Structural Investigations of Colloidal Semiconductor Nanocrystal Heterostructures: Faceting and Epitaxy

1996 ◽  
Vol 452 ◽  
Author(s):  
A. V. Kadavanich ◽  
A. Mews ◽  
S. H. Tolbert ◽  
X. Peng ◽  
M. C. Schlamp ◽  
...  
Keyword(s):  
Point Group ◽  
Group Symmetry ◽  
X Ray Diffraction ◽  
Structural Investigations ◽  
Transmission Microscopy ◽  
Cds Quantum Dot ◽  
Show Evidence ◽  
Multi Wavelength ◽  
Heterogeneous Phase ◽  
Phase Proceeds

AbstractWe use High Resolution Transmission Microscopy (HRTEM) to study CdSe, CdS/HgS/CdS quantum-dot quantum well (QDQW), and CdSe/CdS core-shell nanocrystals, grown by wet-chemical techniques. The nanocrystals have faceted Wulff polyhedron shapes.In addition to HRTEM, we employ multi-wavelength anomalous dispersion (MAD) x-ray diffraction. We use computer modeling to help interpret the experimental data.Growth of a heterogeneous phase proceeds epitaxially preserving the overall shape and point-group symmetry of the original seed nanocrystals, both for wurtzite (CdSe/CdS) and zincblende (CdS/HgS/CdS) type structures.Recently prepared InAs nanocrystals also show evidence of faceting as observed by HRTEM and may lend themselves equally well to epitaxy.

scholarly journals Darstellung und Kristallstruktur von [(NH3)5Rh(H7O4)Rh(NH3)5](S2O6)2,5 · H2O (1). Ein gemischtes Aquopentamminrhodium(III)-hydroxopentamminrhodium(III)- dithionat mit einer neuartigen μ-H7O4-Struktureinheit / Preparation and Crystal Structure of [(NH3)5Rh(H7O4)Rh(NH3)5](S2O6)2,5 · H2O (1). A Mixed Aquopentaamminerhodium(III)-hydroxopentaamminerhodium(III) Dithionate with a Novel μ-H7O4 Structural Unit

1988 ◽  
Vol 43 (2) ◽  
pp. 189-195 ◽  
Author(s):  
Walter Frank ◽  
Thomas Stetzer ◽  
Ludwig Heck
Keyword(s):  
Crystal Structure ◽  
Structural Unit ◽  
Small Difference ◽  
Point Group ◽  
Group Symmetry ◽  
Monoclinic Space Group ◽  
Crystal Data ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray

The title compound 1 can be obtained from an aqueous solution of aquopentaammine rhodium(III) dithionate and hydroxopentaammine rhodium(III) dithionate. The crystal structure has been determined from single crystal X-ray diffraction data and refined to R = 0.035 for 4390 unique reflections. Crystal data: monoclinic, space group P21/c, a = 1300.9(5) pm. b = 1472.3(6) pm. c = 1478.8(9) pm, β = 106.20(4)°, Z = 4.In the crystal dinuclear rhodium cations with point group symmetry 1 (C1) are found. A central μ-H3O2-bridge is formed by strong hydrogen bonding between aquo and hydroxo ligands; this bridge is additionally coordinated by two molecules of water. The entire bridging system is therefore H7O4-(H3O2- · 2 H2O). O-O distances characterizing the strength of the three hydrogen bonds within this new kind of structural unit are O(H2O-Rh 1)-O(HO-Rh2): 248 pm. O(H2O-Rh 1)-O(H2Oa): 273 pm, O(HO-Rh2)-O(H2Ob): 287 pm. The hydrogen atoms involved in these bridges have been located. The small difference in the Rh 1-O(H2O) - (205.4(3) pm) and Rh2-O(OH)- (204.3(3) pm) distances indicates that the entire H7O4-- moiety serves as a μ-bridging unit between Rh 1 and Rh 2

scholarly journals Redetermination of the crystal structure of caesium tetrafluoridobromate(III) from single-crystal X-ray diffraction data

IUCrData ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Artem V. Malin ◽  
Sergei I. Ivlev ◽  
Roman V. Ostvald ◽  
Florian Kraus
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Diffraction Data ◽  
Point Group ◽  
Group Symmetry ◽  
Site Symmetry ◽  
X Ray Diffraction ◽  
Cation Site ◽  
X Ray ◽  
Square Planar

Caesium tetrafluoridobromate(III), CsBrF4, was crystallized in form of small blocks by melting and recrystallization. The crystal structure of CsBrF4 was redetermined from single-crystal X-ray diffraction data. In comparison with a previous study based on powder X-ray diffraction data [Ivlev et al. (2013). Z. Anorg. Allg. Chem. 639, 2846–2850], bond lengths and angles were determined with higher precision, and all atoms were refined with anisotropic displacement parameters. It was confirmed that the structure of CsBrF4 contains two square-planar [BrF4]− anions each with point group symmetry mmm, and a caesium cation (site symmetry mm2) that is coordinated by twelve fluorine atoms, forming an anticuboctahedron. CsBrF4 is isotypic with CsAuF4.

scholarly journals Phase transition sequences in tetramethylammonium tetrachlorometallates by X-ray diffraction and spectroscopic measurements

2017 ◽  
Vol 73 (5) ◽  
pp. 844-855 ◽  
Author(s):  
Jack Binns ◽  
Garry J McIntyre ◽  
José A. Barreda-Argüeso ◽  
Jesús González ◽  
Fernando Aguado ◽  
...  
Keyword(s):  
Phase Transition ◽  
Point Group ◽  
Lone Pair ◽  
Group Symmetry ◽  
First Principles Calculations ◽  
X Ray Diffraction ◽  
Intermediate Phases ◽  
Increasing Temperature ◽  
First Time ◽  
Prototype Phase

The phase transition sequences of two members of the tetramethylammonium tetrachlorometallate(III) family of hybrid organic–inorganic salts have been determined and structurally characterized as a function of temperature for the first time. Unusually, a reduction in point-group symmetry with increasing temperature until reaching a cubic prototype phase is observed. Two additional intermediate phases are observed for Fe3+. First-principles calculations and the presence of short Cl...Cl contacts for Ga3+suggest the [GaCl4]−anion to be conformationally hindered due to stronger lone-pair–σ-hole interactions. The conformationally more flexible Fe3+structures show sublattice melting with the onset of rotational disorder in the [NMe4]+cations occurring 40 K below the corresponding onset of rotational disorder in the [FeCl4]−sublattice.

scholarly journals Group 11 Pincer Oxazoline Complexes

2021 ◽  
Author(s):  
Mahroo T. Seighalani
Keyword(s):  
Point Group ◽  
Diffraction Method ◽  
Binding Mode ◽  
Group Symmetry ◽  
Pincer Complexes ◽  
Pincer Ligands ◽  
Henry Reaction ◽  
X Ray Diffraction ◽  
Pincer Ligand ◽  
Nitroaldol Reaction

The synthesis and characterization of new copper pincer complexes via cyclometallation of potentially anionic pincer ligands with C1 point group symmetry is reported. All of these complexes have been characterized by single crystal X-ray diffraction method, which confirms the proposed tridentate binding mode of pincer ligand and the formation of an amido N-Cu bond. The reactivity of two of the complexes was investigated towards C-C bond formation reaction, notably the Henry reaction. One of the complexes, which was derived from the achiral pincer ligand, is shown to be a suitable catalyst for the Henry reaction under the standard conditions. The Henry or nitroaldol reaction is one of the organic reactions which affords a C-C bond. The product of this reaction is a β-nitro alcohol which is formed by addition of a nitroalkane to a carbonyl compound.

scholarly journals Syntheses and crystal structures of 2-(p-tolyl)-1H-perimidine hemihydrate and 1-methyl-2-(p-tolyl)-1H-perimidine

2022 ◽  
Vol 78 (2) ◽  
Author(s):  
Paulina Kalle ◽  
Sergei V. Tatarin ◽  
Marina A. Kiseleva ◽  
Alexander Yu. Zakharov ◽  
Daniil E. Smirnov ◽  
...  
Keyword(s):  
Water Molecule ◽  
Crystal Structures ◽  
Crystal Packing ◽  
Rotation Axis ◽  
Point Group ◽  
Group Symmetry ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
H Nmr ◽  
Rotation Axes

The title compounds, 2-(4-methylphenyl)-1H-perimidine hemihydrate (1, C18H14N2·0.5H2O) and 1-methyl-2-(4-methylphenyl)-1H-perimidine (2, C19H16N2), were prepared and characterized by 1H NMR and single-crystal X-ray diffraction. The organic molecule of the hemihydrate lies on a twofold rotation axis while the water molecule lies on the intersection of three twofold rotation axes (point group symmetry 222). As a consequence, the hydrogen atoms that are part of the N—H group and the water molecule as well as the CH3 group of the p-tolyl ring are disordered over two positions. In compound 1, the perimidine and the 2-aryl rings are slightly twisted while its N-methylated derivative 2 has a more distorted conformation because of the steric repulsion between the N-methyl group and the 2-aryl ring. In the crystal structures, molecules of perimidine 2 are held together only by C—H...π contacts while the parent perimidine 1 does not exhibit this type of interaction. Its crystal packing is established by intermolecular N—H...O hydrogen bonds with the solvent water molecules and additionally stabilized by π–π stacking.

scholarly journals Formazanate Complexes of Bis-Cyclometalated Iridium

2019 ◽  
Author(s):  
Evanta Kabir ◽  
Ge Mu ◽  
David A. Momtaz ◽  
Noah A. Bryce ◽  
Thomas Teets
Keyword(s):  
Point Group ◽  
Binding Mode ◽  
Group Symmetry ◽  
Binding Modes ◽  
X Ray Diffraction ◽  
Substitution Pattern ◽  
X Ray ◽  
Redox Active ◽  
Symmetric Geometry ◽  
New Compounds

<div>In this work we describe a series of bis-cyclometalated iridium(III) formazanate complexes, expanding the coordination chemistry of the redox-active formazanate class to iridium. A total of 18 new complexes are described, varying the substituent pattern on the formazanate and the identity of the cyclometalating ligand on iridium. Eight of the new compounds are structurally characterized by single-crystal X-ray diffraction, which along with NMR spectroscopy evinces two binding modes of the formazanate. Two of the compounds are isolated in a C2-symmetric geometry where the formazanate is bound in a six-member chelate “closed” conformation, involving the 1- and 5-positions of the 1,2,4,5-tetraazapentadienyl formazanate core. In most of the examples, the major isomer that forms and is exclusively isolated involves the formazanate bound in a five-member chelate “open” form, coordinating through the 1- and 4-positions of the formazanate core and resulting in C1 point-group symmetry. All complexes are characterized by UV-vis absorption spectroscopy and cyclic voltammetry, with these features depending primarily on the substitution pattern on the formazanate, and to a lesser extent on the identity of the cyclometalating ligand and formazanate binding mode.</div>

Das neue komplexe Barium-Mercurid Ba20Hg103 und seine ternären Zink- und Cadmium-Varianten / The New Complex Barium Mercuride Ba20Hg103 and its Ternary Zinc and Cadmium Variants

2012 ◽  
Vol 67 (9) ◽  
pp. 893-906 ◽  
Author(s):  
Marco Wendorff ◽  
Caroline Röhr
Keyword(s):  
Point Group ◽  
Chemical Properties ◽  
Structure Type ◽  
Zinc Atom ◽  
Group Symmetry ◽  
X Ray Diffraction ◽  
Covalent Bonds ◽  
Covalently Bonded ◽  
Small Change ◽  
Diamond Type

Ba20Hg103, the next Hg-rich binary barium mercuride after BaHg11 and BaHg6, was synthesized from melts of the elements, which were slowly cooled from 550 to 200 °C. It forms a new complex cubic structure type (F43m, a = 2333.30(10) pm, Z = 4, R1 = 0.0651) with four Ba und 13 Hg positions as determined by means of single-crystal X-ray diffraction. The structure can be best described by decomposing it into four types (A to D) of space-filling distorted truncated octahedra (sodalite or b-cages) centered at the four sites with 43m point group symmetry of the space group. The cages C and D are centered by [Hg8] tetrahedra stars, which are connected via [Hg(13)Hg8] cubes to form a diamond-type network. The polyhedra B contain a section of the Laves phaseMgCu2 (five [Hg4] tetrahedra sharing corners). The smallest polyhedron A contains a truncated tetrahedron [HgHg12] surrounded by a strongly covalently bonded mercury shell. The ternary cadmium derivative Ba20Cd4Hg99 (a = 2331.57(14) pm, R1 = 0.0465) is isotypic, whereas in the related zinc mercuride Ba20Zn5Hg99 (a = 2332.33(7) pm, R1 = 0.0436) one of the tetrahedra stars is filled by an extra zinc atom and is thus distorted into a [ZnHg8] cube. This extra zinc atom causes the small change in the compounds formula. The four crystallographically different Ba cations are coordinated by 17 or 18 Hg atoms. The mercury atoms themselves are surrounded by 10 to 13, in one case 16, Hg=Ba neighbors. The shortest Hg-Hg distances (dminHg-Hg = 285:8 pm) are found for the strong covalent bonds in the shell around the sodalite cages A and the cubes around Hg(13). The bonding modes (Hg-Hg distances and overall coordinations numbers) of the different Hg atoms of Ba20Hg103 are discussed in comparison with those in the more Hg-rich compounds BaHg6 and BaHg11. According to their crystal-chemical properties, the Hg atoms in Hg-rich mercurides can be classified into four different groups, from mainly covalent to polar intermetallic and pure metallic, to finally cationic centers

scholarly journals Redetermination of the crystal structure of β-zinc molybdate from single-crystal X-ray diffraction data

2015 ◽  
Vol 71 (7) ◽  
pp. i6-i7 ◽  
Author(s):  
Olfa Mtioui-Sghaier ◽  
Rafael Mendoza-Meroño ◽  
Lilia Ktari ◽  
Mohamed Dammak ◽  
Santiago García-Granda
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Diffraction Data ◽  
Point Group ◽  
Structure Type ◽  
Group Symmetry ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Anisotropic Displacement Parameters

The crystal structure of the β-polymorph of ZnMoO4was re-determined on the basis of single-crystal X-ray diffraction data. In comparison with previous powder X-ray diffraction studies [Katikaneani & Arunachalam (2005).Eur. J. Inorg. Chem. pp. 3080–3087; Cavalcanteet al.(2013).Polyhedron,54, 13–25], all atoms were refined with anisotropic displacement parameters, leading to a higher precision with respect to bond lengths and angles. β-ZnMoO4adopts the wolframite structure type and is composed of distorted ZnO6and MoO6octahedra, both with point group symmetry 2. The distortion of the octahedra is reflected by variation of bond lengths and angles from 2.002 (3)–2.274 (4) Å, 80.63 (11)–108.8 (2)° for equatorial and 158.4 (2)– 162.81 (14)° for axial angles (ZnO6), and of 1.769 (3)–2.171 (3) Å, 73.39 (16)–104.7 (2), 150.8 (2)–164.89 (15)° (MoO6), respectively. In the crystal structure, the same type ofMO6octahedra share edges to built up zigzag chains extending parallel to [001]. The two types of chains are condensed by common vertices into a framework structure. The crystal structure can alternatively be described as derived from a distorted hexagonally closed packed arrangement of the O atoms, with Zn and Mo in half of the octahedral voids.

scholarly journals Group 11 Pincer Oxazoline Complexes

2021 ◽  
Author(s):  
Mahroo T. Seighalani
Keyword(s):  
Point Group ◽  
Diffraction Method ◽  
Binding Mode ◽  
Group Symmetry ◽  
Pincer Complexes ◽  
Pincer Ligands ◽  
Henry Reaction ◽  
X Ray Diffraction ◽  
Pincer Ligand ◽  
Nitroaldol Reaction

The synthesis and characterization of new copper pincer complexes via cyclometallation of potentially anionic pincer ligands with C1 point group symmetry is reported. All of these complexes have been characterized by single crystal X-ray diffraction method, which confirms the proposed tridentate binding mode of pincer ligand and the formation of an amido N-Cu bond. The reactivity of two of the complexes was investigated towards C-C bond formation reaction, notably the Henry reaction. One of the complexes, which was derived from the achiral pincer ligand, is shown to be a suitable catalyst for the Henry reaction under the standard conditions. The Henry or nitroaldol reaction is one of the organic reactions which affords a C-C bond. The product of this reaction is a β-nitro alcohol which is formed by addition of a nitroalkane to a carbonyl compound.

scholarly journals Crystal structure of tetrawickmanite, Mn2+Sn4+(OH)6

2015 ◽  
Vol 71 (2) ◽  
pp. 234-237 ◽  
Author(s):  
Barbara Lafuente ◽  
Hexiong Yang ◽  
Robert T. Downs
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Point Group ◽  
The Other ◽  
Group Symmetry ◽  
Tetragonal Symmetry ◽  
Point Group Symmetry ◽  
Natural Sample ◽  
X Ray Diffraction ◽  
X Ray

The crystal structure of tetrawickmanite, ideally Mn2+Sn4+(OH)6[manganese(II) tin(IV) hexahydroxide], has been determined based on single-crystal X-ray diffraction data collected from a natural sample from Långban, Sweden. Tetrawickmanite belongs to the octahedral-framework group of hydroxide-perovskite minerals, described by the general formulaBB'(OH)6with a perovskite derivative structure. The structure differs from that of anABO3perovskite in that theAsite is empty while each O atom is bonded to an H atom. The perovskiteB-type cations split into orderedBandB′ sites, which are occupied by Mn2+and Sn4+, respectively. Tetrawickmanite exhibits tetragonal symmetry and is topologically similar to its cubic polymorph, wickmanite. The tetrawickmanite structure is characterized by a framework of alternating corner-linked [Mn2+(OH)6] and [Sn4+(OH)6] octahedra, both with point-group symmetry -1. Four of the five distinct H atoms in the structure are statistically disordered. The vacantAsite is in a cavity in the centre of a distorted cube formed by eight octahedra at the corners. However, the hydrogen-atom positions and their hydrogen bonds are not equivalent in every cavity, resulting in two distinct environments. One of the cavities contains a ring of four hydrogen bonds, similar to that found in wickmanite, while the other cavity is more distorted and forms crankshaft-type chains of hydrogen bonds, as previously proposed for tetragonal stottite, Fe2+Ge4+(OH)6.

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