Ligand field stabilization

Predicted LFSE for high-spin d° to d10 (inset), and variation in hydration energy for first-row M2+ transition metal ions, which mirrors this trend, superimposed on a general increase with atomic number. 

Coordination chemistry relies heavily on a capacity to separate and/or isolate individual complexes from reaction mixtures, and subsequently to employ an array of physical methods to determine the nature and structure of such complexes. 

Single crystal X-ray crystallography is a key physical method, as it provides an accurate three-dimensional picture of crystalline complexes in the solid state. 

Solid state and solution structures need not be identical, and an array of less definitive physical methods must be employed to probe complex structure and chemistry in solution. 

Key physical methods employed in coordination chemistry are NMR and IR spectroscopy, UV-Vis spectrophotometry and MS. 

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Many of the spinel-type compounds mentioned above do not have the normal structure in which A are in tetrahedral sites (t) and B are in octahedral sites (o) instead they adopt the inverse spinel structure in which half the B cations occupy the tetrahedral sites whilst the other half of the B cations and all the A cations are distributed on the octahedral sites, i.e. (B)t[AB]o04. The occupancy of the octahedral sites may be random or ordered. Several factors influence whether a given spinel will adopt the normal or inverse structure, including (a) the relative sizes of A and B, (b) the Madelung constants for the normal and inverse structures, (c) ligand-field stabilization energies (p. 1131) of cations on tetrahedral and octahedral sites, and (d) polarization or covalency effects. ... 

A considerable number of rhodium(III) complexes exist. Their stability and inertness are as expected for a low-spin d6 ion any substitution leads to a considerable loss of ligand-field stabilization. 

Ligand-Field Stabilization Energies 8.2.3 Contributions to the Chelate Effect - The Entropy... 

Figure 8-7. A comparison of high-spin octahedral and tetrahedral ligand-field stabilization energies for various d" configurations.

Table 1.3 Esti mated values of the four components of the contribution made by ligand field stabilization energy to the lattice enthalpy of KsCuFe, to the hydration enthalpy of Ni (aq), AH (Ni, g), and to the standard enthalpy change of reaction 13.

He compared the infrared spectra of cements with that of zinc polyacrylate salt and found differences. Inspection of his data shows that, unlike the cements, the salt was purely ionic, so that it seems here that cement formation is associated with the formation of coordination complexes. There are no ligand field stabilization effects with the Zn ion because it has a completed d shell (Cotton Wilkinson, 1966). For this reason the... 

In order to compare the structural options for transition metal compounds and to estimate which of them are most favorable energetically, the ligand field stabilization energy (LFSE) is a useful parameter. This is defined as the difference between the repulsion energy of the bonding electrons toward the d electrons as compared to a notional repulsion energy that would exist if the d electron distribution were spherical. 

Table 9.1 Ligand field stabilization energies (LFSE) for octahedral and tetrahedral ligand distributions...

Relative ligand field stabilization energies for 3d ions. Thick lines octahedral field ... 

The ligand field stabilization is expressed in the lattice energies of the halides MX2. The values obtained by the Born-Haber cycle from experimental data are plotted v.v. the d electron configuration in Fig. 9.5. The ligand field stabilization energy contribution is no more than 200 kJ mol-1, which is less than 8% of the total lattice energy. The ionic radii also show a similar dependence (Fig. 9.6 Table 6.4, p. 50). 

Table 17.4 Ligand field stabilization energies for Mn304, Fe304 and Co304. Values for high-spin complexes in all cases except for octahedral Co ...

Decide whether the following compounds should form normal or inverse spinels using the ligand field stabilization energy as the criterion ... 

Hydration of the metal ions produces an enthalpy change that is commensurate with the size and charge of the ion with the addition of the number of Dq units shown in the weak field column in Table 17.4. For d°, d5, and d10 there is no additional stabilization of the aqua complex since these cases have no ligand field stabilization. Figure 17.10 shows a graph of the heats of hydration for the first-row + 2 metal ions. 

Table 17.4 Ligand Field Stabilization Energies in Dq Units. ...

The graph shows what has become known as the "double-humped" appearance that reflects the fact that the ligand field stabilization energy for the aqua complexes begins at 0, increases to 12 Dq, then drops to 0 on going from d° to d5 and repeats the trend on going from d6 to d10 (see Table 17.4). 

Determine the ligand field stabilization energy for d°-d10 ions in tetrahedral complexes. Although there are no low-spin tetrahedral complexes, assume that there are. 

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