Thermodynamic properties and heat capacities of Co (BTC)1/3 (DMF) (HCOO)

A novel metal organic framework [Co (BTC)_1/3 (DMF) (HCOO)] _n (CoMOF, BTC = 1,3,5-benzene tricarboxylate, DMF = N,N-dimethylformamide) has been synthesized solvothermally and characterized by single crystal X-ray diffraction, X-ray powder diffraction, and FT-IR spectra. The molar heat capacity of the compound was measured by modulated differential scanning calorimetry (MDSC) over the temperature range from 198 to 418 K for the first time. The thermodynamic parameters such as entropy and enthalpy versus 298.15 K based on the above molar heat capacity were calculated. Moreover, a four-step sequential thermal decomposition mechanism for the CoMOF was investigated through the thermogravimetry and mass spectrometer analysis (TG-DTG-MS) from 300 to 800 K. The apparent activation energy of the first decomposition step of the compound was calculated by the Kissinger method using experimental data of TG analysis.     

Low-temperature heat capacity and standard thermodynamic functions of 1-butyl-3-methylimidazolium lactate

The heat capacities of 1-butyl-3-methylimidazolium lactate ionic liquids ([C₄mim][Lact]) were measured with a highly accurate automatic adiabatic calorimeter over the temperature range from 79 to 406 K. And the experimental values of molar heat capacities were fitted to a polynomial equation using least square method in the appropriate temperature ranges. The standard molar heat capacity was determined to be 1734.46?±?5.12 J K^?1 mol^?1 at 298.15 K. The molar enthalpy and molar entropy of the transition were determined to be 15.575?±?0.045 and 64.44?±?0.14 J K^?1 mol^?1. Other thermodynamic properties, such as (H_T???H_298.15) and (S_T???S_298.15), were also calculated. Furthermore, when the temperature reaches 241.87 K, the strongest peaks appeared by analysis of the heat capacity curve. This phenomenon could be explained from the interionic interaction, which is the hydrogen bond between the anions and cations.     

Heat capacities and thermodynamic properties of a 3D Cu(II) supramolecular complex

A 3D supramolecule (H₃O)₂[Cu(2,6-pdc)₂]·H₂O (pdc = pyridinedicarboxylate) has been solvothermally synthesized and characterized by X-ray powder diffraction and FT-IR spectrum. The thermal decomposition characteristics of the complex were investigated by thermogravimetric analysis, which revealed a three-step mass loss process. The low-temperature molar heat capacities of crystalline (H₃O)₂[Cu(2,6-pdc)₂]·H₂O were measured by temperature-modulated differential scanning calorimetry for the first time. A phenomenon of glass transition was observed. The thermodynamic parameters such as entropy and enthalpy relative to 298.15 K were calculated based on the above molar heat capacity data.     

Heat capacities and thermodynamic properties of one manganese-based MOFs

A metal-organic framework [Mn(4,4′-bipy)(1,3-BDC)] _n (MnMOF, 1,3-BDC = 1,3-benzene dicarboxylate, 4,4′-bipy = 4,4′-bipyridine) has been synthesized hydrothermally and characterized by single crystal XRD and FT-IR spectrum. The low-temperature molar heat capacities of MnMOF were measured by temperature-modulated differential scanning calorimetry for the first time. The thermodynamic parameters such as entropy and enthalpy relative to reference temperature 298.15 K were derived based on the above molar heat capacity data. Moreover, the thermal stability and the decomposition mechanism of MnMOF were investigated by thermogravimetry analysis-mass spectrometer. A two-stage mass loss was observed in air flow. MS curves indicated that the gas products of oxidative degradation were H₂O, CO₂, NO, and NO₂.     

Heat capacities and thermodynamic properties of Ni9(btz)12(DMA)6(NO3)6

The low-temperature molar heat capacity of crystalline Ni₉(btz)₁₂(DMA)₆(NO₃)₆ (1) (btz = benzotriazolate; DMA = N,N′-dimethylacetamide) was measured by temperature-modulated differential scanning calorimetry for the first time. The thermodynamic parameters such as entropy and enthalpy relative to reference temperature 298.15 K were obtained based on the above molar heat capacity data. The compound was synthesized by solvothermal method and characterized by powder X-ray diffraction and FT-IR spectra. Moreover, the thermal stability and the decomposition mechanism of Ni₉(btz)₁₂(DMA)₆(NO₃)₆ were investigated by thermogravimetry (TG) analysis under air atmosphere from 300 to 873 K. The experimental results through TG measurement demonstrate that the compound has a two-stage mass loss in air flow.     

Thermal behavior and thermodynamic properties of berberine hydrochloride

The low-temperature heat capacities of berberine hydrochloride were measured over the temperature range from 78 to 350 K by an adiabatic calorimeter. The thermodynamic functions H _T ? H _298.15 and S _T ? S _298.15 were derived from the heat capacity data. The results showed that the structure of berberine hydrochloride was stable over the temperature range from 78 to 350 K. The thermal stability of the compound was further tested by DSC and TG measurements. The results were in agreement with those obtained from adiabatic calorimetry experiment. The standard molar enthalpy of formation in the crystalline state of berberine hydrochloride was obtained from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by a rotating-bomb combustion calorimeter.     

Synthesis and mesomorphism behaviour of chalcones and pyrazoles type compounds as photo-luminescent materials

The following organic and organic–inorganic hybrid compounds were prepared as photo-luminescent materials following efficient and practical synthetic methods: 1,3-bis[4-(n-alkoxy)phenyl]-2-propen-1-one (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10); 3,5-bis[4-(n-alkoxy)phenyl]-1H-pyrazole (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10) (in case of n = 7, a mixture of 3,5-bis(4-heptyloxyphenyl)-1H-pyrazole and 3,5-bis(4-heptyloxyphenyl)-4H-pyrazole was detected) and bis(3,5-bis [4-(n-alkoxy) phenyl]-1H-pyrazole) silver(I) nitrate (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10). The prepared compounds have been characterised and their structures were elucidated depending upon (FTIR, UV-Vis, ¹HNMR, ¹³CNMR, 2D ¹H-¹H-COSY, 2D ¹H-¹³C-HSQC and mass spectra) in addition to molar conductivity measurements for silver(I) complexes. The mesomorphism behaviour of the prepared compounds was studied using polarised light optical microscopy and confirmed with differential scanning calorimetry and X-ray powder diffraction techniques. The studies showed that among all of these compounds only the pyrazole derivatives are liquid crystal materials. The luminescent properties of all the prepared compounds were also investigated which confirmed that all of these compounds are photo-luminescent in the crystalline solid state and in the mesophase.     

Molar heat capacities and standard molar enthalpy of formation of pyrimethanil butanedioic salt

A noval anilino-pyrimidine fungicide, pyrimethanil butanedioic salt (C₂₈H₃₂N₆O₄), was synthesized by a chemical reaction of pyrimethanil and butanedioic acid. The low-temperature heat capacities of the compound were measured with an adiabatic calorimeter from 80 to 380 K. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity fitted curve. The thermal stability of the compound was investigated by TG and DSC. The TG curve shows that pyrimethanil butanedioic salt starts to sublimate at 455.1 K and totally changes into vapor when the temperature reaches 542.5 K with the maximal speed of weight loss at 536.8 K. The melting point, the molar enthalpy (Δ_fus H _m), and entropy (Δ_fus S _m) of fusion were determined from its DSC curves. The constant-volume energy of combustion (Δ_c U _m) of pyrimethanil butanedioic salt was measured by an isoperibol oxygen-bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpy of formation was derived and determined to be Δ_f H _m ^o (pyrimethanil butanedioic salt)=?285.4 ± 5.5 kJ mol^?1.     

Vanadium complexes with quadridentate Schiff bases

The Schiff base ligands N,N′-(±)-trans-bis(3,5-dichloro-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L¹) and N,N′-(±)-trans-bis(5-chloro-4-methyl-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L²) were derived from the condensation of trans-1,2-diaminocyclohexane with 3,5-dichloro-2-hydroxyacetophenone or 5-chloro-4-methyl-2-hydroxyacetophenone, respectively. Both these ligands formed well-defined complexes with vanadium (IV) and (V) under suitable experimental conditions. These complexes have been characterized by elemental analysis, molar conductivity, magnetic moments, infrared, electronic spectra, ESR, X-ray diffraction, and thermogravimetric analysis. X-ray diffraction study of [VO(L²)]·H₂O complex indicated its monoclinic crystal system with a = 9.8525, b = 23.6271, c = 9.0904 Å, and β = 97.87°. The complexes [VO(L¹)]·H₂O and [VO(L²)]·H₂O have been examined as catalysts for epoxidation of styrene in the presence of hydrogen peroxide as oxidant. The IR spectral data suggest that both the ligands behave as dibasic tetradentate chelating agent with ONNO donor atoms sequence toward cental metal ion.     

Heat capacities and standard molar enthalpy of formation of pyrimethanil maleic salt and pyrimethanil fumaric salt

Novel anilino-pyrimidine fungicides, pyrimethanil maleic salt, and pyrimethanil fumaric salt (C₂₈H₃₀N₆O₄) were synthesized by a chemical reaction of pyrimethanil with maleic acid/fumaric acid. The low-temperature heat capacities of the two compounds were measured with an adiabatic calorimeter from 80 to 350 K. The heat capacities of pyrimethanil fumaric salt are bigger than that of pyrimethanil maleic salt in the measurement temperature range. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity-fitted curves. The melting points, the molar enthalpies (Δ_fus H _m), and entropies (Δ_fus S _m) of fusion of pyrimethanil maleic salt and pyrimethanil fumaric salt were determined from their DSC curves. The values indicate that pyrimethanil fumaric salt was more thermostable than pyrimethanil maleic salt. The constant-volume energies of combustion (Δ_c U _m ^o ) of pyrimethanil maleic salt and pyrimethanil fumaric salt were measured using an isoperibol oxygen bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpies of formation of the two compounds were derived and determined to be Δ_f H _m ^o (pyrimethanil maleic salt) = ?459.3 ± 4.9 kJ mol^?1 and Δ_f H _m ^o (pyrimethanil fumaric salt) = ?557.2 ± 4.8 kJ mol^?1, respectively. The results suggest that pyrimethanil fumaric salt is more chemically stable than pyrimethanil maleic salt.     

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li₄Ti₅O₁₂ and Li₂TiO₃) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m²/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.     

Variously substituted phenyl hepta cyclopentyl-polyhedral oligomeric silsesquioxane (ph,hcp-POSS)/polystyrene (PS) nanocomposites

A comparative study concerning the thermal stability of polystyrene (PS) and six POSS/PS nanocomposites of general formula R₇R′(SiO_1.5)₈/PS (where R = cyclopentyl and R′ = phenyl, 4-methoxyphenyl, 4-tolyl, 3,5-xilyl, 4-fluorophenyl, and 2,4-difluorophenyl) was carried out in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Nanocomposites were prepared by in situ polymerization of styrene in the presence of 5 % w/w of POSS, but the actual filler concentration in the obtained nanocomposites, determined by ¹H NMR spectroscopy, was in all cases slightly higher than that in the reactant mixtures. FTIR spectra of nanocomposites evidenced the presence of filler-polymer interactions. Inherent viscosity (η _inh) determinations indicated that the average molar mass of polymer in methylated and fluorinated derivatives was lower than neat PS, and were in agreement with calorimetric glass transition temperature (T _g) measurements. Degradations were performed into a thermobalance, in the scanning mode, at 10 °C min^?1, and the temperatures at 5 % mass loss (T _5 %), of various nanocomposites were determined. The effects of various substituents of the POSS phenyl group on the thermal stability of nanocomposites were evaluated. The results were discussed and interpreted.     

The influence of methyl groups on the torsion angle and on the energetics of 1-phenylpyrrole derivatives: a thermodynamic and computational study

Calorimetric and effusion techniques, complemented by computational calculations were combined to determine the standard (p ^o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, $\Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right)$ , at T = 298.15 K, of 1-(3,5-dichlorophenyl)-2,5-dimethylpyrrole and 2,5-dimethyl-1-phenyl-3-pyrrolecarboxaldehyde, as (107.2 ± 2.7) and (25.9 ± 3.2) kJ mol^?1, respectively. These values were derived from the respective standard molar enthalpies of formation, in the crystalline phase, ${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{cr}} \right)$ , at T = 298.15 K, obtained from combustion calorimetry measurements, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined by the Knudsen effusion mass-loss method. The gas-phase enthalpies of formation of both experimentally studied compounds were also estimated by G3(MP2)//B3LYP computations, using a set of working reactions; the results obtained are in good agreement with the experimental data. With this computational approach, the enthalpies of formation of 1-(3,5-dichlorophenyl)pyrrole, 1-(3,5-dichlorophenyl)-2-methylpyrrole, 1-phenyl-3-pyrrolecarboxaldehyde and 2-methyl-1-phenyl-3-pyrrolecarboxaldehyde were also estimated and a value for their ${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right)$ has been defined. Moreover, the molecular structures of the six molecules were established, their geometrical parameters were determined and the influence of methyl groups in the pyrrole ring (2 and 5 positions) on the phenyl/pyrrole torsion angle was analyzed. All the results were also interpreted in terms of enthalpic increments.     

Low-temperature heat capacities, and thermodynamic properties of solid–solid phase change material bis(1-octylammonium) tetrachlorocuprate

A new crystalline complex (C₈H₁₇NH₃)₂CuCl₄(s) (abbreviated as C₈Cu(s)) was synthesized by liquid phase reaction. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the complex. Low-temperature heat capacities of the complex were measured by a precision automatic adiabatic calorimeter over the temperatures ranging from 78 to 395 K, and two solid–solid phase changes appeared in the heat capacity curve. The temperatures, molar enthalpies and entropies of the two phase transitions of the complex were determined to be: T _{trs, 1} = 309.4 ± 0.35 K, Δ_trs H _{m, 1} = 16.55 ± 0.41 kJ mol^?1, and Δ_trs S _{m, 1} = 53.49 ± 1.3 J K^?1 mol^?1 for the first peak; T _{trs, 2} = 338.5 ± 0.63 K, Δ_trs H _{m, 2} = 6.500 ± 0.10 kJ mol^?1, and Δ_trs S _{m, 2} = 19.20 ± 0.28 J K^?1 mol^?1 for the second peak. Two polynomial equations of the heat capacities as a function of the temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex relative to the standard reference temperature of 298.15 K were calculated based on the fitted polynomial equations.     

Heat capacities and thermodynamic properties of MgNDC

One-three-dimensional metal-organic frameworks Mg_1.5(C₁₂H₆O₄)_1.5(C₃H₇NO)₂ (MgNDC) has been synthesized solvothermally and characterized by single crystal XRD, powder XRD, FT-IR spectra. The low-temperature molar heat capacities of MgNDC were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 205 to 470 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range. The thermodynamic parameters of MgNDC such as entropy and enthalpy relative to reference temperature of 298.15 K were derived based on the above molar heat capacities data. Moreover, the thermal stability and decomposition of MgNDC was further investigated through thermogravimetry (TG)?Cmass spectrometer (MS). Three stages of mass loss were observed in the TG curve. TG?CMS curve indicated that the oxidative degradation products of MgNDC are mainly H₂O, CO₂, NO, and NO₂.     

Improved thermal stability of an organic zeolite by fluorination

The thermal stability of an organic zeolite material, namely 2,4,6-tris(4-bromo-3,5-difluorphenoxy)-1,3,5-triazin (Br-3,5-DFPOT), was improved by fluorination of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazin (BrPOT). The open pore structure (van der Waals diameter of 10.5 Å) of the modified zeolite was observed up to 110 °C in comparison to 70 °C for BrPOT. Nitrogen sorption at low temperature showed a type I isotherm and derived pore volumes thereof are in agreement with structural data. It was observed here that Br-3,5-DFPOT crystals preserving the open pore structure could only be obtained below a typical size of about 50 μm. The improved thermal stability of the fluorinated system is attributed to an enhancement of the strength of the Br₃-synthon.     

Ligand preferences in ytterbium ions complexation with carboxylate-based metal-organic frameworks

Two coordination polymers of ytterbium were synthesized by employing 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoic acid (H₃TATB), 4,4′,4-benzene-1,3,5-triyl-tribenzoic acid (H₃BTB), and 3,5-pyridinedicarboxylic acid (3,5-PDC) ligands and were characterized by single-crystal X-ray diffraction analysis. Reaction of ytterbium(III) chloride in the presence of H₃BTB and 3,5-PDC ligands gives preferred complexation with the 3,5-PDC ligand, producing [Yb₂(3,5-PDC)(ClO₄)₃][NH(Me)₃] (1). However, under exactly the same reaction conditions, reaction of ytterbium(III) chloride in the presence of 3,5-PDC and H₃TATB resulted in complexation with H₃TATB to form [(CH₃)₂NH₂][Yb₄(TATB)₄(HCO₂)(H₂O)₂]·3H₂O (2). The crystal structure results showed a layered structure for 1 and a metal-organic framework structure for 2. This indicates that the complexation preference of the ytterbium ion is H₃TATB ≥ 3,5-PDC ≥ H₃BTB. Conversely, the uncomplexed ligand in the metal-organic framework (2) is an auxiliary agent during the synthesis, which shows polytopic linker controls crystal properties, to form suitable crystals for single-crystal structure determination. The prepared coordination compounds were used as heterogeneous catalysts in an oxidation amidation reaction with different aldehydes and benzylamine hydrochloride.     

Syntheses and crystal structures of three pillared complexes based on H2AIP and triazole-bipyridine ligands

Three pillared polymeric complexes, {[Ni₂(AIP)₂(4,4′-bpt)(H₂O)₂]·4H₂O}_n (1), {[Co(AIP)(3,3′-bpt)]·H₂O}_n (2), and {[Ni(AIP)(3,3′-bpt)]·H₂O}_n (3) (H₂AIP = 5-aminoisophthalic, 4,4′-bpt = 1H-3,5–bis(4-pyridyl)-1,2,4-triazole and 3,3′-bpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole), have been hydrothermally synthesized and characterized by X-ray diffraction analysis. Both 1 and 3 have 2-D (6,3) honeycomb layers, which are further interlinked by bent pillared triazole-bipyridine ligands to form a bilayer structure. The structures can be simpli?ed to a (3,4)- and (3,5)-connected geometrical topology, respectively. Compound 2 has a Co-AIP layer structure in which the layers are pillared by 3,3′-bpt spacers to form the 3-D CsCl net.     

Synthesis,structure characterization,and thermochemistry of the coordination compounds of pyridine-2,6-dicarboxylic acid with several metals (Ca and Co)

Two solid state complexes of pyridine-2,6-dicarboxylate with Ca²⁺ and Co²⁺ ions, Ca₂(DPC)₂(H₂O)₆(H₂DPC)₂(s) and Co(DPC)₂·Co(H₂O)₅·2H₂O(s), were synthesized. X-ray crystallography was applied to characterize the crystal structures of the two complexes. The molecular and cell stacking structures of the two complexes were shown; the crystal data and refinement details were summarized, and the selected bond lengths and angles of the title complexes were listed. Low-temperature heat capacities of the two complexes were measured with an automated adiabatic calorimeter in the temperature ranging from 78 to 380 K. Two polynomial equations of experimental molar heat capacities as a function of the temperature were obtained by the least-squares method. The smoothed molar heat capacities and thermodynamic functions of the complexes were calculated based on the fitted polynomial equations. In addition, thermodynamic properties of the two complexes were compared.     

Study on the Interaction of Nicotinic Acid with <Emphasis Type="SmallCaps">l</Emphasis>-Phenylalanine in Buffer Solution by Heat Capacity Measurements at Various Temperatures

The interaction between nicotinic acid (NA) and l-phenylalanine (Phe) was studied in aqueous phosphate buffer solutions (pH = 7.35) by differential scanning calorimetry. Heat capacities of nicotinic acid–buffer, l-phenylalanine–buffer, and nicotinic acid–l-phenylalanine–buffer mixtures were determined at (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K using the microdifferential scanning calorimeter SCAL-1 (Pushchino, Russia). The apparent molar heat capacities, ^? C _p , of nicotinic acid in buffer solution and in buffer 0.0216 mol·kg^?1 amino acid solutions were evaluated. The concentration of NA was varied from (0.0106–0.0701) mol·kg^?1. The interaction of NA with Phe is accompanied by complex formation. The partial molar heat capacities of transfer of nicotinic acid from buffer to buffer amino acid solutions are positive. The results are discussed in terms of various interactions operating in this system.