Simultaneous observation of ν(OO), ν(CoO 2) and δ(CoOO) in resonance Raman spectra of five- and six-coordinate dioxygen adducts of Co(TPP- d8

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The resonance Raman spectra of dioxygen adducts of five- and six-coordinate Co(TPP- d 8) were measured using 406.7 nm excitation. Five-coordinate complexes are produced in low-temperature O 2 matrices, while six-coordinate complexes are formed at low temperature in toluene- d 8 solution in the presence of pyridine which serves as the sixth ligand. The ν(OO), ν(CoO 2) and δ(CoOO) modes of Co(TPP- d 8)O 2 are observed at 1281 (1206),? (369) and 216 (195) cm −1, respectively, where the numbers in parentheses indicate the corresponding 18O 2 adduct vibrations. The ν(OO), ν(CoO 2) and δ(CoOO) modes of Co(TPP- d 8)(py)O 2 are located at 1161 (1097), 511 (489) and 278 (262) cm −1, respectively. The downshift of ν(OO) and ν(CoO 2) of the six- vs. the five-coordinate complex is attributed to electron donation from pyridine to O 2 which strengthens the CoO and concomitantly weakens the OO bond.