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1.
Polymorphism of paracetamol 总被引:1,自引:0,他引:1
G. L. Perlovich Tatyana V. Volkova Annette Bauer-Brandl 《Journal of Thermal Analysis and Calorimetry》2007,89(3):767-774
The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature
dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured
and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications
in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG
sub298=60.0 kJ mol−1; ΔH
sub298=117.9±0.7 kJ mol−1; ΔS
sub298=190±2 J mol−1 K−1. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition
enthalpy at 298 K, ΔH
tr298(I→II)=2.0±0.4 kJ mol−1, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based
on ΔH
tr298 (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value
of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification
II were also estimated (ΔG
sub298=56.1 kJ mol−1; ΔH
sub298=115.9±0.9 kJ mol−1; ΔS
sub298=200±3 J mol−1 K−1). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported
found by classical thermochemical methods. 相似文献
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V.V. Pavlyuk G.S. Dmytriv I.I. Tarasiuk I.V. Chumak H. Pauly H. Ehrenberg 《Solid State Sciences》2010,12(2):274-280
A phase transition from the cubic CsCl-type structure (Pm-3m space group) into a tetragonal UPb-type structure (I41/amd) is observed for the LiAg binary compound at ambient conditions. The crystal structure of the tetragonal modification of the LiAg binary compound was solved by direct methods in SHELXS on the base of structure factors which were extracted from a powder diffraction pattern and refined by SHELXL and the Rietveld method (a = 3.9605(1), c = 8.2825(2) Å, Bragg R-factor = 4.81, Rf-factor = 4.87). Elevated temperatures and/or a small Li-excess versus the equimolar composition favour the cubic structure whereas ambient and lower temperatures and/or a small Li-deficiency stabilize the tetragonal structure. This reconstructive transition is reversible but proceeds slowly. 相似文献
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L. M. Plyasova 《Journal of Structural Chemistry》1977,17(4):637-640
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Christine C. Mattheus Anne B. Dros Jacob Baas Auke Meetsma Jan L. de Boer Thomas T. M. Palstra 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):939-941
Pentacene, C22H14, crystallizes in different morphologies characterized by their d(001)‐spacings of 14.1, 14.5, 15.0 and 15.4 Å. We have studied the crystal structure of the 14.1 and 14.5 Åd‐spacing morphologies grown by vapour transport and from solution. We find a close correspondence between the 14.1 Å structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt [Chem. Eur. J. (1999), 5 , 3399–3412] and the 14.5 Å structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst. (1961), 14 , 705–711]. Single crystals commonly adopt the 14.1 Åd‐spacing morphology with an inversion centre on both molecules in the unit cell. Thin films grown on SiO2 substrates above 350 K preferentially adopt the 14.5 Åd‐spacing morphology, with a slightly smaller unit‐cell volume. 相似文献
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A geometric model of phase equilibria between NaKC4H4O6 · 4H2O crystal hydrate polymorphs was suggested. An analytic equation for its thermodynamic potential was obtained, and the temperature
dependences of heat capacity and polarization were found. An analytic form of the interrelation between the anisotropic characteristics
of NaKC4H4O6 · 4H2O was obtained, and their temperature dependences were calculated over a wide temperature range including polymorphic transition
points. 相似文献
17.
H. Hajmowicz L. Synoradzki K. Bujnowski J. Zachara 《Journal of Thermal Analysis and Calorimetry》1997,48(6):1385-1392
It has been shown that polymorphism is the reason for the occurrence of (+)N-tosyl-L-glutamic acid 1 with various melting points. 1 occurs in two crystalline forms: and . Form -1 (prisms) having a melting point of 145–147°C is chemically pure and stable. Form -1, however, is unstable and is formed as a result of the stabilizing effect of an organic solvent not introduced into the structure of the crystal. At about 125°C the forms is transformed to the form. The melting point of the form depends on the amount and type of solvent contained in the crystal, which, during measurement cannot leave the system. 相似文献
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X-ray crystallography is used to analyze the concomitant polymorphism of KNaNbOF5 crystals. The second ??-modification of the compound, crystallizing in the tetragonal crystal system is found for the first time: space group P4/nmm, a = 5.9352(2) ?, c =8.5487(5) ?, V = 301.14(2) ?3, Z = 2, R1 = 0.0095. Parameters of the orthorhombic noncentrosymmetric structure of the ??-phase, previously described by Poeppelmeier et al. (J. Am. Chem. Soc., 129, 13963?C13969 (2007)), are refined and a comparative analysis of both structures is performed. The structures are characterized by the complete ordering of oxygen and fluorine atoms, the Nb-O distance in the ??-phase (1.738(1) ?) being noticeably longer than that in the ??-phase (1.709(2) ?). In ??-KNaNbOF5, alternating NbOF5 and NaOF5 octahedra share vertices, while in ??-KNaNbOF5, they share both vertices and edges. The existence of the non-polar centrosymmetric ??-modification of KNaNbOF5 cancels the assumption of the substantial contribution of potassium cations to the polar structure of ??-KNaNbOF5. 相似文献
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Béatrice Nicolaï René Céolin Ivo B. Rietveld 《Journal of Thermal Analysis and Calorimetry》2010,102(1):211-216
Indomethacin crystallizes from solutions in tetrahydrofuran as a solvate exhibiting the mole ratio 1 indomethacin:2 tetrahydrofuran. Upon heating, desolvation into indomethacin phase I occurs through partial amorphization and transitory formation of a phase, which is different from the crystallographically known polymorphs. The X-ray powder diffraction pattern of the solvate was tentatively indexed on a triclinic lattice (a = 31.454(5) Å, b = 17.883(3) Å, c = 10.551(2) Å, α = 70.55(2)°, β = 105.31(2)°, γ = 136.70(1)°). Assuming Z = 6 (1 indomethacin + 2 tetrahydrofuran) formula units per unit cell, the solvate’s specific volume is similar to the value calculated using additivity. 相似文献
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German L. Perlovich Svetlana V. Blokhina Nikolay G. Manin Tatyana V. Volkova Valery V. Tkachev 《Journal of Thermal Analysis and Calorimetry》2013,111(1):655-662
Single crystals of the crystallosolvate [bicalutamide + DMSO] with 1:1 stoichiometry were grown, and their structures were solved by X-ray diffraction methods. Polymorphic modifications I and II, the amorphous state, and the DMSO crystallosolvate of bicalutamide were prepared and thermochemistry of fusion processes was studied by DSC technique. The temperature dependence of the saturated vapor pressure of polymorphic form I was obtained and the thermodynamic characteristics of the sublimation process including the crystal lattice energy were calculated. The solution enthalpies of the forms under consideration and the crystallosolvate were acquired by the solution calorimetry procedure. The phase transition enthalpies estimated for form I, form II, and the amorphous state followed the rank order: form I— > form II, form I— > amorphous state, and form II— > amorphous state. The crystal lattice energy of polymorphic form II was determined using the results of sublimation and solution calorimetric experiments. The difference between the crystal lattice energy of the crystallosolvate and unsolvated phases was observed. The dissolution kinetics of forms I, II, the amorphous state, and DMSO solvate in water were investigated. 相似文献