Valence tautomerism interconversion triggers transition to stable charge distribution in solid polymeric cobalt-polyoxolene complexes

The reaction of 3,3,3,3-tetramethyl-5,5,6,6-tetrahydroxy-1,1spiro-bis(indane), L, with cobalt salts inthe presence of diazine ligands affords polymeric derivatives of general formula[CoL(diazine)]∞·nH2O, L being coordinated as a mixed-valence SQ-Cat species. The bipiridyl ando-phenantroline derivatives have been characterised by means of magnetic, EPR and calorimetricmeasurements. The characterisation showed that both systems are obtained in a metastable chargedistribution, presumably trapped due to the class I character of the mixed valence form of the ligand.The occurrence of entropy-driven valence tautomeric interconversion induces the transition to the moststable charge distribution. The photomagnetic characterisation evidenced that valence tautomericprocess can be photoinduced and that the lifetime of the photoinduced metastable state, obtained inlow yield, is of ca. 2 × 105 s at 9 K.