Iron complex energy parameters

As a consequence of these points, the spectra of octahedral Mn high-spin and of tetrahedral iron complexes consist of a number of bands of width 500 cm with e 0.1 lying at fairly high energies [those for Mn(H20)6 " commence at 18000 cm ] and whose positions are not very sensitive to the details of the ligands, Probably because the chemical species present are not well defined in solution, the spectra for octahedral Fe complexes are diffuse and rarely interpretable, Because a number of bands are present for the other cases, it may be possible to deduce several of the ligand field and interelectronic repulsion parameters and even X, although the uncertainty in Dq may be substantial. 

Fig. 3-1.—Energy curves for three states of an iron(II) complex FeX . The sextet curve represents a stable structure for extreme ionic bonds and an excited structure for extreme covalent bonds it has five electrons with unpaired spins. The doublet curve represents an excited structure for extreme ionic bonds and a stable structure for extreme covalent bonds it has one unpaired electron. The dashed curve represents a quartet state, with three electrons with unpaired spins. The parameter representing the ordinate determines the nature of the bonds.

Redfield limit, and the values for the CH2 protons of his- N,N-diethyldithiocarbamato)iron(iii) iodide, Fe(dtc)2l, a compound for which Te r- When z, rotational reorientation dominates the nuclear relaxation and the Redfield theory can account for the experimental results. When Te Ti values do not increase with Bq as current theory predicts, and non-Redfield relaxation theory (33) has to be employed. By assuming that the spacings of the electron-nuclear spin energy levels are not dominated by Bq but depend on the value of the zero-field splitting parameter, the frequency dependence of the Tj values can be explained. Doddrell et al. (35) have examined the variable temperature and variable field nuclear spin-lattice relaxation times for the protons in Cu(acac)2 and Ru(acac)3. These complexes were chosen since, in the former complex, rotational reorientation appears to be the dominant time-dependent process (36) whereas in the latter complex other time-dependent effects, possibly dynamic Jahn-Teller effects, may be operative. Again current theory will account for the observed Ty values when rotational reorientation dominates the electron and nuclear spin relaxation processes but is inadequate in other situations. More recent studies (37) on the temperature dependence of Ty values of protons of metal acetylacetonate complexes have led to somewhat different conclusions. If rotational reorientation dominates the nuclear and/or electron spin relaxation processes, then a plot of ln( Ty ) against T should be linear with slope Er/R, where r is the activation energy for rotational reorientation. This was found to be the case for Cu, Cr, and Fe complexes with Er 9-2kJ mol" However, for V, Mn, and... 

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