Table 2.

Energetic Parameters Computed for O₂ Binding to Complexes 2 and 4, and Comparison of Superoxo Stretching Frequencies in the Resulting [FeO₂] Adducts.

Stot (Fe spin) a	reactants	ΔHrxn	ΔSrxn b	ΔGrxn b	ν(O-O) (cm−1)
S = 3 (HS)	2 + O2	0.5	10.3	10.8	1222
	4 + O2	−1.3	10.6	9.3	1197
S = 2 (HS)	2 + O2	2.3	10.8	13.1	1213
	4 + O2	0.7	11.2	11.9	1198
S = 1 (HS)	2 + O2	1.7	11.2	12.9	1269
	4 + O2	−0.3	12.3	12.0	1243
S = 1 (LS)	2 + O2	−3.3	14.6	11.3	1183
	4 + O2	−7.1	15.1	8.0	1160

^aS_tot is the overall spin of the [FeO₂] adduct, whereas HS and LS indicate the spin-state of the Fe center itself.

^bThermodyanmic parameters were computed assuming a temperature of 298.15 K.