Halide complexes in aqueous solutions

Structures of Aqua and Halide Complexes in Aqueous Solutions Derived from X-ray... 

The isostructural solutions formed by yttrium(III) and erbium(III) have been used to study the structures of their halide complexes in aqueous solutions at different concentrations (35). The RDFs for some erbium(III) bromide and chloride solutions with different metal ion concentration and halide to metal ratios are given in Fig. 20 after elimination of the nonmetal interactions. For comparison those of three perchlorate solutions of similar concentrations are also given. For all of these solutions the peaks at 2.35 A, which correspond to the inner coordination sphere of the metal ion, are nearly the same and are closely reproduced by a theoretical peak calculated for 8.0 Er-H20 interactions. This indicates that the anions do not penetrate the first... 

BrF3 (see below). Many metal ions also form halide complexes in aqueous solution. For a majority... 

AHR/ROS] Ahrland, S., Rosengren, K., The stability of metal halide complexes in aqueous solution. II. The fluoride complexes of divalent nickel, copper and zinc, Acta Chem. Scand., 10, (1956), 727-734. Cited on pages 142, 143, 283. 

Z4< Gerding, P., "Thermochemical studies on metal complexes IX. Free energy, enthalpy, and entropy changes for stepwise formation of zlnc(ll) halide complexes in aqueous solution", Acta Chem. Scand., v23, 5. ppl695-1703 (1969)... 

Table 21.6 Stability of actinide halide complexes in aqueous solution. The values refer to perchlorate media and 25°C, if not otherwise staled. ...

Table 16 Kinetic parameters for base hydrolysis of cobaltija) ammine- or amine-halide complexes in aqueous solution...

Compounds of Tl have many similarities to those of the alkali metals TIOH is very soluble and is a strong base TI2CO3 is also soluble and resembles the corresponding Na and K compounds Tl forms colourless, well-crystallized salts of many oxoacids, and these tend to be anhydrous like those of the similarly sized Rb and Cs Tl salts of weak acids have a basic reaction in aqueous solution as a result of hydrolysis Tl forms polysulfldes (e.g. TI2S3) and polyiodides, etc. In other respects Tl resembles the more highly polarizing ion Ag+, e.g. in the colour and insolubility of its chromate, sulfide, arsenate and halides (except F), though it does not form ammine complexes in aqueous solution and its azide is not explosive. 

Fig. 8. Correlation between Pearson s hardness parameter (7P) derived from gas-phase enthalpies of formation of halide compounds of Lewis acids (19), and the hardness parameter in aqueous solution (/A), derived from formation constants of fluoride and hydroxide complexes in aqueous solution (17). The Lewis acids are segregated by charge into separate correlations for monopositive ( ), dipositive (O), and tripositive ( ) cations, with a single tetrapositive ion (Zr4+, ). The /P value for Tl3+ was not reported, but the point is included in parentheses to show the relative ionicity of Tl(III) to ligand bonds. 

Halides other than fluoride form very weak complexes in aqueous solution there are no reliable equilibrium constants to be found in the literature. The solution chemistry of aqueous solutions of beryllium chloride, bromide, and iodide have been reviewed previously (9). Some evidence for the formation of thiocyanate complexes was obtained in solvent extraction studies (134). 

There is little evidence for the formation of soluble complexes in aqueous solutions of Hg1 halide and pseudohalide systems,12,32 but the mercury(I) halides themselves are well-known substances. X-ray studies on the dimercury(I) dihalides show that all these compounds possess... 

Ammonia and alkyl amines do not form complexes in aqueous solution, but the solid halides can give adducts of the type MC12-hNH3 and magnesium halides give complexes such as MgBr2py4. 

Thallium(I) halides are predominantly ionic, although there is a tendency toward increasing covalent character in the series of compounds TlCl (17%), TlBr (20%), and TII (28%). This increased degree of covalency results in decreased solubility for example, TIF is soluble in water whilst the other Tl halides are only sparingly soluble. The thallium(I) halides are classical examples of incompletely dissociated 1 1 electrolytes. The stability of halide complexes of Tl is low and follows the order TIF < TlCl < TlBr < TII, where for the series of halides, Kx = -, 0.8, 2.1, 5.0 and Ki = -, 0.2, 0.7, 1.5 respectively. The fluoride ion F is preferred to perchlorate as a noncomplexing counterion. Claims have been made for T1X species with n = 3 and 4 however, the formation of complexes in aqueous solution with n > 2 seems unlikely. 

Water-soluble palladium(O) complexes have also been used as homogeneous catalysts in aqueous-solution alkylation reactions. The particular complex that has been used is Pd(TPPMS>3. Aryl or heteroaromatic halides can be coupled with aryl or vinyl boronic acids, alkynes, alkenes, or dialkyl phosphites with this palladium(0) complex. This complex in aqueous solution can also be used for the coupling of alkynes with unprotected iodonucleotides, iodonucleosides, and iodoamino acids (133). 

Very recently, an extensive structural study of Tl(III) chloride, bromide, and cyanide complexes in aqueous solution has been completed in which a combination of EXAFS, LAXS, and IR/Raman techniques were used with the aim of elucidating not only the structure of the remaining Tl(III) halide complexes, but also the number and the Tl-0... 

Rate Constants for the Various Halide Exchange Reactions between the TlX, "" Complexes in Aqueous Solution at 25°C... 

As an example, a new palladium based method has been developed for the alkylation of tyrosine residues [34], In this reaction, allylic carbonates, esters, and carbamates are activated by palladium(O) complexes in aqueous solution, resulting in the formation of electrophilic zr -allyl complexes (such as 16), Fig. 10.3-8(a). These species react at pH 8-10 with the phenolate anions of tyrosine residues, resulting in the formation of aryl ether 17 and regeneration of the Pd(0) catalyst. The reaction requires no organic cosolvent, is catalytic in palladium, and requires P(m-QjH4S03 )3 as a water-soluble phosphine ligand. In contrast to alkyl or allylic halides, the inert character of the allyloxycarbonyl compounds used in this reaction ensures that nonspecific... 

The transition from localized behavior to delocalized behavior is an important one. As an example, nickel oxide (NiO) has about the same color as Ni + complexes in aqueous solution. Cu + complexes in aqueous solution are blue, but teud to be green if the ligands are halide ions or violet if the ligands are ammonia molecules. Copper(II) oxide (CuO), on the other hand, is black. Very likely, the wide absorption in the visible region is from an allowed transition that covers the weak ligand field transitions. It cannot be an LM transition since there is no reason to believe that LM transition are in the visible region just in the case of CuO. 

Zinc halide (chloride and bromide) complexes in aqueous solution up to 400 C were studied by Marley and Gaffney [195]. Although the band positions reported in the Raman spectra of the different zinc bromide complexes are in total agreement with those observed by Irish et al. [193], the calculated scattering coefficients, /, are in clear conflict. According to Marley and Gaffney [195], these coefficients remain constant with temperature, whereas Irish et al. [193] demonstrated systematic and significant increases of the different scat-... 

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