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.     

Anisotropy of lattice distortion of [Co(NH3)5NO2]C2O4 at hydrostatic pressures of up to 4.0 GPa

Variation of the lattice parameters of [Co(NH₃)₅NO₂]C₂O₄ as a function of hydrostatic pressure was studied by powder X-ray diffractom etry in diamond anvils. No phase transitions were observed at pressures below 4.0 GPa, but the structure was anisotropically distorted. The maximal compression was observed in the direction perpendicular to the planes of the oxalate ions and NO₂ ligands.     

Disorder in ICE VI at 1 GPa: A neutron diffraction study on in situ grown single crystals

Abstract

Crystallographic structure determinations of H₂O and D₂O ice VI single crystals were performed between 207 K and ambient temperautre at pressures of 0.9 GPa. A neutron pressure cell of the Marburg-type was used. Single crystals were grown in situ under optical control in the pressure cell. Details of the cell construction, especially the design of the sapphire anvils and zero-scattering gaskets, are described.     

Pressure Effect on the Crystal Structure of Na2C2O4: Deformation Anisotropy During Hydrostatic Compression and Phase Transition at 3.8 GPa

Variation of the unit cell parameters of Na₂C₂O₄ is investigated by powder diffractometry in diamond anvils when hydrostatic pressure is increased to 6.5 GPa. Anisotropic distortion of the structure was observed up to about 3.8 GPa, whereupon a transition to an unknown polymorphous modification occurred. Before the phase transition, the compression was maximal in the direction perpendicular to close-packed layers formed by oxalate ions. Minimal compression was observed in the direction of the specific crystallographic axis b. The anisotropy of compression at elevated pressure is similar, but not identical, to the anisotropy of compression of the same structure at reduced temperature.     

Kinetics of solid state nitrito-nitro bond isomerization in [Co(NH3)5ONO]Br2 at high pressures

The kinetics of the solid state bond isomerization in [Co(NH₃)₅ONO]Br₂ is studied by quantitative IR spectroscopy in diamond anvils at pressures of 1.0, 2.0, 3.0, and 4.0 GPa and atmospheric pressure and at temperatures of 7, 16, 25, and 34°C. The pressure dependence of the reaction rate constant is adequately described by the equation inK = a + bP + cP². Although solid state isomerization is accompanied by an increase in molar volume, the hydrostatic pressure accelerates the reaction. The reason for this unusual effect must be sought in the anisotropy of structure deformation in the course of bond isomerization; the total increment in volume is comparatively small (0.84%), but the structure is drastically compressed (by 3.4%) in a number of crystallographic directions, and the crystal structure is compressed under pressure in the same directions. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 5, pp. 934–946, September–October, 1998.     

Effect of High Pressure on the Polymorphs of Paracetamol

Effect of hydrostatic pressure on the two (I – monoclinic and II – orthorhombic) polymorphs of paracetamol was studied by X-ray diffraction in the diamond anvil cell at pressures up to 4.5 GPa (for the monoclinic form) and up to 5.5 GPa (for the orthorhombic form). The two groups of phenomena were studied: (i) the anisotropic structural distortion of the same polymorph, (ii) transitions between the polymorphs induced by pressure. The anisotropy of structural distortion of polymorphs I and II was well reproducible from sample to sample, also from powder samples to single crystals. The bulk compressibility of the two forms was shown to be practically the same. However, a noticeable qualitative difference in the anisotropy of structural distortion was observed: with increasing pressure the structure of polymorph II contracted in all the directions showing isotropic compression in the planes of hydrogen-bonded molecular layers, whereas the layers in the structure of the polymorph I expanded in some directions. Maximum compression in both polymorphs I and II was observed in the directions normal to the molecular layers. The transitions between the polymorphs induced by pressure were poorly reproducible and depended strongly on the sample and on the procedure of increasing/decreasing pressure. No phase transitions were induced in the single crystals of the monoclinic polymorph at pressures at least up to 4GPa, although a partial transformation of polymorph I into polymorph II was observed at increased pressure in powder samples. Polymorph II transformed partly into the polymorph I during grinding. The transformation could be hindered if grinding was carried out in CCl₄. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anisotropy of lattice distortion in [Co(NH3)5ONO]X2, X=Cl−, Br−, under hydrostatic pressure of up to 5.0 GPA

Variation of the unit cell parameters of [Co(NH₃)₅ONO]X₂ (X=Cl⁻, Br⁻) as a function of hydrostatic pressure is studied by powder X-ray diffractometry in cooled diamond anvils. Pressures of up to 5.0 GPa lead to anisotropic lattice distortion but not to phase transitions. The anisotropy of lattice compression of the nitrito isomers is qualitatively distinct from that of the related structures of the corresponding nitro isomers, which differ mainly in the structure of complex cations. The following specific interactions are responsible for the anisotropy of compression for both nitrito and nitro isomers: hydrogen bonds between the NO₂ and NH₃ ligands of the neighboring cations and between the NH₃ ligands and the halide anions; specific interactions of the NO₂ ligands of the neighboring cations with each other and of the NO₂ ligands with the halide anions. Institute of Solid State Chemistry, Siberian Branch, Russian Academy of Sciences. Novosibirsk State University. Institute of Mineralogy and Materials Science and Technology Center, Marburg University (Germany). Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 424–432, May–June, 1998. This work was supported by the Humboldt Foundation (Germany) and the “Universities of Russia” Program (projects 3H-34-94, 3H-375-92).     

A pressure induced phase transition in pyroxene

Abstract

Two monoclinic pyroxenes of composition Ca(Fe,Mg)Si₂O₆ were studied up to 10 GPa using X-ray powder diffraction and ⁵⁷Fe Mössbauerspectroscopy. The results are indicative of a phase transition at 4 GPa.