Electrochemical and Electronic Structure Investigations of the [S3N3]• Radical and Kinetic Modeling of the [S4N4]n/[S3N3]n (n = 0, −1) Interconversion

Voltammetric studies of S4N4 employing both cyclic (CV) and rotating disk (RDE) methods in CH2Cl2 at a glassy carbon electrode reveal a one-electron reduction at −1.00 V (versus ferrocene/ferrocenium), which produces a second redox couple at −0.33 V, confirmed to be the electrochemically generated [S3N3]− by CV studies on its salts. Diffusion coefficients (CH2Cl2/0.4 M [nBu4N][PF6]) estimated by RDE methods: S4N4, 1.17 × 10−5 cm2 s−1; [S3N3]−, 4.00 × 10−6 cm2 s−1. Digital simulations of the CVs detected slow rates of electron transfer for both couples and allowed for a determination of rate constants for homogeneous chemical reaction steps subsequent to electron transfer. The common parameters (kf1 = 2.0 ± 0.5 s−1, ks1 = 0.034 ± 0.004 cm s−1 for [S4N4]−/0; kf2 = 0.4 ± 0.2 s−1, ks2 = 0.022 ± 0.005 cm s−1 for [S3N3]−/0 at T = 21 ± 2 °C) fit well to a “square-scheme” mechanism over the entire range of data with first order decay of both redox products. An alternate model could also be fit wherein [NS]• liber...