Kinetic method to estimate the reduction potential involving unstable organochromium macrocyclic complex

Abstract

The complex [4-BrC6H4CH2Cr(1,4,8,12-tetraazacyclope ntadecane)(H2O)]2+, (RCrL(H2O)2+) is oxidized to RCrL(H2O)3+ which then rapidly homolyses. The rate constants were determined in aqueous solution at 25.0°C for oxidation by IrCl6 2- and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonate) monoanion, (ABTS.-); the values are (1.29 ± 0.11) × 104 dm3 mol-1 s-1 and (1.51 ± 0.17) × 102 dm3 mol-1 s-1 respectively. The estimates of reduction potential E0 and self-exchange rate constant k11 were made for the couple 4-BrC6H4CH2CrL(H2O)3+/2 +: E0 = 0.8 ± 0.2 V; 5 × 10-2 dm3 mol-1 s-1 < k11 < 7 × 102 dm3 mol-1 s-1. © 1994.