Influence of Excitation of the Lanthanide 4 fShell on Complexation with Organic Substrates in Solutions: 1. The Complexation of the β-Diketonate Tris(heptafluorodimethyloctanedionato)europium(III) with Sulfoxides in Benzene Solutions

Complexation of sulfoxides R¹R²S=O with the -diketonate Eu(fod)₃(fod is heptafluorodimethyloctanedionato) in the ground and excited states in benzene solutions was studied. Excitation of Eu(fod)₃was found to increase the formation constants and to reverse the sign of the enthalpy of complexation. The compensation effect was observed for the thermodynamic parameters: S ₀= (3.4 ± 0.4) × 10^–3H ₀+ (50.0 ± 4.7) in the ground state and S ^* ₀= (3.2 ± 0.4) × 10^–3H ^* ₀+ (62.0 ± 0.6) in the excited state of Eu(fod)₃. The enhancement of the stability of the complexes [Eu(fod)^* ₃· R¹R²S=O] is due to an increase in the entropy of complexation upon excitation of f–ftransitions in Eu(III).     

The Influence of 4f Orbital Excitation in Eu(Fod)3 on Complexation with Sulfones in Benzene Solutions

Complexation of sulfones (S) with the -diketonate Eu(Fod)₃ (Fod–heptafluorodimethyloctanedione) in the ground and excited electronic states in benzene solutions was studied. The stability constants and thermodynamic parameters for the formation of complexes Eu(Fod)₃ · S in the ground state (K, H ₀, S ₀) and Eu(Fod)₃ ^* · S in the excited state (K*, H ₀ ^*, S ₀ ^*) were determined. The excitation of f–f transitions of Eu(III) was found to enhance the stability of Eu(Fod)₃ · S complexes, apparently due to an increase in the acceptor ability of the Eu(III) chelate. This fact confirms the involvement of the 4f orbital in the chemical bond formation. The compensation effect was observed for the thermodynamic parameters: S ₀ = (2.9 ± 0.3) × 10^–3H ₀ + (35.0 ± 4.0) in the ground and S ₀ ^* = (3.3 ± 0.3) × 10^–3H ₀ ^* + (49.0 ± 5.0) in the excited states of Eu(Fod)₃. It was shown that electronic excitation of the 4f orbital of Eu(Fod)₃ influences isotopic effects in complexation with sulfolanes.     

Solvent extraction of thorium from nitric acid solutions using di-N-butyl sulfoxide (DBSO) in xylene

The extraction of thorium(IV) from nitric acid solutions by di-n-butyl sulfoxide (DBSO) in xylene has been investigated as a function of acid, extractant and the metal concentration. The effect of contact time and diverse ions on the extraction has been examined. Phosphate, fluoride, oxalate and perchlorate reduce the extraction to some extent. The extraction of other metal ions, especially impurities associated with thorium in ores, has been measured under optimised conditions selected for thorium extraction. Na(I), K(I), Ca(II), Sr(II), Mn(II), Fe(II), Ni(II), Zn(II), Pb(II), Al(III), Ti(IV) and Hf(IV) are not extracted. Among the stripping solutions employed for back-extraction, deionized water is found to be the best and more than 99% thorium can be back-extracted in three stages. The extracted species is supposed to be Th(NO₃)₄·2DBSO. The extraction is found to be almost independent of the thorium concentration in the range between 4.3·10^–4–4.3·10^–2M and inversely dependent upon the temperature. The values of thermodynamic functions H, G and S for extraction equilibrium have been evaluated to be –19.6±2.9 kJ·mole^–1, –18.1±2.0 kJ·mole^–1 and –5.0±2.9 J·mole^–1·K^–1, respectively.     

Determination of enthalpies of formation of organic free radicals based on bond dissociation energies. 4. Alkyl-substituted derivatives of phenyl and benzyl

The enthalpies of formation (H _f°) of 16 alkyl-substituted phenyl and benzyl radicals (R^·) were determined for the first time by the published values of energies of R—X bond dissociation. For the initial molecules of RX, alkyl-substituted benzenes, the additive-group procedure was developed for the calculation of H _f°. In the framework of the additive-group model for considered R^·, we studied the structure-property interrelation, analyzed the obtained H _f°(R^·) values, and confirmed their reliability. The influence of nonvalent interactions on H _f°(R^·) was systematized and detailed. The parameters, from which it is possible to calculate H _f° of the 51 radicals, were proposed.     

Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

The standard molar enthalpies of formation _f H _m ^° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization _l ^g H ^{m °} of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol^–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.     

Heat of Formation for LiMyMn2−yO4 (M=Co,Cr, Li,Mg, Ni) Spinel Solid Solution

The enthalpy of formation for LiM_yMn_2–yO₄ (M=Co, Cr, Li, Mg, Ni) was measured by a Tian-Calvet type high temperature isothermal microcalorimeter. The standard enthalpy of formation for LiMn₂O₄ at 876 K was evaluated to be H_f⁰=–1404.2±6.4 kJ mol^–1. The partial substitution of Co and Ni for Mn decreased the absolute H_f⁰ value, while that of Cr and Mg for Mn increased the absolute H_f⁰ value. In the case of the partial substitution of Li for Mn, no marked change in H_f⁰ could be observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Role of Intermolecular Interactions in Formation of Linear Polynuclear Platinum Complexes

The electronic and steric structures of cis- and trans-[Pt(NH₃)₂Hlg₂] were calculated by HF and DFT methods, and the differences between their thermodynamic functions H ⁰ 298, S ⁰ 298, G ⁰ 298, and C _4p = f(T) were evaluated on the basis of DFT force fields. The differences between the stabilities of the cis and trans isomers are mainly due to features of molecular structure, namely, to the energy of interligand interaction. The nonvalent interactions Pt···Pt and NH₂-H···Hlg between the mononuclear fragments cis-[Pt(NH₃)₂· Hlg₂], weakening in the order Cl^- > Br^- > I^-, considerably enhance the stability of the cis isomers and provide conditions for formation of linear polynuclear complexes with Pt-Pt bonds.     

The kinetics of the oxidation-reduction reaction between uranium(VI) and titanium(III) in HCl solution

The oxidation-reduction reaction between U(VI) and Ti(III) in HCl solution was studied spectrophotometrically. The reaction is second-order at all concentrations of reactants, HCl, ferrous chloride and mannitol used in this work. In 5M HCl the rate constantk increases with increasing Ti(III) concentration, whereas it decreases with increasing U(VI) concentration, with increasing HCl concentration from 1.00M to 7.17M and increases thereafter from 7.17M to 11.79M. The addition of mannitol causes a consistent decrease in the rate of reaction, whereas ferrous chloride has no effect. The activation energy for this oxidation-reduction reaction was 47.90±0.11 kJ·mol^–1. The values of H , G and S were 45.40±0.11 kJ·mol^–1, 72.50±0.17 kJ·mol^–1 and –91.10±0.22J·k^–1·mol^–1, respectively. The mode of reaction is discussed in the light of kinetic results.     

Additive prediction of thermodynamic functions of hydrofluorides

Summary The experimental data available on the thermodynamic functions ⁰ forMF·nHF hydrofluorides [M=Li, Na, K, Rb, Cs, NH₄, Ag(I) and Tl(I);n=1–3] have been evaluated additively. The unknown values of ⁰ forn=0÷7 are predicted.

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Additive Voraussagen der thermodynamischen Funktionen von Hydrogenfluoriden (Kurze Mitt.)

Zusammenfassung Die vorhandenen experimentellen Daten über die thermodynamischen Funktionen ⁰ von HydrogenfluoridenMF·nHF [M=Li, Na, K, Rb, Cs, NH₄, Ag(I) und Tl(I);n=1–3] werden linear ausgeglichen und die fehlendenden Werte für ⁰ mitn=0÷7 vorausgesagt.

     

On the interaction between gold and copper in mercury

On the base of cyclic voltammetry, chronoamperometry and potentiometry experiments with the use of the hanging mercury drop electrodes, there was found that a solid AuCu compound is formed in the complex Au-Cu amalgam. The stability of AuCu is controlled by its solubility product, which is equal (7.1±1.5)·10^–6 M ² at 298 K. The temperature dependence of the solubility product allowed to determine H _AuCu of formation in mercury. This value is compared with H _AuCu of the reaction in the binary system. On the basis of theBorn-Haber cycle one may conclude that the AuCu formed in mercury phase should have the same structure as in the binary alloy. Some thermodynamic aspects of reactions in the Au-Cu-Ga amalgam are discussed. The solubility of copper in mercury was experimentally confirmed and is equal (1.1±0.1) · 10^–2at.%.

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Über die Wechselwirkung zwischen Gold und Kupfer in Quecksilber

Zusammenfassung Mit Hilfe von voltammetrischen, chronoamperometrischen und potentiometrischen Experimenten mit der hängenden Quecksilbertropfelektrode wurde eine feste AuCu-Verbindung in Au-Cu-Amalgam gefunden. Die Beständigkeit der Verbindung AuCu wird durch das Löslichkeitsprodukt bestimmt, das gleich (7,1 ± 1,5) · 10^–6 M ² bei 298 K ist. Die Temperaturabhängigkeit des Löslichkeitsproduktes erlaubt die Bestimmung der Bildungswärme H _AuCu der Verbindung in Quecksilber. Dieser Wert wird mit der Bildungswärme H _AuCu im binären System verglichen. Auf der Basis desBorn-Haber-Kreisprozesses kann man schließen, daß das in Quecksilber gebildete AuCu dieselbe Struktur wie im binären System hat. Verschiedene thermodynamische Aspekte der Reaktionen in Au-Cu-Ga-Amalgam werden diskutiert. Die Löslichkeit von Kupfer in Quecksilber wurde experimentell bestätigt und beträgt (1,1 ± 0,1) · 10^–2 at.%.

     

ViscosityB-Coefficient of ammonium azide and the enthalpy of formation of the azide anion

Recent determination of the standard enthalpy of formation of the ammonium azide _f H ^O (NH N ₃,c) and the assignment of the viscosity B-coefficient for the azide anion, B(N ₃ ^– ,aq), in aqueous solution enable us to estimate the standard enthalpy of formation of the gaseous azide anion, _f H ^O (N ₃ ^–,g , — a thermochemical magnitude in some dispute — to be 192 kJ-mol^–1.     

Thermochemistry of Alcohols: Experimental Standard Molar Enthalpies of Formation and Strain of Some Alkyl and Phenyl Congested Alcohols

The standard molar enthalpies of formation _f H _m ^° (cr) at the temperature T = 298.15 K were determined using combustion calorimetry for di-tert-butyl-methanol (A), di-tert-butyl-iso-propyl-methanol (B), and di-phenyl-methyl-methanol (C). The standard molar enthalpies of sublimation _cr ⁸ H _m ^° of these compounds and of di-phenyl-methanol (D) were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ¹ H _m ^° of the compounds A–D and of tri-phenyl-methanol (E) were measured by differential scanning calorimeter (DSC). From these data and data available from the literature, the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) for A, (–397.0 ± 1.2); B, (–418.1 ± 2.3); C, (–34.2 ± 1.3); and D, (0.9 ± 2.1) kJ · mol^–1 were derived, which correspond to strain enthalpies (H _S) of 46.1, 114.7, 8.1, and 5.0 kJ · mol^–1, respectively.     

Preparation and Thermochemistry of Complexes of Zinc Nitrate with Threonine

The solubility property of Zn(NO₃)₂–Thr–H₂O system (Thr—threonine) at 25°C in the entire concentration range has been investigated by the phase equilibrium semimicromethod. The corresponding phase diagram and refractive index diagram were constructed. From the phase equilibrium results, the incongruently soluble compounds of Zn(Thr)(NO₃)₂ · 2H₂O, Zn(Thr)₂(NO₃)₂ · H₂O, and Zn(Thr)₃(NO₃)₂ · H₂O were synthesized and characterized by IR, XRD, TG–DTG, chemical and elemental analyses. The constant-volume combustion energies of the compounds, _c E, determined by precision rotating bomb calorimeter at 298.15 K, were –6266.88 ± 3.72, –9263.28 ± 2.23, and –11 423.11 ± 6.81 J/g, respectively. The standard enthalpies of combustion for these compounds, _c H _m ^° (complex, s., 298.15 K), were calculated as –2147.40 ± 1.28, –4120.83 ± 0.99, and –6444.68 ± 3.85 kJ/mol and the standard enthalpies of formation, _f H _m ^° (complex, s., 298.15 K), are –1632.82 ± 1.43, –1885.55 ± 1.50, and –2770.25 ± 4.21 kJ/mol. The enthalpies of dissolution of the complexes in a medium of simulated human gastric juice (37°C, pH 1, in the solution of hydrochloric acid), _dis H _m ^° (complex, s., 310 K), which were also measured by a microcalorimeter to be 13.36 ± 0.06, 15.53 ± 0.06, and 17.04 ± 0.05 kJ/mol, respectively.     

Dissociation quotients of malonic acid in aqueous sodium chloride media to 100°C

The first and second molal dissociation quotients of malonic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of malonic acid/bimalonate solutions was measured relative to a standard aqueous HCl solution from 0 to 100°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a seven-term equation. This treatment yielded the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: logK _1a =-2.852±0.003, H _1a ^/o =0.1±0.3 kJ-mol^–1, S _1a ^o =–54.4±1.0 J-mol^–1-K^–1, and C _p,1a ^o =–185±20 J-mol^–1-K^–1. Measurements of the bimalonate/malonate system were made over the same intervals of temperature and ionic strength. A similar regression of the present and previously published equilibrium quotients using a seven-term equation yielded the following values for the second acid dissociation equilibrium at 25°C: logK_2a=–5.697±0.001, H _2a ^o =–5.13±0.11 kJ-mol^–1, S _2a ^o =–126.3±0.4 J-mol^–1-K^–1, and C _p,2a ^o =–250+10 J-mol^–1-K^–1.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Complexation properties of phosphonocarboxylic acids in aqueous solutions

The concentration formation constants of phosphonoacetic acid (PAA) complexes with the Ca²⁺ and Mg²⁺ ions were determined in aqueous solution at 25°C by potentiometric and coulometric titrations at different ionic strengths and were extrapolated to I=0 in order to obtain thermodynamic values of the formation constants. Complexes were formed by the completely deprotonated K _f (ML) and monoprotonated K _f (MHL) forms of the PAA anion. The respective values for the complexes are: log K _f (CaL)=4.68±0.03, log K _f (CaHL)=2.61±0.08; log K _f (MgL)=5.58±0.09, log K _f (MgHL)=3.0±0.3. The enthalpy and entropy of complexation for the deprotonated Ca²⁺ and Mg²⁺ PAA species, determined from the temperature dependence of the log K _f (ML), are: H⁰(Ca) =0.6±0.2 kcal-mol^–1, S⁰(Ca)=21.4±0.6 cal-mol^–1-K^–1, H⁰(Mg)=3.0±0.7 kcal-mol^–1, and S⁰(Mg)=35±2 cal-mol^–1-K^–1. It is seen there-fore, that the complexes are entropy stabilized but enthalpy destabilized. Formation constants were also determined for Ca²⁺ and Mg²⁺ complexes with PAA analogs, phosphonoformic and 3-phosphonopropionic acids and the complexation of PAA was also studied at a single ionic strength, with Na⁺, Ag⁺, Tl⁺, Sr²⁺, Ba²⁺, Cd²⁺, Cu²⁺, and Pb²⁺ ions.     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

Thermally-induced Transition in Aqueous Solution of Cationic Surfactant Containing Aromatic Ring

Heat capacities of aqueous solutions of cetyltrimethylammonium (CTA) salicylate, of CTA m-hydroxybenzoate and of CTA p-hydroxybenzoate were measured using a scanning microcalorimeter. Only the salicylate solution exhibited heat-capacity anomaly around 330 K, depending on the heating rate. The transition enthalpy was 3.5±0.2 kJ mol^–1, which was similar to that observed in solution of 1:1 intermolecular compound between CTA bromide (CTAB) and o-iodophenol (OIPh). The enthalpy of formation H_f of the 1:1 intermolecular compound from CTAB and OIPh was determined by measuring the enthalpies of solution of the relevant crystals into ethanol. Positive value _fH=3.0±0.3 kJ mol^–1 was explained from a large difference between the heat capacities of the 1:1 compound and 1:1 mixture of the component crystals.This revised version was published online in November 2005 with corrections to the Cover Date.     

Heat capacity measurement of U1?yLayO2 (y=0.044, 0.090, 0.142) from 300 to 1500 K

Heat capacities of U_1–yLa_yO₂ were measured by means of direct heating pulse calorimetry in the temperature range from 300 to 1500 K. An anomalous increase in the heat capacity curve of each sample was observed similarly to the case of U_1–yGd_yO₂, found recently in our laboratory. As the lanthanum content of U_1–yLa_yO₂ increased, the onset temperature of an anomalous increase in the heat capacity decreased and the excess heat capacity increased. The enthalpy of activation (H_f) and the entropy of activation (S_f) of the thermally excited process, which cause the excess heat capacity were obtained to be 2.14, 1.63 and 1.50 eV and 39.4, 34.2 and 31.8 J·K^–1·mol^–1 for U_0.956La_0.044O₂, U_0.910La_0.090O₂ and U_0.858La_0.142O₂, respectively. The values at zero La content extrapolated by using the data of H_f and S_f for U_1–yLa_yO₂ were in good agreement with the experimental values of undoped UO₂ so far reported, similarly to the case of Gddoped UO₂. The electrical conductivities of U_1–yLa_yO₂ (y=0.044 and 0.142) were also measured as a function temperature. No anomaly was seen in the electrical conductivity curve. It may be concluded that the excess heat capacity originates from the predominant contribution of the formation of oxygen clusters and from the small contribution of the formation of electron-hole pairs.     

On the reliability of equilibrium data of the charge-transfer complex between 2,3-dichloro-1,4-naphthoquinone and hexamethylbenzene

In view ofHammond's warning⁶ about the Conspiracy of errors, found in the case of low values of equilibrium constants of charge-transfer complexes a case is made out for redetermining the values for the system hexamethylbenzene—2,3-dichloro-1,4-naphthoquinone. Uncertainties in the parameters were estimated using theLiptay ⁸ matrix procedure. The solvent used was dichloromethane. The following data were obtained at 25°C: vC T = 22,220 cm^–1;E _A=0.99 eV;K =2599±57 l²·cm^–1·mol^–2. _max= 1020 ± 148 cm^–1··1;K=2.55±0.37 l·mol^–1; –H=2.7±0.3 kcal·mol^–1.With 1 Figure