Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Experimental Determination of the Isotherm at 15°C of the System Mg2+/Cl?, SO42–H2O

 The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.     

Inhibition efficiency and adsorption mechanism of 4-aminobenzoic acid for copper corrosion in nitric acid medium: a combined experimental and theoretical investigation

Structural Chemistry - A combined experimental and theoretical study is presented to predict and analyze the inhibition efficiency and adsorption mechanism of 4-aminobenzoic acid molecule for...     

Thermodynamic Study of the Solid-Liquid Equilibria in the Systems MIPO3-Pr(PO3)3 (MI=Na,Rb, Cs OR Ag)

A previously established equation of a stoichiometric phase liquidus curve was applied to determination of the phase diagrams of the systems M^IPO₃-Pr(PO₃)₃ (with M^I=Na, Rb, Cs or Ag). The temperature, enthalpy and entropy of fusion were calculated for each solid phase with the exception of silver polyphosphate, the crystallization field of which was very limited. The enthalpy of fusion of the polyphosphate Pr(PO₃)₃ was determined from the DTA curve. The melting enthalpy of Pr(PO₃)₃ calculated from the different binary systems was approximately equal to the measured value. The calculated temperatures and compositions were in good agreement with those determined experimentally. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ab Initio and DFT Studies on CO2 Interacting with Znq+–Imidazole (q=0, 1, 2) Complexes: Prediction of Charge Transfer through σ‐ or π‐Type Models

Using first‐principles methodologies, the equilibrium structures and the relative stability of CO₂@[Zn^q+Im] (where q=0, 1, 2; Im=imidazole) complexes are studied to understand the nature of the interactions between the CO₂ and Zn^q+–imidazole entities. These complexes are considered as prototype models mimicking the interactions of CO₂ with these subunits of zeolitic imidazolate frameworks or Zn enzymes. These computations are performed using both ab initio calculations and density functional theory. Dispersion effects accounting for long‐range interactions are considered. Solvent (water) effects were also considered using a polarizable continuum model approach. Natural bond orbital, charge, frontier orbital and vibrational analyses clearly reveal the occurrence of charge transfer through covalent and noncovalent interactions. Moreover, it is found that CO₂ can adsorb through more favorable π‐type stacking as well as σ‐type hydrogen‐bonding interactions. The inter‐monomer interaction potentials show a significant anisotropy that might induce CO₂ orientation and site‐selectivity effects in porous materials and in active sites of Zn enzymes. Hence, this study provides valuable information about how CO₂ adsorption takes place at the microscopic level within zeolitic imidazolate frameworks and biomolecules. These findings might help in understanding the role of such complexes in chemistry, biology and material science for further development of new materials and industrial applications.     

Cristallisation de LiFe5O8 dans un verre 0,9 Li2B2O4O,1 LiFe5O8: C. Chaumont and J.C. Bernier,Départment Science des Matériaux,Ecole Nationale Supérieure de Chimie de Strasbourg, 1, rue Blaise Pascal,B.P. 296/R8, 67008 Strasbourg Cédex,France

The LiPO₃-La(P₃O₉) system was studied by microdifferential thermal analysis. The only new compound observed in the system was LiLa(PO₃)₄, melting incongruently at 960°C. A eutectic appears at 640°C, for the mixture containing 5 mole% LaP₃O₉. Crystallographic data and powder diagrams of the new compound are given. The LiLa(PO₃)₄ is an LiNd(PO₃)₄ isotype. It crystallises in the monoclinic system C2/c with a unit cell a = 16.53 (3), b = 7.08 (3), c = 9.88 (2) Å, β = 126.42 (5), and Z = 4.     

Phase equilibrium relations in the binary systems LiPO3CeP3O9 and NaPO3CeP3O9

The LiPO₃CeP₃O₉ and NaPO₃CeP₃O₉ systems have been investigated for the first time by DTA, X-ray diffraction, and infrared spectroscopy. Each system forms a single 1:1 compound. LiCe(PO₃)₄ melts in a peritectic reaction at 980°C. NaCe(PO₃)₄ melts incongruently, too, at 865°C. These compounds have a monoclinic unit cell with the parameters: a = 16.415(6), b = 7,042(6), c = 9.772(7)Å; β = 126.03(5)°; Z = 4; space group $\text{C}{}_2\text{c}$ for LiCe (PO₃)₄; and a = 9.981(4), b = 13.129(6), c = 7.226(5) Å, β = 89.93(4)°, Z = 4, space group $\text{P2}{}_1\text{n}$ for NaCe(PO₃)₄. It is established that both compounds are mixed polyphosphates with chain structure of the type |M^I_IM^III_II (PO₃)₄|_∞M^I_I: alkali metal, M^III_II: rare earth.     

Comparative yield stress determination for pure and interstratified smectite clays

Different experimental devices and operative procedures were used to obtain the main properties of suspensions of two purified clays, a pure smectite and an interstratified illite-smectite natural clay, at different concentrations. The yield stress values derived from flow and creep tests were found to be very consistent, while those derived from dynamic tests were observed to be much more sensitive to experimental conditions. Qualitatively, the two clays exhibit the same rheological behaviour, which can be modelled using the Herschel-Bulkley model; their yield stress increases with clay concentration and they present a thixotropic character for low concentrations, with an inversion of the curves when the clay concentration increases. However, significant differences were observed when considering numerical values. For the same clay concentration in the suspension, the yield stress of the pure smectite is distinctly higher than that of the interstratified one. The rheological properties of the pure smectite clay can be related to the swelling properties and the organisation of the minerals in water, leading to three-dimensional strong but deformable structures. On the other hand, the presence of a small percentage of illite in the natural clay gives it a brittle behaviour which collapses more easily under stress.     

On the Electronic States of S4+ and S4‐ Isomers.

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