Density Functional Study of Calcium Nitride

The high-pressure behavior of Ca3N2 is studied up 100 GPa using density functional theory. Evaluation of many hypothetical polymorphs of composition A3X2 leads us to propose four high-pressure polymorphs for both α- and β-Ca3N2: (1) an anti-Rh2O3−II structure at 5 GPa, (2) an anti-B-sesquioxide structure at 10 GPa, (3) an anti-A-sesquioxide structure at 27 GPa, and (4) a hitherto unknown hexagonal structure (P63/mmc), derived from the post-perovskite structure of CaIrO3, at 38 GPa. The development of the density and bulk modulus under pressure has been examined

N,N'-(p-Phenylene)dibenzamide (PPDB)

C20N202H16, monoclinic, P2~/c, a = 18.065(1), b = 5.247(1), c = 8.027(1) A, fl = 93.99 (1) °, Z = 2. The crystal structure has been refined by least-squares techniques. R w = 7.3%. The structure contains planar phenyl rings which are\ud rotated with respect to the plane of the amide group owing to steric hindrance. The molecules are connected in one dimension by means of hydrogen bonds

Trisodium Trimetaphosphimate Monohydrate

The trimetaphosphimate anion (PO2NH)33- in trisodium cyclo-tri--imidotriphosphate monohydrate, Na3(PO2NH)3.H2O, exhibits a chair conformation. Two trimetaphosphimate rings are linked to each other by six N-HO hydrogen bonds forming pairs. These units are interconnected by O-HO hydrogen bonds through water molecules forming columns

Determination of the relative concentrations of rare earth ions by x-ray absorption spectroscopy: Application to terbium mixed oxides

A method, based on X-ray absorption spectroscopy (XAS) in the range 0.8–1.5 keV, to determine the relative amounts of rare earth ions in different valencies is explained and tested for the case of terbium mixed oxides. The results are in agreement with those obtained by existing analytical methods. The XAS method is advantageous in that it can be applied where other, conventional, methods break down

Hexakis(dimethylformamide)bis(hexaphenylcyclohexasiloxanehexaolato)hexacopper(II) Dimethylformamide Solvate

The sandwich-like title complex, hexakis(dimethylformamide)-1O,2O,3O,4O,5O,6O-bis[2,4,6,8,10,12-hexaphenylsiloxane-2,4,6,8,10,12-hexaolato(6-)-1:22O1,2:32O2,3:42O3,- 4:52O4,5:62O5,1:62O6]hexacopper(II) tetrakis(dimethylformamide) solvate, [Cu6(C3H7NO)6{(C6H5)6O12Si6}2].4C3H7NO, is comprised of two regular crown-shaped macrocyclic hexadentate organosiloxanolate ligands chelating a flat Cu6 hexagon, as in the ethanol-solvated analogue investigated previously. The title complex has a more distorted shape than the trigonal ethanol-solvated analogue, being slightly side-oblated, but still contains a large empty inner channel accessible by small molecules (the diameter of the free cross-section being about 2.5 Å). Each CuII ion has square-pyramidal coordination with four basal siloxanolate O atoms and an apical dimethylformamide (DMFA) molecule (coordinated through its carbonyl group). The average bond lengths are: Cu-O(Si) 1.964 (11) Å and Cu-O(DMFA) 2.215 (10) Å. The structure contains four additional DMFA molecules per complex unit, linked by weak C-HO hydrogen bonds. Unexpectedly, the C=O bond length is longer [1.248 (10) and 1.255 (9) Å] in the uncoordinated DMFA molecules than in the coordinated [1.214-1.227 (7) Å]

Electronic properties of silica nanowires

Thin nanowires of silicon oxide were studied by pseudopotential density functional electronic structure calculations using the generalized gradient approximation. Infinite linear and zigzag Si-O chains were investigated. A wire composed of three-dimensional periodically repeated Si4O8 units was also optimized, but this structure was found to be of limited stability. The geometry, electronic structure, and Hirshfeld charges of these silicon oxide nanowires were computed. The results show that the Si-O chain is metallic, whereas the zigzag chain and the Si4O8 nanowire are insulators