Octahedral metal complexes configuration

Experimentally based intuitive arguments have been presented to arrive at a regional rule for optical activity of d-d transitions of conformational isomers of octahedral metal complexes. Conformational preferences for chelate rings formed by 1,3-pn in its octahedral mono, bis, and tris metal complexes have been studied by calculation of the conformational energies. In all cases, the chair conformation was found to be the most stable. The lowest energy pathway for converting from one chair configuration into another has a barrier to activation of about 7 kcal mol Conformational types of metal-edta complexes have been studied. ... 

Co(ni) acetylacetonates show frequencies closer to the low spin high spin. Co(tfac)3 has an even lower v(Co—O) band than calculated for low spin, i.e. 445 vi. 451 cm , respectively . Therefore, metal-ligand vibrations for a series of octahedral metal complexes are in order Co(II) < Ni(II) and Zn(II) < Ni(II) within the same ligand system. Fe(III) < Mn(III) < Cr(III) is observed, as expected from crystal field theory . 

Table 7.6 Comparison of ligand field splitting energy (A 0) for different ligands bound to d3 electronic configuration octahedral metal complexes [ML6]n+.

Octahedral metal complexes of d , Cr(III) and low spin d , Co(III), have particularly high kinetic stability to ligand replacement or exchange. The activation energy for ligand substitution in such complexes has been shown to be considerably greater than in comparable complexes in which the metal possesses other d° configurations. This kinetic stability is associated with the half filled or filled t2g environments, in which the... 

Polyatomic molecules cover such a wide range of different types that it is not possible here to discuss the MOs and electron configurations of more than a very few. The molecules that we shall discuss are those of the general type AFI2, where A is a first-row element, formaldehyde (FI2CO), benzene and some regular octahedral transition metal complexes. 

A representative molecular orbital diagram for an octahedral d-block metal complex ML6 is shown in Figure 1.8. The MOs are classified as bonding (oL and ttL), nonbonding (jtM) and antibonding (o, nl and ). The ground-state electronic configuration of an octahedral complex... 

Somewhat better data are available for the enthalpies of hydration of transition metal ions. Although this enthalpy is measured at (or more property, extrapolated to) infinite dilution, only six water molecules enter the coordination sphere of the metal ion lo form an octahedral aqua complex. The enthalpy of hydration is thus closely related to the enthalpy of formation of the hexaaqua complex. If the values of for the +2 and +3 ions of the first transition elements (except Sc2, which is unstable) are plotted as a function of atomic number, curves much like those in Fig. 11.14 are obtained. If one subtracts the predicted CFSE from the experimental enthalpies, the resulting points lie very nearly on a straight line from Ca2 lo Zn2 and from Sc to Fe3 (the +3 oxidation state is unstable in water for Ihe remainder of the first transition series). Many thermodynamic data for coordination compounds follow this pattern of a douUe-hunped curve, which can be accounted for by variations in CFSE with d orbital configuration. 

Both mer- and /ac-M(dien)(XYZ)"+ complexes for octahedral metal centers can be formed but the factors determining the relative stabilities have yet to be determined.612 In diamagnetic systems these configurations can be distinguished using NMR.23,613 Table 9 summarizes the available information. 

Rather less work has been done with other transition metal complexes using 3,2,3-tet as a ligand. The Cu11,836 859 Os111 44 and Rum410 complexes have been reported, with trans octahedral configurations assigned to the latter two. 

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