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) (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.