In toluene solutions (–79 °C) dioxygen reversibly binds to Mn(TPP)(py) with replacement of the pyridine to form a five-coordinate complex, rather than by addition to yield a six-coordinate species. The resulting Mn(TPP)(O2) complex surprisingly exhibits the S = 3/2 spin state (D = –2.48 ± 0.07 cm-1; λ = E/D = 0.3257 ± 0.0003; Az = –53.1 (±0.5) × 104 cm-1; Ay = –82.0 (±0.5) × 10-4cm -1; A17O = B17O = 0). The experimental results, in combination with qualitative bonding considerations, indicate (i) extensive Mn ⟶ O2 charge transfer and (ii) the appropriateness of an Mn1v(O22-) valency formalism in which the Mn(IV) is in the 4(t23) ground state. A linear geometry for the complex can be ruled out. Although further definite conclusions as to structure are not presently possible, we tentatively favor the symmetric, “edge-on” mode of binding.
ASJC Scopus subject areas
- Colloid and Surface Chemistry