Vanadium hexacarbonyl

Vanadium hexacarbonyl is the inorganic compound with the formula V₆. It is a blue-black volatile solid. This highly reactive species is noteworthy from theoretical perspectives as a rare isolable homoleptic metal carbonyl that is paramagnetic. Most species with the formula M_x_y follow the 18-electron rule, whereas V₆ has 17 valence electrons.

Synthesis

According to the original synthesis by Calderazzo, V₆ is prepared in two-steps via the intermediacy of. In the first step, VCl₃ is reduced with metallic sodium under 200 atm CO at 160 °C. The solvent for this reduction is typically diglyme, CH₃OCH₂CH₂OCH₂CH₂OCH₃. This triether solubilizes sodium salts, akin to the behavior of a crown ether:
The resulting anion is oxidized with acid:

Reactions

Vanadium hexacarbonyl is thermally unstable. Its primary reaction is reduction to the monoanion, salts of which are well studied. It is also susceptible to substitution by tertiary phosphine ligands, often leading to disproportionation.
V₆ reacts with sources of the cyclopentadienyl anion to give the orange four-legged piano stool complex V₄. Like many charge-neutral organometallic compounds, this half-sandwich species is volatile. In the original preparation of this species, C₅H₅HgCl was employed as the source of.

Structure

V₆ adopts an octahedral coordination geometry and is isostructural with chromium hexacarbonyl, even though they have differing valence electron counts. High resolution X-ray crystallography indicates that the molecule is slightly distorted with two shorter V–C distances of 1.993 Å vs. four 2.005 Å. Even though V is a larger ion than V, the V–C distances in are 0.07 Å shorter than in the neutral precursor.