Calorimetric studies of binary systems of 1,3,5-trinitrobenzene with naphthalene, anthracene and carbazole. II. Phase diagrams

The phase diagrams of the binary systems of 1,3,5-trinitrobenzene (TNB) with naphthalene, anthracene and carbazole have been determined by differential scanning calorimetry and optical microscopy over the temperature range 180 K to just above the melting point. All systems show the same features: (i) systems form nearly ideal double simple-eutectic type phase diagrams with 1 : 1 complex, (ii) each one of three known modifications of TNB may exist as a component of the complex—TNB eutectic mixtures. (iii) measured liquidus lines of complexes agree within experimental error with those calculated by the Vieland equation for a completely dissociated complex in the liquid phase, whereas the experimental liquidus lines for the parent components deviate slightly from those predicted by the Schröder—van Laar equation, indicating some degree of complexing in the liquid phase.

The solubility parameter theory has been used to clarify this discrepancy. Applying this theory to the liquidus lines of complexes, we have found that these TNB complexes are still stable upon fusion, and an approximate degree of dissociation amounted to 90% at the melting point in all three cases.

The enthalpy of complex formation, ΔH⁰, both in the liquid and solid state has been determined. The values of ΔH⁰ show that in the solid state the carbazole—TNB complex is the most stable, and the naphthalene—TNB complex is the least stable.     

Paramagnetic ruthenium(III) cyclometallated complex. Synthesis, spectroscopic studies and electron-transfer properties

The reaction of Ru^II(PPh₃)₃X₂ (X = Cl, Br) with o-(OH)C₆H₄C(H)=N-CH₂C₆H₅ (HL) under aerobic conditions affords Ru^II(L)₂(PPh₃)₂, 1, in which both the ligands (L) are bound to the metal center at the phenolic oxygen (deprotonated) and azomethine nitrogen and Ru^III(L¹)(L²)(PPh₃), 2, in which one L is in bidentate N,O form like in complex 1 and the other ligand is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom (deprotonated) of the benzyl amine fragment. The complex 1 is unstable in solution, and undergoes spontaneous oxidative internal transformation to complex 2. In solid state upon heating, 1 initially converts to 2 quantitatively and further heating causes the rearrangement of complex 2 to the stable RuL₃ complex. The presence of symmetry in the diamagnetic, electrically neutral complex 1 is confirmed by ¹H and ³¹P NMR spectroscopy. It exhibits an Ru^II → L, MLCT transition at 460 nm and a ligand based transition at 340 nm. The complex 1 undergoes quasi-reversible ruthenium(II)—ruthenium(III) oxidation at 1.27V vs. SCE. The one-electron paramagnetic cyclometallated ruthenium(III) complex 2 displays an L → Ru^III, LMCT transition at 658 nm. The ligand based transition is observed to take place at 343 nm. The complex 2 shows reversible ruthenium(III)—ruthenium(IV) oxidation at 0.875V and irreversible ruthenium(III)—ruthenium(II) reduction at −0.68V vs. SCE. It exhibits a rhombic EPR spectrum, that has been analysed to furnish values of axial (6560 cm⁻¹) and rhombic (5630 cm⁻¹) distortion parameters as well as the energies of the two expected ligand field transitions (3877 cm⁻¹ and 9540 cm⁻¹) within the t₂ shell. One of the transitions has been experimentally observed in the predicted region (9090 cm⁻¹). The first order rate constants at different temperatures and the activation parameter ΔH^#/ΔS^# values of the conversion process of 1 → 2 have been determined spectrophotometrically in chloroform solution.     

Low-temperature heat capacity and thermodynamic properties of crystalline [Re2(Ala)4(H2O)8](ClO4)6 (Re = Eu, Er; Ala = alanine)

[Re₂(Ala)₄(H₂O)₈](ClO₄)₆ (Re=Eu, Er; Ala=alanine) were synthesized, and the low-temperature heat capacities of the two complexes were measured with a high-precision adiabatic calorimeter over the temperature range from 80 to 370 K. For [Eu₂(Ala)₄(H₂O)₈](ClO₄)₆, two solid–solid phase transitions were found, one in the temperature range from 234.403 to 249.960 K, with peak temperature 243.050 K, the other in the range from 249.960 to 278.881 K, with peak temperature 270.155 K. For [Er₂(Ala)₄(H₂O)₈](ClO₄)₆, one solid–solid phase transition was observed in the range from 270.696 to 282.156 K, with peak temperature 278.970 K. The molar enthalpy increments, ΔH_m, and entropy increments,ΔS_m, of these phase transitions, were determined to be 455.6 J mol⁻¹, 1.87 J K⁻¹ mol⁻¹ at 243.050 K; 2277 J mol⁻¹, 8.43 J K⁻¹ mol⁻¹ at 270.155 K for [Eu₂(Ala)₄(H₂O)₈](ClO₄)₆; and 4442 J mol⁻¹, 15.92 J K⁻¹ mol⁻¹ at 278.970 K for [Er₂(Ala)₄(H₂O)₈](ClO₄)₆. Thermal decompositions of the two complexes were investigated by use of the thermogravimetric (TG) analysis. A possible mechanism for the thermal decomposition is suggested.     

The enthalpy of formation of IrO2 and thermodynamic functions

The Gibbs energy of formation of IrO₂(s) has been measured by means of oxygen dissociation pressure measurements, and by EMF measurements using ZrO₂ (+ CaO) as the solid electrolyte. In addition, high-temperature enthalpy increments of IrO₂ have ben measured from 416 to 940 K using a drop calorimeter. A “third law” evaluation of the experimental results and data from literature has been made. For the enthalpy of formation of IrO₂(s) the value ΔH°_f (298.15 K) - −(59.60 ± 0.03) kcal mole⁻¹ has been selected. The thermodynamic functions of IrO₂(s) have been calculated in the temperature range 298–1200 K.     

纳米氧化锌的低温热容和热力学性质

用扫描电子显微镜(SEM)测定了纳米氧化锌试样的粒径, SEM结果表明ZnO试样平均粒径为30 nm. 在83～350 K温区, 用精密低温绝热量热计测定了ZnO的等压摩尔热容, 拟合出其等压摩尔热容与热力学温度的函数关系式: C_p＝－3.249＋0.2400T－3.413×10^－4T ²＋4.485×10^－7T ³. 根据热容与热力学函数关系, 计算了以298.15 K为基准的纳米ZnO的热力学函数, 并与粗晶ZnO和18 nm ZnO热容文献报导值进行了比较, 从能量角度分析了不同粒径ZnO热容曲线差别产生的原因.     

Heat capacities of NaNO3 and KNO3 from 350 to 800 K

The heat capacities of NaNO₃ and KNO₃ were determined from 350 to 800 K by differential scanning calorimetry. Solid-solid transitions and melting were observed at 550 and 583 K for NaNO₃ and 406 and 612 K for KNO₃, respectively. The entropies associated with the solid-solid transitions were measured to be (8.43± 0.25) J K⁻¹ mole⁻¹ for NaNO₃ and (13.8±0.4) J K⁻¹ mole⁻¹ for KNO₃. At 298.15 K the values of C⁰_P S⁰_P, {H⁰(T)-H⁰(0)}/T and -{G⁰(T)-H⁰(0)}/T, respectively, are 91.94, 116.3, 57.73, and 58.55 J K⁻¹ mole⁻¹ for NaNO₃ and 95.39, 133.0, 62.93, and 70.02 J K⁻¹ mole⁻¹ for KNO₃. Values for S⁰_T, {H⁰(T)-H⁰(0)}/T, and -{G⁰(T)-H⁰(0)}/T were calculated and tabulated from 15 to 800 K for NaNO₃ and KNO₃.     

Structures and energetics of C3H6S isomers: a Gaussian-3 ab initio study

Twenty-two isomers/conformers of C₃H₆S^+√ radical cations have been identified and their heats of formation (ΔH_f) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their ΔH_f data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4⁺) with C_2v symmetry. In contrast, the least energy C₃H₆O^+√ isomer is the 1-propen-2-ol radical cation. The G3 ΔH_f298 of 4⁺ is calculated to be 859.4 kJ mol⁻¹, ca. 38 kJ mol⁻¹ higher than the literature value, ≤821 kJ mol⁻¹. For allyl mercaptan radical cation (7⁺), the G3 ΔH_f298 is calculated to be 927.8 kJ mol⁻¹, also not in good agreement with the experimental estimate, 956 kJ mol⁻¹. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 ΔH_f298 values for 4⁺ and 7⁺ should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent.

Cation CH₃CHSCH₂^+√ (10⁺) has the least energy among the eleven distonic radical cations identified. Their ΔH_f298 values range from 918 to 1151 kJ mol⁻¹. Nevertheless, only one of them, CH₂=SCH₂CH₂^+√ (12⁺), has been observed. Its G3 ΔH_f298 value is 980.9 kJ mol⁻¹, in fair agreement with the experimental result, 990 kJ mol⁻¹.

A couple of reactions involving C₃H₆S^+√ isomers CH₂=SCH₂CH₂^+√ (12⁺) and trimethylene sulfide radical cation (13⁺) have also been studied with the G3 method and the results are consistent with experimental findings.     

Dynamic, electrooptical and energetic nonequivalency of NH bonds in 1:1 and 1:2 complexes of aminopyridines with proton acceptors

The influence of the –NH₂ group position in the pyridine ring on the proton donor ability of N–H groups in hydrogen bonding as well as on the spectral behaviour of stretching and bending vibrations of aminopyridines has been studied. The proton donor ability was shown to increase in the row: meta-, ortho-, and para-aminopyridines. It was established tha N–H bonds in ortho-aminopyridine were not equivalent, and the evaluation of their dynamic nonequivalence was made.

The influence of temperature on the spectral characteristics of the absorption bands of the stretching vibrations of amine groups in the free and hydrogen bonded molecules in CCl₄ has been studied (in temperature range 290–330 K), the formation constants of the complexes have been determined, enthalpy of the 1:1 complexes formation (−ΔH₁) between ortho- and meta-aminopyridines with dimethylformamide, dimethylsulphoxide and hexamethylphosphoramide has been calculated in temperature range 290–330 K. The 1:2 complexes of ortho-, meta- and para-aminopyridines with acetonitrile, tetrahydrofurane, dimethylsulphoxide, hexamethylphosphoramide were studied at the indoor temperature. Enthalpy of the 1:2 complex (−ΔH₂) was estimated on the basis of ‘intensity rule’; −ΔH₁=ΔB^1/2 assuming that parameter does not depend on the composition of a complex.

The vibrational and electrooptical tasks were solved for the free and H-bounded molecules of aminopyridines as well as its complexes of the 1:1 and 1:2 compositions. Dynamic, electrooptical and energetic nonequivalency of NH bonds of aminogroups in aminopyridines was studied quantitatively. The independent calculations of dynamic constants proved mentioned above nonequivalency of NH bonds.

Correlations between spectral characteristics of the absorption bands, geometric, dynamic and electrooptical parameters of –NH₂ group in aminopyridines in the free and hydrogen bonded molecules have been established. Those correlations allow to determine the most important molecular characteristics obtained on the basis of spectral measurements in the range of the absorption bands of the stretching vibrations of aminogroup.     

Conductivity, calorimetry and phase diagram of the NaHSO4–KHSO4 system

Physico-chemical properties of the binary system NaHSO₄–KHSO₄ were studied by calorimetry and conductivity. The enthalpy of mixing has been measured at 505 K in the full composition range and the phase diagram calculated. The phase diagram has also been constructed from phase transition temperatures obtained by conductivity for 10 different compositions and by differential thermal analysis. The phase diagram is of the simple eutectic type, where the eutectic is found to have the composition X(KHSO₄) = 0.44 (melting point ≈ 406 K). The conductivities in the liquid region have been fitted to polynomials of the form κ(X) = A(X) + B(X)(T − T_m) + C(X)(T − T_m)², where T_m is the intermediate temperature of the measured temperature range and X, the mole fraction of KHSO₄. The possible role of this binary system as a catalyst solvent is also discussed.     

Low-temperature heat capacity and standard molar enthalpy of formation of the complex Zn(Thr)SO4·H2O (s)

Low-temperature heat capacities of the complex Zn(Thr)SO₄·H₂O (s) have been precisely measured with a small sample adiabatic calorimeter over the temperature range from 78 to 373 K. The initial dehydration temperature of the complex (T_d=325.50 K) has been obtained by analysis of the heat-capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation by least square method. The standard molar enthalpy of formation of the complex has been determined from the enthalpies of dissolution (Δ_dH_m^Θ) of [ZnSO₄·7H₂O (s) +Thr (s)] and Zn(Thr)SO₄·H₂O (s) in 100 ml of 2 mol dm⁻³ HCl solvent as: Δ_fH_{m,Zn(Thr)SO4·H2O}^Θ=−2111.7±3.4 kJ mol⁻¹. These experiments were made by using an isoperibol solution calorimeter at 298.15 K.     

Thermodynamic stabilities of NiTeO3 and Ni3TeO6 by solid oxide electrolyte e.m.f. method

The e.m.f. of the galvanic cells Pt,C,Te(l),NiTeO₃,NiO/15 YSZ/O₂ (P_o2 = 0.21 atm),Pt and Pt,C,NiTeO₃,Ni₃TeO₆,NiO/15 YSZ/O₂ (P_o2 = 0.21 atm),Pt (where 15 YSZ=15 mass% yttria-stabilized zirconia) was measured over the ranges 833–1104 K and 624–964 K respectively, and could be represented by the least-squares expressions E₍₁₎±1.48 (mV) = 888.72 − 0.504277 (K) and E_(II) ±4.21 (mV) = 895.26 − 0.81543T (K).

After correcting for the standard state of oxygen in the air reference electrode, and by combining with the standard Gibbs energies of formation of NiO and TeO₂ from the literature, the following expressions could be derived for the ΔG^°_f of NiTeO₃ and Ni₃TeO₆: ΔG_f^°(NiTeO₃) ± 2.03 (kJ mol⁻¹) = −577.30 + 0.26692T (K) and ΔG^°_f(Ni₃TeO₆)±2.54 (kJ mol⁻¹) = −1218.66 + 0.58837T (K).     

Solvent extraction of Fe(III) by dehydrated castor oil fatty acids

The effect of temperature on the extraction of FE(III) by dehydrated castor oil fatty acids (DCOFA) has been studied in the temperature range 283–313 K at 1.0M constant ionic strength (NaClO₄). The temperature dependence of the conditional constant of extraction is given in the form: ln K_ext=31.95 − 12800(1/T). Also, it was found that the average thermodynamic parameters, ΔH°_ext, ΔG°_ext, and ΔS°_ext are 106.5 kJ/mole, 27.3 kJ/mole, and 0.3 kJ. mole⁻¹.K⁻¹, respectively. The extracted species in toluene solution were identified as FeR₃.HR and Fe(OH)R₂, where HR represents the fatty acid used.     

Raman spectroscopic characterization of high temperature MGaCl8 (M = Nb, Ta) dinuclear molecular complexes in the liquid and gaseous state

Raman spectra were obtained at temperatures 375–650 K and pressures up to 4 atm from GaCl₃-NbCl₅ and GaCl₃-TaCl₅ binary mixtures in the liquid and vapour state. The data indicate formation of NbGaCl₈ and TaGaCl₈ liquid and vapour dinuclear addition complexes. The spectra were interpreted in terms of a C_2ν configuration for the MGaCl₈ (M = Nb, Ta) molecules consisting of a MCl₆ octahedron sharing an edge with a GaCl₄ tetrahedron. A comparison of the spectral features of 1 : 1 GaCl₃-NbCl₅ and GaCl₃-TaCl₅ molten mixtures with the spectra of the corresponding polycrystalline samples indicates that the proposed identity for the complexes is maintained in all three phases. The NbGaCl₈ and TaGaCl₈ complexes exist in the liquid state in a wide temperature range beyond their melting points (125 and 150°C, respectively) and are shown to undergo dissociation to their components [Nb₂Cl₁₀(1)/NbCl₅(1), Ga₂Cl₆(1) and Ta₂Cl₁₀(1)/TaCl₅(1)] with increasing temperature. Both complex molecules are identified in the gaseous state in low percentages among the vapours of their components and are almost totally decomposed at temperatures higher than ca 325°C. The enthalpy of the reaction TaCl₅(g) +1/2Ga₂Cl₆(g) TaGaCl₈(g) was determined from accurate relative Raman intensity measurements as ΔH⁰ = −38±2 kJ mol⁻¹.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli.

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

Relative thermodynamic stabilities of isomeric alkyl allyl and alkyl (Z)-propenyl ethers

The relative thermodynamic stabilities of ten allyl ethers (ROCH₂CH=CH₂) and the corresponding isomeric (Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst. From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔGΘ, ΔHΘ and ΔSΘ of isomerization at 298.15 K were evaluated. The propenyl ethers are highly favored at equilibrium, the values of both ΔGΘ and ΔHΘ for the allyl → propenyl reaction being ca. −18 to −25 kJ mol⁻¹. The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxy-substituted alkyl groups. In most cases the entropy contribution is negligible; however, for R = (MeO)₂CH and R = (MeO)₃C the values of ΔSΘ are ca. −5 J K⁻¹ mol⁻¹.     

Electrochemical, HPLC and electrospray ionization mass spectroscopic analyses of peroxycitric acid coexisting with citric acid and hydrogen peroxide in aqueous solution

We successfully determined the molecular structure of peroxycitric acid (PCA) coexisting in the aqueous equilibrium mixture with citric acid (CA; 1,2,3-tricarboxylic-2-hydroxy propane) and hydrogen peroxide (H₂O₂) by a combined use of reversed-phase HPLC (RP-HPLC), potentiometric, hydrodynamic chronocoulometric (HCC) and electrospray ionization mass spectroscopic (ESI-MS) methods. Firstly, the RP-HPLC was employed to separate CA, PCA and H₂O₂ coexisting in the equilibrium mixture and the concentration of CA consumed (ΔC_CA) in the formation of PCA that was evidenced to be fairly stable during the RP-HPLC measurement was quantitatively measured based on the standard calibration curve of CA. Secondly, the total oxidant concentration (C_Ox) corresponding to peroxycarboxylic (–COOOH) group in PCA in the equilibrium mixture was determined using potentiometric measurement. The ratio of C_Ox/ΔC_CA was found to be 1.07, which indicates that only one –COOH group in CA molecule is oxidized to the corresponding –COOOH group in PCA molecule. Thirdly, using the HCC technique the diffusion coefficient of PCA, which could be electroreduced at a more positive potential by 1.0 V than the coexisting H₂O₂, was independently measured as 0.3 × 10⁻⁵ cm² s⁻¹ and at the same time, by considering ΔC_CA as the concentration of PCA, the number of electrons (n) required for the reduction of PCA was determined to be 2. The result obtained from RP-HPLC and HCC, i.e., n = 2 which is equivalent to one –COOOH group in PCA, is in agreement with that obtained from the combination of RP-HPLC and potentiometric measurements. Finally, the structure of PCA was proposed to contain one –COOOH group with a molecular mass of 208 confirmed by negative ion ESI-MS method. A probable molecular structure of PCA was discussed.     

Synthesis and thermodynamic properties of a metal-organic framework: [LaCu6(μ-OH)3(Gly)6im6](ClO4)6

A metal-organic complex, which has the potential property of absorbing gases, [LaCu₆(μ-OH)₃(Gly)₆im₆](ClO₄)₆ was synthesized through the self-assembly of La³⁺, Cu²⁺, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, C_p,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [H_T − H_298.15] and [S_T − S_298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC).     

Microwave spectrum and conformation of isopropyl fluoroformate

The microwave spectrum of isopropyl fluoroformate is characterized by intense a-type R-branch transitions from one conformational species. The rotational constants of the ground state, A₀ = 4967.0(8) MHz, B₀ = 1704.69(2) MHz, C₀ = 1468.86(1) MHz and κ = −0.8651(2) are consistent with a τ₁ (O=COC) = 0°, τ₂(COCH) ˜35° structure. This structure can be viewed as a combination of the two conformational species found in ethyl fluoroformate. Two vibrational satellites having rotational constants A₀ = 4963(5) MHz, B₀ = 1694.11(7) MHz. C₀ = 1471.43(4) MHz and A₀=4998(6) MHz, B₀ = 1705.21(7) MHz, C₀ = 1471.10(4) MHz have been assigned.     

Kinetic study of trifluoromethylation with s-(trifluoromethyl) dibenzothiophenium salts

The kinetic parameters were determined for C-trifluoromethylation of aniline with S-(trifluoromethyl)dibenzothiophenium triflate (1), its 3,7-dinitro derivative (2) and S-(trifluoromethyl)diphenylsulfonium triflate (3) in DMF-d₇. The higher reactivity of heterocyclic 1 compared with non-heterocyclic 3 could be explained on the basis of its greatly enhanced activation entropy (ΔS^≠: −11.2 cal mol ⁻¹ K⁻¹ for 1; −47.1 for 3), but not its enhanced activation enthalpy (ΔH^≠: 21.2 kcal mol⁻¹ for 1; 12.1 for 3). The aromatic delocalization of the heterocyclic ring may thus be only slightly disturbed by the S-trifluoromethyl substituent. The high reactivity of 2 was attributed to the great electron deficiency caused by two nitro groups in addition to the heterocyclic salt system (ΔH^≠ 17.0 kcal mol⁻¹, ΔS^≠ −9.1 cal mol⁻¹ K⁻¹ for 2). The reaction mechanism is discussed; the conventional S_N2 attack mechanism was ruled out and a mechanism for a side-on attack to the CF₃-S bond may possibly be applicable.     

Thermodynamic studies on the interaction of some ureas and salts with micellar triton-X-100 in aqueous solutions

We have determined the enthalpies of solution in the micellar state (ΔH_s) for Triton-X-100 in 1 m aqueous solutions of urea, 1,3-dimethyl urea, tetramethyl urea, sodium chloride and calcium chloride at 298.15 K and 308.15 K. These results were used to evaluate the heat capacities of solution (ΔC_p,s) for Triton-X-100 micelles in these solvent systems. It has been observed that ΔC_p,s values of micellar Triton-X-100 decreases drastically upon transfer from water to these solutions but is positive in all cases. Thus, the heat capacities of transfer of Triton-X-100 micelles (ΔC_p,tr) are negative in all the systems studied. A comparison of the effect of non-electrolytes (ureas) and electrolytes (salts) on the micelle has been presented. The results have been discussed in terms of the relative water-structure-disrupting tendencies of the ureas and the salts.