Vanadium oxide, electron paramagnetic complexation

Components of fluidized cracking catalysts (FCC), such as an aluminosilicate gel and a rare-earth (RE) exchanged zeolite Y, have been contaminated with vanadyl naphthenate and the V thus deposited passivated with organotin complexes. Luminescence, electron paramagnetic resonance (EPR) and Mossbauer spectroscopy have been used to monitor V-support interactions. Luminescence results have indicated that the naphthenate decomposes during calcination in air with generation of (V 0)+i ions. After steam-aging, V Og and REVO- formation occurred. In the presence of Sn, Tormation Of vanadium-tin oxide species enhance the zeolite stability in the presence of V-contaminants. 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

Complexes containing vanadium in low oxidation states, apart from organometallic compounds, are known with ligands such as bipy, phen, nitric oxide, and tertiary phosphines, which stabihze such oxidation states. Depending on their electronic structure, V and V complexes may be diamagnetic, which permits study by NMR spectroscopy, and EPR spectroscopy has been used to study paramagnetic V complexes. 

It can be seen also that the 18-electron rule will tend to break down when the first-row transition metals are in a high oxidation state. There may also be steric limitations to the formation of 18-electron complexes in high oxidation states - consider for example the hypothetical cation [Cr(CO)9] . Steric limitations may also explain why vanadium forms the monomeric, paramagnetic and 17-electron hexacarbonyl, V(CO)6, rather than the dimeric complex [V(CO)6]2 which would be diamagnetic and would obey the 18-electron rule. 

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