Molecular orbitals octahedral

Fig. 2. Simplified molecular orbital diagram for a low spia octahedral complex, such as [Co(NH3 )g, where A = energy difference a, e, and t may be antisymmetric (subscript ungerade) or centrosymmetric (subscript, gerade) symmetry orbitals. See text.

Figure 19.14 Molecular orbital diagram for an octahedral complex of a first series transition metal (only a interactions are considered in this simplified diagram).

The foregoing discussion indicates that while there are difficulties in the way of a bonding role for 3d orbitals, for certain situations at least it is possible to conceive of ways in which these difficulties may be overcome. However, it is necessary to say that even for hypervalent molecules such as SF6 which seem to require the use of d orbitals, there are molecular orbital treatments not involving the use of d orbitals. In fact, as shown by Bent in an elegant exposition12, the MO model of SF6 involving the use of d orbitals is only one of several possibilities. The octahedral stereochemistry of SF6, traditionally explained in... 

FIGURE 16.36 I1ie tear-shaped objects are representations of the six ligand atomic orbitals that are used to build the molecular orbitals of an octahedral complex in ligand field theory. They might represent s- or p-orbitals on the ligands or hybrids of the two. 

We are now ready to apply the ideas in the preceding three sections to the construction of molecular orbitals in octahedral complexes. 

Fig. 4.4 Molecular orbital diagram for octahedral complexes (cr-interaction only)...

A quantitative consideration on the origin of the EFG should be based on reliable results from molecular orbital or DPT calculations, as pointed out in detail in Chap. 5. For a qualitative discussion, however, it will suffice to use the easy-to-handle one-electron approximation of the crystal field model. In this framework, it is easy to realize that in nickel(II) complexes of Oh and symmetry and in tetragonally distorted octahedral nickel(II) complexes, no valence electron contribution to the EFG should be expected (cf. Fig. 7.7 and Table 4.2). A temperature-dependent valence electron contribution is to be expected in distorted tetrahedral nickel(n) complexes for tetragonal distortion, e.g., Fzz = (4/7)e(r )3 for com-... 

Molecules with two or more unpaired electrons may be divided into two classes by far the most common examples are molecules where the unpaired electrons are contained in a set of degenerate atomic or molecular orbitals with qualitatively similar spatial distributions, e.g., an octahedral Cr(m) (4A2g) or Ni(n) (3A2g) complex, a ground state triplet molecule like 02, or the excited triplet states of naphthalene or benzophenone. 

Figure 5 Schematic presentation of a molecular orbital diagram for an octahedral d6 metal complex involving 2,2 -bipyridyl-type ligands, in which various possible transitions are indicated.

Fig. 13. Molecular orbital scheme for octahedral fluoride complexes...

FIGURE 5.13 The molecular orbital diagram for an octahedral molecule. 

FIGU RE 17.14 The coordinate system to designate orbitals used in constructing molecular orbitals for an octahedral complex. 

When describing a complex in terms of molecular orbitals, we need to establish a model by which we can identify the orbitals utilized by both the metal and the ligands. We will first consider an octahedral complex with the positions of the ligands identified on the coordinate system shown in Figure 17.14, and the orbitals will be designated by the numbers assigned to the ligands in the positions indicated. 

FIGURE 17.16 Ihe molecular orbital energy level diagram for an octahedral complex. 

Although we will not write the complete wave functions as we did for the case of an octahedral complex, the molecular orbitals give rise to the energy level diagram shown in Figure 17.20. 

FIGURE 18.9 Interpretation of M—charge transfer absorption in an octahedral complex using a modified molecular orbital diagram.The transitions are from e or t2g orbitals on the metal to orbitals on the ligands. 

The hypervalent chalcogen chemistry has been developed to higher coordinated species with various ligands,7 10 where TBP changes to square pyramidal (SP) or octahedral (Oh), etc. Additional atomic orbitals of E, such as an 5-orbital, may operate to stabilize the structures.10b The concept is also extended over linear a-bonds constructed by m ( > 4) atoms with n electrons (extended hypervalent bonds mc-ne (in > 4)).11 14 The approximate molecular orbital model for mc-ne (m > 4) is also exhibited in Scheme la, exemplified by 4c-6e. 

Information about the possible structures of molybdate and its pro-tonated forms in solution has been obtained from molecular orbital calculations (62). By considering bond orders obtained from a Mulli-ken population analysis and the agreement between experimental and theoretical UV spectra it was concluded that [Mo04]2 and [HMoOt I are tetrahedral and that the neutral acid is octahedral. For the latter a somewhat distorted octahedral structure based on the formula Mo02(OH)2(H20)2 was proposed (62). The alternative structure Mo03(H20)3 was not taken into account in the calculations. 

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