Mixed‐Valence o‐Iminobenzoquinone and o‐Iminobenzosemiquinonate Anion Radical Complexes of Cobalt: Valence Tautomerism

Abstract

2,4‐Di‐tert‐butyl‐N‐[2‐(phenylthio)]phenyl‐o‐iminobenzosemiquinonate anion radical (LSPhISQ·–) and o‐iminobenzoquinone (LSPhIQ) based mixed‐valence complexes of the types trans‐[CoII(LSPhISQ·–)(LSPhIQ)X] defined by Robin–Day Class III states, trans‐[CoII(LSPhISQ0.5·–)2X] {X = Cl–, 1; SCN– (thiocyanato‐kS), 2; N3–, 3; NO2–, 4 and I3–, 5} are reported. The X‐ray bond parameters of 1–5, BS DFT calculations and variable‐temperature X‐band EPR spectra established the electronic states of 1–5. It was confirmed that 1–5 and mixed‐valence ions [1–5]+ and [1–5]– exhibit valence tautomeric equilibria of types: 1–5: trans‐[CoII(LSPhISQ0.5·–)2X] ⇌ trans‐[CoIII(LSPhISQ·–)2X]; [1–5]+: trans‐[CoIII(LSPhISQ0.5·–)2X]+ ⇌ trans‐[CoII(LSPhIQ)2X]+, and [1–5]–: trans‐[CoIII(LSPhISQ0.5·–1.0–)2X]– ⇌ trans‐[CoII(LSPhISQ·–)2X]– (LSPhIQ = o‐iminobenzoquinone state of LSPhISQ·–). In solids and frozen glasses, the contributions of “[MII(LSPhIQ)]” states are larger, whereas in fluid solutions the contributions of the “[MIII(LSPhISQ·–)]” states dominate. In CH2Cl2, 1–5 absorb strongly at ≥ 800 nm due to spin‐allowed LSPhISQ·– → LSPhISQ·– (charge resonance transfer) transitions, whereas in solids, they exhibit MII → LSPhIQ (MLCT) transitions at ≥ 1000 nm.