Ground electronic states metallocenes

Derivative electron transmission spectra for the 3d metallocenes (7) are presented in Fig. 1. Very similar results have been obtained by Modem/ et al. (11). Occupations of the predominantly M3d highest occupied orbitaTs and ground electronic states are given in Table I. 

The final system of the metallocene series, Ni(Cp)2, and its dimethyl derivative, sup-ly only a small amount of information from their photoelectron spectra, since only a single peak due to a d-electron ionisation is observed in each case. This band is obviously due to ionisation of a 7r d-electron from the 32 (o2 tt2 54) ground level to yield a single ion state, 2Il(a2 tt 54), and its intensity relative to the ligand ionisation region rules out the possibility of other d-electron ionisations being coincident with it. 

Ground-State Electronic Configurations of Open-Shell Metallocenes... 

Tables 1 and 2 assume the strong-field limit for configurations of d electrons in ligand fields (16). In Table 1, all ground states have been considered which are likely to occur in tetrahedral and octahedral symmetries. Table 2 was originally intended for D 5 symmetries appropriate to the metallocenes, but it can also be used for Dn where n > 5, and (with some change of notation) for linear symmetries.

A quite different case is presented by the bent metallocene systems, [Cp2MH(alkene)] where M = Nb or Ta. Here the metal-alkene complex is relatively quite stable, so much so that the kinetics of formation of a stable alkyl metal complex cannot be easily studied. Nonetheless it is possible to get a handle on the hydrometallation kinetics by means of dynamic NMR methods (Table 1). The increased rate for propene versus ethylene results from both steric destabilization of the ground state and electronic stabilization of the transition state for the former. The first is typical of alkene complexes the second implies that some partial positive charge develops at the -carbon during the hydrometallation process, also seen in the trend for substituted styrenes. 

We discuss in this section the principal bonding characteristics shown in the metallocene and bis-benzene series and the way in which these trends influence the splittings within the set of 3d-orbitals and consequently determine the electronic ground states of these complexes. A brief account of the bonding of the recently discovered symmetrical bis-cyclobutadiene complex NiCbj will also be summarised. 

Big even though the ground state electronic configurations do not necessarily correspond to sequential filling of these levels, particularly for some of the metallocenes ). 

Table 1 Electronic structure and ground-state as well as Lande g values and reduction potentials (vs. SCE) of metallocenes and decamethylmetallocenes as well as their cations, [MCp2] + ...

Such complex spectra are found for open-shell metallocenes.Whereas ferrocene has two bands arising from ionization of its rf-electron configuration, chromocene, with a triplet ground state and an eia configuration,... 

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