Kinetics of substitution at ternary titanium(IV)–cyclopentadienyl,pyronato or pyridinato–halide or alkoxide complexes

Rate laws and kinetic parameters are reported for substitution at titanium(IV) complexes Ti(LL)₂X₂, where LLH=cyclopentadiene, the 4-pyrone ethylmaltol, several 4-pyridinones, and related ligands, and X=halide or alkoxide, in acetonitrile solution at 298.2 K. Reactivities are discussed in terms of the nature of the leaving group, the entering group and the non-leaving ligand LL^?. Activation volumes of ?15 and ?12 cm³ mol^?1 have been determined for thiocyanate attack at Ti(cp)₂Cl₂ and Ti(etmalt)₂Cl₂ respectively. Substitution mechanisms are discussed in the light of the kinetic parameters obtained.     

Thermodynamic properties of transition metals in aqueous solution:4. The enthalpies of mixing aqueous solutions of CdCl2, CuCl2 and ZnCl2 with MgCl2 at varying ionic strength at 25°C

Enthalpies of mixing ΔH _m of aqueous solutions of CdCl₂, CuCl₂, and ZnCl₂ with MgCl₂ solutions were measured at ionic strengths of 1.0, 2.0, and 3.0 at 25°C. The excess enthalpy equations of Pitzer were then fitted to the resulting ΔH _m data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system.     

Solubility of nonpolar gases in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂) in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas are reported. Gibbs energy for the solution process at 25°C is evaluated from the experimental values of the solubility of gases expressed as mole fraction. Lennard-Jones 6–12 pair potential parameters for 2,2,2-trifluoroethanol are estimated by using the scaled particle theory (SPT); and experimental solubilities are compared with those calculated from the values of these parameters through the SPT model.     

Effects of anharmonicity of molecular vibrations on the diffraction of electrons: Part III. Predictive models

It has long been known how to relate anharmonic vibrational distribution functions to scattered electron intensities when deriving molecular parameters from gas-phase electron diffraction patterns. What has been lacking is a convenient procedure for estimating the characteristic asymmetry parameters of radial distribution functions for polyatomic molecules, particularly in the case of non-bonded internuclear distances. In the present work alternative models of bond distribution functions are discussed briefly and a plausible model is proposed for geminal non-bonded distances. Numerical examples are worked out for the ground-states of CO₂, CS₂, H₂O, and D₂O. Variations of the asymmetry parameters of SO₂ and SF₆ with temperature are examined. It is shown that the effect of asymmetry can become quite large at elevated temperatures.     

Conversion of Parameters Among Variants of Scatchard’s Neutral-Electrolyte Model for Electrolyte Mixtures that Have Different Numbers of Mixing Terms

Various model equations are available for representing the excess Gibbs energy properties (osmotic and activity coefficients) of aqueous and other liquid mixed-electrolyte solutions. Scatchard’s neutral-electrolyte model is among the simplest of these equations for ternary systems and contains terms that represent both symmetrical and asymmetrical deviations from ideal mixing behavior when two single-electrolyte solutions are mixed in different proportions at constant ionic strengths. The usual form of this model allows from zero to six mixing parameters. In this report we present an analytical method for transforming the mixing parameters of neutral-electrolyte-type models with larger numbers of mixing parameters directly to those of models with fewer mixing parameters, without recourse to the source data used for evaluation of the original model parameters. The equations for this parameter conversion are based on an extension to ternary systems of the methodology of Rard and Wijesinghe (J. Chem. Thermodyn. 35:439–473, 2003) and Wijesinghe and Rard (J. Chem. Thermodyn. 37:1196–1218, 2005) that was applied by them to binary systems. It was found that the use of this approach with a constant ionic-strength cutoff of I≤6.2 mol⋅kg⁻¹ (the NaCl solubility limit) yielded parameters for the NaCl+SrCl₂+H₂O and NaCl+MgCl₂+H₂O systems that predicted osmotic coefficients φ in excellent agreement with those calculated using the same sets of parameters whose values were evaluated directly from the source data by least-squares, with root-mean-square differences of RMSE(φ)=0.00006 to 0.00062 for the first system and RMSE(φ)=0.00014 to 0.00042 for the second. If, however, the directly evaluated parameters were based on experimental data where the ionic strength cutoff varied with the ionic-strength fraction, i.e., because they were constrained by isopiestic ionic strengths (MgCl₂+MgSO₄+H₂O) or solubility/oversaturation ionic strengths (NaCl+SrCl₂+H₂O and NaCl+MgCl₂+H₂O), then parameters converted by this approach assuming a constant ionic-strength cutoff yield RMSE(φ) differences about an order of magnitude larger than the previous case. This indicates that for an accurate conversion of model parameters when the source model is constrained with variable ionic strength cutoffs, an extension of the parameter conversion method described herein will be required. However, when the source model parameters are evaluated at a constant ionic strength cuttoff, such as when source isopiestic data are restricted to ionic strengths at or below the solubility limit of the less soluble component, or are Emf measurements that are commonly made at constant ionic strengths, then our method yields accurate converted models. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

A critical review of the chemical kinetics of SF4, SF5, and S2F10 in the gas phase

The gas phase chemical kinetics of SF₄, SF₅, and S₂F₁₀ are reviewed with particular emphasis on relevance to the general problem of the dielectric breakdown of SF₆. Specific reaction systems treated are SF₄ + F₂, SF₅ + SF₅, and the pyrolysis of S₂F₁₀. Computer modeling calculations were carried out to arrive at the best estimates of rate parameters. Based on the results of these calculations, sets of recommended rate parameters are provided. The major discrepancies and problems in establishing the kinetic data base are described. Thermochemical consequences of different model calculations are given.     

Solubility of nonpolar gases in tetrahydropyran at 0 to 30°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, and SF₆) in tetrahydropyran at the temperature range 0 to 30°C and 101.33 kPa partial pressure of gas are reported. Thermodynamic functions for the solution process (Gibbs energy, enthalpy, and entropies) at 25°C are evaluated from the experimental values of the solubility of gases as mole fraction and their variation with the temperature. Lennard-Jones 6–12 pair potential parameters for tetrahydropyran are estimated by using the scale particle theory (SPT); and experimental solubilities are compared with the calculated values using this model. Experimental solubilities of gases in tetrahydropyran and intermolecular potential parameters are compared with those obtained for the same gases in other cycloethers.     

High Pressure Study of NH4Pb2Br5 Type Compounds. I Structural Parameters and Their Evolution under High Pressure

We have investigated the nature of the interactions of ns²‐cations and the possible structure‐determining role of the ns²electron pair at ambient and high pressure in several AB₂X₅ (A = K, Rb, Cs, In, Tl; B = Sn, Pb, Sr; X = Cl, Br, I) compounds. Structural parameters are obtained by high pressure x‐ray diffraction as well as by quantum mechanical methods (DFT‐GGA‐calculations). The structural parameters at ambient and high pressure are discussed and compared to those of Tl₅Se₂I crystallising in the antitype structure. Short cation—cation distances in the NH₄Pb₂Br₅ type structure enable direct cation—cation interactions and the existence of an ns²‐cation in the B‐position is crucial for the stability of these structures. The effect of pressure on the structural parameters of these compounds gives new insights into the interactions of lone pair cations. The pronounced decrease of the cation—cation distances with pressure points to strongly increasing bonding interactions between the lone pair cations.     

Determination of variable atom parameters in ionic crystals by electrostatic calculations

An electrostatic method to determine variable atom parameters in ionic crystals with experimentally determined unit cell parameters and space group is proposed. The atom parameters are usually chosen to give the maximum Madelung constant. However, when these atom parameters generate interatomic distances at least one of which is less than a critical distance, which comes from repulsion between atoms, the atom parameters corresponding to that distance are assigned. Applicability was examined for three cases: TiO₂ (rutile), UCl₃, and β-Rb₂GeF₆. Agreement between the atom parameters of this method and of literature was good. Some discussion is presented on the basis of this method. In ionic crystals, the atoms with variable parameters are set first using the geometrical arrangement which is the most stable in an electrostatic sense, and then “real” distances are fixed under the interaction of repulsive forces.     

Prediction of non-isothermal ternary gas-phase breakthrough experiments based on binary data

The results of breakthrough experiments in an adsorption column packed with commercial activated carbon for three binary CO₂/N₂ mixtures as well as for two ternary CO₂/N₂/H₂ mixtures are presented. The experiments were carried out at two different temperatures (25 and 45 °C), four different pressures (1, 5, 10 and 20 bar) and three different flow rates. To analyze the experiments, the breakthrough profiles are simulated using a one-dimensional model consisting of material and energy balances together with the necessary constitutive equations. Transport parameters such as the heat and mass transfer coefficients are fitted to the results from the experiments with the binary mixtures (CO₂/N₂) and then compared to parameters obtained in a previous work (Adsorption 18: 143–161, 2012) for binary CO₂/H₂ mixtures. Furthermore, the parameters obtained for binary mixtures are used to predict the outcome of breakthrough experiments with ternary CO₂/N₂/H₂ mixtures. These simulations are then tested by experiments, showing that their prediction capability is rather satisfactory for a large range of experimental conditions.     

Molecular structure,vibrational frequencies and ionization potential of tin dihalides: An ab initio SCF and CI study

The geometrical parameters for SnX₂ (X = Cl, Br, I) and SnX₂⁺ have been optimized at the SCF and Cl levels using non-empirical pseudopotentials and a basis set of double-zeta plus polarization quality. For the neutral molecules the geometrical parameters are in agreement with the experimental values, the difference being of only 2%. Vibrational frequencies and ionization potentials are also in agreement with experiment.     

Sorption and partial molar volume of gases in polybutadiene

Sorption of He, H₂, N₂, O₂, Ar, CH₄, C₂H₆, and C₂H₆ in polybutadiene and the dilation of the polymer due to sorption of the gases are investigated over the pressure range 0-50 atm at 25°C. For CO₂ the measurements are made at temperatures ranging from 15 to 80°C. Partial molar volumes of the gases in the polymer are determined. The temperature dependence of partial molar volume is discussed on the basis of the data for CO₂. The Flory-Huggins interaction parameters of CO₂, C₂H₄, and C₂H₆ are also estimated.     

A Study on AB2X5 Compounds. II. Refinement of the Structures of InSn2Br5 and InSn2I5

The refinement of the structure of InSn₂Br₅ and InSn₂I₅ is reported. Both compounds crystallize with the tetragonal NH₄Pb₂Br₅ type arrangement (a = 828.5(9) and 881.0(8) (pm), c = 1443.8(20) and 1524.0(3) (pm) respectively). We discuss the parameters in comparison with those of Tl₅Se₂I crystallizing in the antitype structure, and we derive the parameters of a model structure based on the packing of hard spheres. It can be shown, that bond distances and thermal parameters seeming unusual at first sight are not to be attributed to the interaction of lone pairs, since we find them in our model structure as well.     

Thermodynamics of CoAl2O4-CoGa2O4 solid solutions

CoAl₂O₄, CoGa₂O₄, and their solid solution Co(Ga_zAl_1−z)₂O₄ have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B₂O₃ at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O’Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing.     

Thermodynamic properties of transition metals in aqueous solution: 3. The heats of mixing aqueous solutions of CdCl2, NiCl2 and ZnCl2 with NaCl at varying ionic strength at 25°C

The heat of dilution of aqueous solutions of ZnCl₂ and the heats of mixing H _m of aqueous solutions of CdCl₂, NiCl₂, and ZnCl₂ with NaCl solutions were measured at 25°C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system.     

Thermodynamic properties of transition metals in aqueous solution. 2. The enthalpies of mixing of aqueous solutions of CoCl2, CuCl2, and MnCl2 with NaCl at varying ionic strength at 25°C

Enthalpies of mixing (_m H) aqueous solutions of CoCl₂, CuCl₂, and MnCl₂ with NaCl solutions were measured at constant ionic strengths of 0.5, 1.0, and 3.0 molal at 25°C. The excess enthalpy equations of Pitzer were then fit to the resulting _m H data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system. The heat of mixing data for CoCl₂ and CuCl₂ were in agreement with earlier isomolal results by other workers.     

Phases containing tungsten in Cu(1) positions

A tetragonal (123) phase of composition CdBa₂Cu₂WO₈ with the complete and selective substitution of tungsten atoms for copper in the Cu(1) positions is synthesized from CdWO₄ and BaCuO₂ at 800°C in flowing oxygen. The percentage of the (123) phase in the sample is at least 90%; the unit cell parameters are a = b = 0.4151(3) nm, c = 1.2537(8) nm. The X-ray diffraction pattern shows a superstructure with all three of the unit cell parameters being doubled.     

An EPR study of manganese(II) complexes in potassium chromate single crystal

Electron paramagnetic resonance study of Mn²⁺-doped K₂CrO₄ single crystals at room temperature and liquid nitrogen temperature revealed the presence of two pairs of inequivalent Mn²⁺ complexes. It is concluded that Mn²⁺ ions are incorporated in the host substitutionally at potassium sites, and an equal number of K⁺ vacancies are created for charge compensation. The spin—Hamiltonian parameters are evaluated. The principal directions of the crystalline field experienced by the manganese (II) ion are determined and they are found to be consistent with the electrostatic considerations. The hyperfine parameters indicate the significant extent of covalent bonding of ligands with the metal ion.     

Kinetics and thermodynamics of thermal dehydration of magnesium oxalate dihydrate

The kinetics and thermodynamics of the thermal dehydration of crystalline powders of MgC₂O₄ · 2 H₂O were studied by means of thermal analyses both at constant temperatures and at linearly increasing temperatures. The dehydration of the dihydrate is regulated by one of the Avrami-Erofeyev laws. The kinetic parameters from TG at constant temperatures are in good agreement with those from TG at the lowest rate of rising temperatures. The dynamic dehydration kinetics was also examined, using DSC recorded simultaneously with TG at linearly increasing temperatures. The validity of the estimated mechanism and kinetic parameters is briefly discussed.     

The stability of inclusion compounds under heating

The thermal decomposition of three inclusion compounds: [Zn₂(camph)₂dabco]·DMF·H₂O, [Zn₂(camph)₂bipy]·3DMF·H₂O and [Zn₂(camph)₂bpe]·5DMF·H₂O was studied in the inert atmosphere. TG and DTG curves confirm multi-step decomposition process, the dehydration being the first step. Thermogravimetric data (obtained at different rates of linear heating) were processed with computer program (with ‘Model-free’ approach). Kinetic parameters of decomposition were calculated for the DMF multi-step removal, the processes are described by Avrami–Erofeev equations. The connection between the kinetic parameters and structural features of the host frameworks (ligand linker lengths and porous-free volumes) are discussed.