Electron density at the iron nucleus

Fig. 5.1 Linear regression analysis between calculated electron densities at the iron nucleus and measured isomer shifts for a collection of iron complexes. (From [19])...

However, the division of the electron density at the iron nucleus into contributions arising from Is through 4s contributions can be done conveniently at the level of the canonical molecular orbitals. This arises because the iron Is, 2s, and 3s orbitals fall into an orbital energy range where they are well isolated and hence do not mix with any hgand orbital. Hence, the Is, 2s, and 3s contributions are well defined in this way. The 4s contribution then arises typically from several, if not many, molecular orbitals in the valence region that have contributions from the iron s-orbitals. Thus, the difference between the total electron density at the nucleus and... 

Table 5.2 Contributions to the electron density at the iron nucleus in Fep4 unrestricted B3LYP calculations with the CP(PPP) basis set. Orbitals that electron density at the iron nucleus are printed in boldface...

Table 5.3 Contributions of -orbitals to the total electron density at the iron nucleus (in a.u. ) as a function of oxidation state and configuration. Calculations were done with the spin-averaged Hartree-Fock method and a large uncontracted Gaussian basis set. (17 1 Ip 5d If)... 

Since the iron 4s orbitals are involved in covalent bonding with the ligands, the s-electron density at the iron nucleus is increased compared to high-spin iron(ll) compounds. This is even more tme if tt-accepting ligands like CN are present. Therefore the difference in isomer shift between low-spin iron(ll) and low-spin iron(lll) is much less pronounced than between high-spin iron(n) and high-spin iron(III). 

Figure 20 Calibration of the B3LYP method for the prediction of Fe isomer shifts. The calculated electron density at the iron nucleus is plotted versus the experimentally determined isomer shift for a series of 15 iron-containing compounds. (Reprinted from Neese. 2002, with permission from Elsevier)...

High pressures acting on Fep2 produce a reversible decrease in the chemical isomer shift which is regular in behaviour [9]. This corresponds to an increase in electron density at the iron nucleus. Evidence from optical studies suggests that this results from a decrease in the 3rf-shielding effects with increasing pressure. 

The electric monopole interaction is proportional to the s-electron density at the iron nucleus [Pg.2820]

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