Citation:
Abstract:
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 [(Bu4N)-Bu-n][PF6]) estimated by RDE methods: S4N4, 1.17 x 10(-5) cm(2) s(-1); [S3N3](-), 4.00 x 10(-6) cm(2) 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 (k(f1) = 2.0 +/- 0.5 s(-1), k(s1), = 0.034 +/- 0.004 cm s(-1) for [S4N4](-/0); k(f2) = 0.4 +/- 0.2 s(-1), k(s2) = 0.022 +/- 0.005 cm s(-1) for [S3N3](-/0) at T= 21 +/- 2 degrees 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](center dot) liberated in the first step reacts with formed [S3N3](center dot) to reproduce S4N4 with an apparent second order rate constant k(f2)' = 1.1 +/- 0.3 x 10(3) 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](-center dot) radical anion was detected by the Simultaneous Electrochemical Electron Paramagnetic Resonance (SEEPR) method to give: (a) [S-32(4) N-14(4)](-center dot), 9 lines, a(N-14) = 0.118 mT; (b) [(S4N4)-S-32-N-15](-center dot), 5 lines, a(N-15) = 0.164 mT; (C) [(S4N4)-S-33-N-14](-center dot), estimated a(N-14) = 0.118, a(S-13 = 0.2 mT); g = 2.0008(1). Equivalence of S-33 hyperfine splittings is consistent with dynamic averaging of the C-2v 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](center dot).
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Times Cited: 5Boere, Rene T. Chivers, Tristram Roemmele, Tracey L. Tuononen, Heikki M.