Metal d orbitals

There is (a) cr-donation from a filled oxygen orbital to an empty platinum orbital and (b) 7r back-bonding from a filled metal d orbital into an empty oxygen 7r -anti-bonding orbital. 

Back-bonding, with formation of a 7r-bond, from a filled metal d orbital to an anti-bonding it -ethene orbital. 

The second example in Fig. 4-4 shows how a (spin-allowed or spin-forbidden) band lying close to a charge transfer band may acquire unusually high intensity. We shall discuss charge-transfer bands more in Chapter 6. For the moment, we note that they involve transitions between metal d orbitals and ligands, are often fully allowed and hence intense. On occasion, the symmetry of a charge transfer state... 

In Fig. 6-7, similar procedures are followed for the metal d orbitals. The 42 2orbital-symmetry matches with the in-plane group combination ((Ji-02+molecular orbitals described in Eq. (6-13). 

Figure 3. Molecular-orbital diagrams as obtained by the ROHF method. Dashed lines indicate MOs dominated by the metal d-orbitals, the solid lines stand for doubly occupied or virtual ligand orbitals. Orbitals which are close in energy are presented as degenerate the average deviation from degeneracy is approximately 0.01 a.u. In the case of a septet state (S=3), the singly occupied open-shell orbitals come from a separate Fock operator and their orbital energies do not relate to ionization potentials as do the doubly occupied MOs (i.e. Koopmann s approximation). For these reasons, the open-shell orbitals appear well below the doubly occupied metal orbitals. Doubly occupying these gives rise to excited states, see text.

A particular feature of transition metal porphyrin chemistry is that the energies of the metal d orbitals and the frontier orbitals of the porphyrin ligand arc often quite close, with the result that the redox chemistry of the porphyrin ligand and the... 

For ionic compounds, crystal field theory is generally regarded a sufficiently good model for qualitative estimates. Covalency is neglected in this approach, only metal d-orbitals are considered which can be populated with zero, one or two electrons. To evaluate (Vzz)vai 4t the Mdssbauer nucleus, one may simply take the expectation value of the expression — e(3cos 0 — for every electron in a valence orbital i/, of the Mdssbauer atom and sum up,... 

A T structure with the strongest ct-donor D trans to the empty site (I in Scheme 1) is preferred in the case of three pure cr-donor ligands. The presence of a ir-acceptor ligand also makes the T structure more stable. When one of the ligands is a tt-donor, X, a Y structure of type II (Scheme 1) is observed. This structure permits the formation of a w bond between the empty metal d orbital and the lone pair of X. No such tt bond is present in the T structure since all symmetry adapted d orbitals are filled. This partial M—X multiple bond stabilizes Y over T. 

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