. Author manuscript; available in PMC: 2021 Jan 5.

Published in final edited form as: J Am Chem Soc. 2020 Dec 16;142(52):21679–21690. doi: 10.1021/jacs.0c07914

Table 1.

Isotropic ⁵⁷Fe Hyperfine Couplings^a

E₄(2H)*^b		E₄(4H)^c		E₀^d
⁵⁷Fe	a_iso/δA^e (MHz/%)	⁵⁷Fe	a_iso/δA^e (MHz/%)	⁵⁷Fe	a_iso/δA^e (MHz/%)
a	−30/+17	α	−35/−34	A¹	−18/+41
b	−27/+18	β	−27/+26	A²	−17.1/23
e	+23	κ	~+20^g	A³	−11.8
f	~+25^f	γ1	+17	B¹	+11.7
g	~+25^f	γ2	−16	B¹	+11.7
c	−19	δ	+13	B²	+9.3
d	−17	λ	~+8^g	A⁴	−3.7

Isotropic hyperfine couplings (a_iso) or ⁵⁷Fe sites of photoreduced E₄(2H)*, Janus intermediate E₄(4H), and resting state E₀, arranged in order of absolute values; it is argued in the text that a/b, α/β and A¹/A² refer to the same pair of Fe sites.

Isotropic coupling reported as average of coupling observed at canonical g-values in ENDOR; signs determined by PESTRE measurements.

As reported; obtained through ENDOR, PESTRE, and Triple.¹²

As reported; determined by Mossbauer spectroscopy.⁵³

δA(%) = 100 × (A_m – A₁)/a_iso, where A₁ corresponds to g₁ and is in each case an extreme value (max or min) and m = 2 or 3 is the other extreme, as observed in the 2D plots of ⁵⁷Fe ENDOR spectra for E₄(2H)* and E₄(4H) of Figure 5, Figure S3 and as reported for E₀.⁵³

Calculated from eqs 3 and 4 using a_test = −20 MHz as described in the text; listed below site e because of uncertainties thus introduced.

Sign of a_iso for κ and value for λ calculated from eq 3 and the analogues to eq 4 for one unknown a_iso, using a_test = −20 MHz.