Search results for " bonding"
showing 10 items of 934 documents
CH-Directed Anion-π Interactions in the Crystals of Pentafluorobenzyl-Substituted Ammonium and Pyridinium Salts
2010
Simple pentafluorobenzyl-substituted ammonium and pyridinium salts with different anions can be easily obtained by treatment of the parent amine or pyridine with the respective pentafluorobenzyl halide. Hexafluorophosphate is introduced as the anion by salt metathesis. In the case of the ammonium salt 4, water co-crystallisation seems to suppress effective anion-pi interactions of bromide with the electron-deficient aromatic system, whereas with salts 5 and 6 such interactions are observed despite the presence of water. However, due to asymmetric hydrogen-bonding interactions with ammonium side chains, the anion of 5 is located close to the rim of the pentafluorophenyl group (eta(1) interac…
New anionic cobalt complexes using highly hindered bis-amides with varying donor abilities as ligands.
2007
Four potential tetradentate ligands of formulae 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)ethane (H(4)L(1), 1), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)propane (H(4)L(2), 2), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)benzene (H(4)L(3), 3) and 1,8-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)naphthalene (H(4)L(4), 4) have been prepared and the crystal structures of three of them (1, 3 and 4) determined by single crystal X-ray diffraction. The investigation of their complexing ability toward Co(II) afforded the compounds of formulae [Co(III)(L(3))Na(I)(H(2)O)(2)] (5), [Co(III)(L(n))Li(I)(H(2)O)2] with n = 1 (6), 2 (7) and 3 (8) and [Co(II)(L(4))Li(I)(2)] (9). Complexes 5-8 are squa…
Polyfunctional recognition of pyridinedicarboxylate anions with macrocyclic polyamine receptors containing heteroaromatic groups.
2008
The interaction of the biologically relevant anions deriving from the six pyridinedicarboxylic acids (H2PDC) with two macrocyclic receptors containing a pentamine chain and a bipyridine (1) or a phenanthroline (2) moiety, as well as with the aliphatic analogue [21]aneN7 (3), was studied by means of spectroscopic methods (UV-vis, NMR) and potentiometric titrations affording the stability constants of the adducts formed. All three receptors form stable complexes with the substrates thanks to the formation of several salt bridges and hydrogen bond contacts, as observed in the crystal structure of the H8[3(2,6-PDC)4] x H2O x 0.5 EtOH solid compound. Additional pi-stacking interactions between t…
A highly enantioselective abiotic receptor for malate dianion in aqueous solution
2006
The highly enantioselective molecular recognition of the malate dianion by a synthetic receptor in aqueous solution has been studied by potentiometric titrations, mass spectrometry (ESI-MS), diffusion measurements (PGSE NMR) and molecular modeling. Garcia-España Monsonis, Enrique, Enrique.Garcia-Es@uv.es
Bis(5-tert-butyl-2-hydroxy-3-methylbenzyl)(6-hydroxyhexyl)ammonium chloride monohydrate, an anion receptor complex
2007
In the title compound, C(30)H(48)NO(3)(+) x Cl(-) x H(2)O, the cation acts with a water molecule as a chloride ion receptor. The chloride ion forms three strong intramolecular hydrogen bonds. The water molecule forms both an intramolecular bridge between one phenol H atom and the chloride ion, and an intermolecular link to the aliphatic alcohol O atom. Weak intermolecular C-H...Cl and C-H ...O hydrogen bonds provide additional packing interactions.
Conductance of potassium halides near the temperature of maximum density of water
1981
The conductances of dilute aqueous solutions of KCl, KBr, and KI have been measured over the temperature range 2 to 8°C and have been analyzed by the Fuoss-Hsia equation. The ionic Walden products at infinite dilution have been discussed in terms of local viscosity. The temperature dependence of these products suggest that near the temperature of maximum density of water, the structure-breaking ability of these ions changes in a regular way.
On the Creeping of Saturated Salt Solutions
2013
Creeping is a well-known but annoying phenomenon in the preparation of crystals from solution, where growing crystallites gradually extend up the walls of the growth vessel. In this process, solution is transported toward the tip of the creeping crystallites, where solvent evaporation takes place and solid material is deposited. In this study, the growth of crystal aggregates extending from evaporating droplets of saturated aqueous solutions of ionic salts, placed on different substrate materials, has been investigated using optical microscopy. It is shown that the rate determining step of the crystallization process is the evaporation of solution, following Fick’s laws. Fresh solution, nec…
Speciation of Organic Matter in Natural Waters-interaction of polyacrylates and polymethacrylates with major cation components of seawater
2004
Abstract The speciation of some high molecular weight polycarboxylates was studied in different ionic media. Polyacrylates here investigated ( W =2.0, 5.1 and 20.0 kDa) form weak species with alkali metal cations ( K =10 2 mol l −1 , t =25 °C, I =0 mol l −1 ) and quite stable complexes with alkaline earth metal cations ( K >10 6 mol l −1 , t =25 °C, I =0 mol l −1 ). Results are reported from experiments performed in a multicomponent electrolyte solution simulating the major composition of seawater (artificial seawater). Protonation constants in this medium are expressed as a polynomial function of S 1/2 ( S =salinity) and the sharp lowering with respect to values obtained in non-interacting…
The interaction of amino acids with the major constituents of natural waters at different ionic strengths
2000
Abstract The interaction of amino acids with the major constituents of natural waters has been studied potentiometrically by determining protonation constants at different ionic strengths (e.g., I ≤5.6 mol (kg H 2 O) −1 (NaCl)) and in artificial seawater (containing Na + , K + , Ca 2+ , Mg 2+ , Cl − and SO 4 2− ) at different salinities. For glycine determinations in mixed NaCl–MgCl 2 , electrolyte solutions were also performed. The data included in this work, together with some already published, make it possible to calculate parameters for dependence on ionic strength using different models, i.e. an extended Debye–Huckel type equation and Pitzer equations. The results can be interpreted b…
Hydrolysis of dioxouranium(VI): a calorimetric study in NaClaq and NaClO4aq, at 25°C
2004
Abstract We report the results of a calorimetric study on the hydrolysis of UO 2 2+ in different ionic media (NaClO 4 aq , NaCl aq ) at 25 °C. Experiments in NaCl were performed at different ionic strength, at I ≤1 mol l −1 . The species considered in both ionic media were UO 2 (OH) + , (UO 2 ) 2 (OH) 2 2+ and (UO 2 ) 3 (OH) 5 + , and in addition (UO 2 ) 3 (OH) 4 2+ and (UO 2 ) 3 (OH) 7 − in NaCl aq . The dependence on ionic strength of enthalpy changes in NaCl aq was expressed by the simple linear equation Δ H pq =Δ H ° pq + aI 1/2 ( a , empirical parameter). Comparison with literature findings is given and some recommended values are reported.