Valency orbitals vanadium

A good example of a tetrahedral metal complex is VCU, the coordinate system for which is shown in Fig. 9-16. We have already discussed the role of s and f valence orbitals in a tetrahedral molecule (Chapter V). The 4s and 4p orbitals of vanadium can be used to form tr molecular orbitals. The 34, and orbitals are also situated properly for such use. In valence-bond language, jd and sp hybrid orbitals are both tetrahedrally directed. The and... 

Koopman s theorem is found to be valid only in the case of the vanadium (dA) complex 9. The amount of orbital reorganization is increasing considerably in the series 9-14-15-16. It is also found that strong metal-ligand interaction combined with low symmetry leads to extensive delocalization of the outer valence MO s especially in the cylobutadiene complex 16, only two orbitals with >80% metal character are found for which the convenient term essential 3d metal orbital would be justified. 

UPS studies of supported catalysts are rare. Griinert and coworkers [45] recently explored the feasibility of characterizing polycrystalline oxides by He-II UPS. A nice touch of their work is that they employed the difference in mean free path of photoelectrons in UPS, V 2p XPS and valence band XPS (below 1 nm, around 1.5 nm, and above 2 nm, respectively) to obtain depth profiles of the different states of vanadium ions in reduced V205 particles [45]. However, the vast majority of UPS studies concern single crystals, for probing the band structure and investigating the molecular orbitals of chemisorbed gases. We discuss examples of each of these applications. 

The charge at the vanadium in the usual dithiolene complexes may be estimated49 as less than 2, and these complexes are therefore included in the section on low valence states. Various tris(dithiolene) complexes have been isolated and one-electron oxireductions studied by polarographic and voltammetric techniques. Table 3 summarizes methods of preparation and electrochemical behaviour. Schrauzer and co-workers50 correlated electrochemical data with Taft s constants the observed linear correlation reflected the ligand n orbital origin of the orbitals involved in the redox process. 

In order to discuss the valence electronic state and chemical bonding of lithium vanadium oxide we made calculations using cluster models. The density of states (DOS) and the partial density of states (PDOS) of Li1.1V0.9O2 are obtained by this study as shown in Figure 3.4. The filled band located from —8 to —3 eV is mainly composed of O 2p orbital. The partially filled band located around —2 to 4 eV is mainly composed of V 3d orbital. Unoccupied band located above 5 eV is... 

Stizza et al. (73,274) have investigated amorphous vanadium phosphates, which are also of interest in relation to a XAS study of the butane-maleic anhydride (V, P)0 catalysts (99a). From the V K edge useful information is obtained about the distortions in the vanadium coordination sphere [molecular cage effect on the pre-edge intensity (312)] and on the vanadium oxidation state. Notably, V4+ is silent to most spectroscopic methods. A mixed V4+-V5+ valence state can be measured from the energy shift of the sharp core exciton at the absorption threshold of the Is level of vanadium due to Is -f 3d derived molecular orbitals localized within the first coordination shell of vanadium ions. 

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