Oxidation state V d

Boas and L. C. Pessoa, Vanadium, Chap. 33, pp. 453-583, and L. G. Hubert-Pfalzgraf, M. Postel and 

Niobium and Tantalum, Chap. 34, pp. 585-697 in Comprehensive Coordination Chemistry, Vol. 3, Pergamon Press, Oxford, 1987. 

Niobium(V) is generally considered to be a class-a metal, but the SCN ligand yields a series of both V-bonded thiocyanato and 

However, most complexes of Nb and Ta are derived from the pentahalides. NbFs and TaFs dissolve in aqueous solutions of HF to give [MOFs] and, if the concentration of HF is increased, [MFg]. This is normally the highest coordination number attained in solution though some [NbFy] - may form, and [TaFv] definitely does form, in very high concentrations of HF. However, by suitably regulating the concentration of metal, fluoride ion and HF, octahedral 

Boas and L. C. Pessoa, Vanadium, Chap. 33, pp. 453-583, and L. G. Hubert-Pfalzgraf, M. Postel and J. G. Riess, Niobium and Tantalum, Chap. 34, pp. 585-697 in Comprehensive Coordination Chemistry, Vol. 3, Pergamon Press, Oxford, 1987. 

Niobium(V) is generally considered to be a class-a metal, but the SCN ligand yields a series of both V-bonded thiocyanato and S-bonded isothiocyanato complexes, e.g. [Nb-(NCS) (SCN)6 ]- (n = 0, 2, 4, 5, 6). Furthermore, dithiocarbamates, dodecahedral [M(S2CNR2)4] , and dithiolates,  

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In agreement with the oxidation state V(IV)-d, it has a magnetic moment /ieff = 1.75 /iB- The V-S bond lengths are substantially identical, but the bonding angles are grouped as four smaller and two larger. 

On the other hand, the ratio Hz (ext/obs) < 1 of the EXV catalyst indicates an increase of the amount of hydrogen consumption. The UV-VIS spectra on this catalyst (Fig. 3) support this result, showing a large band in the of d-d transitions region. According to the literature [3,10], the peak at 800 nm corresponds to the octahedral vanadium species in oxidation state V. ... 

In their maximum oxidation state, V(V), Cr(VI), Mo(VI), W(VI) and Mn(Vll) have the d electron configuration, carry a high charge and are relatively small. In an alkaline medium, they exist as tetraoxo [M04] monomers [2] (see Section I.l, charge-pH diagram). 

The passage from the 3d to the Ad and 5d series is also characterised by an increase in the stability of the higher oxidation states. Thus in the 3d series M(IV) complexes tend to be unstable and strongly oxidising and are found only for V, Cr, Mn, Co, and Ni, and of the MF compounds (Ti to Cu) those of Co, Ni, and Cu exhibit similar features. In the 4 d series though a number of quite stable M (IV) species are known as well as examples of M (III) complexes, and MFelectronic spectra is entirely lacking we do not treat them further here. 

In the 5 d series the M(V) oxidation state is the most widely occurring condition as far as hexafluoro salts are concerned. The MF6 anion is thus known for the elements from W to Au, but unlike the M(IV) complexes these are all strongly oxidising species they are unstable towards water and the MF< ions of Re, Os, Ir, and Pt all yield the corresponding quadrivalent salts on hydrolysis. 

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