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

The oxidation of the bis-dioxolene 3,3,3',3'-tetramethyl-5,6,5',6'-tetrahydroxy-1,1'-spiro-bis(indane) (CatH(2)-CatH(2)) in acidic solution yields the o-quinone-catecholate (Q-CatH(2)) 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-CatH(2))(PF(6))(2) (M = Cr(III), Co(III); CTH = tetraazamacrocycle, SQ-CatH(2) = semiquinonato form of CatH(2)-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 M(III) (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.