Octahedral complexes, electron

Kinetically labile and inert complexes Dissociation, association and interchange Activation parameters Substitution in square planar complexes Substitution in octahedral complexes Racemization of octahedral complexes Electron-transfer processes... 

This is the most common and stable state of chromium in aqueous solution. The Cr ion, with 2d electrons, forms mainly octahedral complexes [CrX ], which are usually coloured, and are kweticallv inert, i.e. the rate of substitution of X by another hgand is very slow consequently a large number of such complexes have been isolated (see below, under chromium(III) chloride). 

The chemistry of Cr(III) in aqueous solution is coordination chemistry (see Coordination compounds). It is dominated by the formation of kineticaHy inert, octahedral complexes. The bonding can be described by Ss]] hybridization, and HteraHy thousands of complexes have been prepared. The kinetic inertness results from the electronic configuration of the Cr ion (41). This type of orbital charge distribution makes ligand displacement and... 

In general, octahedral complexes of transition-metal ions possessing 0, 1, or 2 electrons beyond the electronic configuration of the preceding noble gas, ie, i/, (P configurations, are labile. The (P systems are usually inert the relative lability of vanadium(II) may be charge and/or redox related. 

However, high spin (P and (P species, which possess 4, 5, and 4 unpaired electrons, respectively, are labile, as are (P through (P octahedral complexes. In addition to the inert (P systems, low spin (P and (P complexes are inert to rapid substitution. The (P species are the least labile of the configurations classed as labile. 

Thc Crystal l-ield Siabili2ation Energy (CFSl ) is the additional stability which accrues to an ion in a complex, as compared to the free ion, because its d-orbitals are split In an octahedral complex a l2 electron increases the stability by 2/5Ao and an Cf, electron decreases it by 3/5Ao- In a tetrahedral complex the orbital splitting is reversed and an e electron therefore increases the stability by 3/5At whereas a t2 electron decreases it by 2/5Ai. 

As six ligands approach a central metal ion to form an octahedral complex, they change the energies of electrons in the d orbitals. The effect (Figure 15.10, p. 419) is to split the five d orbitals into two groups of different energy. 

Derive the electron distribution of the Fe3+ ion in the low-spin and high-spin octahedral complexes. 

Give the number of unpaired electrons in octahedral complexes with strong-field ligands for... 

When, however, the ligand molecule or ion has two atoms, each of which has a lone pair of electrons, then the molecule has two donor atoms and it may be possible to form two coordinate bonds with the same metal ion such a ligand is said to be bidentate and may be exemplified by consideration of the tris(ethylenediamine)cobalt(III) complex, [Co(en)3]3+. In this six-coordinate octahedral complex of cobalt(III), each of the bidentate ethylenediamine molecules is bound to the metal ion through the lone pair electrons of the two nitrogen atoms. This results in the formation of three five-membered rings, each including the metal ion the process of ring formation is called chelation. 

In practice, these conditions of radial waveforms and bond lengths will not be met exactly, so that a rough rule is that Ad 0.5 Act in real systems. Once again, only one electronic, d-d absorption is expected (and observed), although much shifted towards the red relative to that in an analogous octahedral complex. 

Sometimes, the physicochemical properties of ionic species solubilized in the aqueous core of reversed micelles are different from those in bulk water. Changes in the electronic absorption spectra of ionic species (1 , Co ", Cu " ) entrapped in AOT-reversed micelles have been observed, attributed to changes in the amount of water available for solvation [2,92,134], In particular, it has been observed that at low water concentrations cobalt ions are solubihzed in the micellar core as a tetrahedral complex, whereas with increasing water concentration there is a gradual conversion to an octahedral complex [135],... 

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