Vanadium coordination

The mechanism for such a process was explained in terms of a structure as depicted in Figure 6.5. The allylic alcohol and the alkyl hydroperoxide are incorporated into the vanadium coordination sphere and the oxygen transfer from the peroxide to the olefin takes place in an intramolecular fashion (as described above for titanium tartrate catalyst) [30, 32]. 

Vanadium coordination compounds classification and analysis of crystallographic and structural data. C. E. Holloway and M. Melnik, Rev. Inorg. Chem., 1985,7, 75 (185). 

Although much of the V NMR has been performed on model systems or catalytic materials containing vanadium, 29 >30 compounds such as V2O5 or VOPO4 are used in both the catalysis and lithium battery fields, and many of the results can be used to help elucidate the structures of vanadium-containing cathode materials. V NMR spectra are sensitive to changes in the vanadium coordination number and distortions of the vanadium local environments from regular tetrahedra or octahedra. >33 5>V isotropic chemical shifts of between —400 and —800 ppm are seen for vanadium oxides, and unfortunately, unlike... 

The great recent development in electrochemical techniques will certainly be helpful for the study of redox processes of a metal which can occur in so many oxidation states. Multinuclear NMR spectrometers will allow increased use of 51V resonance as a routine method for the characterization of complexes in solution. Other recent developments are the study of polynuclear complexes, metal clusters (homo and hetero-nuclear) and mixed valence complexes, and it can be anticipated that these topics will soon become important areas of vanadium coordination chemistry, although the isolation of compounds with such complex... 

Reactions of these ligands have not been studied in aqueous solution. However, their complexes are readily synthesized and are stable but reactive towards heteroligands [41,42], The reported structures all show the vanadium coordinated in monomeric units after the fashion depicted in Scheme 4.9. The multidentate thiolato complexes with tri- or tetradentate functionality are sufficient to satisfy the coordination requirements of the vanadium nucleus. Structurally, the compounds are not much different from analogous complexes formed with oxygen ligands (Section 4.4.2). 

The chemistry already described is reproduced by numerous ligands that have not specifically been addressed in the previous discussion. The V-salicylidenehydrazides (Scheme 4.18a) and related compounds provide a good example. The structure [76] of a typical complex, represented in Scheme 4.18b, is not very different from that proposed for the solution structures of dipeptide complexes (Scheme 4.17). Interestingly, other similar complexes, based on Schiff base-derived ligands, form dimeric [VO]2 core complexes (Scheme 4.1) via two long ( 2.4 A) VO bonds [2], The cyclic core is not necessary for dimer formation, and a dimer can form via a linear VOV bond [77], These complexes otherwise are not significantly different in their vanadium coordination from that depicted in Scheme 4.18b. 

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. 

The extant literature of vanadium coordination complexes can be used to shed additional light on the vanadium site of vanadium bromoperoxidase. The known structures of vanadium in a variety of coordination environments provide a wealth of structural detail that can be brought to bear on the proposed enzyme structure. 

The largest vanadium coordination cage reported thus far is nonanu-clear [ V30io (OCH2)3CCH20H Vi6037] (14) 44), which is closely... 

Allylvanadium complexes (see Allyl Complexes) are synthesized by allylation with Grignard reagents as shown in Scheme 25. Another synthetic route lies in the allylation of a vanadium anionic species with allylic chloride. Codimerization of vanadium-coordinated diphenylacetylene (tolane) and 1,3-butadiene affords the allyl complex (49) (Scheme 26). ... 

In this section, selected and representative vanadium coordination compounds will be introduced. The aim is to provide a first overview of those coordination modes which are related - or can be related - to the coordination of vanadium to biogenic ligands in its biologically relevant oxidation states +III, +IV and +V. Additional, and usually more complex, structures will be provided in those sections of Chapters 4 and 5, that are dedicated to model chemistry. For simplicity, the coordination compounds will be grouped according to the type of ligand functions dominating the coordination sphere ... 

Vanadium coordination compounds containing at least one V-C bond. 

Table 3.3 Magnetic ordering temperatures for a series of vanadium coordination polymer magnets using halogen-substituted phenyl tricyanoethylene acceptors. (Explanation of abbreviation numbers indicate substitution position PTCE = phenyl tricyanoethylene)...

The occurrence of different vanadium coordination polyhedra, including tetrahedral [V(V)J, square pyramidal [V(1V) and V(V)], trigonal bipyr-amidal [V(IV)], distorted octahedral [V(1V) and V(V)], and regular octahedral [V(lll)] geometries. 

Compound V/P/O Framework Structure Vanadium Coordination and Linkages Cell Parameters Space Group References... 

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