Spectra nephelauxetic effect

Electronic spectra Nephelauxetic effect Magnetic properties Thermodynamic aspects... 

The numerical values of the interelectronic repulsion parameters, B and C, as determined from the spectrum of an actual transition metal compound (or at least the value of B ) are, in general, lower than the values in a free (gaseous) transition metal ion. This observation which was actually pointed out by several workers in the field (42, 43, 53, 60, 61), is called the nephelauxetic effect (19, 53). In a free 3d metal ion, the interelectronic repulsion integrals are approximately projwrtional to the average reciprocal radius of the partly filled 3d shell. The... 

From this equation, we see that the Racah parameter for the metal ion in a complex, B, is the value for the gaseous ion reduced by a correction (expressed as Bhk) for the cloud-expanding effect. As should be expected, the effect is a function of the nature of the particular metal ion and ligand. As a result, analysis of the spectrum for a complex must be made to determine both Dq and B (which is actually B for the complex). Table 18.7 shows values of the nephelauxetic parameters for ligands and metal ions. 

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