Halide ions shielding data

Deverell [245] has proposed three methods, which do not involve theoretical calculations of halide crystals, to estimate absolute nuclear shielding data of aqueous alkali and halide ions. The first method is based upon the experimental observation of a dependence of aqueous alkali ion and halide ion shieldings upon the isotopic composition of the solvent. The NMR signals of these ions are shifted towards higher fields as the mole fraction of deuterium in the solvent increases (see further Section 6.5). This solvent isotope shift which is particularly notable for the halide ions is attributed to the altered vibration pattern of the hydrated ions in turn affecting the energy difference between excited states and the ground electronic state [369], The U.V. 

The difficulties, described above, in accounting for alkali and halide ion shielding in the simple situation of the ion at infinite dilution may look discouraging for the use of ion shielding data to probe into the interactions of the ions with other species in more complex systems. Indeed, quantitative interpretations of the changes in halide ion chemical shift with changes in solution composition are difficult and considerations in the literature have mainly been confined to... 

Baron s data on the pressure dependence of the nuclear shielding in alkali halide crystals have also been analyzed in terms of the Kondo - Yamashita theory by Hafemeister and Flygare [ 368]. Their estimates of aqueous ion shieldings are summarized in Table 6.1. 

Some Hg chemical shift data are given in Table 3 for some representative compounds whose structures appear to be fairly well defined in solution. As with typical transition metals, such as Pt, and " Cd, the nuclear shielding increases in halide complexes as the halide ion becomes heavier ( normal halide dependence )... 

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