Labile octahedral complexes

Kinetic parameters for alcohol exchange have been deduced from H and studies on Co(ii), (296) Ni(ii), (297) and Mn(ii) (298) systems. The complex [Co(CH30H)5py] (296) provides a clear example of the operation of the trans effect in a labile octahedral complex, in that the exchange rate constants for cis and trans methanol sites with respect to pyridine are 410s and 1200s respectively. 

Since the early 1950 s when systematic studies of the substitution reactions of non-labile octahedral complexes were begun by Taube, Brown, Ingold and Nyholm and Basolo, there has been a preoccupation with features of aquation and base hydrolysis reactions. This work has been excellently summarised in all its features in a progressive series of and at least to this con-... 

Explain inert and labile octahedral complexes according to CFT. 

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. 

The mechanism of octahedral complex formation by labile metal ions. D. J. Hewkin and R. H. Price, Coord. Chem. Rev., 1970, 5, 45-73 (177). 

As the trans effect theory indicates, there should be some relationship between lability of a ligand and its role as a labilizing group in another position in a complex. In an octahedral complex reacting via a dissociative mode of activation, the transition state has five strongly bound ligands. This state will be stabilized... 

There have been few studies of substitution in complexes of nickel(II) of stereochemistries other than octahedral. Substitution in 5-coordinated and tetrahedral complexes is discussed in Secs. 4.9 and 4.8 respectively. The enhanced lability of the nickel(II) compared with the cobalt(II) tetrahedral complex is expected from consideration of crystal field activation energies. The reverse holds with octahedral complexes (Sec. 4.8). 

This account is concerned with the rate and mechanism of the important group of reactions involving metal complex formation. Since the bulk of the studies have been performed in aqueous solution, the reaction will generally refer, specifically, to the replacement of water in the coordination sphere of the metal ion, usually octahedral, by another ligand. The participation of outer sphere complexes (ion pair formation) as intermediates in the formation of inner sphere complexes has been considered for some time (122). Thermodynamic, and kinetic studies of the slowly reacting cobalt(III) and chromium(III) complexes (45, 122) indicate active participation of outer sphere complexes. However, the role of outer sphere complexes in the reactions of labile metal complexes and their general importance in complex formation (33, 34, 41, 111) had to await modern techniques for the study of very rapid reactions. Little evidence has appeared so far for direct participation of the... 

The water molecules are substitutionally labile and the soft M(I)(C0)3+ species reacts with ligands containing both hard and soft ligands, for example, thioethers, histidine, and carboxylates, to form kinetically stable octahedral complexes. In fact, histidine in a peptide is such a strong binding ligand that it often competes with the intended bifunctional ligand. 

The malonato complexes of chromium(III) are analogous to the oxalate complexes of chromium(III). Since malonic acid is a weaker acid than oxalic acid, the malonato complexes are expected to be more labile than the oxalato complexes. The dicarboxylate complexes of chromium(III) form a group of anionic complexes which are suitable for the study of octahedral complex reactivity. 

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