No abstract

No abstract

The bistable cobalt complex containing two symmetrical 3,6 di tert butyl o benzoquinone and one 1,10 phenanthroline moieties as ligands (1) was synthesized. Complex 1 was isolated in the individual state and characterized by IR and ESR spectroscopy, X ray diffraction, magnetochemical studies, and precision calorimetry. A change in temperature causes the re versible metal-ligand electron transfer and spin crossover (redox isomerism) in complex 1 in the crystalline state. The redox isomeric transformation at ∼250 K is accompanied by the phase transition. The structural study at two temperatures confirmed the changes in the molecular and crystal structure associated with the redox isomeric transformation.

No abstract

No abstract

Heat capacities of triphenylantimony dimethacrylate Ph3Sb(O2CCMeCH2)2 were measured by precision adiabatic vacuum calorimetry over the temperature range from T = (6 to 335) K and by differential scanning calorimetry over the temperature range from T = (300 to 470) K. The melting of the sample was observed within the above temperature range. The melting was accompanied by a compound decomposition. On the obtained data, the standard thermodynamic functions of molar heat capacity C p,m o, enthalpy H o(T) – H o(0), entropy S o(T), and Gibbs energy G o(T) – H o(0) of Ph3Sb(O2CCMeCH2)2 were calculated over the range from T = (0 to 400) K. The low-temperature (T < 50 K) heat capacity dependence was analyzed on the basis of Debye's heat capacity theory of solids and its multifractal model, so the characteristic temperatures and the fractal dimension were determined, and some conclusions about the structure topology were made. The standard entropy of formation at T = 298.15 K of Ph3Sb(O2CCMeCH2)2(cr) was calculated.

No abstract

Temperature dependences of the heat capacity of carbosilane dendrimers with butyl termi nal groups of the seventh and ninth generations were determined in the temperature range from 6 to 600 K by precision adiabatic vacuum calorimetry and differential scanning (dynamic) calorimetry. The physical transitions were revealed and their thermodynamic characteristics were analyzed. The experimental data obtained were used to calculate the standard thermo dynamic functions C p (T ), H°(T ) -H°(0), S°(T ), and G°(T ) -H°(0) for the temperature range from T → 0 to 600 K. The thermodynamic function-molar weight isotherms for the dendrimers of the third-ninth generations with terminal butyl groups in the glassy and highly elastic state are linear.Investigation of the synthesis and physicochemical properties of dendrimers, being monodispersed, nano sized, regularly branched macromolecular particles, is a promising direction of the modern chemistry of high molecular weight compounds. 1-11 Since the first reports on the synthesis of carbosilane dendrimers have been pub lished, 6,7 they were used, along with other compounds with dendrite organization of the molecular structure, as objects for the determination of the thermodynamic char acteristics. 12-19 In particular, methods of precision calo rimetry were used to study the low temperature depen dence of the heat capacity in a wide temperature range, and the experimental values were used in calculating the thermodynamic functions in the temperature range from T → 0 to 340-600 K.We have earlier 19 obtained the standard thermody namic functions of the carbosilane dendrimers of the third-sixth generations with the terminal butyl groups in the range from T → 0 to 340-600 K and determined and analyzed changes in these functions depending on the composition and structure of compounds. The systematic studies of the temperature dependence of the heat capac ity of the dendrimers revealed the second relaxation tran sition, which is an important principal result. The appear ance of the transition is consistent with a change in the physical state of the dendrimers. It was of interest to elu cidate whether this transition is characteristic of dendrimer samples of higher generations from the same homological series. The presence of the transition would mean that we deal with a general phenomenon for dendrimers of high generations.The purpose of this work is the calorimetric study of the temperature dependence of the heat capacity C p° = f(T ) of the carbosilane dendrimers of the seventh and ninth generations in the temperature range from 6 to 550-600 K and elucidation and physicochemical inter pretation of possible physical transitions on heating and cooling. We also intended to calculate the standard ther modynamic functions C p (T ), H°(T ) -H°(0), S°(T ), and G°(T ) -H°(0) from the experimental data for the range from T → 0 to 550-600 K and to approximate the calcu lated thermodynamic functions to the corresponding iso therms thermodynamic function-molar weight, which have been determined...