Table 2.

Homolytic vs. heterolytic cleavage of the O—O bond in Fe^III—OOH sites^*

Reactant	Spin	Homolysis							Heterolysis
		Thermodynamics†				Spin densities‡‡			Thermodynamics†				Spin densities‡‡
		ΔE	+solv	−TΔS‡	ΔGsolv	Fe	⩵O	X§	ΔE	+solv	−TΔS‡	ΔGsolv	Fe	⩵O	X§
1. [FeIII(NH3)5OOH]2+	1/2	+40.3	−10.6¶	−17.0	+12.7	+1.1	+1.0	0.0	+269.7	−219.2¶	−9.4	+41.0	+1.8	+1.4	0.0
2. [FeIII(NH3)4(OH)OOH]+	1/2	+31.5	−6.5¶	−15.2	+9.8	+1.2	+0.9	0.1	+136.6	−132.2¶	−6.7	−2.3	+1.6	+1.2	+0.3
3. [FeIII(BLM)OOH]+	1/2	+29.4	−2.6‖/−1.8††	−14.2	+12.8‖/+13.4††	+1.1	+0.9	0.0	+99.3	−103.4‖/−78.8††	−7.1	−11.2‖/+13.3††	+1.1	+1.1	+0.6
4. [FeIII(Por)(SCH3)OOH]−	1/2	+65.2	−2.4††	−13.5	+49.3	+1.1	+1.0	0.0	−75.3	+23.4††	−6.1	−58.0	+1.1	+1.0	+0.8
5. [FeIII(PAH)OOH]**	5/2	+37.9	−3.5††	−8.0	+26.4	+1.2	+0.9	0.0	+47.0	−39.9††	+0.5	+7.6	+1.6	+1.2	+0.3

^*DFT calculations performed by using B3LYP/TZV. 

^† All values in kcal/mol. 

^‡ Includes zero point correction energy. 

^§ Ligand X = NH₃ (1.), OH⁻ (2., 5.), deprotonated amide (3.), heme/SCH₃ (4.). 

^¶ Solvent = CH₃CN. 

^‖ Solvent = H₂O. 

^**(PAH): two NH₃, H₂O, OH⁻, -OCHO⁻. 

^††Solvent with ɛ = 4.0. 

^‡‡ All Fe^IV: S = 1, all Fe^V: S = 3/2.