Ligands octahedral

Methyl-coenzyme M reductase participates in the conversion of CO2 to CH4 and contains 6-coordinate nickel(II) in a highly hydrogenated and highly flexible porphyrin system. This flexibility is believed to allow sufficient distortion of the octahedral ligand field to produce low-spin Ni" (Fig. 27.7) which facilitates the formation of a Ni -CHs intermediate. 

Figure 8-4. Splitting of the d orbitals in an octahedral ligand field.

Figure 8-6. Comparison of LFSE terms for high- and low-spin d" configurations in octahedral ligand fields.

An alternative mechanism that has been suggested [93, 118] for the intersystem crossing process is based on a twist movement of the octahedral ligand arrangement. Two modes designated by M 3 and Ml and illustrated in Fig. 13... 

Table 18.3 Energies of Octahedral Ligand Field States in Terms of A0. ...

Co(en)2(/3-AlaOi-Pr)](C104)3 in aqueous solution (49). We add some further information on these two studies here. Both esters are bound via terminal amino-iV as well as carbonyl-O. Such chelation stabilizes carbonyl-0 coordination and the O-donor is not displaced from the metal at any stage. The other amine ligands surrounding Co(III) provide the necessary octahedral ligand field (27), and we have found the... 

Non-Marcusian linear free energy relationships (if I may again be permitted that barbarism) provide direct evidence for this type of potential surface in octahedral ligand substitution reactions. Both dissociative (e.g., the chloropentaamine of cobalt(III)) and associative systems (e.g., chloropentaaquo chromium(III)) may have values of slopes for the linear free energy relationships indicating non-Marcusian behavior. 

Equations 3—5 can be used to estimate the octahedral ligand-field splitting (Ao) from the slopes of... 

Term labels appropriate for d3 and d6 configurations in octahedral ligand fields will be used in this review to designate the ligand field or d-d excited states of cobalt(III) and chromium(III) complexes. This... 

Figure 3 Effect of an octahedral ligand field on the Figure 4 Effect of a tetrahedral ligand field on the...

Figure 23 Splitting of a SZ> or term by an octahedral ligand field with a large tetragonal component, as from an e -based Jahn-Teller effect...

In ferric iron the electron configuration outside the closed shells is (3d)5. (3d) stands for the five -orbitals d , dx2-y%, dxy, dXz, and dyz, where the z-axis would be perpendicular to, and the x- and y-axes in the heme plane (Fig. 3). Under the influence of an octahedral ligand field the (f-orbitals are split into two groups of symmetries eg and t%g. In low spin ferric compounds the energy separation between the es-orbitals, dz2 and and the three f2p orbitals is large compaired with spin-... 

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