Electrochemical and Electronic Structure Investigations of the [S3N3]• Radical and Kinetic Modeling of the [S4N4]n/[S3N3]n (n = 0, −1) Interconversion
Boeré, R., Chivers, T., Roemmele, T., & Tuononen, H. (2009). Electrochemical and Electronic Structure Investigations of the [S3N3]• Radical and Kinetic Modeling of the [S4N4]n/[S3N3]n (n = 0, −1) Interconversion. Inorganic Chemistry, 48 (15), 7294-7306. doi:10.1021/ic900742q
Published inInorganic Chemistry
DisciplineEpäorgaaninen ja analyyttinen kemia
© 2009 American Chemical Society. This is a final draft version of an article whose final and definitive form has been published by ACS. Published in this repository with the kind permission of the publisher.
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]• liberated in the first step reacts with formed [S3N3]• to reproduce S4N4 with an apparent second order rate constant kf2′ = 1.1 ± 0.3 × 103 M−1 s−1. The crystal structure of [PPN][S3N3] was determined by X-ray crystallography indicating the solvation of the anion by 1 equiv of methanol. The generated [S4N4]−• radical anion was detected by the Simultaneous Electrochemical Electron Paramagnetic Resonance (SEEPR) method to give: (a) [32S414N4]−•, 9 lines, a(14N) = 0.118 mT; (b) [32S415N4]−•, 5 lines, a(15N) = 0.164 mT; (c) [33S414N4]−•, estimated a(14N) = 0.118, a(33S = 0.2 mT); g = 2.0008(1). Equivalence of 33S hyperfine splittings is consistent with dynamic averaging of the C2v geometry in solution. High-level electronic structure calculations provide evidence for an open-shell doublet triradicaloid character to the ground state wave function of [S3N3]•. ...