Vanadium hexacarbonyl

Vanadium hexacarbonyl
Names
IUPAC name
hexacarbonylvanadium(0)
Identifiers
20644-87-5
ChEBI CHEBI:37857 Yes
PubChem 519800
Properties
C6O6V
Molar mass 219.00 g/mol
Appearance blue-green crystals
yellow solutions
Density 1.7 g/cm3
Melting point decomposes
Boiling point sublimes at 50 °C (122 °F; 323 K) (15 mmHg)
insoluble
Solubility in other solvents 5 g/L hexane;
more soluble in dichloromethane
Structure
Crystal structure orthorhombic
octahedral
Dipole moment 0 D
Hazards
Main hazards CO source
Related compounds
Related compounds
Cr(CO)6, VCl3
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Vanadium hexacarbonyl is the inorganic compound with the formula V(CO)6. This highly reactive species is noteworthy from theoretical and scholarly perspectives. It is a rare isolable homoleptic metal carbonyl that is paramagnetic. Most species with the formula Mx(CO)y follow the 18e rule, whereas V(CO)6 has 17 valence electrons.[1]

Synthesis

Traditionally V(CO)6 is prepared in two-steps via the intermediacy of [V(CO)6]−. 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:

4 Na + VCl3 + 6 CO + 2 diglyme → [Na(diglyme)2][V(CO)6] + 3 NaCl

The resulting anion is oxidized with acid:

2 [V(CO)6]− + H3PO4 → 2 V(CO)6 + H2 + 2 H2PO4−

An improved low-pressure synthesis has been developed.[2]

Reactions

Vanadium hexacarbonyl is thermally unstable. Its primary reaction is reduction to the monoanion [V(CO)6]−, salts of which are well studied. It is also susceptible to substitution by tertiary phosphine ligands, often leading to disproportionation.

V(CO)6 reacts with sources of the cyclopentadienyl anion to give the orange, volatile four-legged piano stool complex (C5H5)V(CO)4 (m.p. 136 °C). 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 C5H5−.

Structure

V(CO)6 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 (trans) shorter V-C distances of 1.993(2) vs. four (equatorial) 2.005(2) Å. Even though V(-1) is larger ion than V(0), the V-C distances in [V(CO)6]- are 0.07 Å shorter than in the neutral precursor.[3]

References

  1. ↑ C. Elschenbroich, A. Salzer ”Organometallics : A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
  2. ↑ Liu, X.; Ellis, J. E. "Hexacarbonylvanadate(1−) and Hexacarbonylvanadium(0)" Inorganic Syntheses 2004, volume 34, pages 96-103. doi:10.1002/0471653683.ch3. ISBN 0-471-64750-0
  3. ↑ Bellard, S.; Rubinson, K. A.; Sheldrick, G. M. "Crystal and molecular structure of vanadium hexacarbonyl" Acta Crystallographica 1979. volume B35, pages 271-274 doi:10.1107/S0567740879003332

Further reading