Oxidovanadium Complexes of 2,2′‐Bipyridine, 1,10 Phenanthroline, and p‐Nitro‐o‐aminophenol – Radical versus Nonradical States

Abstract

Abstract2,2′‐Bipyridine (bpy), 1,10‐phenanthronline (phen) and p‐nitro‐o‐aminophenol (NO2LH2) oxidovanadium complexes of the types [(LONO2–)(VO)(bpy)] (1), [(LONO2–)(VO)(phen)] (2) and [(LONO2–)(VO)(NO2LISQ·–)][NHEt3] (3– NHEt3+; NO2LISQ·– = p‐nitro‐o‐iminobenzosemiquinonate radical) were isolated with (E)‐2‐(3‐hydroxy‐3‐phenyltriaz‐1‐en‐1‐yl)benzoic acid (LONOH2) as a coligand. The single‐crystal X‐ray bond parameters and electron paramagnetic resonance (EPR) spectra authenticated that 1 and 2 are the oxidovanadium(IV) complexes of bpy and phen, whereas 3– is the NO2LISQ·– complex of oxidovanadium(IV) and undergoes reversible one‐electron oxidation and reduction at lower potentials. Density functional theory (DFT) calculations established that the closed‐shell‐singlet (CSS) solution of 3– is unstable owing to open‐shell‐singlet (OSS) perturbation. The CSS → OSS charge‐transfer transition that appears at λ = 632 nm is absent for 1 and 2. Complex 3 is a hybrid of the [(LONO2–)(VO2+)(NO2LIQ)] (NO2LIQ = p‐nitro‐o‐iminobenzoquinone) and [(LONO2–)(VO3+)(NO2LISQ·–)] states, whereas 32– is an oxidovanadium(IV) complex of the type [(LONO2–)(VO2+)(NO2LAP2–)]2– (NO2LAP2– = p‐nitro‐o‐amidophenolato).