Fig. 5: UV-vis electronic absorption, ⁵⁷Fe NRVS PVDOS and ⁵⁷Fe Mössbauer spectra of the [8Fe–8S] clusters.

a, UV-vis electronic absorption spectra of 1 × 10⁻⁴ M toluene solutions of lbdc (magenta), ildc (yellow) and ebdc (blue), are shown as bold solid lines. For comparison, the spectra of the canonical and site-differentiated Fe₄S₄ complexes in the relevant oxidation states are also shown: they include K₃[Fe₄S₄(DmpS)₄] (dotted blue), K₂[Fe₄S₄(DmpS)₄] (dotted yellow), K[Fe₄S₄(DmpS)₃(Im*)] (dashed yellow) and [Fe₄S₄(DmpS)₂(Im*)₂] (dotted-dashed yellow), K[Fe₄S₄(DmpS)₄] (dotted magenta) and [Fe₄S₄(DmpS)₃(Im*)] (dashed magenta). b, ⁵⁷Fe NRVS PVDOS spectra of lbdc, ildc and ebdc (solid coloured lines). For comparison, the spectra of the corresponding canonical cubanes in their respective oxidation states are shown alongside, as dotted coloured lines. All spectra were recorded on powdered ⁵⁷Fe enriched (>95%) samples between 30 K and 50 K. c–e, The 80 K Mössbauer spectra (vertical bars) recorded on powder samples of lbdc (c), ildc (d) and ebdc (e). No external magnetic field was applied in d and e, whereas a 0.06 T external magnetic field was applied along the γ ray direction in c. Simulations are overlaid as thick grey solid lines and components are displayed above the spectra as coloured thin solid lines. The nuclear parameters are the following: doublet 1 (violet) δ = 0.48 mm s⁻¹, ∆E_Q = 0.81 mm s⁻¹; doublet 2 (magenta) δ = 0.31 mm s⁻¹, ∆E_Q = 0.92 mm s⁻¹; common linewidth Γ_FWHM = 0.39 mm s⁻¹ (c); doublet 1 (brown) δ = 0.34 mm s⁻¹, ∆E_Q = 0.89 mm s⁻¹; doublet 2 (yellow) δ = 0.68 mm s⁻¹, ∆E_Q = 2.57 mm s⁻¹; common linewidth Γ_FWHM = 0.43 mm s⁻¹ (d) and doublet 1 (light blue): δ = 0.51 mm s⁻¹, ∆E_Q = 0.89 mm s⁻¹, Γ_FWHM = 0.66/0.78 mm s⁻¹; doublet 2 (dark blue): δ = 0.55 mm s⁻¹, ∆E_Q = 1.56 mm s⁻¹, Γ_FWHM = 0.57/0.61 mm s⁻¹ (e). FWHM, full-width at half-maximum.