High-spin configurations tetrahedral coordination

Figure 2.3 Ionic radii for ions commonly found in solids (a) graphical representation (b) periodic table. Note a superscript, indicates a high-spin configuration (Section S4.5) cation radii are those for ions octahedrally coordinated to oxygen, except where marked with a t, which are for ions in tetrahedral coordination...

Fig. 4.3 Ranges of isomer shifts observed for Fe compounds relative to metallic iron at room temperature (adapted from [24] and complemented with recent data). The high values above 1.4-2 mm s were obtained from Co emission experiments with insulators like NaCl, MgO or Ti02 [25-28], which yielded complex multi-component spectra. However, the assignment of subspectra for Fe(I) to Fe(III) in different spin states has never been confirmed by applied-field measurements, or other means. More recent examples of structurally characterized molecular Fe (I)-diketiminate and tris(phosphino)borate complexes with three-coordinate iron show values around 0.45-0.57 mm s [29-31]. The usual low-spin state for Fe(IV) with 3d configuration is 5 = 1 for quasi-octahedral or tetrahedral coordination. The low-low-spin state with S = 0 is found for distorted trigonal-prismatic sites with three strong ligands [30, 32]. Occurs only in ferrates. There is only one example of a molecular iron(VI) complex it is six-coordinate and has spin S = 0 [33]...

Fig. 5. Geometries detected by TAMREAC according to the Angular Overlap and VSEPR models for four- and five-coordinate complexes. Abbreviations SPL = square planar, Td = tetrahedral, SPY = square pyramidal, TBP = trigonal bipyramidal, Is = low spin, hs = high spin, d" = number of electrons in the d configuration of the metal.

Jahn-Teller distortions are also predicted for certain transition metal ions in tetrahedral coordination. The electronic configurations predicted to undergo no Jahn-Teller distortions are the high-spin 3d2, 3d5, 3d7 and low-spin 3d4... 

Figure 3.10 Partial energy level diagram for the Fe3+ or Mn2+ ions with 3tfi configurations in high-spin states in an octahedral crystal field. Only sextet and quartet spectroscopic terms and crystal field states are shown. Note that the same energy level diagram applies to the cations in tetrahedral crystal fields (with g subscripts omitted from the state symbols for the acentric coordination site).

For all models, the configuration of the ligands coordinated to the Ni atom is tetrahedral in the high-spin state and square planar in the low-spin state. The Mulliken atomic spin densities and charges of each state are shown in Table 9-3. In the high-spin state, the SI, S3 and Ni atoms have 0.5-0.8 spin densities, while the SI and Ni atoms in la have hardly any spin. In addition, each of the SI, S3 and Ni atoms in 4b, 4b, and 4b" have 0.4-0.9 spin densities except the atoms abstracting the first H radical. The second H radical is captured easily on atoms with large spin densit. 

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