Vanadium complexes spectroscopy

R spectra, 2, 511 Vanadium tetramethoxide spectroscopy, 2, 347 Vanadyl acetylacetonate, 2, 388 hydrolysis, 2, 379 Vanadyl complexes cupferron... 

Asphaltenes may contain both porphyrin and nonporphyrin metals, depending upon the origin of the crude oil. Yen et al. (1969) characterized the vanadium complexes in a petroleum asphaltene by mass spectroscopy, optical spectroscopy, and ESR. Porphyrins (Etio and DPEP), acid-resistant porphyrin macrocycles of increased aromaticity (Rhodo), and nonporphyrins with mixed donor complexes were identified. Baker (1966) and Baker et al. (1967) extracted porphyrins from Boscan crude oil asphaltenes and also found Etio and DPEP as the two major porphyrin series. These homologous series range in molecular weight by 7 to 18 methylene groups. Gallegos (1967) observed by mass spectroscopy that asphaltenes and maltenes from a Boscan crude oil had nearly identical porphyrins in terms of mass distribution. 

Tullius, T.D., Gillum, W.O., Carlson, R.M.K. and Hodgson, K.O. (1980) Structural study of the vanadium complex in living Ascidian blood cells by X-ray absorption spectroscopy./. Am. Chem. Soc. 102, 5670-5677. 

Bonadies, J.A. and C J. Carrano. 1986. Vanadium phenolates as models for vanadium in biological systems. 1. Synthesis, spectroscopy, and electrochemistry of vanadium complexes of ethylenebis[(o-hydroxyphenyl)glycine] and its derivatives. J. Am. Chem. Soc. 108 4088 1095. 

V NMR spectroscopy is a particularly useful method for solution studies of vanadium(V) complexes. Several correlations of the shielding in vanadium(V) complexes have been reported and have been used as empirical guides to the coordination number of the vanadium.57-64 Application of these correlations should, however, be used cautiously. 170 NMR spectroscopy65 and extended X-ray absorption fine structure (EXAFS) spectroscopy have been used for the characterization of solution complexes.66 Methods including potentiometry, X-ray diffraction, and UV-visible and IR spectroscopic techniques are also widely used in the characterization of the properties of vanadium complexes. Other methods for the characterization of low-level (sub-microgram) vanadium complexes have been described 67,68... 

The solid-state and solution chemistry of triethanolamine complexes has been investigated. While the solid-state structure was maintained in organic solvent (38), a different structure was observed in aqueous solution.262 170 NMR spectroscopy was used to demonstrate that the two oxo groups were different and in combination with H and 13C NMR data, defined the structure as (39).262 Speciation studies and a detailed characterization of this class of compounds were important because the ligand is a commonly used buffer in biology and the complexes are model systems for interactions with proteins.61,263 The thermodynamic parameters were determined for several derivatized diethanolamine ligand-vanadium(V) complexes, and represent some of the few vanadium complexes for which such parameters are known.62 The structure of (nitrilotriacetato)dioxovanadate was reinvestigated.2 4... 

In a related study, Ooms et al. have used solid-state MAS NMR spectroscopy and DFT calculations to characterize the chemical shift and quadrupolar coupling parameters for two eight-coordinate vanadium complexes. DFT calculations of the electric field gradient parameters were in good agreement with the NMR results while the chemical shift parameters showed some deviation from the experimental values. 

Van der Voort et al. [261-263] prepared vanadium oxide species in the meso-porous material MCM-48 by reacting the support with gaseous vanadyl acetyla-cetonate [VO(acac)2]. The vapor deposition was carried out in a vacuum reactor (see Fig. 9). VO(acac)2 is sublimed and reacts with the heated substrate at 150°C until a saturation loading is achieved. This takes approximately 16 h, visible by the formation of crystals of the complex on colder parts of the reactor [261]. Subsequently, the sample is purged with dry nitrogen at reaction temperature and calcined in ambient air at 500 °C. The uncalcined zeolite-supported vanadium complex and the calcined catalyst were characterized by X-ray diffraction, nitrogen absorption, IR and UV-Vis spectroscopy. 

Vanadium(n) Complexes.—Dehydration of VSO. THjO has been shown to proceed via the formation of VS04,mH20 (where n = 6, 4, or 1) and V(OH)-(SO4), which were characterized by X-ray studies. The polarographic behaviour and the oxidation potential of the V -l,2-cyclohexanediamine-tetra-acetic acid complex, at pH 6—12, have been determined.Formation constants and electronic spectra have been reported for the [Vlphen),] " and [V20(phen)] complexes. The absorption spectrum of V ions doped in cadmium telluride has been presented and interpreted on a crystal-field model. The unpaired spin density in fluorine 2pit-orbitals of [VF ] , arising from covalent transfer and overlap with vanadium orbitals, has been determined by ENDOR spectroscopy and interpreted using a covalent model. " ... 

In this paper selectivity in partial oxidation reactions is related to the manner in which hydrocarbon intermediates (R) are bound to surface metal centers on oxides. When the bonding is through oxygen atoms (M-O-R) selective oxidation products are favored, and when the bonding is directly between metal and hydrocarbon (M-R), total oxidation is preferred. Results are presented for two redox systems ethane oxidation on supported vanadium oxide and propylene oxidation on supported molybdenum oxide. The catalysts and adsorbates are stuped by laser Raman spectroscopy, reaction kinetics, and temperature-programmed reaction. Thermochemical calculations confirm that the M-R intermediates are more stable than the M-O-R intermediates. The longer surface residence time of the M-R complexes, coupled to their lack of ready decomposition pathways, is responsible for their total oxidation. 

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