Concomitant polymorphs of 1,3‐bis(3‐fluorophenyl)urea

Hydrogen bonding between urea functionalities is a common structural motif employed in crystal‐engineering studies. Crystallization of 1,3‐bis(3‐fluorophenyl)urea, C₁₃H₁₀F₂N₂O, from many solvents yielded concomitant mixtures of at least two polymorphs. In the monoclinic form, one‐dimensional chains of hydrogen‐bonded urea molecules align in an antiparallel orientation, as is typical of many diphenylureas. In the orthorhombic form, one‐dimensional chains of hydrogen‐bonded urea molecules have a parallel orientation rarely observed in symmetrically substituted diphenylureas.     

DFT calculations as a powerful technique to probe the crystal structure of Al(acac)3

(27)Al, (17)O and (13)C chemical shieldings of aluminum acetylacetonate complex, Al(acac)(3), were calculated at some Density Functional Theory (DFT) levels of theory. In these calculations the X-ray structures of its different polymorphs were used. Using these calculated data observed discrepancies between the X-ray crystallography and solid state NMR experiment were explained in terms of the quality of the NMR data. In this survey we resorted to the simulated spectra using our calculated chemical shifts. In order to confirm our conclusions, electric field gradient (EFG) tensors of the (27)Al and (17)O nuclei were calculated at the same levels of theory as used in the chemical shielding calculations. On the other hand, these calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs) made a correlation between X-ray crystallography and solid state NMR experiments.     

Theoretical study on charge transport of quinacridone polymorphs

The charge carrier transporting ability in the polymorphism of quinacridone (QA) has been studied using density‐functional theory and Marcus charge transport theory. The theoretical results indicated quinacridone has good electron transport ability and electron mobilities of all the polymorphism are at 10^?2 magnitude. But its hole mobility, which varied with the different molecular packing, is at range of 10^?1–10^?3 magnitude. The difference of charge carrier mobilities among the polymorphism is originated from the different packing mode. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Precipitation behavior of 1,1,Di-(p-hydroxyphenyl)-cyclohexane clathrate crystals from acetone solutions containingd-limonene

The precipitation behavior of 1,1-di(p-hydroxyphenyl)cyclohexane (DHC) from acetone solutions containing d-Limonene (1-methyl-4(I-methylethenyl)cyclohexene) was studied. From the pure acetone solution or the solutions containing a small amount of d-Limonene crystals (B) precipitated, which clathrate only acetone with a guest/host (G/H) molar ratio of 1.0. However, when thed-Limonene concentration is increased to more than ca. 2 mol/L, crystals (A) precipitated which had a different habit from the B crystals. In the A crystalsd-Limonene is clathrated together with a large amount of acetone and the G/H value ofd-Limonene increases with the concentration in the solution up to the maximum value of 0.2. As the diffraction patterns of the A and B crystals are similar, it is assumed that a part of the acetone molecules in the B crystals are replaced byd-Limonene molecules. The acetone in the A crystals escapes rapidly, but thed-Limonene remains for a long time. This may indicate that the large molecule ofd-Limonene cannot diffuse rapidly within the host lattice owing to three-dimensional hindrance. It was clear that the solubility of the A crystals is higher than that of the B crystals and the transformation from the'metastable A to the stable B crystals proceeds during the crystallization of A crystals.     

Versatile 2,5‐Pyridinedicarboxylate in Linking Transition‐Metal Atoms into 1D and 2D Coordination Polymers and Concomitant Polymorphs

By employing one bridging ligand, 2,5‐pyridinedicarboxylate (2,5‐pda^2?), in the presence or absence of another bridging ligand, 4,4′‐bipyridine (4,4′‐bpy), one one‐dimensional (1D) {[Co₂(2,5‐pda)(2,5‐Hpda)₂(4,4′‐bpy)(H₂O)₃]·6H₂O}_∞ ( 1 ) and two two‐dimensional (2D) coordination polymers, {[Cu₃(2,5‐pda)₃(H₂O)₃]·6H₂O}_∞ ( 2 ) and {[Co(2,5‐pda)(H₂O)]·2H₂O}_∞ ( 3 ) were synthesized. Complexes 2 and 3 are characterized as concomitant polymorphs from a one‐pot reaction at ambient temperature. A comparison of the coordination geometries of all neutral and anionic coordination polymers containing {M_x(2,5‐pda)_y(H₂O)_z}_∞ available to date is presented.     

Polymorphic transformation of indomethacin in precirol solid dispersion system

The polymorphic transformation of indomethacin (IMC) in the presence of Precirol during heating was investigated by differential scanning calorimetry (DSC), infrared (IR) spectroscopy, microscopic Fourier transform infrared (FT-IR)/DSC system, and powder X-ray diffractometry with heating. The results indicate that in the presence of Precirol the original γ form of IMC was first transformed to a transition state, and then to a new polymorph by heating or exposure to IR radiation. The transition state of the melted sample gave three endothermic peaks, at 34, 48 and 127°C, and one exothermic peak, at 54°C. The stable melted sample exhibited two endothermic peaks, at 58 and 127°C, which were due to the fusion of Precirol and the new polymorph of IMC, respectively. This new polymorph of IMC also exhibited two specific IR absorption peaks, at 1693 and 1675 cm^?1. Microscopic FT-IR/DSC was used to examine the correlation between the structural transformation and its thermal response, and demonstrated the existence of the transition state of the melted sample. X-ray diffractometry with heating confirmed the appearance of the new polymorph of IMC in the presence of Precirol after heating.     

Exploring concomitant/conformational dimorphism in a difluoro‐substituted phosphoramidate derivative

The concomitant occurrence of dimorphs of diphenyl (3,4‐difluorophenyl)phosphoramidate, C₁₈H₁₄F₂NO₃P, was observed via a solution‐mediated crystallization process with variation in the symmetry‐free molecules (Z′). The existence of two forms, i.e. Form I (block, Z′ = 1) and Form II (needle, Z′ = 2), was characterized by single‐crystal X‐ray diffraction, differential scanning calorimetry and powder X‐ray diffraction. Furthermore, a quantitative analysis of the energetics of the different intermolecular interactions was carried out via the energy decomposition method (PIXEL), which corroborates with inputs from the energy framework and looks at the topology of the various intermolecular interactions present in both forms. The unequivocally distinguished contribution of strong N—H…O hydrogen bonds along with other interactions, such as C—H…O, C—H…F, π–π and C—H…π, mapped on the Hirshfeld surface is depicted by two‐dimensional fingerprint plots. Apart from the major electrostatic contribution from N—H…O hydrogen bonds, the crystal structures are stabilized by contributions from the dispersion energy. The closely related melting points and opposite trends in the calculated lattice energies are interesting to investigate with respect to the thermodynamic stability of the observed dimorphs. The significant variation in the torsion angles in both forms helps in classifying them in the category of conformational polymorphs.     

Raman spectroscopy as a tool for long‐term energetic material stability studies

Raman spectroscopy is shown to be useful as a tool for long‐term stability studies. The stability of a novel submicron‐size γ‐polymorph form of the explosive HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) was monitored up to 1 year using Raman spectroscopy. The preparation and characterization of this submicron HMX has been previously discussed. It is important to know the long‐term stability of this submicron γ‐polymorph material under ambient conditions for its eventual utilization. This submicron HMX material has been found to be stable both chemically and polymorphically (to the order of 1% impurity level), even though HMX normally converts to the β‐polymorph at ambient conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

尼群地平晶型转变条件及其影响因素的确定

根据熔化数据推算相变稳定性理论计算了尼群地平不同晶型之间的相变温度, 并分别考察了高温、高温和高湿及高压条件下的晶型转变. 理论推导尼群地平I与II, 尼群地平I与III, 尼群地平II与III的转化温度分别为158.88, 160.50和158.65 ℃, 三者均为单变关系, 且在高温条件下尼群地平II, III都转变为尼群地平I, 在高压条件下, II易转变为I. 试验结果表明室温下尼群地平I为稳定型, II和III为亚稳定型, 3种晶型稳定性顺序为尼群地平I＞II＞III.     

Two novel polymorphic forms of iron‐chelating agent deferiprone

Thalassemia is a genetic blood disorder requiring life‐long blood transfusions. This process often results in iron overload and can be treated by an iron‐chelating agent, like deferiprone (3‐hydroxy‐1,2‐dimethylpyridin‐4‐one), C₇H₉NO₂, in an oral formulation. The first crystal structure of deferiprone, (Ia), was reported in 1988 [Nelson et al. (1988). Can. J. Chem. 66 , 123–131]. In the present study, two novel polymorphic forms, (Ib) and (Ic), of deferiprone were identified concomitantly with polymorph (Ia) during the crystallization experiments. Polymorph (Ia) was redetermined at low temperature for comparison of the structural features and lattice energy values with polymorphs (Ib) and (Ic). Polymorph (Ia) crystallized in the orthorhombic space group Pbca, whereas both polymorphs (Ib) and (Ic) crystallized in the monoclinic space group P2₁/c. The asymmetric units of (Ia) and (Ib) contain one deferiprone molecule, while polymorph (Ic) has three crystallographically independent molecules (A, B and C). All three polymorphs have similar hydrogen‐bonding features, such as an R₂²(10) dimer formed by O—H…O hydrogen bonds, an R₄³(20) tetramer formed by C—H…O hydrogen bonds and π–π interactions, but the polymorphs differ in their molecular arrangements in the solid state and are classified as packing polymorphs. O—H…O and C—H…O hydrogen bonds lead to the formation of two‐dimensional hydrogen‐bonded parallel sheets which are interlinked by π–π stacking interactions. In the three‐dimensional crystal packing, the deferiprone molecules were aggregated as corrugated sheets in polymorphs (Ia) and (Ic), whereas in polymorph (Ib), they were aggregated as a square‐grid network. The characteristic crystalline peaks of polymorphs (Ia), (Ib) and (Ic) were established through powder X‐ray diffraction analysis. The Rietveld analysis was also performed to estimate the contribution of the polymorphs to the bulk material.