Search results for " Crystal"
showing 10 items of 3073 documents
Synthesis, characterization and magnetic study of two new octahedral iron(III) complexes with pendant zwitterionic Schiff bases
2016
Two Schiff bases, HL1 [2-((3-(dimethylamino)propylimino)methyl)-5-bromophenol] and HL2 [2-((2-(diethylamino)ethylimino)methyl)-6-methoxyphenol], have been employed to prepare two new octahedral iron(III) complexes, [Fe(HL1)2(N3)2]ClO4·2H2O (1) and [Fe(HL2)2(NCS)2]ClO4·H2O (2). Both complexes are characterized by spectral and elemental analyses. Single crystal X-ray diffraction studies confirm their structures. In both complexes, Schiff bases are trapped in their zwitterionic forms and coordinated to iron(III) only through the imine nitrogen and phenoxo oxygen, i.e., they behave as bi-dentate ligands, keeping the remaining potential donor sites pendant. The measurement of χM vs. T for both c…
Spontaneous Resolution of an Electron‐Deficient Tetrahedral Fe4L4cage
2015
A highly electron-deficient C3-symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)2, thereby resulting in the homochiral assembly of a new family of robust tetrahedral M4L4 cages. This homochiral T-symmetric cage containing a relatively large cavity of 330 A(3) is capable of encapsulating an anionic guest, as was determined by mass spectrometry, (19)F NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH3CN led to crystals containing both (ΔΔΔΔ and ΛΛΛΛ) enantiomers, while crystallization from CH3 OH resulted in crystals containing only the right-handed (ΔΔΔΔ) cage. The difference in the…
Synthesis and characterization of ethylene-1-hexene copolymers prepared by using MgCl2(THF)2-supported Ziegler-Natta catalysts
2000
Ethylene was copolymerized with 1-hexene over vanadium (VOCl3 and VCl4) and titanium (TiCl4) catalysts supported on MgCl2(THF)2 and activated with Et2AlCl. So far these catalyst systems have not been known as initiators of ethylene-1-hexene copolymerization. The vanadium catalysts were more active than the titanium catalyst and, at identical comonomer concentrations in the feed, gave rise to a greater incorporation of 1-hexene into the copolymer. Even at relatively low fractions of 1-hexene, the MgCl2(THF)2-supported catalysts affected much the copolymer properties like density, melting point and crystallinity.
Synthesis, structural, and thermal characterization of a new binuclear copper(II) chelate complex bearing an amine-hardener for epoxy resins
2016
A new di(μ-carbonato)bis[aqua(diethylenetriamine)copper(II)] hexahydrate complex, [{Cu(NH(C2H4NH2)2)(H2O)(μ-CO3)}2]⋅6H2O (1), was synthesized by direct interaction of malachite with diethylenetriamine (dien). The crystals of 1 were characterized by X-ray powder diffraction and IR spectra, as well as structurally characterized. Compound 1 consists of [{Cu(dien)(H2O)(μ-CO3)}2] discrete units whose CO32– anions play the role of bridging ligands combining two Cu(II) chelate cores into a centrosymmetric dimer. The elongated octahedral environment of Cu2+ consists of three nitrogens of dien and an oxygen from CO32– at the base of the bipyramid; the two apical positions of such polyhedron are occu…
Discrete exterior calculus for photonic crystal waveguides
2022
The discrete exterior calculus (DEC) is very promising, though not yet widely used, discretization method for photonic crystal (PC) waveguides. It can be seen as a generalization of the finite difference time domain (FDTD) method. The DEC enables efficient time evolution by construction and fits well for nonhomogeneous computational domains and obstacles of curved surfaces. These properties are typically present in applications of PC waveguides that are constructed as periodic structures of inhomogeneities in a computational domain. We present a two-dimensional DEC discretization for PC waveguides and demonstrate it with a selection of numerical experiments typical in the application area. …
First results of the experiment to search for 2β decay of 106Cd with the help of 106CdWO4 crystal scintillators
2011
An experiment to search for 2β processes in 106Cd with the help of 106CdWO4 crystal scintillator (mass of 215 g), enriched in 106Cd up to 66 %, is in progress at the Gran Sasso National Laboratories of the INFN (Italy). After 1320 h of data taking, limits on double beta processes in 106Cd have been established on the level of 1019 − 1020 yr, in particular (all the results at 90 % C.L.): T1/2(0ν2ε) > 3.6 · 1020 yr, T1/2(2νεβ+) > 7.2 · 1019 yr, and T1/2(2ν2β+) > 2.5 · 1020 yr. Resonant 0ν2ε processes have been restricted as T1/2(0ν2K) > 1.4 · 1020 yr and T1/2(0νLK) > 3.2 · 1020 yr. A possible resonant enhancement of the 0ν2ε processes is estimated in the framework of the QRPA approach.
Optical investigation of spin-crossover in cobalt(II) bis-terpy complexes
2007
Abstract The spin transition of the [Co(terpy) 2 ] 2+ complex (terpy = 2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy) 2 ](ClO 4 ) 2 shows an asymmetric absorption band at 14 400 cm −1 with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing te…
Lack of cross‐resistance to otherBacillus thuringiensiscrystal proteins in a population ofPlutella xylostellahighly resistant to cryia(b)
1994
Competition experiments were performed with brush border membrane vesicles of diamondback moth larvae using 125I‐labelled CryIA(b) and unlabelled CryIA(a), CryIA(b) and CryIA(c). The results suggested a model with a single binding site for CryIA(b). Heterologous competition showed that CryIA(c) competed as effectively as CryIA(b) for the CryIA(b) binding site, whereas CryIA(a) competed less effectively. Toxicity tests were performed on third instar larvae with trypsin‐activated insecticidal crystal proteins (ICPs) and a commercial formulation of Bacillus thuringiensis (Bt) (Dipel). A laboratory colony was found to be susceptible to all four ICPs tested and to Dipel. CryIA(b), CryIA(c) and C…
A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons
2001
It is shown, by means of Hartree-Fock-type calculations using the intermediate neglect of the differential overlap (INDO) method, that polaronic-type charge transfer vibronic excitons (CTVE) in ferroelectric oxides could lead to the formation of a new phase. The ground-state energy of this phase of strongly correlated CTVE lies within an optical gap of pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as ferroelectric and antiferromagnetic ordering. It is shown also that clusters of the CTVE phase being stabilized by oxygen vacancies could be responsible for the unusually strong optical Second Harmonic Generation (SHG) in nominally pure incipient ferroele…
Active photonic crystals based on surface acoustic waves
2003
An active photonic crystal (PC) based on the modulation of a one-dimensional cavity resonator by electrically-generated surface acoustic waves is described. The high nonthermal population of surface modes combined with the enhanced Brillouin scattering in the cavity increases the intensity of the scattered light to values comparable to the excitation intensity. This process is employed to switch and modulate light beams in PCs.