(SN)xGROWN UNDER UNUSUAL CONDITIONS

Electrochemical and chemical reduction of disulfur dinitride: formation of [S4N4]-*, EPR spectroscopic characterization of the [S2N2H]* radical, and X-ray structure of [Na(15-crown-5)][S3N3]

Voltammetric studies of S(2)N(2) employing both cyclic voltammetry (CV) and rotating disk electrode (RDE) methods on GC electrodes at room temperature (RT) revealed two irreversible reduction processes at about -1.4 V and -2.2 V in CH(3)CN, CH(2)Cl(2), and tetrahydrofuran (vs ferrocene) and no observable oxidation processes up to the solvent limit when the scan is initially anodic. However, after cycling the potential through -1.4 V, two new couples appear near -0.3 V and -1.0 V due to [S(3)N(3)](-/0) and [S(4)N(4)](-/0) respectively. The diffusion coefficient D for S(2)N(2) was determined to be 9.13 x 10(-6) cm(2) s(-1) in CH(2)Cl(2) and 7.65 x 10(-6) cm(2) s(-1) in CH(3)CN. Digital modeling of CVs fits well to a mechanism in which [S(2)N(2)](-*) couples rapidly with S(2)N(2) to form [S(4)N(4)](-*), which then decomposes to [S(3)N(3)](-). In situ electron paramagnetic resonance (EPR) spectroelectrochemical studies of S(2)N(2) in both CH(2)Cl(2) and CH(3)CN resulted in the detection of strong EPR signals from [S(4)N(4)](-*) when electrolysis is conducted at -1.4 V; at more negative voltages, spectra from transient adsorbed radicals are observed. In moist solvent or with added HBF(4), a longer-lived spectrum is obtained due to the neutral radical [S(2)N(2)H](*), identified by simulation of the EPR spectrum and density functional theory (DFT) calculations. The chemical reduction of S(2)N(2) with Na[C(10)H(8)] or Na[Ph(2)CO] produces [Na(15-crown-5)][S(3)N(3)], while reduction with cobaltocene gives [Cp(2)Co][S(3)N(3)]. The X-ray structure of the former reveals a strong interaction (Na...N = 2.388(5) A) between the crown ether-encapsulated Na(+) cation and one of the nitrogen atoms of the essentially planar six-membered cyclic anion [S(3)N(3)](-).