Oxygen— metal charge transfer

The molecular orbital energy level calculations have yielded relative energies of OMCT transitions (Loeffler et al., 1974, 1975 Sherman, 1985a,b Sherman and Waite, 1985). Peak maxima are centred well into the ultraviolet region. However, since OMCT transitions are fully allowed by both the 

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The electronic spectra of a variety of transition metal-bearing oxide and silicate minerals have been measured at high pressures and/or elevated temperatures. Trends for absorption bands originating from crystal field (CF), metal-metal intervalence charge transfer (IVCT) and oxygen —> metal charge transfer (OMCT) transitions are summarized in tables 9.2,9.3 and 9.4, respectively. 

Table 9.4. Oxygen —> metal charge transfer transitions in minerals at high pressures and temperatures... 

Fig. 3-1. Band assignment for the diffuse reflectance spectrum of a goethite. Note that one band eould not be assigned. EPT electron pair transition OMCT oxygen-metal charge transfer. From Seheinost et al., 1999 with permission.

Chromium v). Ab initio MO calculations and electronic spectral studies on the CrO group show that the second lowest energy electronic absorption is due to an oxygen-metal charge transfer rearrangement within the CrO " group. ... 

The desorption energy of the a - and a2-CO species was estimated to be 72 and 56 kJ mol respectively. The difference, 16 kJ mol can be ascribed to the electronic modification effect due to one oxygen atom, since the steric blocking is considered to be very small for both Mo. and Mo,. . This electronic effect is restricted to Mo atoms directly coordinated by 0(a) and can be explained in terms of the electrostatically-enhanced fiirough-metal charge transfer (13). 

Hexaalkoxides are only known for the two elements tungsten and uranium. In both cases, physical and spectroscopic data are consistent with monomeric, octahedral complexes. Tungsten hexaalkoxides are pale yellow or colorless substances that readily sublime and exhibit the expected H NMR and mass spectra.189 The totally symmetric v(W—O) stretch occurs between 530 and 600 cm-1 in the IR spectrum, depending on the alkyl substituents. In contrast, the homoleptic phenoxide W(OPh)6 is intense red in color due to the presence of a strong oxygen-to-metal charge transfer band in this d° complex which absorbs in the visible part of the spectrum.36... 

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