Isomer shift electronegativity effect

FIGURE 7 Isomer shift vs. Pauling electronegativity for anhydrous ferrous halides. The IS values are corrected for the effects of temperature, assuming no intrinsic thermal contribution. The uncertainty limits are represented by the size of the dots. 

In view of this uncertainty, the two halides have been remeasured in these laboratories (117), giving the values 1.09 and 1.44 mm sec . Use of these values shows that the sensitivity of the isomer shift to ligand electronegativity is effectively the same for both sets of compounds (see Fig. 8). The least-squares lines through these points have the equations... 

Two complementary effects could explain the constancy of the isomer shifts (116). When eui organic group in Ri Sn is replaced by a more electronegative ligand, some rehybridization might be expected, which... 

Electric monopole interaction between nucleus and electrons at the nuclear site Isomer shift 6 a. Oxidation state (nominal valency) of the Mossbauer atom b. Bonding properties in coordination compounds (covalency effects between central atom/ion and ligands. Delocalization of d-electrons due to back-bonding effects, shielding of s-electrons by p-and d-electron ) c. Electronegativity of ligands... 

R atoms. This follows from the isomer shift results obtained by means of Eu, Dy and Gd Mdssbauer effect spectroscopy, which indicate that the R atoms donate electrons to the H atoms. These findings are in agreement with the fact that there is virtually no difference in electronegativity between H and the 3d metals but a considerable electronegativity difference between R and H. 

Some heteropolycycloalkanes, e.g. indolizidine, quinolizidine, tropane, and decahydro-quinoline, are parent skeletons of alkaloids. Carbon-13 shifts of these and other parent polycycloalkanes [408] (Tables 4.64 and 4.65) are predominantly determined by heteroatom electronegativity, ring size, stereoisomerism, and dynamic effects. Aza- and thiade-calins are representative examples (Table 4.64). As described for cis- and trans-decalin (Section 4.1.3), carbon nuclei in the cis isomers of aza- and thiadecalins are shielded... 

---