Atomic positions in geological aragonite and biogenic aragonite, obtained from several mollusk shells, were precisely measured by high-resolution neutron diffraction, which is more sensitive than X-ray diffraction to the positions of light atoms, C and O, in the CaCO3 structure. Comparable analysis of atomic positions revealed, for the first time, the changes in some bond lengths and atomic configurations in biogenic specimens with respect to geological ones. Most pronounced are modifications in the aplanarity of the carbonate groups. These modifications correlate with the observed shifts of the ν2 frequency in the IR absorption spectra. The changes in atomic positions as well as the changes in lattice parameters detected by high-resolution X-ray diffraction are attributed to the interaction between organic macromolecules and growing crystallites during biomineralization. The obtained results allow us deeper understanding of the specific routes used by nature for growing bio-composites with superior chara...

Atomic Structure of Biogenic Aragonite

Tetraaqua metal squarate complexes, M(C4O4)(H2O)4, (M = Fe, Co, Ni, Zn), are known to have a polymeric chain structure with C4O42- as a bridge (μ-2) ligand between two metal ions in the trans position. Each metal ion is bonded to two C4O42- and four water molecules. They are all isostructural with space group C2/c. A complete Ewald sphere of data is measured at 120 K up to 2θ of 100−120° using Mo Kα radiation for each complex. Such carefully measured intensities are used to investigate the detailed electron density distribution in order to understand the chemical bonding and the d-orbital splitting of the metal ions subjected in such a ligand field. Results on the electron density distribution will be presented in the form of deformation density and of Laplacian maps. Deformation density will be presented in terms of experimental Δρx-x, Δρm-a (multipole model), and of theoretical Δρ derived from the HF and DFT calculations. The interesting bent bond feature on the four-membered ring ligand C4O42- is expli...

Bond Characterization of Metal Squarate Complexes [MII(C4O4)(H2O)4; M = Fe, Co, Ni, Zn]

Large single crystals of cesium-nickel sulfate hexahydrate Cs2Ni(SO4)2 · 6H2O of optical quality were grown for the first time. The crystal structure and the optical and thermogravimetric properties of this compound were investigated.

Cs2Ni(SO4)2 · 6H2O (CNSH) crystal: Growth and some properties

Chapter 5. Charge densities from X-ray diffraction data

Crystals of the simple and complex nickel and cobalt sulfates as optical filters for the solar-blind technology

The electron density at room temperature has been determined for α-nickel sulfate hexahydrate, α-NiSO 4 .6H 2 O: tetragonal, P4 1 2 1 2, M r =262.86, a=6.783 (1), c=18.288 (2) A, V=841.4 (3) A 3 , Z=4, D x =2.075 Mg m -3 , Mo Kα, λ=0.71069 A, μ=2.58 mm -1 , F(000)=544. R=0.023, wR=0.026 from 1864 independent reflections using X-ray diffraction data from a previous study of its structure, absolute chirality and optical activity [Stadnicka, Glazer & Koralewski (1987). Acta Cryst. B43, 319-325]

K. Stadnicka

Papers

Jahn–Teller distortion of the electron density in α-nickel sulfate hexahydrate

Jahn-Teller distortion of the electron density in a-nickel sulfate hexahydrate