Table 1.

g- and A-tensors (in megahertz) experimentally observed for 2, 2-H⁺, and [Fe^V(O)(TAML)]^1- and calculated for 2 and 2-H⁺

Compound	g			A (57Fe)			A (17O)			A (14N)
	x	y	z	x	y	z	x	y	z	x	y	z
HRP Cpd I	–	–	–	−26*	−26*	−8*	35†	36†	ND	–	–	–
1	–	–	–	−28‡	−28‡	−4	−27§	−27§	+61§	–	–	–
2¶	2.053	2.010	1.971	−47(2)	−17(2)	0(5)	25(15)	128(3)	≈20	29(2)	11(3)	11(3)
2 (DFT) ∥	2.03	2.00	1.97	−43.5	−18.5	3.3	−1.0	−70.8	75.7	−39.3	10.8	6.1
2-H+¶	2.054	2.011	1.975	−47(2)	−17(2)	0(5)	25(15)**	133(3)	23(10)	30(2)**	11(3)	10(3)
2-H+ (DFT)∥	2.03	2.00	1.97	−45.1	−14.0	−6.0	18.4	−91.4	84.7	−35.5∥	−1.2	3.9
[FeV(O)(TAML)]1-††	1.99	1.97	1.74	−49.3	−1.5	−16.3‡‡	ND	ND	ND	–	–	–

ND, not determined.

^*From Mössbauer data analyzed with an S = 1 Hamiltonian (34).

^†From ENDOR data, S = 1 (19).

^‡Refit of Mössbauer data reported in ref. 15 using g values and zero-field splitting parameters derived from more recent high-field EPR data reported in ref. 35.

^§This work; B3LYP calculations yield a good match for A(⁵⁷Fe).

^¶This work; data analyzed with Eq. 1; 4.2 K Mössbauer spectra recorded at 2.0, 4.0, and 8.0 T show that A_x(⁵⁷Fe) and A_y(⁵⁷Fe) of 2 and 2-H⁺ are negative, see SI Appendix, Fig. S4. The z axis is along the Fe─O bond in all systems. Results for 2 apply to the majority species.

^∥Values for the model obtained from DFT calculations using BP86 functionals (see below).

^**Relative to g, A(¹⁷O) and A(¹⁴N) are rotated 8º around the z axis of the g-tensor.

^††From ref. 14.

^‡‡Correcting A_z for the orbital contribution, which is proportional to (g_z - 2), would yield A_z ∼ 0.