Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

A series of mononuclear non-oxido
vanadium­(IV) [VIV(L1–4)2]
(1–4), oxidoethoxido vanadium­(V)
[VVO­(L1–4)­(OEt)] (5–8), and dinuclear μ-oxidodioxidodivanadium­(V) [VV2O3(L1)2] (9) complexes with tridentate aroylazine ligands are reported
[H2L1 = 2-furoylazine of 2-hydroxy-1-acetonaphthone,
H2L2 = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone,
H2L3 = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone,
H2L4 = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone].
The complexes are characterized by elemental analysis, by various
spectroscopic techniques, and by single-crystal X-ray diffraction
(for 2, 3, 5, 6, 8, and 9). The non-oxido VIV complexes (1–4) are quite stable
in open air as well as in solution, and DFT calculations allow predicting
EPR and UV–vis spectra and the electronic structure. The solution
behavior of the [VVO­(L1–4)­(OEt)] compounds
(5–8) is studied confirming the formation
of at least two different types of VV species in solution,
monomeric corresponding to 5–8,
and μ-oxidodioxidodivanadium [VV2O3(L1–4)2] compounds. The μ-oxidodioxidodivanadium
compound [VV2O3(L1)2] (9), generated from the corresponding mononuclear
complex [VVO­(L1)­(OEt)] (5), is
characterized in solution and in the solid state. The single-crystal
X-ray diffraction analyses of the non-oxido vanadium­(IV) compounds
(2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the
VVO complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium­(V) (9) reveal that the metal center is in a distorted square pyramidal
geometry with O4N binding sets. For the μ-oxidodioxidodivanadium
species in equilibrium with 5–8 in
CH2Cl2, no mixed-valence complexes are detected
by chronocoulometric and EPR studies. However, upon progressive transfer
of two electrons, two distinct monomeric VIVO species are
detected and characterized by EPR spectroscopy and DFT calculations.