Distorted octahedral crystal fields

The series of deviation from a strictly octahedral crystal field follows the sequence ammonium tungstate > tungstic acid > WO3 [14]. The s->d transition becomes allowed as distortion of the octahedral environment increases. Viewed as a fingerprint technique. Figure 6 shows that the bulk of W present in both WZ (calcined) and PtWZ(acac, reduced) behaves as WO3, as also shown by our XRD data [10], sugesting that only a small extent of W reduction is expected to have taken place during catalyst conditioning prior to reaction. 

Figure 29.2 (a) Octahedral and (b) tetrahedral crystal fields represented as point charges around a central ion. Arrows show the effect of a tetrahedral distortion to the crystal field, (c) d-Orbital energy level diagrams for octahedral crystal field and octahedral crystal field with tetragonal distortion, and (d) tetrahedral crystal field and tetrahedral crystal field with tetragonal distortion. 

It is known1 that in octahedral crystal field the ground orbital D-term of Cu2+ ion is split on doublet and triplet where doublet is the lowest level. The doublet degeneration is lifted by joint influence of both axial component of crystal field and spin-orbital interaction. The sign of axial distortion determines what orbital state z2> or x2-y2> (they are Kramers doublets) will be the lowest. For spin doublet z2> effective g-factor components are... 

Figure 6.7 The Jahn-Teller effect and the effect of a tetragonal distortion of an octahedral crystal field on the energies of d orbitals...

A Copper(II) is a Jahn-Teller ion and normally sits in a distorted lattice site. The configuration of copper is which leads to an unpaired electron in the e level in an octahedral crystal field. The Cg level consists of the degenerate and d, orbitals. According to the Jahn-Teller theorem, the system distorts to remove the degeneracy and lower the overall energy of the system. Hence one set of bonds (four in plane, or two axial) become longer than the others and the copper ion has a distorted geometry. 

Centres in octahedral symmetry with rhombic distortion Strong crystal field... 

In an octahedral crystal field, the ground state is and spin-orbit coupling splits this into Fg, F, and 2rg, with Fg lowest. Since a Kramer s doublet is lowest, no Jahn-Teller distortions are possible. Axial fields split the ground state into A 2 and E. Since there are Kramer s doublets in either level, an ESR spectrum is obtainable, but spin-orbit coupling may mix these states and cause short spin-lattice relaxation times. In practice, the ground state is 2 and the system behaves in a similar fashion to the d Of,) case. Distortions are unlikely and spectra readily seen. The g values vary in a complex manner (14). 

The zero field splitting parameter D was found to be in the range 0.2 < D < 1 cm by a perturbation theory calculation which assumed trigonal (or tetragonal) distortion of the predominately octahedral crystal field symmetry. It was necessary to include in the calculation a lower symmetry zero field splitting E(S/ — 8 ) in addition to the axially symmetric term in order to explain the spectrum,... 

The Jahn-Teller distortion has another consequence. The d states that split in energy in an octahedral crystal field into the tj and e pair are further spilt in a Jahn-Teller environment (Figure 1.7). In the case of an elongated octahedron, the most common situation is that the set are split slightly, but there is a bigger splitting for the e pair, with the d j orbital at an appreciably lower energy than the d 2 2 orbital. This means that the orbital that is preferentially occupied will be d 2 and orbital... 

Generation of the square planar crystal field splitting pattern by starting with an octahedral crystal field and removing the ligands along the z-axis by way of a tetragonal distortion. 

The and 72 states are broadened as a result of slight variations in the crystal field. The 72 and E states are sharper but the E state is split into two components, 29 cm apart, because of the slight distortion of the octahedral field. Population inversion and... 

A quantitative consideration on the origin of the EFG should be based on reliable results from molecular orbital or DPT calculations, as pointed out in detail in Chap. 5. For a qualitative discussion, however, it will suffice to use the easy-to-handle one-electron approximation of the crystal field model. In this framework, it is easy to realize that in nickel(II) complexes of Oh and symmetry and in tetragonally distorted octahedral nickel(II) complexes, no valence electron contribution to the EFG should be expected (cf. Fig. 7.7 and Table 4.2). A temperature-dependent valence electron contribution is to be expected in distorted tetrahedral nickel(n) complexes for tetragonal distortion, e.g., Fzz = (4/7)e(r )3 for com-... 

Foyt et al. [137] interpreted the quadrupole-splitting parameters of low-spin ruthenium(II) complexes in terms of a crystal field model in the strong-field approximation with the configuration treated as an equivalent one-electron problem. They have shown that, starting from pure octahedral symmetry with zero quadrupole splitting, A q increases as the ratio of the axial distortion to the spin-orbit coupling increases. 

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