Group vanadium

Complexes of the titanium and vanadium groups are searee but mainly follow the routine eoordination modes. Sometimes for the dihydrobis(pyrazol-l-yl) borates, the role of M - - - H—B agostie interaetions is signifieant. 

The unsubstituted complexes [Mo(R2dtc>4] and [W(R2dtc)4] have been prepared by methods described earlier for synthesis of the vanadium-group complexes. They are 8-coordinate, with four bidentate dithiocar-bamate ligands (157). 

Hydrogen reacts at elevated temperatures with many transition metals and their alloys to form hydrides. The electropositive elements are the most reactive, that is, scandium, yttrium, the lanthanides, the actinides and members of the titanium and vanadium groups (Figure 5.20). 

III. Complexes with Scandium, Titanium, and Vanadium Group Metals. 182... 

HYDRIDE COMPOUNDS OF THE TITANIUM AND VANADIUM GROUP ELEMENTS... 

The atoms of the vanadium group metals have five valence electrons. In vanadium (Z — 23) and niobium (columbium, Z = 41), these valence electrons lie beyond ra re-gas cores, whereas in tantalum (Z = 73), they lie beyond the xenon core which has been augmented by fourteen 4/ electrons. The +5 oxidation state is characteristic of this family for niobium and tantalum it is the only oxidation state of importance. Oxidation is often regarded as removal of five valence electrons, followed by coordination of the pentapositive ion (which cannot exist for appreciable time in chemical systems) to basic groups which are present (H2O, OH, Cl, etc.). Although such a description almost certainly has very little resemblance to the actual path of oxidation of these metals, it is clerically convenient and may be used if not taken literally. In the same way, the lower oxidation states of vanadium may be considered vanadium atoms with the two 4s electrons removed, and with additional removal of one or two 3d electrons. 

Up to the end of 1972, more than 350 compounds containing silicon-transition-metal bonds had been synthesized, but their distribution among the d-block elements is by no means uniform. It can be inferred that the stability of such complexes decreases from right to left in a transition series and with increasing oxidation state of the transition metal. Nevertheless, it is remarkable that no silyl derivatives of the vanadium group have been prepared and that there are few nickel or palladium derivatives, as can be seen in the complete list of compounds given in Section 6. 

There appears to be no chemistry of tetrazenes or tetrazadienes with metals of the scandium, titanium, and vanadium groups. 

Hydride Compounds of the Titanium and Vanadium Group Elements... 

The vanadium group comprises vanadium, niobium and tantalum. Vanadium... 

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