21.6A: The Metal

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The discovery of vanadium is attributed to Andres Manuel del Rio (a Spanish mineralogist working in Mexico City) who prepared a number of salts from a material contained in "brown lead" around 1801. Unfortunately, the French chemist Collett-Desotils incorrectly declared that del Rio's new element was only impure Chromium. Del Rio thought himself to be mistaken and withdrew his claim. The element was rediscovered in 1830 by the Swedish chemist Nils Gabriel Sefström who named it after the Norse goddess Vanadis, the goddess of beauty and fertility.

Metallic vanadium was not isolated until 1867 when Sir Henry Enfield Roscoe (1833-1915), Professor of Chemistry at Owens College (later the University of Manchester) from 1857 to 1885, reduced vanadium chloride (VCl₅) with gaseous hydrogen to give vanadium metal and HCl.

Properties of vanadium
An excellent site for finding the properties of the elements, including vanadium is at

Introduction

Vanadium has been found to play a number of roles in biological systems. It is present in certain vanadium dependent haloperoxidase and nitrogenase enzymes.

A tunicate (Clavelina Puertosecensis) discovered near Discovery Bay, Jamaica

Many sea squirts, such as Ciona Intestinalis accumulate vanadium in very high concentration, although the reason is not known.

The mushroom Amanita muscaria accumulate vanadium in the form of a coordination complex called amavadin, whose function is still unknown.
A number of vanadium complexes have been shown to alleviate many of the symptoms of diabetes in both in vitro and in vivo (in rats and mice) studies. These complexes are being studied as potential alternatives to insulin therapy.

Vanadium Halides

Vanadium(V) halides
Formula	Colour	MP	BP	m (BM)	Structure
VF₅	white	19.5	48.3	0	trigonal bipyramid in gas phase

Preparations:

Prepared by reaction of V with F₂ in N₂ or with BrF₃ at 300C.
In the solid state it is an infinite chain polymer with cis-fluoride bridging.

Vanadium(IV) halides
Formula	Colour	MP	BP	m (BM)	Structure
VF₄	lime-green	100 ^(a)	-	1.68	-
VCl₄	red-brown	-25.7	148	1.61	tetrahedral (monomeric)
VBr₄	purple	-23d	-	-	-

^(a) sublimes with decomposition at 100 C.
Preparations:

VCl₄ is prepared by reaction of V with chlorinating agents such as Cl₂, SOCl₂, COCl₂ etc.
Reaction of VCl₄ with HF in CCl₃F at -78C gives VF₄.

Vanadium Oxides and Aqueous Chemistry

Vanadium oxides
Formula	Colour	Common name	Oxidation State	MP	V-O distance (pm)
V₂O₅	brick-red	pentoxide	V⁵⁺	658	158.5-202
V₂O₄	blue	dioxide	V⁴⁺	1637	176-205
V₂O₃	grey-black	sesquioxide	V³⁺	1967	196-206

Preparations:
V₂O₅ is the final product of the oxidation of V metal, lower oxides etc.

Aqueous Chemistry very complex:

a VO₂⁺
b VO(OH)₃
c V₁₀O₂₆(OH)₂^4-
d V₁₀O₂₇(OH)^5-
e V₁₀O₂₈^6-
f V₃O₉^3-
g VO₂(OH)₂^-
h V₄O₁₂^4-
i V₂O₆(OH)^3-
j VO₃(OH)^2-
k V₂O₇^4-
l VO₄^3-

a VO₂⁺
b V₁₀O₂₆(OH)₂^4-
c V₁₀O₂₇(OH)^5-
d V₁₀O₂₈^6-
e V₄O₁₂^4-
f V₃O₉^3-
g V₂O₆(OH)^3-
h V₂O₇^4-
i VO₃(OH)^2-
j VO₄^3-

In alkaline solution,

VO₄^3- + H⁺ → HVO₄^2-
2HVO₄^2- → V₂O₇^4- + H₂O
HVO₄^2- + H⁺ → H₂VO₄^-
3H₂VO₄^- → V₃O₉^3- + 3H₂O
4H₂VO₄^- → V₃O₁₂^4- + 4H₂O

In acidic solution,

10V₃O₉^3- + 15H⁺ → 3HV₁₀O₂₈^5- + 6H₂O
H₂VO₄^- + H⁺ → H₂VO₄
HV₁₀O₂₈^5- + H⁺ → H₂V₁₀O₂₈^4-
H₃VO₄ + H⁺ → VO₂⁺ + 2H₂O
H₂V₁₀O₂₈^4- + 14H⁺ → 10VO₂⁺ + 8H₂O

VO(H₂O)₄SO₄
The crystal structure of this salt was first determined in 1965. The V=O bond length was 159.4 pm, the aquo group trans to this had the longest V-O bond length (228.4pm) and the equatorial bond lengths were in the range 200.5-205.6 pm. Note that SO₄^2- was coordinated in an equatorial position.

The IR stretching frequency for the V=O in vanadyl complexes generally occurs at 985 +/- 50 cm^-1.

Redox properties of oxovanadium ions:

VO₂⁺ + 2H⁺ + e- → VO²⁺ + H₂O E=1.0 V

VO²⁺ + 2H⁺ + e- → V³⁺ + H₂O E=0.34 V

References

"Inorganic Chemistry", 3rd Edition, Catherine Housecroft, Alan G. Sharpe, Publisher: Prentice Hall
"Complexes and First-Row Transition Elements", D. Nicholls
"Basic Inorganic Chemistry", F.A. Cotton, G. Wilkinson and P.L. Gaus
"Advanced Inorganic Chemistry", F.A. Cotton, G. Wilkinson, C. A. Murillo, and M. Bochmann
"Chemistry of the Elements", Greenwood and Earnshaw
"Hydrolysis of Cations", Baes and Messmer

Contributors and Attributions

Prof. Robert J. Lancashire (The Department of Chemistry, University of the West Indies)