Vanadium complexes spectra

FIGURE 5.4 Vanadium NMR spectrum showing the formation of various hydroxamidova-nadium(V) complexes. Experimental conditions 3.0 mM total vanadate, 5.0 mM total hydrox-ylamine, 20 mM HEPES buffer, 1.0 M KC1, pH 6.9. 

A vanadium complex can be precipitated from a concentrated acetonitrile solution of (HPS)VO(OEt)(EtOH) by the addition of a small amount of water. This complex has an elemental analysis consistent with the formulation [(HPS)V0]20 MeCN. Its 51V NMR spectrum shows only the three upheld resonances. Addition of ethanol results again in complete conversion to the —530 ppm form (HPS)VO(OEt) (35). 

Vanadium complex luminescence may be supposed in chrysoberyl where artificial chrysoberyl activated by V exhibits read broad band luminescence with decay time of approximately 5 ps under UV excitation (Fig. 5.98). Similarly, pyromorphite usually has orange to yeUow UV excited luminescence characterized by broadband peaking at 580 nm (Fig. 4.60). It was earlier supposed that such luminescence is connected with (V04) emission center (Gaft 1984), but the possible role of Ag also may be considered (Gorobets and Rogojine 2001). Beside, blue emission band in beryl luminescence spectrum with short decay time of 1 ps (Fig. 4.122a) can also be connected with (V04) complex, especially because the similar emission has been found in radioluminescence spectrum of beryl with elevated ccmcentration of vanadium (Chithambo et al. 1995). 

The magnetic moment of the ytterbium-vanadium complex = 1.4 jiB) indicates the presence of one unpaired d-electron. Its ESR spectrum ( 8 lines, gj - 1.982, ... 

The adsorption spectrum of aerosil containing admixture vanadium ions exhibits a maximum within the band 290 - 380 nm which was attributed by authors of [97] to the charge transfer transitions in oxygen-containing complexes of five valance vanadium = O -... 

Studies of V4+, which is also a 3d1 ion, have been carried out by several investigators (151, 162, 163). The spectra are often complex due to a nuclear spin of i however, good resolution has been achieved for the ion in a particular symmetry. After a vacuum treatment of vanadium on silica gel at 500° van Reijen and Cossee (151) observed the spectra shown in Fig. 33. Both spectra were obtained with the sample at 20°K. The authors attributed the first spectrum to the (V04)4" ion and the second to the... 

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. " ... 

Oxovanadium(IV) complexes with dithiophosphate ligands have been extensively examined <8,121.161,252,386) x typical ESR spectrum is shown in Fig. 7. In addition to the eight vanadium 1=112 hyperfine lines phosphorus (/ = 1/2) superhyperfine splitting is also observed. The phosphorus superhyper-fine splitting can be considered a bit unusual since the phosphorus is located about 3 A or more away from the metal ion. P and As superhyperfine splitting has been observed in the ESR spectra of ill-defined vanadium phosphine 388) and arsine 389) complexes but in those cases, presumably, direct V-P and V—As interactions occur. ESR parameters have been tabulated for a large number of dithiophosphate 121,252) dithiophosphinate 121.252) complexes. Evaluation 3i) of the fractional 3s character of unpaired electron in dithiophosphate complexes yielded a value of 1.35%. The vanadyl(IV) complexes possess approximate C2V symmetry. The unpaired d electron resides... 

The blue emission band in the beryl liuninescence spectrum with a short decay time of 1 ps (Fig. 4.52a) can be connected with the (V04) complex, especially because a similar emission has been foimd in the radioluminescence spectrum of beryl with an elevated concentration of vanadium (Chithambo et al. 1995). 

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