Stability constants crystal field stabilization energy

The conditional stability constants (log K<.) obtained for copper with humic compounds extracted from soils and natural waters are invariably greater than those for other transition metals (see Table IV). This is expected from the enhanced levels of crystal field stabilisation energy which result fi-om the splitting of the 3d electronic orbitals on Cu by an octahedral field (Mackay and Mackay, 1969). The divei ence in the values of log Kc shown in Table IV, may, in part, have arisen from intrinsic variations in the copper-binding properties of the various humic samples. However, these deviations may also be explained in terms of the different experimental conditions employed (pH, ionic strength, temperature, for example) and the assumptions made in the calculations. For example, an increase in the pH will enhance the availability of dissociated binding sites (see Section 6) which are then free to participate in further complexation of copper and... 

Another factor that affects trends in the stability constants of complexes formed by a series of metal ions is the crystal field stabilization energy. As was shown in Chapter 17, the aqua complexes for +2 ions of first-row transition metals reflect this effect by giving higher heats of hydration than would be expected on the basis of sizes and charges of the ions. Crystal field stabilization, as discussed in Section 17.4, would also lead to increased stability for complexes containing ligands other than water. It is a pervasive factor in the stability of many types of complexes. Because ligands that form tt bonds... 

The M-ferrihydrite coprecipitate contains M-O/OH-Fe and M-O/OH-M as well as Fe-O/OH-Fe linkages. The transition elements stabilize ferrihydrite in the order, Mn < Ni < Co < Cu < Zn (Cornell, 1988 Giovanoli Cornell, 1992). This order does not correspond with that of the electronegativities or the crystal field stabilization energies (CFSE) of these elements, nor does it match the order of binding constants for the M-surface complexes. If Zn is omitted from the series, however, there is a reasonable cor-... 

Fig. 7.27. It is seen from Fig. 7.27 that the rate constant for the exchange reaction [Ce. +-Ce(EDTA)-] is much lower than the expected value. It is to be noted that the crystal field stabilization energy including spin-orbit interaction reaches a maximum for cerium in the cerium sub group and the ligand field strength is in the order H2O < CH3COO. The...

How would you attempt to (a) estimate the crystal field stabilization energy of FeF, and (b) determine the overall stability constant of [Co(NH3)g] in aqueous solution given that the overall formation constant for... 

In Copenhagen an early interest in "crystal field" theory centered around the stabilization of partly filled shells d in octahedral conplexes. Jannik,being fully aware of the dependence of observed constants on (perhaps minute) differences of energy, wrote a short (34) note and presented a paper ( ) in Amsterdam cotiparing 3d-group M(II)... 

The dissociative mechanism tends to be most favored in TBP d , followed by tetrahedral and then d octahedral. For example, d Co2(CO)s has a half-life for CO dissociation of a few tens of minutes at 0 , but for d Mn2(CO)io at room temperature the half-life is about 10 years This order is consistent with the relative stabilities of the stereochemistries of the starting material and of the intermediates in each case, as predicted by crystal field arguments (Section 1.4). Substitution rates tend to follow the order 3rd row < 2nd row > 1st row. For example, at 50 , the rate constants for CO dissociation in M(CO)5 are Fe, 6 x 10 " Ru, 3 x 10 Os, 5 x 10 . The rate for Fe is exceptionally slow, perhaps because Fe(CO)4, but not the Ru or Os analog, is high-spin and less stable, leading to a higher activation energy. 

The dependence of the heat terms on the crystal field stabilization energies discussed in the previous sections will presumably be reflected in the corresponding free-energy values. Now, free-energy differences are related to equilibrium constants by equations of the form... 

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