The layer silicate Cs2SnIVSi6O15

Single crystals of Cs2SnSi6O15, dicaesium tin(IV) hexasilicate, were serendipitously obtained from a CsCl/NaCl flux at 923 K, starting from mixtures of CaO, SnO and TeO2 in a closed silica ampoule. The crystal structure of Cs2SnSi6O15 is constructed from {Si6O15}6– layers extending parallel to (101), and CsI cations with a coordination number of eleven as well as isolated [SnO6] octahedra situated between the silicate layers. Each of the nine different SiO4 tetrahedra in the silicate layer has a connectedness of Q 3 (three bridging and one terminal O atom), which leads to the formation of five- and eight-membered rings. The same type of silicate layer is found in the crystal structure of the mineral zeravshanite. Comparison with other silicates of the type Cs2 M IVSi6O15 (M IV = Ti, Zr, Th, U) revealed a klassengleiche group–subgroup relationship of index 2 between Cs2ZrSi6O15 (Z = 6, space group C2/m) and Cs2SnSi6O15 (Z = 12, space group I2/c).

Crystal structure of phenanthrenide salts stabilized by 15-crown-5 and 18-crown-6

Potassium 15-crown-5 phenanthrenide and potassium 18-crown-6 phenanthrenide were synthesized and characterized by powder X-ray diffraction and 39K solid state NMR spectroscopy. While the radical carbanion is very reactive in solution, the crystals are stable and storable under inert atmosphere. For 15-crown-5, a sandwich-like complex of potassium is formed with two molecules of crown ether per potassium resulting in a coordination number of 10. For the larger 18-crown-6 ligand, a 1:1 complex is obtained and a coordination number of 6 for the potassium cation. In neither crystal structure solvent molecules are incorporated. The 15-crown-5 compound crystallizes faster and is less soluble in THF as compared to the 18-crown-6 compound. Both compounds form solid phenanthrenide that is easy to handle and can be applied for reduction reactions.

DEM investigation on strain localization in a dense periodic granular assembly with high coordination number

Strain localization is one of key phenomena which have been studied extensively in geomaterials and for different kinds of materials including metals and polymers. This well-known phenomenon appears when structure/material is closed to failure. Theoretical, experimental, and numerical research have been dedicated to this subject for a long while. In the numerical aspects, strain localization inside the periodic granular assembly has not been well studied in the literature. In this paper, we investigate the occurrence and development of strain localization within a dense cohesive-frictional granular assembly with high coordination number under bi-periodic boundary conditions by Discrete Element Modeling (DEM). The granular assembly is composed of 2D circular disks and subjected to biaxial loading with constant lateral pressure. The results show that the formation of shear bands is of periodic type, consistent with the boundary conditions. This formation has the origins of the irreversible losing of cohesive contacts, viewed as micro-crackings which strongly concentrated in the periodic shear zones. This micromechanical feature is therefore strongly related to the strain localization observed at the sample scale. Finally, we also show that the strain localization is in perfect agreement with the sample’s displacement fluctuation fields.

Study of the influence of MoO3 concentration on the chemical structure, physical properties, and radiation absorption prowess of alumino lead borate glasses

The present study established a glass system with composition of 55B2O3 -30Pb3O4-(15 - x) Al2O3- xMoO3, where x: (0≤x≤5 mol %) by melt quenching conventional method. The structure of the synthesized samples was examined by XRD and FT-IR techniques. It is found that the molybdenum acts as a modifier and enhances the change between BO3 and BO4 structural units. Increasing MoO3 in the sample improved the glass network compactness and enhanced the coherence of the glass network and the structure stiffening. Some physical parameters were studied with increasing MoO3 content in the samples such as Ri, ri, rp, dB-B average coordination number, number of bonds, field strength of (Mo+3), the floppy modes, the cross-linking density and effective coordination number and found to be enhanced. Increasing MoO3 dopingconcentration from 0 – 5 mol % produced corresponding increase in fast neutron effective removal cross section ΣR from 0.07127 – 0.10825 cm-1, total cross section for thermal neutrons σT from 68.35875 – 105.7526 cm-1, and an increment in the cold neutron scattering cross section. Furthermore, the influence of MoO3 doping in the glasses is such that the stopping powers (Sp) and ranges RCSDA /Rp of electrons, proton, alpha particles, and carbon ion follows the trend: (Sp)BPAM-G1 > (Sp)BPAM-G2 > (Sp)BPAM-G3 >(Sp)BPAM-G4 > (Sp)BPAM-G5, and(RCSDA /Rp)BPAM-G1 > (RCSDA /Rp)BPAM-G2 > (RCSDA /Rp)BPAM-G3 > (RCSDA /Rp)BPAM-G4 > ((RCSDA /Rp)BPAM-G5 respectively. On the other hand, the doping produced no noticeable differences in the equivalent atomic number and the exposure buildup factor of the glasses.

Surface Stability and Morphology of Calcium Phosphate Tuned by pH Values and Lactic Acid Additives: Theoretical and Experimental Study

The ubiquitous mineralization of calcium phosphate (CaP) facilitates biological organisms to produce hierarchically structured minerals. The coordination number and strength of Ca2+ ions with phosphate species, oxygen-containing additives, and solvent molecules played a crucial role in tuning nucleation processes and surface stability of CaP under the simulated body fluid (SBF) or aqueous solutions upon the addition of oligomeric lactic acid (LACn, n=1, 8) and changing pH values. As revealed by ab initio molecular dynamics (AIMD), density functional theory (DFT), and molecular dynamics (MD) simulations as well as high-throughput experimentation (HTE), the binding of LAC molecules with Ca2+ ions and phosphate species could stabilize both pre-nucleation clusters and brushite (DCPD, CaHPO4·2H2O) surface through intermolecular electrostatic and hydrogen bonding interactions. When the concentration of Ca2+ ions ([Ca2+]) is very low, the amount of the formed precipitation decreased with the addition of LAC based on UV-Vis spectroscopic analysis due to the reduced chance for the LAC capped Ca2+ ions to coordinate with phosphates and the increased solubility in acid solution. With the increasing [Ca2+] concentration, the kinetically stable DCPD precipitation was obtained with high Ca2+ coordination number and low surface energy. Morphologies of DCPD precipitation are in plate, needle, or rod, depending on the initial pH values that tuned by adding NH3·H2O, HCl, or CH3COOH. The prepared samples at pH ≈ 7.4 with different Ca/P ratios exhibited negative zeta potential values, which were correlated with the surface electrostatic potential distributions and potential biological applications.

Crystal structure and Hirshfeld surface analysis of the anionic tetrakis-complex of lanthanum(III) NMe4LaL 4 with the CAPh-ligand dimethyl (2,2,2-trichloroacetyl)phosphoramidate

The anionic tetrakis-complex of lanthanum(III) NMe4LaL 4 with the CAPh-ligand dimethyl (2,2,2-trichloroacetyl)phosphoramidate (HL), namely, tetramethylammonium tetrakis{2,2,2-trichloro-1-[(dimethoxyphosphoryl)imino]ethanolato}lanthanum(III), (C4H12N)[La(C4H6Cl3NO4P)4], has been synthesized, crystallized and structurally characterized by X-ray diffraction. The lanthanide ion is surrounded by four anionic, bis-chelating CAPh ligands forming the complex anion with a coordination number of eight for La3+ and NMe4 + as the counter-ion. The coordination polyhedron of the La3+ ion was interpreted as a triangular dodecahedron.

Microstructural differences between naturally-deposited and laboratory beach sands

The orientation of, and contacts between, grains of sand reflect the processes that deposit the sands. Grain orientation and contact geometry also influence mechanical properties. Quantifying and understanding sand microstructure thus provide an opportunity to understand depositional processes better and connect microstructure and macroscopic properties. Using x-ray computed microtomography, we compare the microstructure of naturally-deposited beach sands and laboratory sands created by air pluviation in which samples are formed by raining sand grains into a container. We find that naturally-deposited sands have a narrower distribution of coordination number (i.e., the number of grains in contact) and a broader distribution of grain orientations than pluviated sands. The naturally-deposited sand grains orient inclined to the horizontal, and the pluviated sand grains orient horizontally. We explain the microstructural differences between the two different depositional methods by flowing water at beaches that re-positions and reorients grains initially deposited in unstable grain configurations.