Crystal structure of [Co(NH3)5NO2]C2O4. Analysis of specific contacts and structural effects hindering inner-spheric nitro-nitrito isomerization

The structure of [Co(NH₃)₅NO₂]C₂O₄ is solved and refined (space group Immm, a=7.428(2), b=9.790(3), c=6.568(1) Å, V=477.6(2) ų, Z=2; R₁=0.0177, wR₂=0.0279 for F²>4σ(F²); R₁=0.1177, wR₂=0.0643 for all data; residual electron density from 0.125 to ?0.140 e/ų). Specific contacts in the structure are analyzed. Crystal chemical interpretation is suggested to explain the occurrence of photodecomposition rather than photochemical bond isomerization under the action of light in cobalt(III) nitropentammoniate oxalate crystals, in contrast to all previously investigated cobalt(III) nitropentammoniates.     

Crystal Structure Study of the Metastable β-modification of Glycine and its Transformation into the α-modification

Crystal structure refinement was performed of the metastable modification of glycine (space gr. P2₁, a = 5.092(2) , b = 6.273(3) , c = 5.384(3), = 113.17(4)°, Z = 2, R = 0.0274). The crystals were obtained by a new method (not described in the literature): they were precipitated from a water solution with the addition of glacial acetic acid. The crystal structure of the glycine modification [space gr. P2₁/n, a =5.106(1) , b = 11.979(5) , c = 5.463(2) , = 111.75(2)°:, Z =4] was refined for comparison. Transition from the to the modification in a damp atmosphere was revealed, resulting in the formation of a strongly strained crystal of a mosaic structure. The orientation of the crystallographic axes in the newly formed crystal of the modification relative to the axes in the initial crystal of the modification was determined. It is shown that as in glycine, the lengths of the intramolecular C—O bonds in the modification are fairly similar [1.248(2) and 1.253(2) ] and the previously found significant difference between them is most likely due to the errors of the photomethod. A comparative analysis of the crystal structures of the and glycine modifications (glycine zwitterion packings and structure of intermolecular hydrogen bond networks) was performed. Data of the analysis are used to discuss the properties of the glycine modifications, the possible reasons for the stability of the modification in dry air, the difficulties of crystal growth from solutions, and the ease of crystallization of the modification under various conditions.     

Effects of specific interactions on the anisotropy of crystal structure distortion of [Co(NH3)5NO2]Cl2 under hydrostatic pressure

Using some special experimental techniques for anisotropic refinement of the crystal structure of [Co(NH₃)₅NO₂]Cl₂ at high pressures gave results with an accuracy comparable to that obtained in normal conditions. The anisotropy of lattice compression under pressure is determined by specific interactions in crystals, in particular, by NH-Cl and NH-O hydrogen bonds. The anisotropy of compression at increased pressure is qualitatively distinct from that caused by lowered temperature for the same structure. This difference is also due to specific interactions (hydrogen bonds) in the structure. Institute of Solid State Chemistry, Siberian Branch, Russian Academy of Sciences (Novosibirsk). Novosibirsk State University. Marburg University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 433–447, May–June, 1998. This work was supported by A. Humboldt Foundation.     

Effect of the nature of the support on the activity of palladium catalysts for oxidation of carbon monoxide

We have studied the catalytic activity of TiN_0.65, TiO₂, Al₂O₃, and palladium catalysts supported on them in the oxidation of carbon monoxide. The order in which the activities of the supported catalysts vary, Pd/Al₂O₃>Pd/TiO₂>Pd/TiN_0.65, is the reverse of the activity series for the supports. This is explained by the effect of transfer of electron density from the palladium to the substrate. Taras Shevchenko Kiev University, 64 Vladimirskaya ul., Kiev 252033, Ukraine, G. V. Kurdyumov Institute of the Physics of Metals, National Academy of Sciences of Ukraine, 36 Akademika Vernadskogo bul’var, Kiev-142 252642, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 118–121, March–April, 1998.     

Betaine 0.77‐perhydrate 0.23‐hydrate and common structural motifs in crystals of amino acid perhydrates

The title compound, betaine 0.77‐perhydrate 0.23‐hydrate, (CH₃)₃N⁺CH₂COO⁻·0.77H₂O₂·0.23H₂O, crystallizes in the orthorhombic noncentrosymmetric space group Pca2₁. Chiral molecules of hydrogen peroxide are positionally disordered with water molecules in a ratio of 0.77:0.23. Betaine, 2‐(trimethylazaniumyl)acetate, preserves its zwitterionic state, with a positively charged ammonium group and a negatively charged carboxylate group. The molecular conformation of betaine here differs from the conformations of both anhydrous betaine and its hydrate, mainly in the orientation of the carboxylate group with respect to the C—C—N skeleton. Hydrogen peroxide is linked via two hydrogen bonds to carboxylate groups, forming infinite chains along the crystallographic a axis, which are very similar to those in the crystal structure of betaine hydrate. The present work contributes to the understanding of the structure‐forming factors for amino acid perhydrates, which are presently attracting much attention. A correlation is suggested between the ratio of amino acid zwitterions and hydrogen peroxide in the unit cell and the structural motifs present in the crystal structures of all currently known amino acids perhydrates. This can help to classify the crystal structures of amino acid perhydrates and to design new crystal structures.     

Influence of pyridine-based ligands on photostability of MAPbI3 thin films

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Low-temperature heat capacity and thermodynamic parameters of γ-aminobutyric acid

Thermodynamic properties of γ-aminobutyric acid were studied in the temperature interval from 5.7 to 300 K using a vacuum adiabatic calorimeter. The curve C _p (T) in the mentioned temperature interval is S-shaped without any anomalies. Based on the smoothed values of heat capacity, the calorimetric entropy $ S_{m}^{0} (T) - S_{m}^{0} (0) $ and the difference in the enthalpies $ H_{m}^{0} (T) - H_{m}^{0} (0) $ were calculated and tabulated. At the standard temperature 298.15 K, these values are equal to 158.1 ± 0.3 J K^?1 mol^?1 and 23020 ± 50 J mol^?1, respectively. At temperatures from 5 to 10 K, the function C _p (T) was found to obey the Debye law C = AT ³. Contrary to what has been supposed previously, the empirical Parks–Huffman rule for estimating entropy in the homologous series was shown to be not valid for the series glycine–β-alanine–γ-aminobutyric acid.     

New interpretation of heat effects in polymorphic transitions

Overlapping endothermic and exothermic effects in DSC measurements of polymorphic transitions is often detected in molecular crystals and drugs. It is explained by the sequence of melting and crystallization. In this paper, we argue that this explanation is incorrect. In revealing the kinetic nature of the endo/exo thermal effect, we suggest another explanation, based on the nucleation. New interpretation does allow us to measure the energetic barrier in the nucleation of bulk sample, thus providing a tool for testing the nucleation models.