pH-Triggered intramolecular electron transfer in asymmetric bis-dioxolene adducts

The oxidation of the bis-dioxolene 3,3,3ʹ,3ʹ-tetramethyl-5,6,5ʹ,6ʹ-tetrahydroxy-1,1ʹ-spiro-bis(indane)(CatH2-CatH2) in acidic solution yields the o-quinone-catecholate (Q-CatH2) as a product. The mixed valence character of the molecule is removed on deprotonation yielding the paramagnetic bis-semiquinonato species due to a formally intramolecular electron transfer. Complexes of formula M(CTH) (SQ-CatH2)(PF6)2(M = CrIII, CoIII; CTH = tetraazamacrocycle, SQ-CatH2= semiquinonato form of CatH2-Q) were also prepared. They are six-coordinate, the semiquinonato being coordinated to the metal ion. Evidences are given that intramolecular electron transfer follows deprotonation of the non-coordinated catecholate, yielding the MIII(CTH)(Cat-SQ) species, the catecholato being coordinated to the metal ion. The obtained results provide significant examples of systems showing pH-controlled magnetic properties.