Synthesis and Crystal Structures of Cobalt(II/III) Tris-Phenanthrolines with Various Polyiodide Anions

Cobalt (II) tris-phenanthroline perchlorate and similar salts with polyiodide anions were synthesized and structurally characterized. The complex cations are packed in the crystals through numerous C–H···π and π···π contacts, while iodine-containing anions are isolated and interact with the π-system of aromatic ligands. Spontaneous oxidation of cobalt(II) tris-phenanthroline with iodine gives a crystalline product containing a triply charged complex cation, triiodide anions, and molecular iodine. The anions and iodine molecules in the crystal form a framework of iodine atoms linked via halogen–halogen interactions, while complex cations are held in this framework by C‒H⋅⋅⋅I and I⋅⋅⋅π contacts and do not directly interact with one another. The study gives some insights into the nature of interactions that can occur during operation of dye-sensitized solar cells containing tandem iodine and cobalt redox mediators.