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.