Donor spin-orbit interaction

The introduction of heteroatoms into the hydrocarbon diradicals is a frequently applied strategy to tune the spin preference and relative stabilities of diradicals. The heteroatoms may change the energies of donor or acceptor orbitals, and consequently affect the donor-acceptor interaction involved in the cyclic orbital interaction. Take 2-oxopropane-l,3-diyl, or so-called oxyallyl (OXA, 18) as an example [29]. It is a hetero analog of TMM, as shown in Fig. 14. The replacement of CH with oxygen in the central fl unit leads to a decrease in energies of Jt and k orbitals. This may enhance the orbital interaction through one path (denoted by bold lines) and weaken that via the other (denoted by wavy lines) relative to the continuous cyclic orbital interaction in the parent species 1 (Fig. 14). As a result, the p-Jt -q... 

In a similar fashion the bonding in H2 might be formally regarded as a complementary pair of one-electron donor-acceptor interactions, one in the ot (spin up ) and the other in the 3 (spin down ) spin set.8 In the long-range diradical or spin-polarized portion of the potential-energy curve, the electrons of ot and (3 spin are localized on opposite atoms (say, at on HA and 3 on HB), in accordance with the asymptotic dissociation into neutral atoms. However as R diminishes, the ot electron begins to delocalize into the vacant lsB(a) spin-orbital on HB, while (3 simultaneously delocalizes into Isa on HA, until the ot and (3 occupancies on each atom become equalized near R = 1.4 A, as shown in Fig. 3.3. These one-electron delocalizations are formally very similar to the two-electron ( dative ) delocalizations discussed in Chapter 2, and they culminate as before (cf. Fig. 2.9) in an ionic-covalent transition to a completely delocalized two-center spin distribution at... 

We can also verify that the usual ECAO-MO description (3.2) and (3.4) leads to predicted hybridizations that are generally consistent with the donor-acceptor estimates (3.8). Suppose that each H atom is associated with a valence spin-orbital of hybridized form (3.6). According to Eq. (3.2), the optimal electronic energy of bond formation is obtained by choosing the hybridization parameter k to maximize the magnitude of the interaction element... 

The occupancies of metal 4d and 5s orbitals correspond to an overall s015d515 configuration, deviating noticeably from the nominal s°d5 assignment. The d spin-orbitals of a spin are essentially completely filled (0.993-0.995), and thus chemically inert. However, the nominally empty spin-orbitals of (3 spin exhibit significant non-zero occupancies (0.063 in each member of the eg set and 0.017 in each member of the t2g set), and appreciable occupancy of both spins is also found in the 5s orbital (0.088 a, 0.082 (3). These unexpected occupancies (which would be strictly absent in the isolated ion) can be associated with the leading donor-acceptor interactions, namely... 

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