Ligand field stabilization energy formation

The ligand field stabilization energy is only one aspect of the formation of a transition state. Because the reactions are carried out in solutions, solvation of the transition state and the entering ligand may have enough effect to assist in the formation of a particular transition state. Also, the fact that some... 

Another manifestation of ligand field stabilization energy can be seen from the heats of hydration of the transition metal ions. For example, the hydration of a gaseous ion results in the formation of an aqua complex as represented by the equation... 

The equilibrium constants for complex formation in aqueous solution are not high compared to those for Fe2+—Cu2+ because the Mn11 ion is the largest of these and it has no ligand field stabilization energy in its complexes (except in the few of low spin). 

Alfred Werner studied the "strengthening of the primary valence force by the saturation of the secondary valence force," but he failed to explain fully this phenomenon. To elucidate the stabilization of unstable oxidation states by complex formation two aspects should be taken into account the thermodynamic stability of complexes and their kinetic redox lability. Such factors as ligand field stabilization energy for M" and and the geometry of the donor atoms spatial orientation also affects the stability of a given oxidation state. Macrocyclic ligands are especially suitable for the stabilization of unstable metal oxidation states, both from the thermodynamic and kinetic viewpoints. 

In aqueous solution, the complexes of most metal cations exist in dynamic equilibrium with their components. If we disturb this equilibrium, another one is instantly formed. It is quite otherwise with robust complexes which persist for hours (or even days) under conditions favourable to their decomposition any biological properties that they may have are strikingly different from those of their components. Robust complexes are formed where metal ions have 3,4 (low spin), 5, or 6 d electrons provided that formation of the complex involves large values of ligand-field stabilization energy. Metals most prone to form robust complexes are the transition metals platinum, iridium, osmium, palladium, rhodium, ruthenium, also (but not so frequently) nickel, cobalt, and iron. The halide and, particularly, the cyanide anions most readily form robust complexes with these transi-... 

Fig. 13.6 (a) Octahedral crystal field stabilization energies of the tripositive lanthanide ions, (b) Enthalpy data related to the formation of (octahedral) complexes of the ligand shown in Fig. 13.7 (see also the caption to Fig. 13.2). 

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