Intermacrocyclic Interactions upon Stepwise Oxidations in a Monometallic Porphyrin Dimer: Ring versus Metal-Center Oxidations and Effect of Counter Anions

The effect of intermacrocyclic interactions was studied by controlled and stepwise oxidations of a monometallic silver(II) porphyrin dimer that contains a highly flexible ethane bridge. Monometallic dimers are unique systems and behave differently from their dimetallic analogues on the basis of their available sites for storing oxidizing equivalents. UV-visible spectrometry,H- 1 NMR spectroscopy, XPS and single crystal X-ray diffraction studies clearly suggest the removal of the first electron from the metal center. The removal of the second electron occurred from the ring center to form a pi-cation radical and, thereby, form a very unique mixed-valent species. However, unlike in all other ethane-bridged metalloporphyrin dimers reported earlier, the 2e-oxidized species showed quite unusual structures depending on the nature of counter ions. Ions, such as SbF6, SbCl6 and PF6, are engaged in strong interactions with the porphyrin pi-cation radical and causes substantial structural changes, including large deformation of the ring. The solid-state structure remains intact in solution as well. The observations are further supported by DFT calculations.