Search results for "ionic"
showing 10 items of 2016 documents
Crystal and molecular structures of hexaaquazinc(II)isonicotinate n-oxide and catena-diaquabis-μ-(isonicotinato n-oxide)cadmium(II)
1984
Abstract [Zn(H2O)6](N-inicO)2 is an ionic compound made up of hexaaqua metal cations and isonicotinate N-oxide anions. It forms an isomorphic series with the corresponding Mg2+, Fe2+, Co2+ and Ni2+ compounds. In [Cd(N-inicO)2(H2O)2]n complex, coordination takes place through the NO oxygen and one of the (COO) oxygens with ligand forming thus a double bridge between Cd2+ ions. The structure is an endless chain stretching diagonally through the unit cell. The coordination polyhedron in both compounds is almost undistorted octahedron.
Viologen-based ionic liquid crystals: induction of a smectic A phase by dimerisation.
2014
The stability of thermotropic ionic liquid crystals is essentially due to micro-phase segregation between the ionic heads and the long alkyl chains. Here we show, using newly synthesized viologen dimers, that the structure of the central core is another key parameter to play with in order to tune the mesomorphic behaviour. © 2014 the Owner Societies.
Buildup of ultrathin multilayer films by a self-assembly process: III. Consecutively alternating adsorption of anionic and cationic polyelectrolytes …
1992
A solid substrate with a positively charged planar surface is immersed in a solution containing an anionic polyelectrolyte and a monolayer of the polyanion is adsorbed. Since the adsorption is carried out at relatively high concentrations of polyelectrolyte, a large number of ionic residues remain exposed to the interface with the solution and thus the surface charge is effectively reversed. After rinsing in pure water the substrate is immersed in the solution containing a cationic polyelectrolyte. Again a monolayer is adsorbed but now the original surface charge is restored. By repeating both steps in a cyclic fashion, alternating multilayer assemblies of both polymers are obtained. The bu…
Controlling the dimensionality of oxalate-based bimetallic complexes: The ferromagnetic chain {[K(18-crown-6)][Mn(bpy)Cr(ox)3]}∞(18-crown-6=C12H24O6,…
2007
Abstract The bimetallic ferromagnetic chain {[K(18-crown-6)][Mn(bpy)Cr(ox)3]}∞ (1) has been synthesized and characterized. It crystallizes in the orthorhombic chiral space group P212121 [a = 9.0510(2) A, b = 14.4710(3) A, c = 26.8660(8) A, V = 3510.97(1) A3, Z = 2]. Compound 1 is made up by anionic [Mn(bpy)Cr(ox)3]− 1D chains and cationic [K(18-crown-6)]+ complexes. The magnetic exchange within the chain is ferromagnetic [J = +7.8(7) cm−1]. In the solid state, the ferromagnetic chains are well isolated magnetically and no long range magnetic ordering has been observed above 2 K.
Isolation of enantiomerically pure organometallic palladium compounds: synthesis of the triangles prepared from enantiopure [cis-Pd2(C6H4PPh2)2(NCCH3…
2009
Reaction of the racemic [Pd(C(6)H(4)PPh(2))Br](4) () with the silver salt of 1R-(1alpha,2beta,3alpha)]-3-methyl-2-(nitromethyl)-5-oxocyclopentaneacetate, (R)-AgO(2)CR*, results in the formation of a mixture of diastereoisomers (RRR)- and (SRR)- of the formula Pd(2)(C(6)H(4)PPh(2))(2)(O(2)CR*)(2) that were separated by standard chromatographic methods. Each diastereoisomer was readily converted into the tetrametallic stereoisomers (SS)- and (RR)-, of the formula [Pd(C(6)H(4)PPh(2))Br](4) that were isolated and characterized by X-ray crystallography. The R enantiomer of the solvated cationic species [cis-Pd(2)(C(6)H(4)PPh(2))(2)(NCCH(3))(4)](2+), obtained from (RR)-, was reacted with ammonium…
Bis(oxalato)chromium(III) complexes: Versatile tectons in designing heterometallic coordination compounds
2011
Abstract The mononuclear oxalato-containing chromium(III) complexes of general formula [Cr(AA)(C2O4)2]− (AA = α-diimine type ligand) are able to produce a large variety of heterometallic complexes by acting as ligands towards either fully solvated metal ions or preformed cationic complexes with available coordination sites. This review focuses on the structural diversity of the polynuclear complexes (oligonuclear and coordination polymers) which are generated by the bis(oxalato)chromate(III) species, with a special emphasis to their magnetic properties.
Solution properties of polyelectrolytes
1991
Abstract Chromatographic data for sodium polystyrene sulphonate were obtained on both silica- and polymer-based size-exclusion supports using mobile phases of various pH and ionic strength. Deviations of the elution volume were observed towards both lower and higher values relative to the reference calibration graph obtained with uncharged standards. An empirical correlation is proposed in order to account for all the secondary effects observed. The general applicability of this correlation was further tested for chromatographic data obtained for a series of peptides and proteins on a silica-based support under very different eluent conditions. Deviations from ideal elution behaviour such a…
Application of a weakly basic dimethylamino-modified silica ion exchanger to the separation of oligonucleotides
1979
Abstract LiChrosorb RP-8, RP-18 and Diol as well as a newly synthesized basic dimethylamino-modified silica ion-exchanger (DMA-silica) were applied for the separation of adenylic acid, cytidylic acid and uridylic acid oligoribonucleotides. On LiChrosorb RP-8 and RP-18, respectively, in aqueous buffered eluents (K 2 HPO 4 - H 3 PO 4 ), the retention of oligonucleotides was increased with decreasing number of nucleotide units in the solute, i.e., with increasing hydrophobic character. The elution behaviour of ologonucleotides on LiChrosorb Diol followed the same order but took place according to a size-exclusion mechanism. The retention of oligonucleotides on DMA-silica is assumed to be based…
Hydrophobicity of Ionizable Compounds. A Theoretical Study and Measurements of Diuretic Octanol−Water Partition Coefficients by Countercurrent Chroma…
1999
Countercurrent chromatography was used to determine the octanol−water partition coefficients (Po/w) of 23 diuretic drugs. The measured Po/w values ranged over 4 orders of magnitude from 0.05 to 550 (−1.3 < log Po/w < +2.7). All the compounds, except spironolactone, were ionizable. The Po/w values were strongly depending on the aqueous-phase pH. A theoretical model linking these values with the pH was derived for four cases: (i) molecular acid−anionic base, (ii) cationic acid−molecular base, (iii) biprotic systems with two acidic or basic groups showing the same charge sign, and (iv) biprotic systems with ionizable groups showing different charges with special attention to the amino acid ca…
Influence of the presence of surfactants and humic acid in waters on the indophenol-type reaction method for ammonium determination.
2005
Abstract This work has evaluated the influence of humic acid and/or surfactants in the quantification of ammonium in waters with the indophenol-type reaction method. Thymol has been employed with the colorimetric method for sample ammonium concentrations between 0.25 and 1 mg L −1 . In addition, SPE/diffuse reflectance method has been used for quantification of ammonium at low concentrations (between 0.025 and 0.25 mg L −1 ). Matrix effect owing to humic substances were observed with the colorimetric method when the concentration was equal or higher than 25 mg L −1 . Lower concentrations of humic compounds produced matrix effects with the more sensitive SPE/diffuse reflectance method. Gener…