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[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazole (1) is synthesized in 62% yield by fluoride ion-induced condensation of 3,4-difluoro-1,2,5-thiadiazole with (Me3SiN=)2S. The reversible electrochemical reduction of 1 leads to the long-lived [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion (2) and further to the dianion (3). The radical anion 2 is also obtained by the chemical reduction of the precursor 1 with t-BuOK in MeCN. The radical anion 2 is characterized by ESR spectroscopy in solution and in the crystalline state. The stable salts [K(18-crown-6)][2] and [K(18-crown-6)][2]·MeCN (8 and 9, respectively) are isolated from the spontaneous decomposition of the [K(18-crown-6)][PhXNSN] (6, X = S; 7, X = Se) salts in MeCN solution followed by XRD characterization. The radical anion 2 acts as a bridging ligand in 8 and as chelating ligand in 9. The structural changes observed by XRD in going from 1 to 2 are explained by means of DFT/(U)B3LYP/6-311+G* calculations. [ABSTRACT FROM AUTHOR]

The conformational and structural properties of N-trifluoroacetylimidosulfurous difluoride, CF3C(O)N&z.dbnd6;SF2, have been studied by vibrational spectroscopy (IR(gas) and Raman(liquid)), by gas electron diffraction and by quantum chemical calculations (HF, MP2 and B3LYP with 6-31G* and 6-311G* basis sets). Only a single conformer with a syn–syn structure and CS symmetry was observed in the gaseous and liquid states. The CF3C(O) group is oriented syn relative to the SF2 group and the C&z.dbnd6;O and N&z.dbnd6;S double bonds are synperiplanar to each other. The preference of this conformation has been rationalized based on a natural bond orbital analysis. Conformations with anti orientations around the N&z.dbnd6;S and N–C bonds correspond to stable structures according to quantum chemical calculations, but are higher in energy by 2.4 kcal/mol or more. The skeletal parameters, N&z.dbnd6;S=1.481(7) A˚, N–C=1.406(16) A˚, S–F=1.585(2) A˚, C–N&z.dbnd6;S=128.2(16)°, N&z.dbnd6;S–F=110.4(12)° and F–S–F=89.3(11)° (ra values with 3σ uncertainties), are very similar to those in other imidosulfurous difluorides. Whereas the HF approximation reproduces the geometric parameters satisfactorily, the MP2 and B3LYP methods predict some bonds too long by up to 0.07 A˚. [Copyright &y& Elsevier]