Table 1.

Effective unpaired electron density from CASSCF

Species	Redox and spin state	EUED
		Fe	Ligand*
Heme
deoxy	Fe(II) HS	4.000 (4)	—
carboxy	Fe(II) LS	0.001 (0)	0.352
oxy	Fe(II) IS†	2.014 (2)	0.302
Porphyrin
1	Fe(II) LS	0.000 (0)	0.000
2	Fe(II) HS	4.000 (4)	0.092
3	Fe(III) HS	5.000 (5)	0.001

^*Axial CO (carboxy), O₂ (oxy), N_Py (1), O_THF (2), or Cl⁻ (3) ligand on top of the porphyrin in Fig. 1 and SI Appendix, Fig. S14.

^†Simplified annotation (see text); formal unpaired Fe(d) spins in parentheses. The EUED on the ring systems in all heme and porphyrin species was zero.