51V NMR spectroscopy

These equilibria have been studied by various methods of which potentiometry and 51V NMR spectroscopy proved to be particularly useful for the identification of species and the determination of stability constants (8-10,13-16,18,20,22,24). Values obtained for stability constants by different research groups under the same conditions usually show good agreement, e.g., for 0.60 M NaCl medium (Table II). In some cases so-called Bronsted (or mixed) constants (25) are... 

Traditionally, the principal tools for the study of vanadate speciation in aqueous solution were UV/vis and electrochemistry. Unfortunately, the complex chemistry associated with vanadate has rendered much, but certainly not all, of the earlier work obsolete. The reaction solutions often contained numerous products that, a priori, could not be specified. Properly describing the chemistry was somewhat like doing a jigsaw puzzle without knowing what the pieces looked like or how many there were. Only with the advent of 51V NMR spectroscopy in high field NMR spectrometers was there a tool in place that allowed a coherent picture of V(V) chemistry to be fully developed. The combination of potentiometry with NMR spectroscopy has proven a certain winner. Additionally, x-ray diffraction studies have provided an invaluable source of information, but it is information that, in all cases, must be used with extreme caution when attempting to describe the chemistry in solution. 

Tracey, A.S. 2003. Applications of 51V NMR spectroscopy to studies of the complex -ation of vanadium(V) by a-hydroxycarboxylic acids. Coord. Chem. Rev. 237 113-121. 

Rehder, D. 1988. Interaction of vanadate (H2V04 ) with dipeptides. Investigated by 51V NMR spectroscopy. Inorg. Chem. 27 4312 -316. 

This book does not follow a chronological sequence but rather builds up in a hierarchy of complexity. Some basic principles of 51V NMR spectroscopy are discussed this is followed by a description of the self-condensation reactions of vanadate itself. The reactions with simple monodentate ligands are then described, and this proceeds to more complicated systems such as diols, -hydroxy acids, amino acids, peptides, and so on. Aspects of this sequence are later revisited but with interest now directed toward the influence of ligand electronic properties on coordination and reactivity. The influences of ligands, particularly those of hydrogen peroxide and hydroxyl amine, on heteroligand reactivity are compared and contrasted. There is a brief discussion of the vanadium-dependent haloperoxidases and model systems. There is also some discussion of vanadium in the environment and of some technological applications. Because vanadium pollution is inextricably linked to vanadium(V) chemistry, some discussion of vanadium as a pollutant is provided. This book provides only a very brief discussion of vanadium oxidation states other than V(V) and also does not discuss vanadium redox activity, except in a peripheral manner where required. It does, however, briefly cover the catalytic reactions of peroxovanadates and haloperoxidases model compounds. 

NMR spectroscopy can also be used to determine the formation constants of various complexes. We illustrate this by quantificating the distribution of vanadate oligomers in aqueous solution by 51V NMR spectroscopy. Moreover, the chemical shifts are very sensitive to protonation of the oxovanadium species, and 51V spectra can provide information on the specific protonation state of the anions in solution. 

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... 

Group 5 Systems. 51V NMR spectroscopy was used to follow the a-cis to (3-cA isomerisation of the Vv- propylenediaminetetraacetate complex.1036 The presence of isomerisation equilibria for (220) was studied by 3H, 13C and 51V NMR spectroscopy in solution,1037 51V solution NMR spectra were used to determine the species present in the systems II+/II2V04 /I I202/L-(+)-lactate or picolinate.1038,1039... 

Groups 5 and 6. The complexation of Vv02+ by the Schiff base N,N -ethylenebis(pyridoxyl-aminato) was followed by 111 and 51V NMR spectroscopy.1121 13C, 14N and 51V NMR spectra were used to follow reactions of vanadate(V) with dipeptides (Val-Glu, Ala-Gly etc.).1122 The reaction of TaF5... 

Mixed (Ru/V) sulfides were studied by 51V NMR spectroscopy.125 Variable-temperature 51V NMR studies of spin relaxation rates show that the vanadium lattice in CuV2S4 behaves as a nearly antiferromagnetic metal.126... 

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