Ligand field splitting parameter

Here we discuss two topics the relationship between octahedral and tetrahedral ligand field splitting parameters, and the pressure-dependence of the octahedral parameter a common feature of these is the use of the AOM to determine the variation of orbital splittings with the intemuclear distance. 

Table 42 Ligand field splitting parameter A/he (103 cm 1) obtained from the electronic spectra of octahedral and tetrahedral (4C1-) complexes ...

For the pseudo-tetragonally elongated Ml octahedral site in the olivine structure, an alternative method for obtaining the CFSE of Fe2+ ions in this site is to evaluate the ligand field splitting parameters in the equatorial plane and along the axial direction using eqs (3.14) to (3.16). The crystal field spectral data for the fayalite Ml site (see fig. 5.11a) yield values for 10 Dq(m) and 10 Dq(eq) of 8,172 cm-1 and 9,327 cm-1, respectively. The mean 10 Dq value of 8,942 cm-1 and the CFSE of 4,133 cm-1 compare favourably with A0 = 8,830 cm-1 and CFSE = 4,250 cm-1 for Fe2+ in the fayalite Ml sites determined by the baricentric method (fig. 5.11a). 

Figure 5. The lowest states of an Fe(III) d5 ion in a porphyrin as a function of the ligand-field splitting parameter A...

Axial and rhombic zero-field splitting parameters of Kramers doublet ground states and ligand field splitting parameters of non-Kramers doublet degenerate ground states can be determined from the variable temperature variable field data. 

The extent of mixing of different spin-orbital states expressed by the angle (x) is determined by the ratio of the trigonal ligand field splitting parameter A (positive if [Pg.193]

The separation A = e — Et is called the ligand field splitting parameter. As we shall see in Chapter 12, this parameter is related to the energy of the electronic transitions responsible for the colour of many complexes, because the splitting is usually small enough to involve transitions by absorption of visible radiation. 

For the octahedral complexes of transition metals studied in Chapter 11, important transitions are those of energy A (the ligand field splitting parameter) between the non-bonding tzg orbitals and the anti-bonding Cg orbitals. The simplest example is provided by the hexaquotitanium(in) ion, [Ti(H20)6] , whose fundamental valence configuration is (t2g) The absorption band at 493 nm, responsible for the purple colour of the complex, is assigned to the t2g e transition (Fig. 12.9). 

V02+ is nearly as great as that of the hg- eg excitation in Ti(OH2)63+ [9, 10] emphasizes the importance of VO 71-bonding. The shoulder at 16,000 cm-1 arises from the 2B2(xy) —> 2Bi(x2 — y2) transition and provides a direct estimate of the octahedral ligand field splitting parameter (lODq). For comparison, lODq values for the V2+ [10,11] and V3+ [10,12-14] hexaaqua ions are estimated to be -12,000 and 18,800 cm-1, respectively. The absorption spectrum reveals that the strength of the V-OH2(equatoriai) interaction in the vanadyl ion lies somewhere between that of V2+ and V3+. 

Fig. 3 TS-type diagrams correlating the energies of electronic states in d2 and S oxo-metal complexes with the strength of the An ligand field splitting parameter. Gray areas correspond to forbidden An zones for ground-state complexes...

Table 19-1. DFT values for energies/eV of all 45 Slater determinants (SD) due to the d configuration of Fe in tetrahedral Fe04 in terms of interelectronic repulsion B and C and the cubic ligand-field splitting parameter 0Dq... 

The transition energies corresponding to the three d- -d bands of octahedral d systems are listed in Eq. (7). Since the ground term is the ligand field splitting parameter, 10 Dq, is not determined directly by the energy of the first band, cf. d and rf systems. 

B. Ligand Field Splitting Parameters for Molybdenum Hexacarbonyl... 

We conclude by reconsidering what we must now call the ligand field splitting parameter of an octahedral transition metal complex. A, since the factors affecting its magnitude are evidently more complicated than we at first supposed. We have encountered three such factors ... 

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