Thermodynamic investigation on M–Te–O (M = Sc, Y) system

The standard Gibbs energy of formation of M₂TeO₆ and M₆TeO₁₂ (where M = Sc, Y), was determined from its vapor pressure measurements by employing thermogravimetry-based transpiration technique. This technique was validated by measuring the vapor pressure of well-studied substances such as TeO₂(s) and CdCl₂(s). The temperature dependence of the vapor pressure of TeO₂(g) over the mixtures M₆TeO₁₂ + M₂O₃ (where M = Sc, Y), generated by the incongruent vaporization reaction, M₆TeO₁₂(s) → 3M₂O₃(s) + TeO₂(g) + ½O₂(g) were measured in the temperature range 1,413–1,473 K and 1,623–1,743 K for Sc₆TeO₁₂(s) and Y₆TeO₁₂(s), respectively. Similarly, the vapor pressure of TeO₂(g) over the mixtures M₂TeO₆(s) + M₆TeO₁₂(s) generated by the vaporization reaction, 3M₂TeO₆(s) → M₆TeO₁₂(s) + 2TeO₂(g) + O₂(g) was measured in the temperature range (1,223–1,293 K) and (1,333–1,423 K) for Sc₂TeO₆(s) and Y₂TeO₆(s), respectively. From the vapor pressure measurements, the standard Gibbs energy of formation of M₆TeO₁₂ and M₂TeO₆ were derived.     

Modification of the electronic properties of zigzag (n = 5–10) and armchair (n = 3, 5) carbon nanotubes by K atom adsorption

The adsorption of the potassium atom onto the surface of (n,0) zigzag nanotube (n = 5–10) and (n,n) armchair nanotubes (n = 3, 5) has been studied by density functional theory. The local density approximation calculation of adsorption energy (E _ads) emphasized on the dependency of E _ads to the diameter and chirality of the nanotube. E _ads decreases when the diameter increases. So the (5,0)-K system has the highest adsorption energy among all structures. Furthermore, a significant change was observed in the electronic properties of potassium-adsorbed single-walled carbon nanotube (SWCNT) and the metallic behavior of the nanotube improved. Therefore, our results showed that such modified SWCNTs can be applied in nanodevices such as transistors.     

Electrochemical studies on organometallic compounds: XLI. Electrogeneration and ESR characterization of [Nb(η5C5H4SiMe3)2Cl{P(OMe)3}]+

In tetrahydrofuran with 0.2 M NaBPh₄ as supporting electrolyte, the one-electron oxidation at −0.4 V relative to an aqueous saturated calomel electrode (SCE) of the electrogenerated species [Nb(η⁵-C₅H₄SiMe₃)₂{ClP(OMe)₃}] (3) yields the cationic niobium(IV) complex [Nb(η⁵-C₅H₄SiMe₃)₂-Cl{P(OMe)₃}]⁺ (4), which has been characterized by ESR spectroscopy. 4 can also be obtained by chemical oxidation of 3.     

Low-temperature thermodynamics of Ln(Me2dtc)3(C12H8N2) (Me2dtc = dimethyldithiocarbamate, Ln = La, Pr, Nd, Sm)

The heat capacities of Ln(Me₂dtc)₃(C₁₂H₈N₂) (Ln = La, Pr, Nd, Sm, Me₂dtc = dimethyldithiocarbamate) have been measured by the adiabatic method within the temperature range 78–404 K. The temperature dependencies of the heat capacities, C _p,m [La(Me₂dtc)₃(C₁₂H₈N₂)] = 542.097 + 229.576 X ? 27.169 X ² + 14.596 X ³ ? 7.135 X ⁴ (J K^?1 mol^?1), C _p,m [Pr(Me₂dtc)₃(C₁₂H₈N₂)] = 500.252 + 314.114 X ? 17.596 X ² ? 0.131 X ³ + 16.627 X ⁴ (J K^?1 mol^?1), C _p,m [Nd(Me₂dtc)₃(C₁₂H₈N₂)] = 543.586 + 213.876 X ? 68.040 X ² + 1.173 X ³ + 2.563 X ⁴ (J K^?1 mol^?1) and C _p,m [Sm(Me₂dtc)₃(C₁₂H₈N₂)] = 528.650 + 216.408 X ? 16.492 X ² + 12.076 X ³ + 4.912 X ⁴ (J K^?1 mol^?1), were derived by the least-squares method from the experimental data. The heat capacities of Ce(Me₂dtc)₃(C₁₂H₈N₂) and Pm(Me₂dtc)₃(C₁₂H₈N₂) at 298.15 K were evaluated to be 617.99 and 610.09 J K^?1 mol^?1, respectively. Furthermore, the thermodynamic functions (entropy, enthalpy and Gibbs free energy) have been calculated using the obtained experimental heat capacity data.     

1H, 13C and 31P NMR studies of some (C6H5)3−nPRn and (C6H5)3−nPRn Cr(CO)5 (n = 0–3; R  H,CH3, C2H5, i-C3H7, t-C4H9) derivatives

The ³¹P chemical shift of the (C₆H₅)_3−nPR_n and (C₆H₅)_3−nPR_nCr(CO)₅ (n = 0–3; R  H, CH₃, C₂H₅, i-C₃H₇, t-C₄H₉) derivatives is dominated by the steric effect. A small inductive effect is also operative but there are no indications of notable (d_Cr→d_P)π back-bonding. The ¹³C chemical shift of the phenyl carbon atoms indicates that (p_ring-d_P)π electron delocalization is unimportant.The ¹³C chemical shift of the carbonyl carbon atoms, which is mainly governed by the mean excitation energy, confirms the conclusion that there are no notable changes in (d_Cr→d_P)π back-bonding in this series of compounds.     

A systematic density functional and wavefunction-based study on dicarboxyl dianions −O2C–R–CO2 − with R = C2, C2X2, C2X4, and C6X4 (X = H, F)

The possible existence of the gas phase cis- and trans-maleate, i.e. completely deprotonated maleic acid (O₂C–CΗ=CΗ–CO₂)^2–, is investigated by density functional (B3LYP) and ab-initio quantum chemical methods (MP2, CCSD(T)) using large basis sets. The calculations reveal that only the trans-isomer is Coulomb stable with respect to electron loss. The results are compared to other previously investigated dicarboxylate dianions of the general form ^?O₂C–R–CO₂ ^? with R = C₂, C₂X₂, C₂X₄, and C₆X₄ (X = H, F). Fluorine substitution on the carbon framework helps to stabilize these doubly charged systems, and we predict that all of the aromatic fluorine substituted dicarboxylate dianions are Coulomb stable in the gas phase. Only the highest levels of theory reveal the slight stabilization of both the succinate dianion and the ortho-isomer of the phthalic acid dianion in unprecedented agreement with experiments.     

Critical temperatures,pressures, and densities for the mixtures CO2–C3H8, CO2–nC4H10, C2H6–C3H8, and C3H8–nC4H10

A simple method is developed to estimate mixture critical temperatures (T_c), pressures (P_c), and densities (ρ_c) as a function of overall composition (X) from near critical region experimental coexistence data. This three-step method is applied to four mixtures, CO₂–C₃H₈, CO₂–nC₄H₁₀, C₂H₆–C₃H₈, and C₃H₈–nC₄H₁₀. Isothermal liquid–vapor coexistence data, which includes temperature, vapor pressure, coexisting densities (ρ^ℓ and ρ^v), and coexisting compositions for the more volatile component (x₁^v and x₁^ℓ) are used. In the first step, the difference of the saturated liquid and vapor densities (ρ^ℓ−ρ^v) is fitted to an empirical function in ((P_c−P)/P_c) to obtain P_c. Then P/P_c and ((ρ^ℓ+ρ^v)/2ρ_c) are simultaneously fitted to functions of a polynomial in (X₁−(x₁^v+x₁^ℓ)/2) yielding estimates of ρ_c and X₁. Finally, the discrete estimated critical data points are fitted with an equation to provide a continuous representation of the critical lines. The method is successfully tested for the mixtures, CO₂–C₃H₈ and CO₂–nC₄H₁₀, for which there is a reasonable amount of isothermal data. The procedure is then applied to the mixtures, C₂H₆–C₃H₈ and C₃H₈–nC₄H₁₀, for which there are sparse data. For all four mixtures, the critical temperature line, T_c vs. X₁, matches literature values within ±0.5%. The critical pressure line, P_c vs. X₁, and critical density line, ρ_c vs. X₁, match literature values, in general, within ±2%.     

New Quasi-One-Dimensional Crystals of Metallocarbohedrenes (Sc,Ti,V)8C12 in (12,0) Boron–Nitrogen Nanotubes: Quantum-Chemical Simulation

A quantum-chemical model was made of new quasi-one-dimensional crystals, consisting of regular chains of metallocarbohedrenes Sc₈C₁₂, Ti₈C₁₂, and V₈C₁₂ (isomers with T _h symmetry) inside a single-wall (12,0) boron–nitrogen nanotube. Their electronic characteristics, the nature of the interatomic bonds, and the relative stability in relation to the electronic concentration in the (Sc₈C₁₂@(12,0)BN-NT Ti₈C₁₂@(12,0)BN-NT V₈C₁₂@(12,0)BN-NT) systems and the mutual arrangement of the metallocarbohedrenes and the nanotube are discussed.     

Thermodynamic studies on the systems M–Te–O (M = Nd,Sm)

The standard Gibbs energies of formation of Nd₂TeO₆ and M₆TeO₁₂ (where M = Nd, Sm) were determined from vapour pressure measurements. The vapour pressure of TeO₂(g) was measured by employing thermogravimetry-based transpiration technique. The temperature dependence of the vapour pressure of TeO₂(g) over the mixtures Nd₂TeO₆+Nd₆TeO₁₂, generated by the incongruent vapourisation reaction, 3Nd₂TeO₆(s) → Nd₆TeO₁₂(s)+2TeO₂(g)+O₂(g), was measured in the temperature range 1,408–1,495 K. Similarly, the vapour pressure of TeO₂(g) over the mixtures M₆TeO₁₂+M₂O₃ (where M = Nd, Sm), generated by the incongruent vapourisation reaction, M₆TeO₁₂(s) → 3M₂O₃(s)+TeO₂(g)+½O₂(g), was measured in the temperature range 1,703–1,773 and 1,633–1,753 K for Nd₆TeO₁₂(s) and Sm₆TeO₁₂(s), respectively. Enthalpy increments of M₂TeO₆(s) (where M = Nd, Sm) were determined by inverse drop calorimetric method in the temperature range 573–1,273 K. The thermodynamic functions, viz., heat capacity, entropy and free energy functions, were derived from the measured values of enthalpy increments. A mean value of ?2,426.2 ± 0.6 and ?2,417.9 ± 1.1 kJ mol^?1 was obtained for $ \Updelta_{\text{f} } H_{298}^{\text{o}} $ (Nd₂TeO₆, s) and $ \Updelta_{\text{f}} H_{298}^{\text{o}} $ (Sm₂TeO₆, s), respectively, by combining the value of $ \Updelta_{\text{f}} G^{\text{o}} $ (Nd₂TeO₆, s) and $ \Updelta_{\text{f}} G^{\text{o}} $ (Sm₂TeO₆, s) derived from vapour pressure data and the free energy functions derived from the drop calorimetric data.     

Thermal decomposition of RE(C2H5CO2)3·H2O (RE = Dy,Tb, Gd,Eu and Sm)

The thermal decomposition of Dy(III), Tb(III), Gd(III), Eu(III), and Sm(III) propionate monohydrates was studied in argon by means of simultaneous differential thermal analysis and thermogravimetry, infrared-spectroscopy, X-ray diffraction, and optical microscopy. After dehydration, which takes place below 120 °C, all salts decompose into dioxycarbonates with simultaneous release of CO₂ and C₂H₅COC₂H₅ (3-pentanone) between 250 and 460 °C. However, whereas the anhydrous Dy-, Tb-, and Gd-propionates appear to transform into RE₂O₂CO₃ (rare earth [RE] = Dy, Tb, Gd) in a single step, an intermediate stage involving a RE₂O(C₂H₅CO₂)₄ composition was evidenced in the case of the Eu- and Sm-propionates. For all compounds, further decomposition of RE₂O₂CO₃ into the corresponding sesquioxides (RE₂O₃) is accompanied by the release of CO₂. The thermal decomposition of Dy- and Tb-propionates occurs entirely in the solid state. In contrast the dehydrated Gd-, Eu-, and Sm-propionates melt at increasingly higher temperatures. Evidence for recrystallization was found in conjunction with the onset of decomposition of these three propionates.     

Density-Functional Theory Study on Neutral and Charged M n C2 (M = Fe, Co, Ni, Cu; n = 1–5) Clusters

The ground-state geometrical and electronic properties of neutral and charged M _n C₂ (M = Fe, Co, Ni, Cu; n = 1–5) clusters are systematically investigated by density-functional calculations. The growth evolution trends of neutral and charged Fe _n C₂, Co _n C₂, Ni _n C₂ and Cu _n C₂ (n = 1–5) clusters are all from lower to higher dimensionality, while it is special for Cu _n C ₂ ^± (n = 1–5) clusters which favor planer growth model. The space directional distributions of Co and Ni indicate stronger magnetic anisotropy than that in Cu atoms. Compare with experimental data (photoelectron spectroscopy), our results are in good agreement. The interaction strengths between metal and carbon atoms in TM–C (TM = Fe, Co, Ni) clusters are comparable and are obviously larger than that in Cu–C clusters, and this interaction strengths also decrease through the sequence: cation > neutral > anion, which may be crucial in exploring the differences in the growth mechanisms of metal–carbon nano-materials.     

NMR study (1H, 13C and 31P) of the {(C2H5)2N}nPX3−n compounds (X = Cl,C2H5; n = 0, 1, 2, 3)

¹H, ¹³C and ³¹P NMR data of the compounds {(C₂H₅)₂N}_nPX_3−n, (X = Cl, C₂H₅; n = 0, 1, 2, 3) are reported. While the ¹H and ¹³C resonances from the PEt moiety rather follow the electron-withdrawing effect of the NEt₂ substituent, ¹H and ¹³C chemical shift data from the NEt₂ moiety reveal a quite important shift contribution originating from sterically induced polarization of the CH bonds . ³¹P chemical shift data are interpreted in terms of inductive effects but the anomalous diamagnetic shift deviation from linearity for X = Cl suggests a minor contribution from

multiple bonding. The general trend observed in the ³¹P-couplings is quite straightforward and can be qualitatively explained by Bent's rule.     

The Synthesis of the Arene Clusters Ru6C(CO)14(η6-Arene) (Arene = C6H5CHMe2, C6H5C4H9, C6H5C3H7, and C6H5C3H5)

On reaction with Ru₃(CO)₁₂, isopropenylbenzene and 4-phenyl-l-butene undergo hydrogenation, to yield the clusters, Ru₆C(CO)₁₄(⁶-C₆H₅CHMe₂) 1 and Ru₆C(CO)₁₄(⁶-C₆H₅C₄H₉) 2, respectively. With allylbenzene, both hydrogenation and isomerization occurs affording Ru₆C(CO)₁₄(⁶-C₆H₅C₃H₇) 3 and Ru₆C(CO)14(⁶-C₆H₅C₃H₅) 4. The structures of 1 and 2 have been established by single crystal X-ray diffraction. One of the Ru–Ru bond lengths in 2 is unusually long and extended Hückel molecular orbital calculations have been used in an attempt to rationalize this feature.     

Substituent effects on the compounds CX1X2•− (X1, X2 = H, F, Cl, Br, I) from theoretical investigation

The electronic and molecular structures of mono- and dihalocarbene anions constructed by model CX¹X^2?? (X¹, X² = H, F, Cl, Br, I), as well as the corresponding carbenes CX¹X² and analogous silicon-anions SiX¹X^2??, have been studied in detail using the B3LYP, MP2, and QCISD(T) levels of theory. Our calculated findings suggest that stabilization of the compounds is associated with the size of the halogen substituent X, which is further confirmed by ionization energies, the spin density (S _d), and the second-order perturbative energies (E(2)). Besides, we have also explored the source of the anions’ proton affinity difference.     

Rb[C6H3(COOH)2(COO–)] · [C6H3(COOH)3] · 2H2O: Synthesis,Crystal Structure,and Properties

The salt Rb[C₆H₃(COO)₂(^–)] · [C₆H₃(COOH)₃] · 2H₂O (I) of trimesic acid was synthesized and its thermal stability and conductivity (10^–11 ohm^–1 cm^–1 at 298 K) were measured. Molecular and crystal structures of I were established by X-ray diffraction analysis. Hydrogen bonding system in complex I was detected by IR and Raman spectroscopies. X-ray diffraction data agree with vibration spectroscopy data.     

Structural and electrical properties of chemical solution deposited (Bi0.9Tb0.1)(Fe0.975 TM 0.025)O3±δ (TM = Ni, Mn and Ti) thin films

Effects of Tb and transition metal (TM = Ni, Mn and Ti) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO₃ thin films prepared by using a chemical solution deposition method were reported. From X-ray diffraction and Raman scattering analyses, distorted rhombohedral perovskite structures were observed for all thin films. Improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 2.67 × 10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2P _r ) of 82.2 μC/cm² and low coercive field (2E_c) of 680 kV/cm (at 1,036 kV/cm) were measured for the (Tb, Mn) co-doped thin film.     

Kinetics of Intramolecular Hydrogen Atom Transfer in the Radicals >Si(O·)(R) (R = H,D, CH3, CD3, and C2H5)

Methods are developed for obtaining oxy radicals by the photodecomposition and thermal decomposition of precursors (Si–O)₂Si(N=N–O^·)(R) and (Si–O)₂Si(O–C^·=O)(R). The mechanism of these processes is established. Kinetic data are obtained for the reaction of hydrogen atom transfer in oxy radicals (Si–O)₂Si(O^·)(R) (R = H, D, CH₃, CD₃, and C₂H₅). The activation energies of hydrogen atom transfer are found for three-, four-, and five-membered transition states: 13.5 ± 1, 18 ± 1, and <10 kcal/mol, respectively. For the reaction of H(D) atom transfer in the (Si–O)₂Si(O^·)(H(D)) radical, the kinetic isotope effect is found. Quantum-chemical calculations were used to determine the structures of transition states in the studied processes. Experimental studies were carried out using ESR spectroscopy.     

Stepwise TiCl,TiCH3, and TiC6H5 bond dissociation enthalpies in bis(pentamethylcyclopentadienyl)titanium complexes

Reaction-solution calorimetric studies involving the complexes Ti[η⁵-C₅(CH₃)₅]₂-(CH₃)₂, Ti[η⁵-C₅(CH₃)₅]₂(CH₃), Ti[η⁵-C₅(CH₃)₅]₂(C₆H₅), Ti[η⁵-C₅(CH₃)₅]₂Cl₂, and Ti[η⁵-C₅(CH₃)₅]₂Cl, have enabled derivation of titaniumcarbon and titaniumchlorine stepwise bond dissociation enthalpies in these species.     

Density functional theory study on (F2AlN3) n (n = 1–4) clusters

Possible geometrical structures and relative stabilities of (F₂AlN₃) _n (n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F₂AlN₃) _n (n = 2–4) possess cyclic structure containing Al–N_α–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F₂AlN₃) _n (n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm⁻¹, and the vibrational modes are N₃ asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters (2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K.