sp3)C7-H7AC•••C3' 2.789(3) 2.726(2) 2.667(2) 2.668(6) x-1, y, z (sp2)C6-H6•••C5' 2.706(2) 2.661(2) 2.642(2) 2.632(5) x-0.5, y, 0.5-z

No abstract

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.

On the basis of a multipole refinement of single-crystal X-ray diffraction data collected using an Ag source at 90 K to a resolution of 1.63 Å, a quantitative experimental charge density distribution has been obtained for fluorite (CaF). The atoms-in-molecules integrated experimental charges for Ca and F ions are +1.40 e and -0.70 e, respectively. The derived electron-density distribution, maximum electron-density paths, interaction lines and bond critical points along Ca...F and F...F contacts revealed the character of these interactions. The Ca...F interaction is clearly a closed shell and ionic in character. However, the F...F interaction has properties associated with the recently recognized type of interaction referred to as `charge-shift' bonding. This conclusion is supported by the topology of the electron localization function and analysis of the quantum theory of atoms in molecules and crystals topological parameters. The Ca...F bonded radii - measured as distances from the centre of the ion to the critical point - are 1.21 Å for the Ca cation and 1.15 Å for the F anion. These values are in a good agreement with the corresponding Shannon ionic radii. The F...F bond path and bond critical point is also found in the CaF crystal structure. According to the quantum theory of atoms in molecules and crystals, this interaction is attractive in character. This is additionally supported by the topology of non-covalent interactions based on the reduced density gradient.

Two tourmaline samples occurring in quartz veinlets, which crosscut an amphibolite body at the Budniki camp near the Kowary town, in the south-west part of the Karkonosze Mountains (SW Poland), were studied through microprobe and single crystal X-ray diffraction. Samples were extracted from core and rim regions of crystals with a concentric zoning, respectively.Chemical and structural data revealed that the core tourmaline is characterized by a draviteoxy-dravite composition, with formula: X (Na0.82Ca0.07K0.01Sr0.010.09)Σ1 Y (Mg1.73Fe 2+ 0.81Fe 3+ 0.41Ti0.04V0.01)Σ3 . Z (Al5.85Fe 3+ 0.15)Σ6 ( T Si6O18) (BO3)3 (OH)3 W (OH0.50O0.50)Σ1 and unit cell parameters a = 15.97377(14) Å and c = 7.22644(7) Å. The rim part of the crystals has a magnesio-lucchesiite composition, described by the formula: X (Ca0.49Na0.41K0.04Sr0.020.04)Σ1 Y (Mg1.87Fe 2+ 0.95Ti0.15Fe 3+ 0.02V0.02)Σ3 Z (Al5.49Fe 3+ 0.51)Σ6 (BO3)3