1,721,036 research outputs found
New anilino tropone-based titanium complexes: synthesis, characterization and application as catalysts for olefin polymerization
No full textNew titanium(IV) dichloride complexes containing 2-anilinotropone ligands have been synthesized and characterized.
Bis(ligand)titanium dichloride complexes 1 and 2 were synthesized from reaction of TiCl4(THF)2 with 2 equivalents
of the corresponding sodium salts of 2-(2,6-diisopropylanilino)tropone (L1) and 2-(2,3,4,5,6-pentafluoroanilino)-
tropone (L2), respectively. The mixed cyclopentadienyl–anilinotropone compound 3 was synthesized by reaction of
the lithium salt of L2 with CpTiCl3. The Cp-mixed l-O bimetallic complex 4 was also isolated as a by-product owing
to the adventitious presence of moisture. The molecular structures of 1–4 have been determined by single-crystal
X-ray diffraction studies. Complexes 1 and 2 are isostructural and exhibit a C2-symmetric octahedral geometry, with
a trans (N,N), cis (O,O) arrangement in complex 1, but with a trans (O,O), cis (N,N) arrangement in complex 2. The
Cp-mixed complex 3 has a distorted square-pyramidal structure with the Cp ligand in the apical position. Bimetallic
complex 4 shows a similar coordination geometry for the five-coordinate titanium atom and a pseudo-tetrahedral
coordination for the second metallic centre. All new complexes, when activated with methylaluminoxane, are active in
the polymerization of ethylene and propene
Two tridentate pyridinyl-hydrazone zinc(II) complexes as fluorophores for blue emitting layers
No full textTwo new complexes were obtained by reaction of zinc (II) acetate with 4-fluoro-N'-(pyridin-2-ylmethylene) benzohydrazide or with 4-(hexyloxy)-N'-(pyridin-2-ylmethylene)benzohydrazide ligands in pyridine. Both ligands have a pyridinyl-hydrazone moiety able to act as a mono-negative tridentate ligand toward zinc ion in 2:1 stoichiometric ratio, producing an octahedral environment. The derived complexes are poor emitters in diluted solution. Instead, they exhibit intense blue fluorescence in the solid state due to AIE (aggregation induced emission) effect. The crystalline complexes are bright yellow in natural light and blue under UV–visible light with remarkable Stokes Shifts. Their photoluminescence quantum yields are ranging 20–30%, making them very promising as fluorophore dopants for blue emissive layers. One ligand and its complex were characterized by single crystal X-ray diffraction analysis that revealed an almost planar conformation of two ligands coordinated to the metal and the presence of significant π-π stacking of molecules at about 3.4 Å
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A highly water-soluble fluorescent and colorimetric pH probe
Full text linkA new 5-(4-((2-(benzothiazole-2-carbonyl)hydrazono)methyl)-3-hydroxyphenoxy)N,N,N-trimethylpentan-1-aminium bromide (BTABr) fluorescent and colorimetric pH probe was easily synthesized by the condensation reaction of benzothiazole-2-carbohydrazide with 5-(4-formyl-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1-aminium bromide. The benzothiazole moiety provided the emissive part of the molecule and the charged trimethyl amino group guaranteed outstanding solubility in water, for an organic molecule. pH titration experiments indicated that the probe is useful for monitoring acidic and alkaline solutions, turning reversibly in color/fluorescence just at a neutral pH value. Naked-eye colorimetric response was observed both in solution and in the solid state. In addition, the probe showed high stability and selectivity and large Stokes shifts. Because of these features, BTABr can potentially work as an on-off real-time pH sensor for intracellular pH imaging. The crystal structure of BTABr examined by single-crystal analysis showed a planar geometry of the molecule and confirmed the presence of a molecular stacking between molecules joined in a complex tridimensional hydrogen bonding pattern
Structure and stereochemical assignment of sphaeropsidone, a phytotoxic from Diplodia cupressi
No full textSphaeropsidone is a phytotoxin produced in very large amount from Diplodia cupressi. It crystallizes in the monoclinic P21 space group with two molecules in the asymmetric unit. Cell parameters are: a = 4.1280(6) Å, b = 13.161(1) Å, c = 13.333(3) Å, β = 90.14(1)°, Z = 4, Dcalc = 1.432 mg/m3 at 173 K. The final refinement converged to R1 = 0.0413, wR2 = 0.0730 for 1684 observed reflections. In sphaeropsidone, the hydroxyl group and oxirane oxygen atoms are mutually cis positioned. The absolute stereochemistry at the three chiral centres turns out to be 1S,5R,6S. The stereochemical assignment of spaeropsidone is a fundamental basis for the assignment of the absolute configuration of some of its derivatives used in structure-activity relationship studies. No intramolecular hydrogen bonds are found. In the crystal packing, the hydroxyl and carbonyl oxygen atoms are involved in head-to-tail intermolecular hydrogen bonds to form infinite linear chains of molecules running along c. The linear chains are arranged into layers of molecules stacked along a
Structure and electronic properties of extended chromophores for application in second order non linear optics
No full textA new donor-acceptor crosslinkable l-shape chromophore for NLO applications
No full textA new nonlinear-optical (NLO) chromophore containing L-Shape 2-benzofuranyldiazene in π-electron bridge has been synthetized and its chemical and thermal properties examined. Evaluation of the second order NLO properties was performed by EFISH measurements of μβ on chloroform solution and by SHG measurements on amorphous spin-coated thin films obtained from a blend of polymer and chromophores crosslinked “in situ”. The value of 830∙10−48 esu for μβ measured on the dye and of 10 pm/V for the d33 for the poled network are in medium range for similar systems, confirming the proper employ of the molecule to build NLO active networks. The crystal structures dye and its precursor examined by single-crystal analysis show a planar geometry and bond lengths pattern confirm the push pull L-shape nature of the D-π-A systems
- …
