Thermal behaviour of malonic acid,sodium malonate and its compounds with some bivalent transition metal ions

Characterization, thermal stability and thermal decomposition of transition metal malonates, MCH₂C₂O₄·nH₂O (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)), as well as, the thermal behaviour of malonic acid (C₃H₄O₄) and its sodium salt (Na₂CH₂C₂O₄·H₂O) were investigated employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), infrared spectroscopy, TG-FTIR system, elemental analysis and complexometry. The dehydration, as well as, the thermal decomposition of the anhydrous compounds occurs in a single step. For the sodium malonate the final residue up to 700 °C is sodium carbonate, while the transition metal malonates the final residue up to 335 °C (Mn), 400 °C (Fe), 340 °C (Co), 350 °C (Ni), 520 °C (Cu) and 450 °C (Zn) is Mn₃O₄, Fe₂O₃, Co₃O₄, NiO, CuO and ZnO, respectively. The results also provided information concerning the ligand's denticity, thermal behaviour and identification of some gaseous products evolved during the thermal decomposition of these compounds.     

Synthesis of nanosized rubidium ferrite by thermolysis of ferricarboxylate precursors and combustion method

Nanosized pure rubidium ferrites have been successfully prepared by thermal decomposition of rubidium hexa(carboxylato)ferrate(III) precursors, Rb₃[Fe(L)₆]·xH₂O (L = formate, acetate, propionate, butyrate), in flowing air atmosphere from ambient temperature to 1000 °C. Various physico-chemical techniques i.e. simultaneous TG–DTG–DTA, XRD, Transmission Electron Microscope (TEM), IR and Mössbauer spectroscopy etc. have been employed to characterize the intermediates and end products. After dehydration, the anhydrous precursors undergo exothermic decomposition to yield various intermediates i.e. rubidium carbonate/acetate/propionate/butyrate and α-Fe₂O₃. A subsequent decomposition of these intermediates, followed by solid state reaction, lead to the formation of nanosized rubidium ferrite (RbFeO₂). The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature and in less time than that of the conventional ceramic method (>1200 °C).     

Ni–Al hydrotalcite-like material as the catalyst precursors for the dry reforming of methane at low temperature

Nickel–aluminium and magnesium–aluminium hydrotalcites were prepared by co-precipitation and subsequently submitted to calcination. The mixed oxides obtained from the thermal decomposition of the synthesized materials were characterized by XRD, H₂-TPR, N₂ sorption and elemental analysis and subsequently tested in the reaction of methane dry reforming (DRM) in the presence of excess of methane (CH₄/CO₂/Ar = 2/1/7). DMR in the presence of the nickel-containing hydrotalcite-derived material showed CH₄ and CO₂ conversions of ca. 50% at 550 °C. The high values of the H₂/CO molar ratio indicate that at 550 °C methane decomposition was strongly influencing the DRM process. The sample reduced at 900 °C showed better catalytic performance than the sample activated at 550 °C. The catalytic performance in isothermal conditions from 550 °C to 750 °C was also determined.     

Synthesis,crystal structure modeling and thermal decomposition of yttrium propionate [Y2(CH3CH2COO)6·H2O]·3.5H2O

An yttrium propionate complex was synthesized and characterized for its application as precursor for Y₂O₃ based oxide thin films deposition and YBa₂Cu₃O_7 − x superconducting thin films. The TG–DTA and FT-IR analyses have revealed the formation of an yttrium propionate complex with the formula [Y₂(CH₃CH₂COO)₆·H₂O]·3.5H₂O. The molecular structure of the yttrium propionate complex was determined by modeling the FT-IR spectra. The coordination numbers for the yttrium ions are eight and nine, respectively being coordinated by bridging bimetallic triconnective and chelating bidentate propionate groups.The thermal decomposition of yttrium propionate has been investigated by thermogravimetric (TG) and differential thermal analysis (DTA) coupled with quadrupole mass spectrometry (QMS), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR) techniques.     

(Liquid + solid) metastable equilibria in quinary system Li2CO3 + Na2CO3 + K2CO3 + Li2B4O7 + Na2B4O7 + K2B4O7 + H2O at T=288 K for Zhabuye salt lake

An experimental study on metastable equilibria at T=288 K in the quinary system Li₂CO₃ + Na₂CO₃ + K₂CO₃ + Li₂B₄O₇ + Na₂B₄O₇ + K₂B₄O₇ + H₂O was done by isothermal evaporation method. Metastable equilibrium solubilities and densities of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagram under the condition saturated with Li₂CO₃ was plotted, in which there are four invariant points; nine univariant curves; six fields of crystallization: K₂CO₃ · 3/2H₂O, K₂B₄O₇ · 5H₂O, Li₂B₂O₄ · 16H₂O, Na₂B₂O₄ · 8H₂O, Na₂CO₃ · 10H₂O, NaKCO₃ · 6H₂O. Some differences were found between the stable phase diagram at T=298 K and the metastable one at T=288 K.     

Natural gas permeation in polyimide membranes

Polyimide membranes derived from 6FDA-DAM:DABA and 6FDA-6FpDA:DABA copolymers have been used to separate 50/50 CO₂/CH₄ mixtures and multicomponent synthetic natural gas mixtures at 35 °C and feed pressures up to 55 atm. For 6FDA-DAM:DABA 2:1 membranes the effects of thermal annealing and covalent crosslinking are decoupled with respect to effects on permeabilities and selectivity. Crosslinking at 295 °C with 1,4-butylene glycol and 1,4-cyclohexanedimethanol increases CO₂ permeabilities by factors of 4.1 and 2.4, respectively, at 20 atm feed pressure, without a loss in selectivity, relative to crosslinking at 220 °C. Thermal annealing and crosslinking also reduce CO₂ plasticization effects. Crosslinking of DABA-containing copolymers, therefore, can produce membranes with tunable transport properties that offer significantly higher performance with better plasticization-resistance than that reported in the literature for the commercial polymers Matrimid^® and cellulose acetate for CO₂ removal from natural gas mixtures. Separation of complex mixtures containing CO₂, CH₄, C₂H₆, C₃H₈, and C₄H₁₀ or toluene results in a significant decrease of the CO₂ permeability, but only a moderate decrease in the CO₂/CH₄ selectivity.     

A simple synthesis and room temperature magnetic properties of new binary Mn0.5Fe0.5(H2PO4)2·xH2O obtained from a rapid co-precipitation at ambient temperature

A new binary Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O powder was synthesized by simple and cost-effective method using phosphoric acid, manganese and iron metals as starting chemicals. The synthesized solid shows the complex thermal transformations and the final decomposition product is a new binary manganese iron cyclo-tetraphosphate, MnFeP₄O₁₂. The X-ray diffraction and FTIR results indicate that the synthesized new binary Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and the decomposition MnFeP₄O₁₂ powders are a pure monoclinic phase with space group P2₁/n (Z = 2) and C2/c (Z = 4), respectively. The particle morphologies of Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and MnFeP₄O₁₂ powders appear as the rod-like tetragonal shape and show a high agglomeration of small particles, which are similar to the case of Mn(H₂PO₄)₂·2H₂O and Fe₂P₄O₁₂, respectively. Room temperature magnetization results show a ferromagnetic behavior of the Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and MnFeP₄O₁₂ powders, having the hysteresis loops in the range of ?10,000 Oe < H < +10,000 Oe with the specific magnetization values of 25.63 and 13.14 emu/g at 10 kOe, respectively. The lower magnetizations of Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and MnFeP₄O₁₂ than those of Fe(H₂PO₄)₂·2H₂O and Fe₂P₄O₁₂ powders indicate the presence of Mn ions in substitution position of Fe ions.     

New α,ω-dicarboxylate coordination polymers with 4,4′-bipyridine: Cu(bpy)(C5H6O4), Zn(bpy)(C5H6O4), Zn(bpy)(C6H8O4) and Mn(bpy)(C8H12O4) · H2O

Four 4,4′-bipyridine α,ω-dicarboxylate coordination polymers Cu(bpy)(C₅H₆O₄) (1), Zn(bpy)(C₅H₆O₄) (2), Zn(bpy)(C₆H₈O₄) (3) and Mn(bpy)(C₈H₁₂O₄) · H₂O (4) have been synthesized and structurally characterized by single crystal X-ray diffraction methods (bpy = 4,4-bipyridine, (C₅H₆O₄)²⁻ = glutarate anion, (C₆H₈O₄)²⁻ = adipate anion, (C₈H₁₂O₄)²⁻ = suberate anion). Their crystal structures are featured by dimeric metal units, which are co-bridged by 4,4′-bipyridine ligands and dicarboxylate anions such as glutarate, adipate and suberate anions to generate 2D layers with a (4,4) topology in 1, 2 and 4 as well as to form 3D frameworks in 3. Two 3D frameworks in 3 interpenetrate with each other to form a topology identical to the well-known Nb₆F₁₅ cluster compound. Over 5–300 K, the paramagnetic behavior of 4 follows the Curie–Weiss law χ_m(T − Θ) = 4.265(5) cm³ mol⁻¹ with the Weiss constant Θ = −6.3(2) K. Furthermore, the thermal behavior of 3 and 4 is also discussed.     

Synthesis of new substituted benzaldazine derivatives,hydrogen bonding-induced supramolecular structures and luminescent properties

Syntheses of three benzaldazine compounds 1–3 with the general formula Ar₁(CH = N–N = HC)Ar₂ (Ar₁ = Ar₂ = 2-OH-3,5-^tBu₂C₆H₂ (1), Ar₁ = Ar₂ = 2-BrC₆H₄ (2), Ar₁ = ortho-C₆H₄(NHC₆H₃-Me₂-2,6), Ar₂ = C₆H₄F-2 (3)) are described. All compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, IR spectroscopy and single-crystal X-ray crystallography. The different supramolecular structures were obtained through different weak interactions (C ? H···O, O ? H···N and π···π interactions for 1; C ? H···Br and Br···Br interactions for 2; C ? H···F and C ? H···N interactions for 3). Compound 1 shows solvent-dependent fluorescent properties with blue to green emission on the increasing of the solvent polarity. Compounds 2, 3 show blue photoluminescence in different solvents.     

Synthesis,structure and thermochemical study of a cobalt energetic coordination compound incorporating 3,5-diamino-1,2,4-triazole and pyridine-2,6-dicarboxylic acid

An energetic coordination compound [Co₂(C₂H₅N₅)₂(C₇H₃NO₄)₂(H₂O)₂]·2H₂O (Hdatrz(C₂H₅N₅) = 3,5-diamino-1,2,4-triazole, H₂pda(C₇H₅NO₄) = pyridine-2,6-dicarboxylic acid) has been synthesized and characterized by elemental analysis, chemical analysis, IR spectroscopy, single-crystal X-ray diffraction and thermal analysis. X-ray diffraction analysis confirmed that the compound possessed a di-nuclear unit and featured a 3D super-molecular structure. Furthermore, a reasonable thermochemical cycle was designed based on the preparation reaction of the compound and the standard molar enthalpy of dissolution of reactants and products was measured by the RD496-2000 calorimeter. Finally, the standard molar enthalpy of formation of the compound was determined to be −(2475.0 ± 3.1) kJ · mol⁻¹ in accordance with Hess’s law. In addition, the specific heat capacity of the compound at T = 298.15 K was determined to be (1.13 ± 0.02) J · K⁻¹ · g⁻¹ by RD496-2000 calorimeter.     

Preparative resolution of (±)-trans-1,2-diaminocyclohexane by means of preferential crystallization of its citrate monohydrate

Even if (±)-trans-1,2-diaminocyclohexane crystallizes as a conglomerate, its low melting point (?10 °C) and its sensitivity to light, CO₂, O₂, and moisture make this molecule difficult to resolve. It has been shown that the citrate monohydrate of this compound crystallizes as a stable conglomerate with a high thermal stability (up to 163 °C) with no drawbacks as to those listed above for the pure diamine. The crystal structure of this salt, resolved by single crystal X-ray diffraction, reveals structural features consistent with the thermal stability of this phase. Several preferential crystallization attempts (AS3PC) have been performed at a 100 ml scale and at a one liter scale in water with and without additives. Finally a productivity of 40 g per batch per liter of solvent per hour was achieved with a crude enantiomeric purity better than 90%. A simple recrystallization of the crude crops gives quantitatively the crystalline compound with an ee >99% proving the absence of partial solid solution at room temperature.     

An investigation on the solid state pyrolytic decomposition of bimetallic oxalate precursors of Ca,Sr and Ba with cobalt: A mechanistic approach

The mixed metal oxalate precursors, calcium(II)bis(oxalato)cobaltate(II)hydrate (COC), strontium(II)bis(oxalato)cobaltate(II)pentahydrate (SOC) and barium(II)bis(oxalato)cobaltate(II)octahydrate (BOC) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR spectral and X-ray powder diffraction studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound COC decomposed mainly to CaC₂O₄ and Co₃O₄ at 340 °C, and a mixture of CaCO₃ and Co₃O₄ identified at 510 °C. A mixture of CaCO₃ and Ca₃Co₂O₆ along with the oxides and carbides of both the cobalt and calcium were attributed at 1000 °C as end products. DSC study in nitrogen ascertained the formation of a mixture of CaO and CoO along with a trace of carbon at 550 °C. The mixture species, SrC₂O₄, CoC₂O₄ and Co₃O₄ were generated at 255 °C in case of SOC in air, which ultimately changed to CoSrO₃, SrCO₃ and oxides of strontium and cobalt at 1000 °C. The several mixture species also generated as intermediate at 332 and 532 °C. The DSC study in nitrogen indicated the formation of CoSrO_x (0.5 < x < 1) as end product. In case of BOC in air, a mixture of BaCoO₂, BaO, CoO and carbides are identified as end product at 1000 °C through the generation of several intermediate species at 350 and 530 °C. A mixture of BaO and CoO is identified as end product in DSC study in nitrogen. The kinetic parameters have been evaluated for all the dehydration and decomposition steps of all the three compounds using four non-mechanistic equations. Using seven mechanistic equations, the kind of dominance of kinetic control mechanism of the dehydration and decomposition steps are also inferred. The kinetic parameters, ΔH and ΔS of all the steps are explored from the DSC studies. Some of the decomposition products are identified by IR and X-ray powder diffraction studies.     

Solvothermal synthesis and crystal structure of the Mo(VI)-bridged helical chain containing Mo2(V) dimers: (C4H12N2)2[(MoV2O4)(MoVIO4)(C2O4)2]·2H2O

A new molybdenum complex (C₄H₁₂N₂)₂[(Mo^V₂O₄)(Mo^VIO₄)(C₂O₄)₂]·2H₂O, was solvothermally synthesized and characterized by single-crystal X-ray diffraction. The structure of the compound consists of oxalate acid-coordinated mixed-valent [Mo^V₂O₄][Mo^VIO₄] helical chains and protonated piperazine cations. The helical chains are built up from the [Mo^V₂O₄] units and [Mo^VIO₄] tetrahedral. The central axis about helical chain is a 2-fold screw axis. The compound crystallizes in the space group P2₁/n of monoclinic system with a = 11.396(2) Å, b = 14.107(3) Å, c = 15.805(3) Å, β = 102.09(3)°, V = 2484.6(9) Å³, Z = 4. Other characterizations by elemental analysis, IR, and thermal analysis for this compound are also given.     

Thermodynamic properties of chloropinnoite

The molar enthalpies of solution of 2MgO · 2B₂O₃ · MgCl₂ · 14H₂O in approximately 1 mol · dm⁻³ aqueous hydrochloric acid (HCl) and of MgCl₂ · 6H₂O(s) in aqueous (approximately 1 mol · dm⁻³ HCl + MgCl₂ + H₃BO₃) at T=298.15 K were determined. From a combination of these results with measured enthalpies of solution of boric acid (H₃BO₃) in HCl(aq) and of magnesium oxide (MgO) in aqueous (HCl + H₃BO₃) solution, together with the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), MgCl₂ · 6H₂O(s) and H₂O(l), the standard molar enthalpy of formation of −(8812 ± 3) kJ · mol⁻¹ of 2MgO · 2B₂O₃ · MgCl₂ · 14H₂O was obtained. Thermodynamic properties of this compound were also calculated by group contribution method.     

A calorimetric and thermodynamic investigation of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb and calculated phase relations in the system (K2MoO4 + UO3 + H2O)

A calorimetric and thermodynamic investigation of two alkali-metal uranyl molybdates with general composition A₂[(UO₂)₂(MoO₄)O₂], where A = K and Rb, was performed. Both phases were synthesized by solid-state sintering of a mixture of potassium or rubidium nitrate, molybdenum (VI) oxide and gamma-uranium (VI) oxide at high temperatures. The synthetic products were characterised by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of K₂[(UO₂)₂(MoO₄)O₂] was determined using HF-solution calorimetry giving Δ_fH° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = −(4018 ± 8) kJ · mol⁻¹. The low-temperature heat capacity, С_р°, was measured using adiabatic calorimetry from T = (7 to 335) K for K₂[(UO₂)₂(MoO₄)O₂] and from T = (7 to 326) K for Rb₂[(UO₂)₂(MoO₄)O₂]. Using these С_р° values, the third law entropy at T = 298.15 K, S°, is calculated as (374 ± 1) J · K⁻¹ · mol⁻¹ for K₂[(UO₂)₂(MoO₄)O₂] and (390 ± 1) J · K⁻¹ · mol⁻¹ for Rb₂[(UO₂)₂(MoO₄)O₂]. These new experimental results, together with literature data, are used to calculate the Gibbs energy of formation, Δ_fG°, for both phases giving: Δ_fG° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = (−3747 ± 8) kJ · mol⁻¹ and Δ_fG° (T = 298 K, Rb₂[(UO₂)₂(MoO₄)], cr) = −3736 ± 5 kJ · mol⁻¹. Smoothed С_р°(Т) values between 0 K and 320 K are presented, along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)], for both phases. The stability behaviour of various solid phases and solution complexes in the (K₂MoO₄ + UO₃ + H₂O) system with and without CO₂ at T = 298 K was investigated by thermodynamic model calculations using the Gibbs energy minimisation approach.     

Thermal degradation and evolved gas analysis: A polymeric blend of urea formaldehyde (UF) and epoxy (DGEBA) resin

A polymeric blend has been prepared using urea formaldehyde (UF) and epoxy (DGEBA) resin in 1:1 mass ratio. The thermal degradation of UF/epoxy resin blend (UFE) was investigated by using thermogravimetric analyses (TGA), coupled with FTIR and MS. The results of TGA revealed that the pyrolysis process can be divided into three stages: drying process, fast thermal decomposition and cracking of the sample. There were no solid products except ash content for UFE during combustion at high temperature. The total mass loss during pyrolysis at 775 °C is found to be 97.32%, while 54.14% of the original mass was lost in the second stage between 225 °C and 400 °C. It is observed that the activation energy of the second stage degradation during combustion (6.23 × 10⁻⁴ J mol⁻¹) is more than that of pyrolysis (5.89 × 10⁻⁴ J mol⁻¹). The emissions of CO₂, CO, H₂O, HCN, HNCO, and NH₃ are identified during thermal degradation of UFE.     

Preparation and characterization of NiO(core)/Fe2O3(shell) composite particles

A novel hydrothermal coating process has been developed to deposit amorphous Ni(OH)₂·H₂O over octahedral α-Fe₂O₃ particles by treating aqueous dispersion of the preformed cores in Ni(NO₃)₂/CH₃COONa solution. NiO_(core)/Fe₂O_3(shell) composite particles were prepared by air sintering of the Ni(OH)₂·H₂O_(shell)/Fe₂O_3(core) particles at 200–500°C for 1–6 h. The changes of morphology, structure and weight of the hydrothermal and sintering products were studied by means of TEM, XRD, XPS, TG and IR analyzers. The nucleation and growth model was suggested for the non-isothermal decomposition of Ni(OH)₂·H₂O coatings and the kinetic equation was derived from the non-linear regression of the TG data. The activation in the thermal-decomposition process is 73.8 kJ mol⁻¹ and the pre-exponential factor is 1.95×10⁴ s⁻¹.     

Thermal decomposition of Ln(C2H5CO2)3·H2O (Ln?=?Ho, Er, Tm and Yb)

The thermal decomposition of Ho(III), Er(III), Tm(III) and Yb(III) propionate monohydrates in argon was studied by means of thermogravimetry (TG), differential thermal analysis (DTA), IR-spectroscopy and X-ray diffraction (XRD). Dehydration takes place around 90?°C. It is followed by the decomposition of the anhydrous propionates to Ln₂O₂CO₃ (Ln?=?Ho, Er, Tm or Yb) with the evolution of CO₂ and 3-pentanone (C₂H₅COC₂H₅) between 300 and 400?°C. The further decomposition of Ln₂O₂CO₃ to the respective sesquioxides Ln₂O₃ is characterized by an intermediate plateau extending from approximately 500?C700?°C in the TG traces. This stage corresponds to an overall composition of Ln₂O_2.5(CO₃)_0.5 but is more probably a mixture of Ln₂O₂CO₃ and Ln₂O₃. The stability of this intermediate state decreases for the lighter rare-earth (RE) compounds studied. Full conversion to Ln₂O₃ is achieved at about 1,100?°C. The overall thermal decomposition behaviour of the title compounds is similar to that previously reported for Lu(C₂H₅CO₂)₃·H₂O.     

Quantum-dots containing Fe/SBA-15 silica as “green” catalysts for the selective photocatalytic oxidation of alcohol (methanol,under visible light)

Fe/SBA-15 catalysts containing iron oxide nanoparticles confined inside silica pores (replicated, internal, poorly crystalline) and grown outside silica grains (external, mainly crystalline hematite) in different proportions are prepared using a single silica support. Fe-species are deposited by the two-solvent technique with two iron salts precursors (Fe(NO₃)₃·9H₂O, FeCl₃·6H₂O) and two solvents (cyclohexane, hexane) for 11 wt% of iron. Calcination is performed in reproducible conditions (700 °C, 2 °C/min, thin bed, in air). SAXS measurements are used to show that the 2D hexagonal structure of the used silica is maintained after Fe-loading and calcination. Ar sorption measurements show that the pores are partially plugged. The oxidation of pure methanol is used as a test reaction to compare photocatalytic properties. H₂O₂ and visible light both activate the reaction. More active catalysts are formed with hexane associated with FeCl₃·6H₂O than with Fe(NO₃)₃·9H₂O. A reversed situation is observed with cyclohexane. Iron leaching (after 1 h 30 of test, up to 3 mg of Fe by mL) is important. These results are expected to be of interest in the exploration of size and shape “nanocatalysis” and to provide a further understanding for the reactions that take place when porous silicas are used as supports.     

Hydrothermal synthesis and thermodynamic properties of 2ZnO · 3B2O3 · 3H2O

The important zinc borate of 2ZnO · 3B₂O₃ · 3H₂O has been synthesized and characterized by means of chemical analysis, XRD, FT-IR, and DTA–TG techniques. The molar enthalpies of solution of H₃BO₃(s) in HCl · 54.561H₂O, of ZnO(s) in the mixture of HCl · 54.561H₂O and calculated amount of H₃BO₃, and of 2ZnO · 3B₂O₃ · 3H₂O(s) in HCl · 54.604H₂O were measured, respectively. With the use of the standard molar enthalpies of formation for ZnO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of ?(5561.7 ± 4.9) kJ · mol^?1 for 2ZnO · 3B₂O₃ · 3H₂O(s) was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.