Table 1. The Fe–O and O–O stretching frequencies (ν_Fe–O/cm^–1, ν_O–O/cm^–1) in the O₂ complexes of native CcO and synthetic PFe/CuL_n compounds.

	ν Fe–O/cm–1 16O2 (18O2)	ν O–O/cm–1 16O2 (18O2)	Medium
Superoxo group
CcO (beef heart) a	572 (548)	—	H2O, pH 7.4
CcO (bovine heart) b	571 (545)	—	H2O, pH 7.2
Fe/Cu[NMePr] c	570 (544)	—	CH2Cl2
FeCuArOH d	575 (549)	—	DMF
[(LN4-OH)Cu/Fe(TMPIm)] e	574 (548)	—	CH3CN/THF
FeTPPS/CuTerpyCD2 f	578 (551)	—	H2O, pH 7.0
μ-Peroxo group
LS-4DCHIm g	585, 591 (564)	876, 863 (820)	MeTHF
[LOHFe/Cu] h	—	799 (752)	CH3CN/toluene
[(LN4-OH)Cu/Fe(TMPIm)] e	611 (584)	787, 803 (751)	CH3CN/THF

^a Ref. 34.

^b Ref. 6.

^c Ref. 14.

^d Ref. 35.

^e Ref. 15.

^fThis work.

^g Ref. 37.

^h Ref. 36.