Voltammetric studies have been conducted on chlorobis[2-(2'-hydroxyphenyl)-2-oxazolinato]oxorhenium(V) (1, (hoz)(2)Re(0)Cl) and related complexes. These complexes are potentially useful catalysts for the conversion of perchlorate to chloride using chemical reductants such as sulfides. The possible use of an electrode as the reducing agent in the catalytic cycle is explored here. In anhydrous acetonitrile, 1 undergoes a reversible one-electron oxidation to a cation, 1(+), that is stable on the voltammetric time scale. The formal potential of this couple is +0.58 V versus the potential of the ferrocenium/ferrocene couple. When 1 was studied in the presence of low concentrations of water (0.06-6 M), chloride was not displaced by water at an appreciable rate. However, the cation formed upon one-electron oxidation of I reacted fairly rapidly with water with a rate law that was second-order in water (k = 0.94 M-2 s(-1)) by displacement of chloride to form the aquated dication, [(hoz)(2)Re(O)(OH2)](2+) (2(2+)). This species was detected on the return sweep by its reduction to the aquo Re(V) complex, i.e. 2(2+) + e(-) reversible arrow2(+), whose formal potential is +0.1 V. The triflate salt of 2(+), bis[2-(2'-hydroxyphenyl)-2-oxazolinato]aquo-oxorhenium(V) triflate, [(hoz)(2)Re(O)(OH2)][Otf] was also studied. When this triflate salt was dissolved in acetonitrile, the water ligand was replaced by acetonitrile and the resulting complex, [(hoz)(2)Re(O)(NCCH3)](+) (3(+)) showed a one-electron oxidation with an estimated formal potential of +1.15 V. The potential was difficult to determine accurately as the dication, 3, underwent very rapid displacement of acetonitrile by adventitious water to give 2(2+). In the catalytic cycle for destruction of perchlorate, the rhenium(VII) complex, (hoz)(2)Re(O)(2)(+) (4(+)), is formed by reaction of perchlorate with [(hoz)(2)Re(O)(NCCH3)](+) or [(hoz)(2)Re(O)(OH2)](+). We have attempted the in-situ preparation of (hoz)(2)Re(O-2)(+) (4(+)), by reaction of 1 with pyridine N-oxide. The voltammetry of the resulting solutions is complex and only one well-behaved, quasireversible couple is observed near +0.1 V. This couple may involve the 4+/4 reaction or the reduction of a rhenium(VI) species formed in the reaction. The latter has a precedent in the literature.