Racemic vanadium(v) oxo monoperoxo complexes with two achiral bidentate heteroligands. Synthesis, characterization, crystal structure and stereochemistry of K[VO(O2)(ox)(bpy)]·3H2O and Pr4N[VO(O2)(ox)(phen)]

Abstract

Two new racemic monoperoxo complexes of vanadium(V), K[VO(O₂)(ox)(bpy)]·3H₂O (1) and Pr₄N[VO(O₂)(ox)(phen)] (2) [bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, ox = oxalate(2−) and Pr₄N = tetra(n-propyl)ammonium(1+)], were synthesized. The solid complexes were characterized by X-ray structure analysis and IR and Raman spectroscopies. The coordination polyhedron of vanadium is a distorted pentagonal bipyramid. The five equatorial positions are occupied by the η²-peroxo oxygen atoms, two oxygen atoms of the ox ligand and one nitrogen atom of bpy (resp. phen). The oxo ligand and the second nitrogen atom of bpy (resp. phen) are in axial positions. In each structure, the intermolecular distance, 3.5 Å, between the pairs of parallel bpy or phen ligands indicates a π-π interaction between the aromatic rings. The UV-vis spectra of aqueous solutions exhibit characteristic peroxo-to-vanadium CT bands at 422 nm (ε = 32 m² mol⁻¹) for 1 and 428 nm (ε = 29.4 m² mol⁻¹) for 2. From the ⁵¹V NMR measurements, the isomerization based on a mutual ox ↔ bpy or ox ↔ phen position change does not occur in aqueous solutions. The structure of both complex anions is maintained at 295 K for about 6 h after dissolution in water.