STABLE TITANIUM SUPEROXIDE RADICALS IN AQUEOUS TI-PEROXY GELS AND TI-PEROXIDE SOLUTIONS

Titanium superoxide radicals (Ti(IV)O2-) were for the first time observed in situ by electron spin resonance methods in aqueous Ti-peroxy gels made from metallic titanium and hydrogen peroxide and in Ti(III)- and Ti(IV)-salt peroxides. The hyperfine splitting g-values (g1 = 2.002, g2 = 2.009, and g3 = 2.022) found were identical in aqueous and in dried Ti-peroxy gels. The radicals in the gels were detectable at both neutral and low pH. The radicals in Ti(III or IV)-peroxide solutions escaped detection at neutral pH but reappeared upon lowering the pH. Excess hydrogen peroxide at preparation of Ti peroxide at pH 7 gave rise to formation of a detectable radical with a differing g3 (g3 = 2.037), but the radical escaped detection at pH 2. The detectability and g3-values of the Ti-superoxide radicals formed in Ti(III,IV)-peroxide solutions depend on pH and on the method of preparation. This indicates that Ti-superoxide radicals reside in different forms of polymeric Ti-peroxide complexes and may be formed through charge-transfer reactions. © 1991.