A Coordination Chemistry Study of Hydrated and Solvated Cationic Vanadium Ions in Oxidation States +III, +IV, and +V in Solution and Solid State

The coordination chemistry of hydrated and solvated vanadium­(III),
oxovanadium­(IV), and dioxovanadium­(V) ions in the oxygen-donor solvents
water, dimethyl sulfoxide (DMSO), and N,N′-dimethylpropyleneurea (DMPU) has been studied in solution
by extended X-ray absorption fine structure (EXAFS) and large-angle
X-ray scattering (LAXS) and in the solid state by single-crystal X-ray
diffraction and EXAFS. The hydrated vanadium­(III) ion has a regular
octahedral configuration with a mean V–O bond distance of 1.99
Å.
In the hydrated and DMSO-solvated oxovanadium­(IV) ions, vanadium
binds strongly to an oxo group at ca. 1.6 Å. The solvent molecule
trans to the oxo group is very weakly bound,
at ca. 2.2 Å, while the remaining four solvent molecules, with
a mean V–O bond distance of 2.0 Å, form a plane slightly
below the vanadium atom; the mean OVOperp bond angle is ca. 98°. In the DMPU-solvated
oxovanadium­(IV) ion, the space-demanding properties of the DMPU molecule
leave no solvent molecule in the trans position to the oxo group,
which reduces the coordination number to 5. The OVO
bond angle is consequently much larger, 107°, and the mean
VO and V–O bond distances decrease to 1.58 and 1.97
Å,
respectively. The hydrated and DMSO-solvated dioxovanadium­(V) ions
display a very distorted octahedral configuration with the oxo groups
in the cis position with a mean VO bond distance of 1.6 Å
and a OVO bond angle of ca. 105°. The solvent
molecules trans to the oxo groups are weakly bound, at ca. 2.2 Å,
while the remaining two have bond distances of 2.02 Å. The experimental
studies of the coordination chemistry of hydrated
and solvated vanadium­(III,IV,V) ions are complemented by summarizing
previously reported crystal structures to yield a comprehensive description
of the coordination chemistry of vanadium with oxygen-donor ligands.