Tetraphenylarsonium ions structure

The tetrahedral ions of tetraphenylarsonium tetraphenylboride are of comparable structure and size. It is proposed, therefore, that the anion and the cation are similarly influenced on transfer from one solvent to another. This assumption makes it possible to calculate reasonable values for single-ion solvent-transfer activity coelficients (and single-ion Gibbs energies of transfer cf. Table 2-9 in Chapter 2.3) between solvent pairs. Table 5-19 shows some selected values of Ig for anions and cations. These have been... 

X-ray and spectroscopic studies indicate that the arsonium halides are ionic. Mc4AsBr consists of tetrahedral Mc4As+ units and separate bromide ions. X-ray structures have also been obtained on a series of tetraphenylarsonium salts. " A regular tetrahedral stmcture is found about the arsenic atom when the counterion is a halide or ion of similar size. However, as the size of the counterion increases, the crystals become more disordered. In solution, tetraphenylarsonium salts are almost completely dissociated, but ion pairing can be significant and is dependent primarily on the dielectric constant of the solution. 

The uranyl ion, (U02), forms yellow azido complexes that are stable in dilute (0.01 M) aqueous solutions in the presence of excess azide a cation structure [(U02)(N3)] has been established and was used in the analysis of uranium [137,138]. The anion tetraazido complex has been isolated as the tetraphenylarsonium salt, [As(Ph)4]2 [(U02)(N3)4], by admixing a solution of 1 g uranyl nitrate in 2 N nitric acid in nitrogen environment to a solution of 7 g sodium azide. At 80°C the red solution was precipitated with tetraphenylarsonium chloride to obtain yellow crystallites that decomposed at 171°C [139]. 

Clem and Huffman [210] studied the chemical structure of solutions containing Au(III) and azide ions. It was found that a tetraazidoaurate(III) anion, [Au (N3)4]", is formed when the molar ratio of Au(III) to azide is at least 1 to 10. The complex is light sensitive, especially in solution e.g., a tetrahydrofuran solution of the tetraphenylarsonium tetraazidoaurate(III), when exposed to daylight, is quantitatively reduced to the diazidoaurate(I) complex [139] ... 

Recent x-ray powder data indicate that K2lr2(CO)4Ci4.s and presumably the bromo and iodo analogue are in fact K o-6lr(CO)2X2 with KX impurities (515). In 1970 Cleare and Griffith (94) reported that the reaction of concentrated hydrohalic and formic acids with hexachloroiridate(IV) results in the formation of diamagnetic needle crystals of [ 2(00)4X4]- stoichiometry which exhibit a metallic luster. In accord with the work of Malatesta and Canziani (283) they prepared the bromo complexes as well as complexes containing different cations. Table X. The chloro potassium salt exhibits Vco absorptions at 2115, 2080, and 1985 cm i while the bromo tetraphenylarsonium salt exhibits Vco absorbances at 2105,2085,2047, and 1957 cm-i. To account for the observed diamagnetism they proposed a planar tetranuclear structure, [Ir4-(CO)sX8]2", based on the structure of the isoelectronic Re4(CO) ion. 

Nevertheless, the additivity of ionic properties in dilute solution ensures that all the relevant properties of the solute are correctly represented. Tremillon (1974) and Marcus (1985, pp. 96-105) present discussions of the various ways that partitioning of this and other ionic properties may be made, using arguments outside thermodynamics. The large size and similar structure of tetraphenylarsonium (2) and tetrap-henylborate (3) ions have led to suggestions that they should have the same size in most solvents, and be nearly equally solvated. 

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