X-ray diffraction studies of crystals under pressure and quantitative experimental charge density analysis are among the most demanding types of crystallographic research. A successful feasibility study of the electron density in the mineral grossular under 1 GPa pressure conducted at the CRISTAL beamline at the SOLEIL synchrotron is presented in this work. A single crystal was placed in a diamond anvil cell, but owing to its special design (wide opening angle), short synchrotron wavelength and the high symmetry of the crystal, data with high completeness and high resolution were collected. This allowed refinement of a full multipole model of experimental electron distribution. Results are consistent with the benchmark measurement conducted without a diamond-anvil cell and also with the literature describing investigations of similar structures. Results of theoretical calculations of electron density distribution on the basis of dynamic structure factors mimic experimental findings very well. Such studies allow for laboratory simulations of processes which take place in the Earth's mantle.
Crystal structures of 4-chlorotoluene and 4-bromotoluene under high pressure have been determined. In the case of 4-chlorotoluene, two high-pressure forms of this compound exist in the same range of pressure. However, no direct phase transition between them at high pressure has been observed. It has been confirmed that the symmetry of the high-pressure structure of 4-iodotoluene is the same as its symmetry determined at low temperature. Finally, we have extended the pressure range in which the high-pressure structure of 4-fluorotoluene was investigated. We have found that the space group previously reported (Pna21) as the proper one for the high-pressure form of 4-fluorotoluene is not correct as Pnma seems to be a better choice. 4-Bromotoluene formed only P21/c space group crystals isostructural with the α form of 4-chlorotoluene. For the single crystals of 4-iodotoluene under high pressure, we only managed to determine the cell parameters. These values correspond with those determined previously at low temperature measurement.
New [2]rotaxanes composed of dibenzo-24-crown-8 wheel and the axle containing two metal-complexing 14- and/or 16-membered tetraazamacrocyclic units, coordinating the same or different metal ions (Ni and/or Cu) were synthesized and investigated.
As a result of external compression applied to crystals, ions relax, in addition to shortening the bond lengths, by changing their shape and volume. Modern mineralogy is founded on spherical atoms, i.e., the close packing of spheres, ionic or atomic radii, and Pauling and Goldschmidt rules. More advanced, quantum crystallography has led to detailed quantitative studies of electron density in minerals. Here we innovatively apply it to high-pressure studies up to 4.2 GPa of the mineral hsianghualite. With external pressure, electron density redistributes inside ions and among them. For most ions, their volume decreases; however, for silicon volume increases. With growing pressure, we observed the higher contraction of cations in bonding directions, but a slighter expansion towards nonbonding directions. It is possible to trace the spatial redistribution of the electron density in ions even at the level of hundredths parts of an electron per cubic angstrom. This opens a new perspective to experimentally characterise mineral processes in the Earth’s mantle. The use of diamond anvil cells with quantum crystallography offers more than interatomic distances and elastic properties of minerals. Interactions, energetic features, a branch so far reserved only to the first principle DFT calculations at ultra-high-pressures, become available experimentally.
The first [3]rotaxane based on a tetraazamacrocyclic nickel(ii) complex was synthesized and investigated.
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