Aerial Oxidation of a V<sup>IV</sup>–Iminopyridine
Hydroquinonate Complex: A Trap for the V<sup>IV</sup>–Semiquinonate
Radical Intermediate
Marios Stylianou
Chryssoula Drouza
John Giapintzakis
Georgios I. Athanasopoulos
Anastasios D. Keramidas
10.1021/acs.inorgchem.5b00571.s007
https://acs.figshare.com/articles/dataset/Aerial_Oxidation_of_a_V_sup_IV_sup_Iminopyridine_Hydroquinonate_Complex_A_Trap_for_the_V_sup_IV_sup_Semiquinonate_Radical_Intermediate/2144935
The
reaction of 2,5-bis[<i>N</i>,<i>N</i>′-bis(2-pyridyl-aminomethyl)aminomethyl]-<i>p</i>-hydroquinone (H<sub>2</sub>bpymah) with VO<sup>2+</sup> salts in acetonitrile or water at a low pH (2.2–3.5) results
in the isolation of [{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymah)],
the <i>p</i>-semiquinonate complex [{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymas)](OH), the cyclic mixed-valent hexanuclear
compound [{V<sup>V</sup>(O)(μ-O)V<sup>IV</sup>(O)}(μ-bpymah)]<sub>3</sub>, and [(V<sup>V</sup>O<sub>2</sub>)<sub>2</sub>(μ-bpymah)].
[{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymas)](OH) is an intermediate
of the radical-mediated oxidation of [{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymah)] from O<sub>2</sub>. At lower pH values (2.2),
a reversible intramolecular electron transfer from the metal to the
ligand of [{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymas)](OH)
is induced with the concurrent substitution of chlorine atoms by the
oxygen-bridging atoms, resulting in the formation of [{V<sup>V</sup>(O)(μ-O)V<sup>IV</sup>(O)}(μ-bpymah)]<sub>3</sub>. The
metal complexes were fully characterized by X-ray crystallography,
infrared (IR) spectroscopy, and magnetic measurements in the solid
state, as well as by conductivity measurements, UV–vis spectroscopy,
and electrochemical measurements in solution. The oxidation states
of the metal ions and ligands were determined by the crystallographic
data. The [{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymah)]–[{V<sup>IV</sup>(O)(Cl)}<sub>2</sub>(μ-bpymas)](OH) redox process is
electrochemically reversible. The V<sup>IV</sup> ion in the semiquinonate
compound exhibits a surprisingly low oxophilicity, resulting in the
stabilization of OH<sup>–</sup> counterions at acidic pH values.
An investigation of the mechanism of this reaction reveals that these
complexes induce the reduction of O<sub>2</sub> to H<sub>2</sub>O<sub>2</sub>, mimicking the activity of enzymes incorporating two redox-active
centers (metal–organic) in the active site.
2015-08-03 00:00:00
metal complexes
chlorine atoms
semiquinonate compound exhibits
VVO
metal ions
conductivity measurements
OH
VIV ion
UV
oxidation states
O 2.
H 2O
O 2
Aerial Oxidation
acidic pH values
H 2bpymah
electrochemical measurements
IR
VO
VV
intramolecular electron transfer