The cyanogel system involving PdCl42- and the mixed-valence complex [(NC)(5)Fe-II-CN-Pt-IV(NH3)(4)-NC-Fe-II(CN)(5)](4-) is reported. The system has been characterized by UV-vis absorption, diffuse reflectance infrared, and resonance Raman spectroscopies. Gelation occurs through coordination of Pd(II) to the nitrogen atom of terminal cyanide ligands in the mixed-valence complex. Irradiation into the Fe(II) --> Pt(IV) intervalent electron transfer (IT) band of [(NC)(5)Fe-II-CN-Pt-IV(NH3)(4)-NC-Fe-II(CN)(5)](4-) results in the formation of a variety of Prussian-blue-like species within the rigid cyanogel matrix. Photochemical and dark mechanisms involving coupled cyanide loss and Fe(ll) oxidation are proposed for the formation of Prussian-blue-like species. The optical contrast between irradiated and nonirradiated regions of the gel enables photochemical image generation with at least 12 mum resolution. This capability is demonstrated through the production of a series of diffraction gratings in cyanogel samples.