Search results for "tetrahedron"
showing 10 items of 75 documents
Computational chemistry meets experiments for explaining the geometry, electronic structure, and optical properties of Ca10V6O25
2018
In this paper, we present a combined experimental and theoretical study to disclose, for the first time, the structural, electronic, and optical properties of Ca10V6O25 crystals. The microwave-assisted hydrothermal (MAH) method has been employed to synthesize these crystals with different morphologies, within a short reaction time at 120 °C. First-principle quantum mechanical calculations have been performed at the density functional theory level to obtain the geometry and electronic properties of Ca10V6O25 crystal in the fundamental and excited electronic states (singlet and triplet). These results, combined with the measurements of X-ray diffraction (XRD) and Rietveld refinements, confirm…
High-pressure transition to the post-barite phase in BaCrO4hashemite
2012
A recent high-pressure study on barium chromate BaCrO${}_{4}$ reported a phase transition but the structure of the high-pressure phase structure could not be identified. This high-pressure phase was suggested to have a monoclinic structure different from other high-pressure forms of $AB$O${}_{4}$-type compounds. In this work, we have carried out x-ray diffraction measurements up to 46 GPa using He as the quasihydrostatic pressure medium and density-functional theory calculations. Our studies allow us to identify the high-pressure phase as the $P$2${}_{1}$2${}_{1}$2${}_{1}$ post-barite-type phase, recently reported for BaSO${}_{4}$. The equations of state of both, the low- and the high-press…
First principles simulation of amorphous InSb
2013
Ab initio molecular dynamics simulations based on density functional theory have been performed to generate a model of amorphous InSb by quenching from the melt. The resulting network is mostly tetrahedral with a minor fraction ($10%$) of atoms in a fivefold coordination. The structural properties are in good agreement with available x-ray diffraction and extended x-ray-absorption fine structure data and confirm the proposed presence of a sizable fraction of homopolar In-In and Sb-Sb bonds whose concentration in our model amounts to about $20%$ of the total number of bonds.
Effect of Substituents on the Molecular Shapes of π-Basic Macrotricyclic Receptors
2010
Molecular recognition between receptor and substrate is optimized when these compounds show complementary shapes, sizes, and interacting moieties. A family of C3v-symmetric macrotricycles 1–4 is presented that incorporate resorcinol- and mesitylene-derived “walls” and “cap”, respectively. These compounds feature, in principle, a tetrahedral π-basic cavity. This paper reports the effect of substituents in the “walls” and the “cap” on the shapes of the macrotricycles in solution (1H NMR), the solid state (X-ray diffraction), and gas phase (calculations). Substitution of the lower position of the “walls” by Br (in 3) or MeS (in 4) has the same effect as ethyl substitution of the “cap” (in 2), …
Electron-deficient trifluoromethyl-substituted sub-components affect the properties of M4L4 tetrahedral cages
2017
Two supramolecular tetrahedral cages based on a new electron-deficient trifluoromethyl-substituted pyridylimine ligand are synthesised by sub-component self-assembly. Their structures are characterised by NMR und UV-Vis spectroscopy, high-resolution mass spectrometry and single crystal X-ray diffraction. The iron(II) complex shows host–guest chemistry, complex-to-complex transformations and novel electronic properties.
Some Improvements on Relativistic Positioning Systems
2018
[EN] We make some considerations about Relativistic Positioning Systems (RPS). Four satellites are needed to position a user. First of all we define the main concepts. Errors should be taken into account. Errors depend on the Jacobian transformation matrix. Its Jacobian is proportional to the tetrahedron volume whose vertexes are the four tips of the receiver-satellite unit vectors. If the four satellites are seen by the user on a circumference in the sky, then, the Jacobian and the tetrahedron volume vanish. The users we consider are spacecraft. Spacecraft to be positioned cannot be close to a null Jacobian satellites-user configuration. These regions have to be avoided choosing an appropr…
Structure and Magnetic Properties of the Ferromagnetic Cu3Cl126- Trimer in [(NH3C2H4)3NH]2Cu3Cl14
2004
The crystal structure consists of a strongly hydrogen bonded network of tris(N-ethylammonium)ammonium cations, Cu3Cl12(6)- trimeric species, and Cl- anions. The Cu3Cl12(6)- trimers are formed by two distorted tetrahedral CuCl4(2)- anions linked to a central square planar CuCl4(2)- anion via semicoordinate Cu-Cl...Cu mu1 bridges. The central copper ion shows only small deviations from ideal D4h symmetry, while the terminal copper ions show a mild distortion from D2d symmetry with an average trans Cl-Cu-Cl angle of 136.0 degrees. The semicoordinate linkages provide a ferromagnetic exchange pathway between the copper ions with J/k = 6.91(3) K. Short Cl...Cl contacts (3.67-3.90 angstoms) lead t…
Über zinn-haltige heterocyclen
1983
Abstract The crystal structure of 2,2,6-trimethyl-1,3-dithia-6-aza-2-stannocane has been determined and refined to R = 0.043. The transannular 1,5-distance Sn ⋯ N = 256.6(6) pm exceeds the respective single bond by 49 pm. A comparison with analogous eight-membered rings exhibits a clear-cut correlation of such differences with angle deformations in the transition tetrahedron to trigonal-bipyramid. The axial distance SnC is 2 pm longer than the equatorial one.
Molekül- und kristallstruktur von hexamethylcyclo-tristannaselenan [(CH3)2SnSe]3
1978
Hexamethylcyclotristannaselenane [(CH3)2SnSe]3 forms tetragonal crystals, space groups P41212, with a 986.5(2), c 1769.7(4) pm, Z 4. The complete X-ray structural analysis (two independent determinations) shows the six-membered ring to have a twist-boat conformation similar to [(CH3)2SnS]3. The SnSe2C2 tetrahedra are only slightly distorted, the mean bond distances being SnSe 253.1 (251.7⋯254.0(4)) pm, Sn C 2.13 (2.09⋯2.17(3)) pm. Conformational details are discussed.
Heterocyclic systems containing tin(IV)—XIII [1]. Possible ceasing or inversion of the structuraltrans influence during the course of a bimolecular n…
1997
Abstract In the series of the heterocycles X[(CH2)3]2SnR2 (16 newly synthesized compounds and two taken from the literature) and in the germanium analog BuiN[(CH2)3]2GeCl2, the donor group X (= NMe, NBz, NBui, NPri, O, S) intramolecularly attacks the Lewis acidic atoms Sn or Ge. Eight structure determinations (and, in addition, 2 taken from the literature) are compared. The nucleophilic attack at Sn is stronger for the ligands R2 =Cl2 than for the more electronegative R2 = (OSiPh3)2. Overall the familiartrans influence holds: simultaneous approach of X and weakening of the ligand R (trans). In three cases of subtly graded donor strength a slight inversion or ceasing is observed: shorter dis…