Figure 4: Manganese hexacyanomanganate physical characterization.

(a) Fourier transform infrared spectroscopy of oxidized Mn^II—N≡C—Mn^III and reduced Mn^II—N≡C—Mn^II confirm that the C-coordinated manganese is changing valence state. The in situ synchrotron X-ray diffraction experiment (c,d) shows no change in crystal structure for Mn^II—N≡C—Mn^III, Mn^II—N≡C—Mn^II and Mn^II—N≡C—Mn^I except for a small peak shift corresponding to a decrease in lattice parameter during reduction. The broad background peak is due to the scattering by the water electrolyte (Supplementary Information). These results are confirmed by X-ray Powder Diffraction spectra (b) of oxidized Mn^II—N≡C—Mn^III and reduced Mn^II—N≡C—Mn^II.