Complex solvation

The spectra of the initial saturated solution, with a F Nb of approximately 6, are of particular interest because of the presence of a weak band at about 900-930 cm 1. This band can be attributed to NbO bonds in oxyfluoride complexes. Even small additions of HF lead to the disappearance of the above effect. This can be explained based on a complex solvatation model. In solutions with a F Nb ratio of about 6, hexafluoroniobate complex, NbF6, initiates the formation of HF that interacts with complex ions as a solvate. This process is called autosolvatation and is represented by two interactions. The first is a hydrolysis process that leads to the formation of HF ... 

The crystalline complex solvated with 2DMSO explodes with extreme violence if rubbed or scratched. 

Co-extraction of Mo and Cu is potentially a problem with certain feed solutions,14 and again selectivities are very dependent on the nature of modifiers present in formulated reagents.142 The Mo species extracted have not been fully characterized, but may include a neutral dioxo complex, [Mo02L2], which can be assumed to have an N2022 donor set similar to that in the Cu11 complex, and molybdate complexes solvated by neutral phenolic oxime ligands such as [M0O4112 LI l].143 Formation of solvated forms of molybdic acid is supported by evidence that extraction is favorable at very low pH values and that the complexes are readily stripped by aqueous ammonia to produce ammonium molybdate,144... 

In accordance with the limited aim of this article, in the following subsections we shall consider only two of the individual contributions to the highly complex solvation process dealing with structural problems of solutions. No attempt is made to treat other aspects, which might well be of considerable theoretical interest, like electronic spectra 189 244> or dynamic properties 13> of liquid mixtures. 

One of the most unambiguous and simple methods of investigating the association of molecules, as in charge-transfer complexes, solvates, etc. is by means of the freezing point or the vapour pressure of the mixture as a function of its composition. These classical methods have been displaced to some extent by spectroscopic methods, which, however, fail if one is dealing... 

The study of ILs in GLC has yielded important information regarding solute-solvent interactions providing valuable insights into their complex solvation interactions and thermodynamic properties for mixed solvent systems. Moreover, ILs have proven to be an important new class of stationary phases for the separation of a wide variety of different analytes. IL stationary phases will soon be commercially available which will inevitably promote further improvements in separation selectivity, thermal stability, immobilization bonding chemistry/stationary phase stability, and will broaden the range of separated compounds. IL-based stationary phases also hold great promise in GC mass spectrometry where the dual-nature selectivity of the stationary phase eliminates the need for frequent changing of columns. 

Complex solvation. Enthalpically Ihvounbk. cmropiculiy unfavourable. 

Ln-Halides. The complexation/solvation criteria is just one reason why lanthanide halides are the most common precursors in organolanthanide chemistry. In this evaluation, lanthanide iodides are often preferred to bromides and chlorides, however the former are more difficult to synthesize and are much more expensive [96f. Waterfree, solid Ln-halides are ionic substances with high melting points which immediately absorb water when exposed to air, forming hydrates (I > Br > Cl ). Therefore, they have to be handled under an inert gas atmosphere. The main use of the halides is for the production of pure metals [96]. Some methods of preparing Ln(III)-chlorides are summarized in Scheme IV [96],... 

Indications of the occurrence of cycloaddition were first obtained from reactions of specifically deuterated allyl anions with tetrafluoroethylene. Assuming that no hydrogen/deuterium exchange occurs in the collision complex as shown for the allyl anions themselves (Dawson el al., 1979a), the results obtained (Nibbering, 1979) may be interpreted as indicating that 65% of the allyl anions react by a linear addition (51), 20% by a [2 + 2] atom cycloaddition (52) and 15% by a [2 + 3] atom cycloaddition. (53). It should be noted here that the precise mechanistic details of the losses of HF molecules from the collision complexes in eqns (51)—(53) are not known. However, in view of the nucleophilic aromatic substitution discussed in the previous section, it is quite likely that they occur in a stepwise fashion in which complexes solvated by fluoride anions play a role. 

The free radical polymerization is probably initiated by the reaction of the peroxide with a metal—carbon bond which has been modified through complexation, solvation, or even chemical interaction with a proper monomer. This "site is interacted with the peroxide molecule, which is then decomposed in a metal-catalyzed manner to form a free radical terminus on the polymer chain along with an inert metal—peroxide interaction product. Whether the metal in question is aluminum, titanium, or a complex of the two is uncertain since the mechanism of Ziegler type reactions is still uncertain and since all three have been found in separate studies to promote the polymerization of methyl methacrylate in the presence of peroxides. However, the complex between AlEt>Cl and TiCl3 has been observed to have a much greater effect in accelerating the polymerization of methyl methacrylate than either component by itself hence, the complex appears to be the most likely species. 

The complexes may also be prepared by the addition of a solution of carboxylic ligand to an equivalent amount of (i) a lanthanide carbonate [28], (ii) hydroxide [29] or (iii) oxide [30] with a slight excess of the latter. The insoluble part is filtered and the filtrate evaporated to obtain crystalline complex. Anhydrous lanthanide complexes of small chain carboxylic acids may be prepared by (i) the dissolution of lanthanide carbonate in excess of the carboxylic acid, followed by heating to obtain complete dissolution of the suspension and partial evaporation of the solution to obtain the crystals [31], (ii) anhydrous lanthanide is converted into the corresponding monochloroacetate by the addition of an excess of monochloroacetic acid, followed by heating under reflux at reduced pressure for 2 h. Then ether is added to precipitate the salt [32], (iii) the addition of dimethyl formamide and benzene to lanthanide acetates and distillation of the water azeotropes to obtain anhydrous complexes. The last procedure yielded lighter lanthanide complexes solvated with dimethyl formamide [33], The DMF may be removed by heating in a vacuum at 120°C. 

The equihbria (426) are reversible, and on the side of the ammonia-iodine charge transfer complex. Solvation of NI3 NH3 in diethylether in the presence of ammonium iodide yields the ether-soluble charge transfer complex NH3 I2. 

Direct reactions of anhydrous triflic acid with lanthanide chlorides or oxides often resulted in complexes solvated by the acid, which are viscous liquids with a very low vapor pressure. Thus it is advisable to perform reactions with diluted trific acid in an aqueous solution. If anhydrous lanthanide chlorides are used, they are to be hydrated with care in water before use in order to avoid contamination by side products. For instance, anhydrous ScCl reacts violently with water, the sample is first cooled at -180 °C and water is added slowly. The mixture is then warmed in 12 h to room temperature. The anhydrous compound, ScCl -nH O (n= 3.7) is obtained as a white solid after boiling the solution to dryness. 

Relatively large, complex lignin molecules can be extracted by complexation, solvation, and coordination with the correct solvents. The black liquor produced by the Kraft pulping process is an alkaline mixture of lignin-bearing micelles. It is essentially opaque and darkly colored, hence its name. When acidified with dilute sulfuric or hydrochloric acid, the micelles are acidified, and the oily lignin is liberated. It floats to the top of the aqueous phase to form an interfacial precipitate. 

It has soon been found that solvent effects are particularly large for reactions in which charge is either developed or localized or vice versa, that is, disappearance of charge or spreading out of charge. In the framework of electrostatic considerations, which have been around since Berzelius, these observations led to the concept of solvation. Weak electrostatic interactions simply created a loose solvation shell around a solute molecule. It was in this climate of opinion that Hughes and Ingold presented the first satisfactory qualitative account of solvent effects on reactivity by the concept of activated complex solvation. 

The determination of the absolute configuration of a chiral substance is a very important part of the characterization of that molecule. That is also true for chiral solvents. Circular dichroisms induced in the UV spectra of metal complexes solvated by a chiral solvent can be used for the determination of the absolute configuration of the solvent [Br 80]. This method is attractive in that the experiments are easy to carry out. 

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