Thermodynamic Properties of Polyphenylquinoxaline in the Temperature Range of <Emphasis Type="Italic">T</Emphasis> → 0 to 570 K

The thermodynamic properties of amorphous polyphenylquinoxaline in the temperature range of 6 to 570 K are studied via precision adiabatic vacuum calorimetry and differential scanning calorimetry. The thermodynamic characteristics of glass transition are determined. Standard thermodynamic functions C^°_p, H°(T) ? H°(0), S°(Т) ? S°(0), and G°(T) ? H°(0) in the range of T → 0 to 570 K and the standard entropy of formation at T = 298.15 K are calculated. The low-temperature (T ≤ 50 K) heat capacity is analyzed using a multifractal model for the processing of heat capacity, fractal dimension D values are determined, and conclusions on the topological structure of the compound are drawn.     

Researches by the method of low-temperature adiabatic calorimetry and quantum chemical computation of vibrational states

The temperature dependence of heat capacity of a natural zinc silicate, hemimorphite Zn₄Si₂O₇(OH)₂·H₂O, over the temperature range 5–320 K has been investigated by the method of low-temperature adiabatic calorimetry. On the basis of the experimental data on heat capacity over the whole temperature interval, its thermodynamic functions C _p (T), S(T) and H(T) ? H(0) have been calculated. The existence of a phase transition in the area of 90–105 K determined on the basis of vibrational spectra has been confirmed, and changes of entropy ΔS _tr. and enthalpy ΔH _tr. of the phase transition have been calculated. Hemimorphite heat capacity has also been determined by the calculation methods according to the valence force field model in LADY program. The values of force constants of valence bonds and angles have been calculated by semi-empirical method PM5. The calculated IR and Raman spectra concordant with the experimental spectra have been obtained. The heat capacity values calculated according to the found vibrational states satisfactorily agree with those experimentally obtained with an accuracy of ±1.7% in the area of 120–200 K, and not more than ±0.8% for the interval of 200–300 K. This fact testifies that the calculation of thermodynamic characteristics is correct.     

The heat capacity and thermodynamic functions of Ca0.5Zr2(PO4)3 crystalline phosphate from T → 0 to 650 K

The temperature dependence of the heat capacity C _p ^o = f(T) of crystalline calcium-zirconium phosphate was studied over the temperature range 7–650 K by precision adiabatic vacuum and dynamic scanning calorimetry. The experimental data were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o(T) ? H ^o(0), S ^o(T), and G ^o(T) ? H ^o(0) at temperatures from T → 0 to 650 K and the standard entropy of formation of Ca_0.5Zr₂(PO₄)₃ at T = 298.15 K. The data on low-temperature (30 K ≤ T ≤ 50 K) heat capacity were used to calculate fractal dimension D. Conclusions about the character of the topology of the structure of the phosphate were drawn.     

The heat capacity and standard thermodynamic functions of Ni<Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphate over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 664 K

The temperature dependence of the heat capacity of crystalline nickel zirconium phosphate C°_p = f(T) was measured over the temperature range 6–664 K. The experimental data obtained were used to calculate the standard thermodynamic functions of Ni_0.5Zr₂(PO₄)₃ from T → 0 to 664 K. The standard entropy of phosphate formation from simple substances at 298.15 K was calculated from the absolute entropy of the compound. The data on the low-temperature heat capacity were used to determine the fractal dimension of Ni_0.5Zr₂(PO₄)₃ over the temperature range 30–50 K. Conclusions concerning the heterodynamic characteristics of the structure of Ni_0.5Zr₂(PO₄)₃ were drawn.     

Thermodynamic properties of carbosilane dendrimers of the third and sixth generations with ethyleneoxide terminal groups

The temperature dependences of the heat capacities of carbosilane dendrimers of the third and sixth generations with ethyleneoxide terminal groups are examined for the first time by means of precision adiabatic vacuum calorimetry at temperatures between 6.5 and 350 K. In this temperature range, physical transformations are observed and their standard thermodynamic characteristics are determined and discussed. The standard thermodynamic functions are calculated per nominal mole of a chosen unit using the obtained experimental data: C° _p (T), H°(T) - H°(0), S°(T) - S°(0), and G°(T) - H°(0) in the interval T → 0 to 350 K, and the standard entropies of formation at T = 298.15 K. The low-temperature (T ≤ 50 K) heat capacity is analyzed using the Debye theory of specific heat and a multifractal model. The values of fractal dimension D are also determined, and conclusions on the investigated structures’ topology are drawn. The corresponding thermodynamic properties of the studied dendrimers are compared as well.     

Thermodynamic properties of o-semiquinone complex of Co with Di-(2-pyridyl)amine in the temperature range T → 0 to 370 K

The heat capacity of di-(2-pyridyl)amine-bis-(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt in the temperature range from 7 to 370 K was investigated by means of precise adiabatic vacuum calorimetry. It was established that the phase transition associated with the redox-isomeric transformation of the semiquinone-catecholate form of the complex into the bis-semiquinone form is observed above 260 K; this transition is not completed due to thermal destruction that begins at 367 K. The magnetic moment values in the temperature range from 5 to 350 K and the EPR spectra in the temperature range from 130 to 290 K, which confirm the nature of the phase transition, were obtained for the investigated complex. The standard thermodynamic functions C _p ^pO (T), H○(T)-H○(0), S○(T), and G○(T)-H○(0), were calculated from the data on heat capacity in the temperature range from T → 0 to 260 K. Analysis of the low temperature heat capacity on the basis of Debye’s theory of the heat capacity of solids and the multifractional model testifies to the chain-layered structural topology of the investigated complex.     

Heat capacity and thermodynamic functions of theRFe2 compounds (R =Gd,Tb, Dy,Ho, Er,Tm, Lu) over the temperature region 8 to 300 K

Experimental heat capacity data for the Laves phaseRFe₂ intermetallic compounds (R =Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been determined over the temperature range 8 to 300 K. The error in these data is thought to be less than 1%. Smoothed heat capacity values and the thermodynamic functions, (H°_T ? H°₀) and S°_T, are reported throughout the temperature range for theRFe₂ series. In addition, (G°₂₉₈ ? H°₀) at 298 K is reported for all theRFe₂ compounds. These data were analyzed and it was shown that the maxima in the thermodynamic functions near HoFe₂ are due to the magnetic contribution of the lanthanide element. The lattice contribution to the entropy at 300 K was estimated, and from this quantity the Debye temperature was calculated to be about 300 K, which is in good agreement with the low-temperature heat capacity. Furthermore, this analysis indicates that the apparent electronic specific heat constants, γ′, for TbFe₂, DyFe₂, and HoFe₂, reported earlier, are in error.     

Thermodynamics of fluorinated derivatives of carbosilane dendrimers of high generations

The temperature dependences of the heat capacities of fluorinated derivatives of carbosilane dendrimers of high (4.5 and 7.5) generations were studied by adiabatic vacuum calorimetry in the range from 6 to 340 K for the first time. The standard thermodynamic characteristics of devitrification were estimated. The experimental results were used to calculate the standard thermodynamic functions C _p °(T), H°(T)?H°(0), S°(T)?S°(0), and G°(T)-H°(0) over the range from T??0 to 340 K and standard entropies of formation of dendrimers at T = 298.15 K. The low-temperature (T ?? 50 K) heat capacity was analyzed by using Debye??s heat capacity theory of solids and the multifractal model. The values of fractal dimensionality D were determined, and some conclusions about topology of the studied structures were made. The standard thermodynamic characteristics of the studied fluorinated derivatives of carbosilane dendrimers were compared.     

The thermodynamic properties of bis(η6-o-xylene)chromium(I) fulleride over the temperature range from T → 0 to 340 K

The temperature dependence of the heat capacity of bis(η⁶-o-xylene)chromium(I) fulleride, [(η⁶-(o-xylene))₂Cr]^+?[C₆₀]^??, over the temperature range 6–340 K was measured on an adiabatic vacuum calorimeter. The low-temperature (20 K ≤ T ≤ 50 K) heat capacity was subjected to multifractal processing; conclusions about the heterodynamic character of the structure were drawn. The experimental data were used to calculate the standard thermodynamic functions C _p ^° (T), H ^°(T)-H ^°(0), S ^°(T), and G ^°(T)-H ^°(0) over the temperature range from T → 0 to 340 K and estimate the standard entropy of fulleride formation from simple substances at 298.15 K. The standard thermodynamic characteristics of [(η⁶-(o-xylene))₂Cr]^+?[C₆₀]^?? were compared with those of the initial fullerene C₆₀.     

The thermodynamic properties of star-shaped fullerene-containing poly-N-vinylpyrrolidone

The temperature dependence of the heat capacity of star-shaped fullerene-containing poly-N-vinylpyrrolidone was studied over the temperature range 6–390 K by precision adiabatic vacuum and dynamic scanning calorimetry. The temperature intervals and thermodynamic characteristics of phase transitions were determined. The low-temperature dependence of the heat capacity of the substance was analyzed according to the Debye theory of the heat capacity of solids and its multifractal generalization. The data obtained were used to calculate the standard thermodynamic functions C _p ^o (T),H ^o(T)-H ^o(0), S ^o(T), and G ^o(T)-H ^o(0) of fullerene-containing poly-N-vinylpyrrolidone from T → 0 to 390 K. The standard entropy of formation of the polymer from simple substances and the entropy of its synthesis from poly-N-vinylpyrrolidone and fullerite C₆₀ at 298.15 K were calculated. The thermodynamic characteristics of fullerene-containing poly-N-vinylpyrrolidone are compared with those of the polymer-analogue without C₆₀.     

Thermodynamic Properties of a First-Generation Carbosilane Dendrimer with Terminal Phenylethyl Groups

The heat capacity of a first-generation carbosilane dendrimer with terminal phenylethyl groups as a function of temperature in the range from 6 to 520 K is studied for the first time via precision adiabatic vacuum calorimetry and differential scanning calorimetry. Physical transformations, such as low-temperature structural anomaly and glass transition are detected in the above-mentioned range of temperatures, and their standard thermodynamic characteristics are determined and analyzed. The standard thermodynamic functions of the studied dendrimer in the range of T → 0 to 520 K are calculated from the experimental data, as is the standard entropy in the devitrified state at T = 298.15 K. The standard thermodynamic characteristics of the carbosilane dendrimers studied in this work and earlier are compared.     

Heat capacity and thermodynamic properties of Mg(Fe<Subscript>0.6</Subscript>Ga<Subscript>0.4</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> in the 0–800 K temperature range

The heat capacity of Mg(Fe_0.6Ga_0.4)₂O₄ in the temperature range of 4.56–804.9 K is measured by adiabatic and differential scanning calorimetry. The temperature dependence of the heat capacity of Mg(Fe_0.6Ga_0.4)₂O₄ in the 0–800 K range is determined by generalizing the experimental data. The temperature dependences of thermodynamic functions (entropy, enthalpy change, and the reduced Gibbs free energy) are calculated. The abnormal contribution to the heat capacity C _p ^an(T) in the temperature range of 5–52 K is estimated.     

Thermodynamics of G-3(D4) and G-6(D4) carbosilanecyclosiloxane dendrimers

Temperature dependences of the heat capacity of G-3(D₄) and G-6(D₄) carbosilanecyclosiloxane dendrimers are studied for the first time by precision adiabatic vacuum and differential scanning calorimetry in the range of 6 to 350–450 K. Physical transformations in the investigated temperature range are observed and their standard thermodynamic characteristics are determined and discussed. Standard thermodynamic functions for a mole unit are calculated from the experimental data: C _p ^○ (T), H ^○(T), ? H ^○(0), S ^○(T) ? S ^○(0), and G ^○(T) ? H ^○(0) in the range of T → 0 to (350–449) K and standard entropies of formation at 298.15 K. Low-temperature (T ≤ 50 K) heat capacity is analyzed using the Debye theory of heat capacity of solids and the multifractal model. The values of fractal dimensionality D are determined and some conclusions on the topology of the investigated structures are drawn. The corresponding thermodynamic properties of the investigated carbosilanecyclosiloxane dendrimers under study are compared.     

Thermodynamic properties of pyridine-containing polyphenylene dendrimers of the first-fourth generations

The temperature dependence of the heat capacity C _p° = f(T) of hard pyridine-containing polyphenylene dendrimers of the first, third, and fourth generations was studied for the first time in an adiabatic calorimeter at 6–300 K. Using the experimental data obtained, the standard thermodynamic functions, viz., heat capacity, enthalpy, entropy, and Gibbs energy in the range from T → 0 to 300 K, were calculated for these dendrimers and the value of standard entropy of formation of the studied compounds at T = 298.15 K was estimated. The low-temperature heat capacity of the dendrimers was analyzed on the basis of the Tarasov and Debye theories of heat capacity of solids and by the multifractal method. The characteristic temperatures and fractal dimensionality D were determined, and some conclusions about the type of structure topology were drawn. The isotherms of the dependence of thermodynamic functions of the dendrimers on the molecular weight were obtained.     

Thermodynamic properties of second generation poly(phenylene-pyridyl) dendrimer

The temperature dependence of heat capacity C _p ^o = f (T) of second generation hard poly(phenylene-pyridyl) dendrimer (G2-24Py) was measured by a adiabatic vacuum calorimeter over the temperature range 6–320 K for the first time. The experimental results were used to calculate the standard thermodynamic functions: heat capacity C _p ^o (T), enthalpy H ^o(T)–H ^o(0), entropy S ^o(T)–S ^o(0) and Gibbs function G ^o(T)–H ^o(0) over the range from T → 0 K to 320 K. The standard entropy of formation at T = 298.15 K of G2-24Py was calculated. The low-temperature heat capacity was analyzed based on Debye’s heat capacity theory of solids. Fractal treatment of the heat capacity was performed and the values of the temperature characteristics and fractal dimension D were determined. Some conclusions regarding structure topology are given.     

Thermodynamic properties of crystalline phosphate Ba0.5Zr2(PO4)3 over the temperature range from T → 0 to 610 K

The temperature dependence of the heat capacity of crystalline barium zirconium phosphate C _p ^o  = f(T) was measured over the temperature range 6–612 K. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H°(T) ? H°(0), S°(T), G°(T) ? H°(0) over the temperature range from T → 0 to 610 K and standard entropy of formation at 298.15 K. The data on the low-temperature (6 ≤ T/K ≤ 50) heat capacity were used to determine the fractal dimension of Ba_0.5Zr₂(PO₄)₃. Conclusions concerning the topology of the structure of phosphate were drawn. Thermodynamic properties of M_0.5Zr₂(PO₄)₃ (M = Ca, Sr, Ba) were compared.     

Standard thermodynamic functions of CaNi0.5Zr1.5(PO4)3 crystalline phosphate in the range of T → 0 to 640 K

The temperature dependence of the heat capacity C _p ^○ = f(T) of CaNi_0.5Zr_1.5(PO₄)₃ crystalline phosphate is studied by precision adiabatic vacuum and differential scanning calorimetry over the temperature range of 7–640 K. Its standard thermodynamic functions C _p ^○ (T), H ^○(T)-H ^○(0), S ^○(T), and G ^○(T)-H ^○(0) for the region T → 0 to 640 K and the standard entropy of formation at T = 298.15 K are calculated from the obtained experimental data. Using data on the low-temperature (30–50 K) heat capacity, the D fractal dimension of phosphate is determined and conclusions about the character of the topology of its structure have been made. The final results are compared to data from thermodynamic investigations of the structurally related crystalline phosphates Zr₃(PO₄)₄, Ni_0.5Zr₂(PO₄)₃, and Ca_0.5Zr₂(PO₄)₃.     

Heat capacity and thermodynamic functions of MnBr2 · 4D2O and MnCl2 · 4D2O

The heat capacities of MnBr₂ · 4D₂O and MnCl₂ · 4D₂O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°_TH°₀) and S°_T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl₂ · 4D₂O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K.