO₄and NiSeO₄· 6H₂O, as well as the standard molar Gibbs energy of formation Δ_rG_m^ohave been determined.     

ns2np4 (n = 4, 5) lone pair triplets whirling in M*F2E3 (M* = Kr,Xe): Stereochemistry and ab initio analyses

The stereochemistry of ns²np⁴ (n = 4, 5) lone pair LP characterizing noble gas Kr and Xe (labeled M*) in M*F₂ difluorides is examined within coherent crystal chemistry and ab initio visualizations. M*²⁺ in such oxidation state brings three lone pairs (E) and difluorides are formulated M*F₂E₃. The analyses use electron localization function (ELF) obtained within density functional theory calculations showing the development of the LP triplets whirling {E₃} quantified in the relevant chemical systems. Detailed ELF data analyses allowed showing that in α KrF₂E₃ and isostructural XeF₂E₃ difluorides the three E electronic clouds merge or hybridize into a torus and adopt a perfect gyration circle with an elliptical section, while in β KrF₂ the network architecture deforms the whole torus into an ellipsoid shape. Original precise metrics are provided for the torus in the different compounds under study. In KrF₂ the geometric changes upon β → α phase transition is schematized and mechanisms for the transformation with temperature or pressure are proposed. The results are further highlighted by electronic band structure calculations which show similar features of equal band gaps of 3 eV in both α and β KrF₂ and a reorganization of frontier orbitals due to the different orientations of the F-Kr-F linear molecule in the two tetragonal structures.     

Coupling of terminal alkynes by RuHXL2 (X = Cl or N(SiMe3)2, L = PiPr3)

The compounds RuL₂HX, where L = PⁱPr₃ and X = Cl or N(SiMe₃)₂, are catalyst precursors for dimerization of terminal alkynes to enynes and also to cumulenes at 23 °C; selectivity among these products is X-dependent, but not high. Conversion of Ru species onto the catalytic cycle was undetectably small, so alternative approaches to understanding the catalytic mechanism were employed: stoichiometric reactions, independent synthesis of candidate intermediates, and trapping with CO. These show the intermediacy of vinylidenes and vinyl compounds, and reveal conversion of cumulenes to the thermodynamically more stable enynes.     

Thermochemistry of the biochemical reaction: { pyrophosphate(aq) + H2O(l) = 2 phosphate(aq)}

Calorimetric enthalpies of reaction have been measured for the overall biochemical reaction{pyrophosphate(aq)  +  H₂O(l)  =  2phosphate (aq)} . The reaction was catalyzed by alkaline phosphatase and, to simplify the thermochemistry, was carried out in the absence of Mg ^2 + (aq). Measurements were performed with phosphate buffer ( pH  =  7.19 and 7.94), PIPES buffer ( pH  =  7.13), and HEPES buffer ( pH  =  7.86). The results of these measurements were analyzed by using an equilibrium model. These calculations lead to the standard molar enthalpy changeΔ_rH_m^o =  − (17.3  ±  0.6)kJ·mol ^− 1 (temperature T =  298.15 K and ionic strengthI =  0) for the reference reaction{HP₂O₇^3 − (aq)  +  H₂O(l)  =  2HPO₄^2 − (aq)  +  H ⁺ (aq)} . Values of the apparent equilibrium constantK^′ for the overall biochemical reaction from the literature were also analyzed by using the equilibrium model in order to obtain what is believed to be a reliable value for the equilibrium constantK =  4.7 · 10 ^− 4 for the reference reaction. The values ofK and Δ_rH_m^o for the reference reaction have been used together with values from the CODATA tables to calculate standard molar formation properties for the pyrophosphate species.     

Single crystal synthesis and magnetism of the BaLn2O4 family (Ln = lanthanide)

The series of compounds in the BaLn₂O₄ family (Ln = La–Lu, Y) has been synthesized for the first time in single crystalline form, using a molten metal flux. The series crystallizes in the CaV₂O₄ structure type with primitive orthorhombic symmetry (space group Pnma, #62), and a complete structural study of atomic positions, bonds, angles, and distortions across the lanthanide series is presented. With the exception of the Y, La, Eu, and Lu members, magnetic susceptibility measurements were performed between 2 K and 300 K. BaCe₂O₄ and BaYb₂O₄ display large crystal fields effects and suppression of magnetic ordering. All compounds show signs of magnetic frustration due to the trigonal arrangements of the trivalent lanthanide cations in the structure.     

Excess molar enthalpies of (acetonitrile + butan-2-one) and (methanol + acetonitrile + butan-2-one) atT = 298.15 K

The excess molar enthalpies of (acetonitrile  +  butan-2-one) and (methanol  +  acetonitrile  +  butan-2-one) were measured atT =  298.15 K and atmospheric pressure using a flow microcalorimeter. The experimental results are correlated with polynomial equations and compared with those calculated from associated solution models taking account into self-association of methanol and acetonitrile as well as solvation between unlike molecules and a non-polar interaction term.