Table 4.

Mulliken spin densities (∣ρ_s^(Fe)∣), quadrupole splittings (∣ΔE_Q∣) and isomer shifts (δ) averaged over the Fe sites; hyperfine couplings of Fe (a^test) and X (a(X)); and RMS deviations of the individual site hyperfine couplings (a_i) for a series of oxidation states and compositions, where +H indicates O_hydroxyl-protonated models.

level of theory	model	δ1 (mm s−1)a	δ2 (mm s−1)a	δ3 (mm s−1)a	∣ρs(Fe)∣	∣ΔEQ∣ (mm s−1)	atest (MHz)	RMS dev. ai(MHz)	a(X) (MHz)
BP86b	2FeII-5FeIII-N3−	0.41	0.29c	0.45	2.92	1.13	−25.1	4.2	1.1
	4FeII-3FeIII-N3−	0.53	0.38c	0.54	3.06	1.03	−27.3	5.6	−0.3
	6FeII-1FeIII-N3−	0.68	0.52c	0.66	2.98	0.95	−29.6	5.0	−0.3
	2FeII-5FeIII-C4−	0.35	0.24c	0.40	2.73	0.90	−24.3	3.5	3.7
	4FeII-3FeIII-C4−	0.48	0.34c	0.50	2.89	0.94	−25.1	4.7	−0.7
	4FeII-3FeIII-O2−	d		d	3.27	d	−29.5	6.8	d
	2FeII-5FeIII-C4−+H	0.32	0.22	0.38	2.68	0.86	−23.8	3.3	2.7
	4FeII-3FeIII-C4−+H	0.45	0.32c	0.48	2.85	0.93	−24.4	4.5	−1.0
	4FeII-3FeIII-N3−+H	0.51	0.45	0.52	3.03	0.97	−27.0	5.5	−0.4
B3LYPb	2FeII-5FeIII-C4−+H				3.42	1.16	−25.4	5.9	6.1
	4FeII-3FeIII-N3−+H				3.50	1.43	−31.8	8.0	−0.7
B(5HF)P86/ 6-311+G(d)	2FeII-5FeIII-C4−+H				2.44		−24.1	2.7
	4FeII-3FeIII-N3−+H				2.77		−25.1	4.5
	Exp	0.41e		0.41e		0.69e	−17.9e		< 0.07f

^aSubscripts refer to the methods employing a training data set with (1) crystal structures, (2) BP86/STO-TZP optimized structures, or (3) crystal structures without outliers.

^bSDD-VTZ(d) basis set for ∣ρ_s(Fe)∣ and a^test; STO-TZP for ∣ΔE_Q∣, a(X) and δ.

^cEstimated based on range of δ for [2Fe^II-5Fe^III-C⁴⁻+H].

^dCalculations did not converge.

^eRef. 15

^fRef. 25