Anomalous chemical shifts in X-ray photoelectron spectra of sulfur-containing compounds of silver (I) and (II)

Anomalous chemical shifts, i.e. cases when binding energy decreases with the increase of the oxidation state, have been well-documented for selected compounds of silver, and well understood based on analysis of initial- and final-state effects in the XPS spectra. Here we report two examples of even more exotic behaviour of chemical shifts for two silver compounds. The first one is Ag2S2O7 which exhibits both positive and negative substantial shifts with respect to metallic Ag for two distinct Ag(I) sites in its crystal structure, which differ by as much as 3.6 eV. Another is AgSO4, a rare example of oxo silver (II) salt, which exhibits “normal” chemical shift but the Ag 3d5/2 binding energy takes the largest value measured for a silver (II) compound (370.1 eV). This property is connected predominantly with the extremely strongly oxidizing nature of Ag(II) species.