Thermodynamics of the Mixed-Ligand Complex Formation of Mercury(II) Ethylenediaminetetraacetate with Dipyridine and Phenanthroline in Aqueous Solution

The formation of the mixed-ligand complexes HgEdtaL^2?, where L = 2,2′-dipyridine (Dipy) or 1,10-phenanthroline (Phen), was studied by calorimetry and pH titration at 298.15 K and the ionic strength I = 0.5 (NaClO₄, KNO₃). The heats of the formation of the dipyridine and phenanthroline complexes of mercury(II) determined at 298.15 K and the ionic strength I = 0.1 (NaNO₃, KNO₃). A probable coordination mode of the ligands in a mixed complex was discussed.     

Die Bildungsenthalpie von Zinndijodid,SnJ2 (c)

The heat of reaction for SnJ₂ (c)+J₂ (c)+4045 CS₂ (l)=[SnJ₄; 4045 CS₂] (sol) has been determined to be (?41.12±0.55) kJ mol^?1, [(?9.83±0.13) kcal mol^?1] by isoperibol solution calorimetry. Combining this result with the heat of formation of SnJ₄ in CS₂ determined in a previous investigation¹¹ the value (?153.9±1.40) kJ mol^?1, [(?36.9±0.33) kcal mol^?1] has been derived for the heat of formation, ΔH _f ^ι (SnJ₂;c; 298.15 K), of tin diiodide.     

Determination calorimetrique de l'enthalpie de formation des alliages (Al,Ba) riches en aluminum

The heats of formation of some aluminium-barium alloys have been determined by drop calorimetry at high temperature. The heats of mixing of pure liquid Al and Ba to give the liquid alloy are Δ_mH(x_Ba=O.056, 1215 K)=?6.6 kJ mole^?1 and Δ_mH(x_Ba=O.333, 1215 K)=?31.0 kJ mole^-1. To measure its heat of formation, the solid compound Al₄Ba was precipitated by addition of pure barium from a liquid (Al, Ba) bath. It was found that Δ_fH(Al_0.8Ba_O.2, solid, 1215 K)=-(37.1 ? 1.5) kJ mole^?1 with reference to the pure metals in the solid state.     

Zur Thermochemie der Zinnhalogenide

The enthalpy change of the reaction at 298 K between Br₂ (l) and Sn(c) in CS₂ as solvent giving SnBr₄ (s) has been determined by calorimetry to be (?374, 2±1.4) kJ·mol^?1, [(?89.45±0.33) kcal·mol^?1]. By the same method the heat of solution of SnBr₄ (c) in CS₂ has been found to be (11.9±0.3) kJ·mol^?1, [(2.84±0.08) kcal·mol^?1]. Combining these results, a value of (?386.1±1.5) kJ·mol^?1, [(?92.3±0.4) kcal·mol^?1] is derived for the standard heat of formation of SnBr₄ (c). Substituting this figure in the thermochemical cycle hitherto used for calculating the heat of formation of SnBr₄ (c) gives ?124.3 kcal·mol^?1 for the standard heat of formation of SnCl₄ (l), which is in reasonable agreement with a recent determination of this quantity⁸.     

Bildungsenthalpien ternärer Lavesphasen vom MgCu2-Typ im System MgCu2MgZn2

The heats of formation of the ternary cubic Laves phases of the pseudobinary system MgCu₂MgZn₂ were determined by solution calorimetry methods. Replacing copper atoms with zinc atoms increases the negative heat of formation. This change is mainly due to the change of interatomic interactions within the copper sublattice. Relative minima appearing in the ΔH^B vs composition-curve are interpreted in terms of ordering of copper and zinc atoms on the copper sublattice.     

Novel α-spirocyclic (alkyl)(amino)carbenes at the theoretical crossroad of flexibility and rigidity

Spirocyclic (alkyl)(amino)carbenes (CAACs) with reasonable conformations of cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl substituents in the position α to the carbenic center are investigated at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G*. The singlet–triplet energy separations (?E _s?t), HOMO–LUMO energy gaps (?E _HOMO?LUMO), hydrogenation energies (?E _H), heats of methylene formation (?E) as well as philicity indices (N and ω) of these carbenes are compared and contrasted. The highest ?E _s?t is encountered for the cyclopropyl substituted CAAC (54.2 kcal/mol), while the other ones lay in a narrow range of 48.2–51.8 kcal/mol. Assignment of the barriers for ring inversions is carried out in order to probe the “flexible steric bulk” of cyclic substituents, showing negligible differences with those of the unsubstituted rings. The calculated N and ω indices indicate that in contrast to the popular belief, CAACs appear less electrophilic than N-heteorcyclic carbenes (NHCs).     

The thermorchemistry of the di-η5-cyclopentadienyl derivatives of the first transition series and their unipositive ions

The heats of formation [△H⁰f(MCp₂, c, 298)] have been determined for the di-η⁵-cyclopentadienyl derivatives of magnesium, vanadium, chromium, manganese, iron, cobalt and nickel, by static-bomb calorimetry. They are (in kJ mol^-1) (M =) Mg, 77.0 ± 3; V, 123 ± 4; Cr, 186 ± 3; Mn, 198 ± 2; Fe, 158 ± 4; Co, 205 ± 4; and Ni, 262 ± 3.the heats of formation [△H⁰_f(M(CO)_xCp, c, 298)] of tricarbonylcyclopentadienylmanganese and dicarbonylcyclopentadienylcobalt have also been determined as —478 ± 1 and —169 ± 10 kJ mol^?1, respectively.By using the measured heats of formation of the metallocenes of the first transition series and other enthalpy values from the literature in Hess's law cycles, the feasibility of the process MCp₂ → MCp⁺₂ + e (obtained from the photoelectron ionisation energies) has been analysed and shown to be the result of the interplay of exchange energy and ligand-field stabilisation energy terms in these low-spin complexes. The feasibility order, V < Cr > Mn > Fe < Co > Ni is associated with the special stability associated with half-filled and filled shelss, which, because of the large ligand-field splitting, occur at d³, d⁶, d⁸ and d¹⁰.It is shown that bond energy additivity does not occur for the above cyclopentadienylmetal carbonyls.     

Heat of adsorption of carbon dioxyde and ethene on zeolites a exchanged with Li+, Ni2+ and Cu2+

Various contents of Li⁺, Ni²⁺ or Cu²⁺ were introduced in zeolite NaA by conventional cation exchange. Crystal damages are observed on samples having suffered the lowerpH. The heat of adsorption of CO₂ and C₂H₄ was determined by isothermal calorimetry. Very high initial heats (100–120 kJ mol^?1) are found in NaA as well as in Li⁺ exchanged samples, perhaps due to chemisorption on alkaline cations; they vanish when Ni²⁺ or Cu²⁺ replaces more than 20% of Na⁺, in like manner with Co²⁺ or ZnI²⁺. For the adsorption of C₂H₄, high initial heats are absent in the case of NaA, but gradually appear when divalent cations are introduced. Apart from these strong initial values, the heats of adsorption present a plateauvs. the adsorbed amount. Abnormal low values at the plateau are indicative of crystal damages.     

Thermochemical study of coordination equilibria in the zinc(II)-β-alanine-water system in aqueous solution

The heats of formation of β-alanine (HAla) complexes with Zn²⁺ ion at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 mol/l (KNO₃) were determined by calorimetry; the heats of dilution of a zinc nitrate solution in supporting electrolyte solutions were found for introduction of appropriate corrections. The standard heats of complexation in the zinc(II)-β-alanine-water system were determined. The standard thermodynamic characteristics of zinc(II) complexation with β-alanine and standard enthalpies of formation of ZnAla⁺ and ZnAla₂ complex species were calculated.     

Photoacoustic determination of heats of formation and reaction of 5-chloro-1,2-didehydro-1H-azepine,a seven-membered cyclic ketenimine

The heats of formation and trapping by diethylamine of 5-chloro-1,2-didehydro-1H-azepine have been determined by time-resolved photoacoustic calorimetry (PAC). The results are compared with predictions from semiempirical calculations.     

Thermodynamic characteristics of formation reactions of the vanadium(V) malonate complex

The coordination equilibria in the vanadium(V)-malonic acid system were studied by calorimetry. The heats of formation reactions of the complex VO₂CH₂(COO) ₂ ^? at 298.15 K and I = 0.50, 0.75, and 1.00 (NaC1O₄) were determined. The standard thermodynamic characteristics of the studied equilibria were calculated.     

Enthalpy of solution of tigogenin saponin in dioxane and the temperature dependence of its heat capacity

The heats of solution of tigogenin C₂₇H₄₄O₃ in dioxane at dilutions equal to 1: 9000, 1: 18 000, and 1: 36 000 (mol solute/mol solvent) have been studied by isothermal calorimetry. The standard enthalpy of C₂₇H₄₄O₃ solution in dioxane at infinite dilution was derived by the mathematical processing of the calorimetric data. Dynamic calorimetry over the range 173–423 K has been used to study the heat capacity of tigogenin. The C _p ^o ～ f(T) plot has a jump at 298.15. K. The standard enthalpies of formation and combustion and the heat of melting of tigogenin have been indirectly calculated.     

Dibenzofuran and methyldibenzofuran derivatives: assessment of thermochemical data

Thermochemical data of dibenzofuran, a compound of considerable industrial and environmental significance, obtained from experimental calorimetric and computational techniques are reported in this work. The enthalpy of fusion, (19.4 ± 1.0) kJ mol^?1, at the temperature of fusion, (355.52 ± 0.02) K, was determined by differential scanning calorimetry measurements of dibenzofuran. From the standard (p° = 0.1 MPa) molar enthalpies of formation of crystalline dibenzofuran, (?29.2 ± 3.8) kJ mol^?1, and of sublimation, (84.5 ± 1.0) kJ mol^?1, determined at T = 298.15 K by static bomb combustion calorimetry and by vacuum drop microcalorimetry, respectively, it was possible to calculate the enthalpy of formation of the gaseous compound, (55.0 ± 3.9) kJ mol^?1, at the same temperature. The enthalpy of formation in the gaseous phase was also determined from G3(MP2)//B3LYP calculations. The same computational strategy was employed in the calculation of the standard molar enthalpies of formation, at T = 298.15 K, in the gas-phase, of single methylated derivatives of benzofuran and dibenzofuran.     

Thermochemical study of equilibria in the Cu<Superscript>2+</Superscript>-D,L-threonine system in an aqueous solution

The heats of interaction of Cu²⁺ ions with D,L-threonine in an aqueous solution were determined by direct calorimetry at ionic strengths of 0.50, 0.75, 1.00 (KNO₃) and temperatures of 288.15, 298.15, and 308.15 K and the corresponding heats of dilution were found. In calculation of the equilibrium composition of the system, side protolytic processes were taken into account along with the complexation reactions. The standard heats of formation of the CuThr⁺ and CuThr₂ species were found. The results were analyzed on the basis of Gurney views. The standard enthalpies of formation of complex species in the hypothetical undissociated state in an aqueous solution were calculated.     

Thermodynamic properties of biologically active substances: 3-acetyl-9-methoxy-2-phenyl-11H-indolizino[8,7-b]indole and 8-acetylharmine

The enthalpies of solution of 3-acetyl-9-methoxy-2-phenyl-11H-indolizino[8,7-b]indole and 8-acetylharmine in dimethyl sulfoxide were measured by isothermal calorimetry at solute: solvent molar ratios of 1: 9000, 1: 18000, and 1: 36000. From the data obtained, the standard enthalpies of solution of the compounds in dimethyl sulfoxide at infinite dilution were calculated. The heat capacities of 8-acetylharmine were determined by dynamic calorimetry in the interval 298.15–673 K, and the C _p ^o = f(T) equations were obtained. The standard enthalpies of combustion of the compounds were estimated by approximate methods, and their heats of melting were calculated. From the data obtained, using Hess cycle, the standard enthalpies of formation of the compounds were calculated.     

Dynamic differential calorimetry of intermetallic compounds: III. Heats of formation,heats and entropies of fusion of REIn3 and RETl3 compounds

Dynamic differential calorimetry has been employed to evaluate the heats of formation, heats and entropies of fusion of REIn₃ and RETl₃ compounds. The results obtained have been estimated to be corrected to within ±5–6%. The general trend, for both these series, is a decrease in the heat of formation from La to Lu which is correlated with the magnitude of the lanthanide contraction in these compounds. A simple correlation has been found between the heats of formation of REX₃ compounds and the ionic radii of the elements involved.     

Heat of hydration as a method for determining the composition of calcined gypsum

The heat of hydration of a fresh, locally produced sample of some industrial gypsum (plaster of Paris, CaSO₄ · 0.5 H₂O) was determined. An adiabatic calorimeter was used for this purpose. The obtained heat of hydration was ?9 cal g^?1, which is higher than that for the hemihydrate (?5 cal g^?1). The calculated heat of hydration for calcium sulphate hemihydrate from the known heats of formation, and using ordinary thermochemical equations, is ?5 cal g^?1. In the same manner, however, the calculated heat of hydration for the anhydrite (CaSO₄) is ?29 cal g^?1. The higher heat of hydration (?9 cal g^?1) for the tested sample than that for the ordinary hemihydrate (?5 cal g^?1) was attributed to the presence of a certain percent of anhydrite. The composition of the tested sample was proposed by applying conventional chemical and rational analyses. The present work suggests the use of the heat of hydration as a tool for determining the composition of calcined gypsum.     

Thermodynamic characteristics of Cu<Superscript>2+</Superscript> complexation processes with L-phenylalanine in an aqueous solution

The heats of interaction of Cu²⁺ ions with L-phenylalanine in aqueous solution were determined by calorimetry at ionic strengths of 0.50, 0.75, 1.00 (KNO₃) and a temperature of 298.15 K. The results of thermochemical study were interpreted taken into account complexation reactions, protolytic processes, and complexation with the competing ligand (OH^?) taking place in parallel. The effect of supporting electrolyte concentration on the heats of Cu²⁺ complexation with the amino acid was considered. The standard enthalpies of complexation were found by extrapolation to zero ionic strength. The standard enthalpies of formation of complex species in an aqueous solution were calculated.     

Thermodynamic characteristics of protolytic equilibria of L-serine in aqueous solutions

The heat effects of the reaction of aqueous solution of L-serine with aqueous solutions of HNO₃ and KOH were determined by calorimetry at temperatures of 288.15, 298.15, and 308.15 K, and ionic strength values of 0.2, 0.5, and 1.0 (background electrolyte, KNO₃). Standard thermodynamic characteristics (Δ_r H ^o, Δ_r G ^o, Δ_r S ^o, ΔC _p ^o) of the acid-base reactions in aqueous solutions of L-serine were calculated. The effect of the concentration of background electrolyte and temperature on the heats of dissociation of amino acid was considered. The combustion energy of L-serine by bomb calorimetry in the medium of oxygen was determined. The standard combustion and formation enthalpies of crystalline L-serine were calculated. The heats of dissolution of crystalline L-serine in water and solutions of potassium hydroxide at 298.15 K were measured by direct calorimetry. The standard enthalpies of formation of L-serine and products of its dissociation in aqueous solution were calculated.     

Synthesis and Promising Properties of a New Family of High‐Nitrogen Compounds: Polyazido‐ and Polyamino‐Substituted N,N′‐Azo‐1,2,4‐triazoles

A new family of high‐nitrogen compounds, that is, polyazido‐ and polyamino‐substituted N,N′‐azo‐1,2,4‐triazoles, were synthesized in a safe and convenient manner and fully characterized. The structures of 3,3′,5,5′‐tetra(azido)‐4,4′‐azo‐1,2,4‐triazole ( 15 ) and 3,3′,5,5′‐tetra(amino)‐4,4′‐azo‐1,2,4‐triazole ( 23 ) were also confirmed by X‐ray diffraction. Differential scanning calorimetry (DSC) was performed to determine their thermal stability. Their heats of formation and density, which were calculated by using Gaussian 03, were used to determine the detonation performances of the related compounds (EXPLO 5.05). The heats of formation of the polyazido compounds were also derived by using an additive method. Compound 15 has the highest heat of formation (6933 kJ kg^?1) reported so far for energetic compounds and a detonation performance that is comparable to that of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX), while compound 23 has a decomposition temperature of up to 290 °C.