In situ thermo-TOF-SIMS study of thermal decomposition of zinc acetate dihydrate

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used for an in situ thermal decomposition study of Zn(CH₃COO)₂·2H₂O forming ZnO nanoparticles. TOF-SIMS spectra were recorded at regular temperature intervals of 25 °C in positive and negative detection modes in a dynamic thermal process. Controlled heating (5 °C min⁻¹) of Zn(CH₃COO)₂·2H₂O was also carried out using thermogravimetric analysis (TGA) in an oxygen atmosphere (20 ml min⁻¹). Nearly spherical ZnO nanoparticles with no agglomeration and a narrow size distribution (diameter ∼50 nm) were observed, which were characterized using scanning electron microscopy, transmission electron microscopy and x-ray diffraction. In situ thermo-TOF-SIMS was used to monitor the ⁶⁴Zn⁺ and ⁶⁶Zn⁺ ion abundances as a function of temperature, which showed a similar profile to that observed for weight loss in TGA during decomposition. Based on the experimental results, a possible decomposition mechanism for the formation of ZnO is proposed. Copyright © 2004 John Wiley & Sons, Ltd.     

Enthalpy changes in formation reactions of zinc and cadmium trimethylenediaminetetraacetates

Calorimetric enthalpy changes in reactions have been measured for the formation of zinc and cadmium trimethylenediaminetetraacetates at 298.15 K and ionic strengths of 0.1. 0.5, 1.0 mol L⁻¹ (KNO₃). The standard thermodynamic parameters of the reactions studied were evaluated from calorimetric and potentiometric measurements under the same conditions. The results obtained were compared with the corresponding data on related compounds.     

The study of thermal decomposition kinetics of zinc oxide formation from zinc oxalate dihydrate

This study is devoted to the thermal decomposition of ZnC₂O₄·2H₂O, which was synthesized by solid-state reaction using C₂H₂O₄·2H₂O and Zn(CH₃COO)₂·2H₂O as raw materials. The initial samples and the final solid thermal decomposition products were characterized by Fourier transform infrared and X-ray diffraction. The particle size of the products was observed by transmission electron microscopy. The thermal decomposition behavior was investigated by thermogravimetry, derivative thermogravimetric and differential thermal analysis. Experimental results show that the thermal decomposition reaction includes two stages: dehydration and decomposition, with nanostructured ZnO as the final solid product. The Ozawa integral method along with Coats–Redfern integral method was used to determine the kinetic model and kinetic parameters of the second thermal decomposition stage of ZnC₂O₄·2H₂O. After calculation and comparison, the decomposition conforms to the nucleation and growth model and the physical interpretation is summarized. The activation energy and the kinetic mechanism function are determined to be 119.7 kJ mol^?1 and G(α) = ?ln(1 – α)^1/2, respectively.     

Hindered rotation of methylene groups in irradiated zinc acetate dihydrate: a double modulation ESR study

Hindered rotational motion of methylene groups in irradiated zinc acetate has been studied by the double modulation ESR technique. Two excited levels, at E₀ = 6.7 ± 0.6 kJ mol⁻¹ and E_j = 18.4 ± 1.0 kJ mol⁻¹, corresponding respectively to the torsional oscillation and full Jump rotation of the methylene group, were determined.     

Enthalpy of formation of triphenylphosphine sulfide

The first measurements of the enthalpies of combustion, sublimation, and fusion of an organo-phosphorus sulfide, triphenylphosphine sulfide, are reported: _c H _m ^o (C₁₈H₁₅PS, cr)=–(10752.58 ±2.90), _sub H _m ^o (C₁₈H₁₅PS, 403 K)=(136.80±6.09), and _fus H _m ^o (C₁₈H₁₅PS, T_m=435.92 K) =(30.53±0.21) kJ·mol^–1. Correction of the phase change enthalpies toT=298.15K and p^o =0.1 MPa results in the standard phase change enthalpy values of _sub H _m ^o (298.15 K)=(142.8 ±6.8) and _fus H _m ^o (298.15 K)=(19.28±0.21) kj·mol^–1. Accordingly, the enthalpies of formation of solid, liquid, and gaseous triphenylphosphine sulfide are derived: _f H _m ^o (C₁₈H₁₅PS, cr) =(63.20±2.56), _fH _m ^o (C₁₈H₁₅PS, l)=(82.48±2.57), and _fH _m ^o (C₁₈H₁₅PS, g)=(206.0±7.3) kJ·mol^–1. From these ancillary data, the P=S double-bond enthalpy is 394 kJ-mol^–1 and in good agreement with earlier reaction calorimetry results. These phosphorus sulfide values are compared with those for the arsenic sulfides. Plausibility arguments are given for our results.     

Enthalpy of formation of thiophene derivatives

The enthalpy of formation in the gas phase has been calculated for 21 carbonyl compounds of the thiophene series with the aid of the PM3, MINDO, AM1, and MNDO semiempirical quantum-chemical methods. Comparison of them with experimental data showed that the best linear correlation was achieved with the PM3 method. The latter in conjunction with a developed linear regression equation has been used to predict the enthalpy of formation of 22 carboxylic acids and ketones of the thiophene series.     

Enthalpy of formation of dimethyltriazanium chloride

Conclusions We determined the enthalpies of solution (5.53 ± 0.03 kcal/mole) and formation (21.7 ± 0.28 kcal/mole) of dimethyltriazanium chloride.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2392–2394, October, 1981.     

Novel dihydrate formation in p-nitrophenylglyoxal

It is novel that the reaction of p-nitrophenyl-glyoxal with biochemically relevant compounds has a long lag time before the reaction commences. While utilizing NMR spectroscopy to investigate factors that may affect the lag, it has been discovered that a dihydrate form of pNPG is in equilibrium with a monohydrate while in the presence of water. This behavior is not present in the related phenylglyoxal molecule. Quantum chemical computations on the nonhydrated, hydrate, and dihydrate forms of pNPG, as well as phenylglyoxal and its hydrated forms, using both the B3LYP and MP2 levels of theory indicate that nitro group creates the necessary environment for hydration of pNPG whereas this is not present in standard phenylglyoxal. The equilibrium constants and their relationship with temperature as well as the heat of reaction and change in entropy have been determined experimentally. This data should provide new insights into the behavior of this and related systems in biochemical processes.     

Sodium hydrogen nitrilo­tri­acetate dihydrate

In the title compound, Na⁺·C₆H₈NO₆^?·2H₂O, the sodium ion is coordinated in a distorted octahedral manner by two carboxyl­ate O atoms and two water O atoms. Each of these water mol­ecules bridges two adjacent Na ions, resulting in two four‐membered rings of the type Na–O–Na–O.     

Infrared spectra of protiated and deuterated cobalt acetate dihydrate

The infrared spectra of cobalt acetate dihydrate provide a direct evidence for the existence of quite strong hydrogen bonds formed by the water protons. An intense band is, namely, found around 2750 cm^?1, several additional bands are present at lower frequencies and bands originating from water librations appear above 1000 cm^?1. The existence of a band around 3310 cm^?1 on the other hand, indicates that much weaker hydrogen bonds are also present. On deuteration the protons involved in stronger hydrogen bonds are apparently replaced by deuterons to a higher degree than those forming weaker H-bonds.     

Enthalpy of formation of adamantane alkyl derivatives

The enthalpies of formation of adamantane alkyl derivatives were calculated by the semiempirical quantum chemical methods PM3, MINDO, AM1 and MNDO of the MOPAC software package. Comparison of the calculated values with the experimental data showed that the best correlation gave the PM3 method. Using this method and linear regression equation derived by us we calculated enthalpies of formation of twenty-two alkyl derivatives of adamantane.     

Enthalpy of formation for natural paulingite zeolite

Natural paulingite zeolite of the composition (K_4.48Na_0.56Ca_2.95Ba_0.87Mg_0.06)[Al_11.04Fe _0.04 ³⁺ Si_30.49O₈₄] · 35.25H₂O (Vinariská Hora, Czechia) was studied calorimetrically on a high-temperature Tian-Calvet microcalorimeter. Enthalpies of formation from oxides (?1969 ± 128 kJ/mol) and elements (?52393 ± 132 kJ/mol) were determined for this mineral by melt dissolution calorimetry. The obtained experimental results and the literature data were used to calculate the Gibbs free energy of formation from elements.     

Enthalpy of formation of acyclic saturated ketones

The dependences of Δ_f H on the size of molecule, position of carbonyl group, and branching of molecule are investigated at the PM5 level of theory. The major part of Δ_f H is determined with the size of molecule, whereas fine structure of Δ_f H is determined with the branching of molecule and position of carbonyl group. The article is published in the original.