TITANIUM(III) CHEMISTRY - ELECTRON-TRANSFER REACTIONS WITH GROUND-STATE POLY(PYRIDINE)OSMIUM(III) COMPLEXES, QUENCHING REACTIONS WITH EXCITED-STATE POLY(PYRIDINE)RUTHENIUM(II) COMPLEXES, AND FORMAL REDUCTION POTENTIALS

Potentiometric titrations of aquotitanium(III) with ferric ions have been performed in hydrochloric acid solution. The potentiometric data are described by E (V vs. NHE) = 0.03-0.059 log ([Ti(III)]/[Ti(IV)][H+]2) at 25 °C and 3.0 M ionic strength and are consistent with the interpretation that Ti3+(aq) and Ti02+are the principal titanium(III) and titanium(IV) species, respectively, present at acid concentrations of 0.1-3.0 M. Rate constants for the oxidation of titanium(III) by a series of osmium(III) complexes, OsL33+, where L is a bipyridine or phenanthroline derivative, have been determined at 25 °C and 3.0 M ionic strength. The rates are interpreted in terms of the reactions of Ti3+(aq) and TiOH2+. The rate constants are correlated with the Marcus theory, and the exchange rate constants for the Ti4+,3+(aq) and TiOH3+,2+couples are estimated. The rate constants for the reaction of titanium(III) with the excited states of the ruthenium(II) complexes RuL32+are insensitive to the reduction potentials of the ruthenium(II) complexes. Arguments are presented to show that the quenching reactions proceed predominantly by energy-transfer mechanisms. The implications of these results for the production of Ti2+(aq) in quenching reactions are discussed. © 1979, American Chemical Society. All rights reserved.