Search results for "Crystal Structure"
showing 10 items of 15036 documents
Optical properties and microstructure of 2.02-3.30 eV ZnCdO nanowires: effect of thermal annealing
2013
International audience; ZnCdO nanowires with up to 45% Cd are demonstrated showing room temperature photoluminescence (PL) down to 2.02 eV and a radiative efficiency similar to that of ZnO nanowires. Analysis of the microstructure in individual nanowires confirms the presence of a single wurtzite phase even at the highest Cd contents, with a homogeneous distribution of Cd both in the longitudinal and transverse directions. Thermal annealing at 550 C yields an overall improvement of the PL, which is blue-shifted as a result of the homogeneous decrease of Cd throughout the nanowire, but the single wurtzite structure is fully maintained.
Tetrahedral versus octahedral Mn site coordination in wurtzite and rocksalt Zn1−xMnxO investigated by means of XAS experiments under high pressure
2007
Abstract We present the results of x-ray absorption measurements carried out in Zn 1− x Mn x O thin films under high pressure. The Mn environment remains essentially the same for nominal Mn concentrations given by x = 0.05 , 0.1, 0.15 and 0.25. Both the XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) indicate that Mn occupies the Zn site, being surrounded by four oxygen atoms at 2.02±0.01 A. The substitutional hypothesis is reinforced by comparing the differences between the ambient (wurtzite) and high pressure (rocksalt) spectra, which correspond to tetrahedral and octahedral Mn environments.
The substituent effect of π-electron delocalization in N-methylamino-nitropyridine derivatives: crystal structure and DFT calculations
2020
AbstractThe crystal and molecular structures of 3-(N-methylamino)-2-nitropyridine, 5-(N-methylamino)-2-nitropyridine and 2-(N-methylamino)-5-nitropyridine have been characterized by X-ray diffraction. To perform conformational analysis, the geometries of the compounds as well as their conformers and rotamers were optimized at the B3LYP/6-311++G(3df,3pd) level. The resulting data were used to analyze the π-electron delocalization effect in relation to the methylamino group rotation in ortho-, meta- and para-substitution positions. Quantitative aromaticity indices were calculated based on which we estimated the electronic structures of the analyzed compounds. The substituent effect of the met…
A novel MALDI-MS approach for the analysis of neutral metallosupramolecular architectures
2011
Matrix assisted laser desorption/ionisation mass spectrometry (MALDI-MS) methods have been developed for the characterisation of neutral [2×2] metallogrids derived fromdiimine, dihydrazone and diacylhydrazone ligands. Such grids may be protonated in solution to give cationic species but in most cases these are labile, so that rather delicate conditions are required for observation of the intact metallogrids as monoprotonated derivatives in the gas phase. As a MALDI matrix, 2,4,6-trihydroxyacetophenone (THAP) is sufficiently acidic to enable monoprotonation of the grids unaccompanied by dissociation, and if the grid sample is initially deposited by a layering technique to avoid any prelimina…
Two bimetallic layered materials with “Cu4Fe3” defective cubane units: syntheses, structures and magnetic properties of {[CuII(tn)]2[FeII(CN)6]}3·[Na…
2005
Abstract Reactions of the [Fe III (CN) 6 ] 3− anion with the [Cu II (tn)] 2+ ion (tn = 1,3-diaminopropane) afford the compounds {[Cu II (tn)] 2 [Fe II (CN) 6 ]}3·[Na 3 Fe III (CN) 6 ]·12H 2 O (1) and {[Cu n (tn)] 2 [Fe II (CN) 6 ]}·KCl·5H 2 O (2). Despite the differences concerning their asymmetric units, both structures present strong similar features: in both structures, the Cu(II) ion presents a square-base pyramidal CuN 5 environment and each [Fe II (CN) 6 ] 4− anion is linked to six Cu(II) ions through its six N atoms leading to infinite [Cu II (tn)] 2 [Fe II (CN) 6 ] layers which can be viewed as 2-D layered arrangement generated by the defective cubane units Cu 4 Fe 3 involving Fe-CN…
A versatile rigid binucleating ligand for Rh2(μ-Cl)2 moieties: its application as a catalyst in hydrogenation and cyclopropanation
2003
A rigid non-deforming "MCl 2 M" binucleating ligand [7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 ] - able to held the two rhodium atoms in a cooperative distance has been synthesized. The original two bridging chlorides are retained in [Rh 2 (C 5 Me 5 ) 2 Cl 2 {7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 }] + . Hydrogenation of 1-hexene is 10 times faster with [Rh 2 (C 5 Me 5 ) 2 Cl 2 {7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 }] + than with [Rh 2 (C 5 Me 5 ) 2 Cl 4 ]. A hydrogenation mechanism has been proposed which assumes that [Rh 2 (C 5 Me 5 ) 2 (Cl)(H){7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 }] + is the first generated species in the process.
Identification and H(D)-bond energies of C-H(D)Cl interactions in chloride-haloalkane clusters: a combined X-ray crystallographic, spectroscopic, and…
2016
The cationic (1,3,5-triazapentadiene)Pt(II) complex [Pt{NH[double bond, length as m-dash]C(N(CH2)5)N(Ph)C(NH2)[double bond, length as m-dash]NPh}2]Cl2 ([]Cl2) was crystallized from four haloalkane solvents giving [][Cl2(CDCl3)4], [][Cl2(CHBr3)4], [][Cl2(CH2Cl2)2], and [][Cl2(C2H4Cl2)2] solvates that were studied by X-ray diffraction. In the crystal structures of [][Cl2(CDCl3)4] and [][Cl2(CHBr3)4], the Cl(-) ion interacts with two haloform molecules via C-DCl(-) and C-HCl(-) contacts, thus forming the negatively charged isostructural clusters [Cl(CDCl3)2](-) and [Cl(CHBr3)2](-). In the structures of [][Cl2(CH2Cl2)2] and [][Cl2(C2H4Cl2)2], cations [](2+) are linked to a 3D-network by a syste…
Hydrogen-bonded networks of [Fe(bpp)2]2+spin crossover complexes and dicarboxylate anions: structural and photomagnetic properties
2016
The paper reports the syntheses, crystal structures, thermal and (photo)magnetic properties of spin crossover salts of formula [Fe(bpp)2](C6H8O4)·4H2O (1·4H2O), [Fe(bpp)2](C8H4O4)·2CH3OH·H2O (2·2MeOH·H2O) and [Fe(bpp)2](C8H4O4)·5H2O (2·5H2O) (bpp = 2,6-bis(pyrazol-3yl)pyridine; C6H8O4 = adipate dianion; C8H4O4 = terephthalate dianion). The salts exhibit an intricate network of hydrogen bonds between low-spin iron(II) complexes and carboxylate dianions, with solvent molecules sitting in the voids. Desolvation is accompanied by a low-spin (LS) to high-spin (HS) transformation in the materials. The dehydrated phase 2 undergoes a two-step transition with a second step showing thermal hysteresis…
A Ferroelectric Iron(II) Spin Crossover Material
2017
A dual-function material in which ferroelectricity and spin crossover coexist in the same temperature range has been obtained. Our synthetic strategy allows the construction of acentric crystal structures in a predictable way and is based on the high directionality of hydrogen bonds. The well-known iron(II) spin crossover complex [Fe(bpp)₂]²+ (bpp = 2,6-bis(pyrazol-3-yl)pyridine), a four-fold noncentrosymmetric H-bond donor, was combined with a disymmetric H-bond acceptor such as the isonicotinate (isonic) anion to afford [Fe(bpp)₂](isonic)₂·2H₂O. This low-spin iron(II) compound crystallises in the acentric nonpolar I-4 space group and shows piezoelectricity and SHG properties. Upon dehydra…
A new hydrogen bonding motif involved in self-recognition in the solid state by functionalised macrocycles
2011
Self-recognition within the crystal lattices of three functionalised macrocycles results in the formation of arrays of remarkably similar hermaphroditic pairs of macrocycles. In the case of two of the macrocycles containing acylhydrazine substituents, a hitherto unknown recognition pattern is found in the interaction of the hydrazine moiety with crown-ether oxygen atoms.