Table 5.

Magnetic, electronic, geometric, and energetic preference for oxidation states of the iron centers and composition of the interstitial ligand. HC(O⁻_hydroxyl) and HC(HO_hydroxyl) indicate the deprotonated and protonated states of homocitrate, respectively.

criterion	oxidation state	interstitial atom
		HC(O−hydroxyl)	HC(HOhydroxyl)
resting St = 3/2	no preference	no preference	no preferencea
oxidized St = 0	MoIV-2FeII-5FeIII	C4−, N3−	C4−a, N3−a
geometry	MoIV-2FeII-5FeIII	C4−, N3−	C4−
	MoIV-4FeII-3FeIII		C4−, N3−
charge	MoIV-2FeII-5FeIII	N3−	C4−
	MoIV-4FeII-3FeIII		O2−
reduction potential	MoIV-2FeII-5FeIII	C4−	C4−
	MoIV-4FeII-3FeIII	O2−	N3−, O2−
isomer shift (all)	MoIV-2FeII-5FeIII	C4−, N3−	C4−, N3−b
	MoIV-4FeII-3FeIII	C4−, N3−	C4−, N3−
isomer shift (δ3)	MoIV-2FeII-5FeIII	C4−, N3−	C4−, N3−b
quadrupole splitting	MoIV-2FeII-5FeIII	C4−	C4−
	MoIV-4FeII-3FeIII	C4−	C4−, N3−
	MoIV-6FeII-1FeIII	N3−	N3−b
Fe hyperfine coupling	MoIV-2FeII-5FeIII	C4−	C4−
X hyperfine coupling	no preference	no preference	no preference

^aEstimated based on results for deprotonated models. The S_t = 0 and 1 states of [2Fe^II-5Fe^III-C⁴⁻+H] were tested and the results were consistent with the deprotonated case.

^b[2Fe^II-5Fe^III-N³⁻+H] and [6Fe^II-1Fe^III-N³⁻+H] results estimated.