1,721,068 research outputs found
Transition metals complexed to ordered mesophases. Synthesis, characterization, and mesomorphic properties of new potentially ferroelectric liquid crystals: chiral p,p'-dialkoxyazobenzenes and their cyclopalladated dinuclear complexes
No full textTo prepare chiral metallo-mesogens with ferroelectric properties, new azobenzene compounds, HLN(n), bearing a chiral substituent have been synthesized. These ligands consist of two aliphatic chains of variable length, one of which contains a stereogenic center located in the para and para′ positions of an azobenzene core. The chiral groups (R*O) are as follows: N = 1, (R)-(-)-menthol; N = 2, (S)-(-)-β-citronellol, and N = 3, (R)-(-)-2-octanol; the aliphatic chains are linear n-alkoxy groups CnH2n+1O (n = 7, 10, 12, 14). Only the HL2(n) species display liquid-crystalline properties giving cholesteric or smectic A mesophases. The HLN(n) ligands react with [Pd(PhCN)2Cl2], to give the corresponding chloro-bridged dinuclear cyclopalladated products {Pd[LN(n)](μ-Cl)}2 as 1:1 mixtures of isomers arising from the nonselective attack of the palladium on the benzene ring bearing the chiral alkoxy group or on the benzene with the aliphatic alkoxy chain. The (Pd[L2(n)](μ-Cl)}2 compounds and the (Pd[L3(n)](μ-Cl)}2 (n = 10, 12, 14) exhibit smectic mesophases (Sc* in {Pd[L2(7)] (μ-Cl)}2, {Pd[L2(10)](μ-Cl)}2, {Pd[L3(10)](μ-Cl)}2, and {Pd[L3-(14)](μ-Cl)}2,SA in {Pd[L2(12)] (μ-Cl)}2, {Pd[L2(14)](μ-Cl)}2, {Pd[L3(12)]μ-Cl)}2). The Pd[LN(n)]-(μ-Cl)}2 compounds have been converted into the corresponding iodo analogues {Pd[LN(n)] (μ-I)}2. The chloro complexes display a richer mesomorphism than the respective iodo compounds
Macrocyclic Metallomesogens: Thermotropic Double-chained Silver Amphiphiles
No full textMesomorphic [Ag(2)][TfO] (TfO=CF3SO3) and [Ag(2)][TsO] (TsO=p-CH3C6H4SO3) have been prepared by silver complexation of the novel N,N'-bis(hexadecanoyl)-1,10-diaza-4,7,13,16-tetrathiacyclooctadecane, 2. The phase behaviour of the silver complexes is described and a lamellar mesophase is proposed for [Ag(2)][TfO] by means of X-ray evidence
Transition metals complexed in ordered mesophases. XV. Synthesis, characterization and mesomorphic properties of new potentially ferroelectric liquid crystals: acetylacetonate p,p'-dialkoxyazobenzene mononuclear palladium(II) complexes
No full textOn the thermal behaviour of palladium(II) macrocyclic polycatenars
No full textPolycatenar saturated macrocycles 1,10-bis[3,4,5-tris(4-dodecyloxy)benzoyl]-1,10-diaza-4,7,13,16-tetrathiacyclo-octadecane (3b) and 1,10-bis[3,4-bis(4-dodecyloxy)benzoyl]-1,10-diaza-4,7,13,16-tetrathiacyclo-octadecane (3d) reacted with [Pd(MeCN)(4)][BF4](2) led to the cationic complexes [4b][BF4](2) and [4d][BF4](2), respectively. Complexes [4b][BF4](2) and [4d][BF4](2) showed smectic mesomorphism on heating as confirmed by small angle X-ray diffraction. A concurrent, irreversible structural change of the complex cations was observed and a tentative explanation is suggested
Heteroligand Palladium Complexes with One or Two Chiral Centres
No full textA series of chiral mononuclear palladium(II) complexes, [(Az(n))Pd(L-m)], I-VIII, have been synthesized. Herein the Az(n)Pd fragments represent the cyclopalladated 4-tetradecyloxy-4'-alkoxyazobenzene bearing an optically active carbon atom in a terminal alkoxy chain while HLm is the anion arising from the achiral N-[4'(dodecyloxy)resorcylidene]-4-(alkyl)anilines or the N-[4'-(dodecyloxy) resorcylidene]-4-(alkoxy)anilines containing a stereogenic center in a lateral chain. The optically active alkoxy tails are derived by S-(-)-beta-citronellol and R-(-)-2-octanol. Thermotropic mesomorphism, namely nematic and smectic phases, has been observed for almost all the complexes, with higher thermal stability and clearing temperatures of the same order or lower than those of the corresponding organic ligands
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
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