TABLE 1.

Vacuum structures of the Fe(Por)(His)(O/OH/H₂O) model and relative energies of the various spin states (ΔE)

Ox. state		# Unpaired spin	Distance to Fe (pm)			ΔE kJ/mol
			Ligand		NPor		NHis	O
III	H2O	5	205–208	215	240
III	OH−	1	201–202	206	182	0.0
III		3	202–203	261	191	75.6
III		5	208–210	256	188	106.2
III	O2−*	1	203–204	219	166	0.0
III		3	203–204	218	165	5.8
IV	OH−	0†	196–205	204	179	24.2
IV		2	196–203	205	178	0.0
IV		4	196–213	218	183	101.2
IV	H2O	0†	200	194	205	3.1
IV		0	194–204	194	204	38.2
IV		2	198–199	194	205	0.0
IV		4	198	218	241	22.2
IV	O2−	0†	202	217	165	32.0
IV		2	202	217	165	0.0
IV		4	209	217	164	90.5
V	OH−	1	201–202	205	181	0.0
V		3	202–203	262	191	76.1
V		5	208–210	257	188	106.6
V	O2−	1	197–206	213	163	5.5
V		3	199	213	165	0.0
V		5	199	214	165	181.5
Crystal			197–205	214	192

^*The His ligand dissociates in the sextet state.

^†Open-shell singlet.