The thermodynamic properties of fullerene hydrides C<Subscript>60</Subscript>H<Subscript>2<Emphasis Type="Italic">n</Emphasis></Subscript>

The equilibrium geometric parameters and normal vibration frequencies of the C₆₀H₂, C₆₀H₁₈, and C₆₀H₆₀ molecules were determined using density functional theory at the B3LYP/6-31G* level. The results were used to calculate the thermodynamic properties of the substances in the ideal gas state. The heat capacity of crystalline hydrofullerenes was modeled and the enthalpies of their sublimation estimated. The thermodynamic parameters of the hydrogenation of fullerene C₆₀ were analyzed.     

Theoretical study of metal tetrahydroborates and alanates L(MH<Subscript>4</Subscript>)<Subscript>3</Subscript>, HL(MH<Subscript>4</Subscript>)<Subscript>2</Subscript>, and H<Subscript>2</Subscript>L(MH<Subscript>4</Subscript>)(L = Be,Mg, Al,Sc, Ti,V, Zn; M = B,Al)

The structural and energetic characteristics of the lowest-lying structures for isolated molecules and ions of light-metal boro-and aluminohydrides L (MH₄)₃, HL(MH₄)₂, and H₂L(MH₄)(L = Be, Mg, Al, Sc, Ti, V, Zn; M = B, Al) with different coordination modes of and groups were calculated by the perturbation theory (MP2), coupled cluster (CCSD(T)), and density functional theory (B3LYP) methods using the 6-31G*, 6-311+G**, and 6-311++G** basis sets. The preferable coordination modes of the ligands in these complexes, as well as the differences and trends in the behavior of the structural parameters and dissociation energies for the loss of BH₃ (AlH₃) molecules and BH ₄ ^? (AlH ₄ ^? ) ions were analyzed in various related series of hydroborates and hydroaluminates.     

Structure and internal rotation in molecules Cl<Subscript>3</Subscript>P=NCOCX<Subscript>3</Subscript> (X = F and Cl)

Applying the quantum-chemical calculations by MP2/6-31G* method molecular structures of trichlorophosphazenes Cl₃P=NCOCX₃ with X = F and Cl were determined and barriers to intramolecular reorientation of PCl₃ group relative to P=N bond and of CF₃ and CCl₃ groups relative to C-C bond were estimated. The values of potential barriers to internal rotation calculated for isolated molecules were compared with the values of the barriers obtained from the data of NQR and NMR spectroscopy of the compounds in the crystalline state. The structural and dynamic features of the studied molecules are discussed.     

Thermodynamic characterization of the amphoteric oxides M<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = Cr,Fe, Co) and their hydrates in aqueous media

The molar solubilities of solid oxides M₂O₃ and their hydrates at 25°C as functions of pH of aqueous media, as well as the acid-base equilibrium constants were calculated for crystalline oxides and dissolved M(OH)₃ hydroxides, where M = Cr, Fe, Co, by the thermodynamic method, taking into account the formation of mono- and polynuclear hydroxo complexes.     

Complex amidoboranes M<Superscript>2</Superscript>[M<Superscript>1</Superscript>(NH<Subscript>2</Subscript>BH<Subscript>3</Subscript>)<Subscript>4</Subscript>] (M<Superscript>1</Superscript> = Al,Ga; M<Superscript>2</Superscript> = Li,Na, K,Rb, Cs)

Structural, spectral, and thermodynamic characteristics of complex amidoboranes M²[M¹(NH₂BH₃)₄] (M¹ = Al, Ga; M² = Li, Na, K, Rb, Cs) were calculated by the B3LYP/def2-SVPD quantum-chemical method. The procedure for the synthesis of these compounds by reactions of alkali metal amidoboranes with aluminum and gallium chlorides was suggested and experimentally tested. Reaction products were characterized by the NMR and IR spectroscopy and X-ray phase analysis.     

The molecular designs and properties of asymmetric heterocycles (HBrBN<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1-4)

The structures and properties of asymmetric heterocycles (HBrBN₃) _n (n = 1-4) are systematically studied at the B3LYP/6-31G* level. The molecules (HBrBN₃) _n (n = 2-4) have the core structures of a 2n-membered ring with alternating boron and α-nitrogen atoms. The relationships between geometrical parameters and oligomerization degree n are discussed. The calculated IR spectra have four main characteristic regions. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed. Thermodynamic analysis of the gas-phase oligomerizations shows that formation of the most stable heterocycles (HBrBN₃) _n (n = 2-4) is enthalpy driven in the range of 200-800 K.     

Avoiding gas-phase calculations in theoretical p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> predictions

CBS-QB3, two simplified and less computationally demanding versions of CBS-QB3, DFT-B3LYP, and HF quantum chemistry methods have been used in conjunction with the CPCM continuum solvent model to calculate the free energies of proton exchange reactions in water solution following an isodesmic reaction approach. According to our results, the precision of the predicted pK _a values when compared to experiment is equivalent to that of the thermodynamic cycles that combine gas-phase and solution-phase calculations. However, in the aqueous isodesmic reaction schema, the accuracy of the results is less sensitive to the presence of explicit water molecules and to the global charges of the involved species since the free energies of solvation are not required. In addition, this procedure makes easier the prediction of pK _a values for molecules that undergo large conformational changes in solvation process and makes possible the pK _a prediction of unstable species in gas-phase such as some zwitterionic tautomers. The successive pK _a values of few amino acids corresponding to the ionization of the α-carboxylic acid and α-amine groups, which is one of the problematic cases for thermodynamic cycles, were successfully calculated by employing the aqueous isodesmic reaction yielding mean absolute deviations of 0.22 and 0.19 pK _a units for the first and second ionization processes, respectively.     

Thermodynamic study of Ag<Subscript>8</Subscript>GeSe<Subscript>6</Subscript> by EMF with an Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> solid electrolyte

The Ag–Ge–Se system was studied in the range of compositions Ag₂Se–GeSe₂–Se by measuring the EMF of the concentration (relative to the silver electrode) circuits with a solid electrolyte Ag₄RbI₅ in the temperature range 290–430 K. The polymorphic transition temperature of Ag₈GeSe₆ (320 K) was determined and the partial molar functions of silver were calculated for both crystal modifications of this compound based on the EMF measurements. The thermodynamic functions of formation and entropy of both modifications of Ag₈GeSe₆ and the thermodynamic functions of its polymorphic transition were calculated.     

Cu<Subscript>4</Subscript>RbCl<Subscript>3</Subscript>I<Subscript>2</Subscript> solid superionic conductor in thermodynamic study of three-component copper chalcogenides

The Cu-B-Se (B = In, As, Sb, Bi) systems are studied by measurement of EMF for concentration circuits vs. a copper electrode in the temperature range of 300–430 K. A solid superionic Cu₄RbCl₃I₂ conductor is used as an electrolyte. Diagrams of solid-phase equilibriums in the studied systems are constructed. Partial molar functions of alloyed copper are calculated on the basis of the equations of the temperature dependences of EMF. Potential-forming reactions corresponding to the measured EMF values are determined on the basis of the phase diagrams and standard thermodynamic formation functions and standard entropies of ternary compounds are calculated.     

Thermodynamic functions and the enthalpies of formation of gaseous VOX<Subscript>3</Subscript> vanadium oxotrihalides

A critical analysis of experimental and theoretical data on the structure and vibrational frequencies of gaseous VOX₃ vanadium oxotrihalides is performed. The values of molecular constants are selected and the thermodynamic functions are calculated within a “rigid rotator–harmonic oscillator” approximation. Equations that approximate a temperature dependence of heat capacity within the temperature range of 298.15–3000 K are obtained. Analysis of the available experimental data allows the enthalpy of formation to be determined for gaseous VOCl₃ molecules. The enthalpies of formation for VOF₃, VOBr₃, and VOI₃ molecules are determined for the first time using this value and quantum-chemical calculations of energy of exchange reactions involving VOCl₃. The obtained results are added to the database of the IVTANTERMO software.     

Heat capacity,entropy of Ln<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> (Ln = La,Sm, and Gd), and the high-temperature enthalpy of Ln<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> (Ln = Eu,Dy, and Ho)

The low-temperature heat capacity of Ln₂(MoO₄)₃ (Ln = La, Sm, and Gd) is investigated by means of adiabatic calorimetry within the range of 60–300 K. The temperature dependences of the heat capacity are found and the values of the standard entropy are calculated, based on extrapolations to 0 K. Characteristic temperatures for molybdates are determined from the results of IR spectroscopic studies. The high-temperature enthalpy of Ln₂(MoO₄)₃ (Ln = Eu, Dy, and Ho) is measured via high-temperature microcalorimetry, and the temperature dependence of heat capacity is calculated in the range of 298–1000 K. Since samarium and gadolinium molybdates are of the same structural type as terbium molybdate, we can estimate the anomaly of the heat capacity in the low-temperature region using the data for terbium molybdate and find the entropy of samarium and gadolinium molybdates.     

Quantum-chemical modeling of the electronic structure and chemical bond of Sn<Subscript>0.875</Subscript>M<Subscript>0.125</Subscript>O<Subscript>2</Subscript> (M = Cr,Mn, Co)

The electronic structure of the Sn_0.875M_0.125O₂ compounds (M = Cr, Mn, Co) with a rutile structure and magnetic moments of the transition metal atoms in them were calculated by the ab initio spin-polarized linear muffin-tin orbital method. The electron density and electron localization function maps for these compounds were constructed. Based on these data, the effect of the composition of these phases on the electronic spectrum, chemical bond, and magnetic and transport properties were analyzed.     

High-temperature heat capacity of stannates Er<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> and Tm<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Erbium stannate Er₂Sn₂O₇ and thulium stannate Tm₂Sn₂O₇ with a pyrochlore-type structure were produced by solid-phase synthesis by calcining stoichiometric mixtures of the respective oxides in air at 1473 K for 240 and 200 h. The high-temperature heat capacity of Er2Sn2O7 and Tm₂Sn₂O₇ was studied by differential thermal calorimetry at 353–1000 K. From the experimental dependences C _P = f(T), the thermodynamic functions (enthalpy change, entropy change, and reduced Gibbs free energy) of oxide compounds were calculated.     

Electronic structure and quadrupole interactions in triple molybdates Li<Subscript>2</Subscript>M<Subscript>3</Subscript>Al(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>, M = Cs,Rb

Within the density functional theory the electronic structure of triple molybdates Li₂M₃Al(MoO₄)₄, where M = Cs, Rb, is studied for the first time. It is found that all molybdates studied belong to wide band insulators with a band gap of ~4 eV. Quadrupole frequencies and asymmetry parameters of the electric field gradient near magnetic ⁷Li, ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei are calculated and experimental NMR spectra are interpreted.     

Modeling of the mechanism of one-electron transfer from the perylene molecule to the oxygen molecule <Superscript>3</Superscript>O<Subscript>2</Subscript> in the HF medium

The thermodynamic parameters of the formation of the perylene radical cation in anhydrous hydrogen fluoride containing dissolved dioxygen were calculated by the ab initio method MP2. The protonated product of HF autoprotolysis was modeled as the H(FH)₃⁺ cluster. The ³O₂ molecule was found to bind to the linear H(FH)₃⁺ cluster via a hydrogen bond. As the charge and multiplicity of the system change upon the capture of an electron, the oxygen-hydrogen fluoride cluster complex undergoes rearrangement to yield the hydroperoxyl radical OOH incorporated in a cycle formed by HF molecules. The free energy of electron transfer from the perylene molecule to the ³O₂ molecule in the HF medium is about −38 kcal/mol.     

Probing the imine silylenoid HN=SiNaF and its insertions reaction with R–H (R=F,OH, NH<Subscript>2</Subscript>, CH<Subscript>3</Subscript>) using DFT

The geometries and isomerization of the imine silylenoid HN=SiNaF as well as its insertion reactions with some R–H molecules have been systematically investigated theoretically, where R=F, OH, NH₂, and CH₃, respectively. The barrier heights for the four insertion reactions are 67.7, 115.6, 153.5, and 271.5 kJ/mol at the B3LYP/6-311+G* level of theory, respectively. Here, all the mechanisms of the four reactions are identical to each other, i.e., a stable intermediate has been formed during the insertion reaction. Then, the intermediate could dissociate into the substituted silylene (HN=SiHR) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies for the four reactions are 71.8, 95.5, 123.3, and 207.6 kJ/mol, respectively, which are linearly correlated with the calculated barrier heights. Furthermore, the effects of halogen substitutions (F, Cl, and Br) on the reaction activity have also been discussed. As a result, the relative reactivity among the four insertion reactions should be as follows: H–F > H–OH > H–NH₂ > H–CH₃.     

Structure of the Cu(Salen) molecule Cuo<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript> according to gas-phase electron diffraction data and quantum chemical calculations

In the framework of synchronous gas-phase electron diffraction and mass spectrometry experiment, the saturated vapor of N,N′-ethylenebis(salicylaldiminate) copper(II) CuO₂N₂C₁₆H₁₄ is studied at a temperature T 574(5) K. It is found that evaporation is congruent and the saturated vapor consists of monomeric molecules. Electron diffraction data are proved to correspond to the geometric model for the CuO₂N₂C₁₆H₁₄ molecule of C ₂ symmetry with an almost planar structure of the CuN₂O₂ coordination fragment and internuclear distances \(r_{h_1 } \)(Cu-O) = 1.917(13) Å and \(r_{h_1 } \)(Cu-N) = 1.931(15) Å. The stuctural parameters obtained are compared to those quantum chemically calculated and molecular parameters in crystals.     

Synthesis,hydration, and electric properties of chlorine-substituted brownmillerite Ba<Subscript>1.95</Subscript>In<Subscript>2</Subscript>O<Subscript>4.9</Subscript>Cl<Subscript>0.1</Subscript>

Chlorine-substituted brownmillerite Ba_1.95In₂O_4.9C_l0.1 was obtained from barium indate Ba₂In₂O₅ by solid-phase synthesis. The ability to absorb water from the gas phase was confirmed by thermogravimetric studies. The transport properties were studied while varying the thermodynamic parameters of the external environment (T, pO₂, pH₂O). The chloride ions in the oxygen sublattice of barium indate Ba₂In₂O₅ were found to affect the ion conductivity. In a humid atmosphere, the sample exhibited proton conductivity (E _a = 0.54 eV), whose contribution became dominant below 300°C.     

Molecular structure of ErCl<Subscript>3</Subscript> and YbCl<Subscript>3</Subscript> according to the data of the simultaneous electron diffraction and mass spectrometric experiment

The saturated vapors of ErCl₃ and YbCl₃ were studied in a simultaneous electron diffraction and mass spectrometric experiment at 1165 K and 1170 K, respectively. In the vapors of these compounds, we found up to 3 mol.% dimers along with the monomers. The parameters of the r _g effective configuration of the monomer molecules were determined. For ErCl₃ and YbCl₃, the internuclear distances r _g(Ln-Cl) were 2.436(5) Å and 2.416(5) Å, and the bond angles ∠_g(Cl-Ln-Cl) were 117.0(10)° and 117.2(10)°, respectively. The equilibrium configurations and vibration frequencies of the monomer and dimer molecules were calculated by the HF, B3LYP, and MP2 methods using the combination of the ECP_D energy-consistent quasirelativistic core potential, including 4f electrons [Kr4d ¹⁰4f ⁿ ], and the contracted [5s4p3d] valence basis set for Er and Yb atoms and the MIDIX [4s3p1d] basis set for Cl atoms. The parameters of the effective r _g configuration of the monomer molecules corresponding to the temperature of the experiment were calculated. The difference between the calculated equilibrium r _e(Ln-Cl) and temperature-averaged r _g(Ln-Cl) distances was found to be 0.001–0.002 Å and did not exceed the error of the r _g(Ln-Cl) parameter determined in the electron diffraction experiment. The experimental parameters of the r _g structure were shown to be consistent with the idea about the planar equilibrium geometrical configuration of ErCl₃ and YbCl₃ molecules.     

Phase equilibria in the Tl-TlCl-Te system and thermodynamic properties of the compound Tl<Subscript>5</Subscript>Te<Subscript>2</Subscript>Cl

The Tl-Te-Cl system was studied in the Tl-TlCl-Te composition region by differential thermal analysis, X-ray powder diffraction, and emf and microhardness measurements. A series of polythermal sections, an isothermal section at 400 K, and a projection of the liquidus surface of the phase diagram were constructed. The ternary compound Tl₅Te₂Cl characterized by a wide homogeneity region and incongruent melting by a syntectic reaction at 708 K was shown to exist. This compound was found to crystallize in tetragonal lattice (space group I4/mcm) with the parameters a = 8.921 Å, c = 12.692 Å, Z = 4. Wide phase separation regions were also found in the system, including a three-phase separation region in the Tl-TlCl-Tl₂Te subsystem. Regions of primary crystallization of phases, and the types and coordinates of in- and monovariant equilibria in the T-x-y diagram were determined. From emf measurement data, the standard thermodynamic functions of formation and the standard entropy were calculated for the compound Tl₅Te₂Cl, as follows: ?ΔG ₂₉₈ ⁰ = 355.9 ± 1.1 kJ/mol, ?ΔH ₂₉₈ ⁰ = 377.1 ± 5.0 kJ/mol, and S ₂₉₈ ⁰ = 474.1 ± 6.8 J/(mol K).