[1,2,5]Selenadiazolo[3,4‐<i>c</i>][1,2,5]thiadiazole and [1,2,5]Selenadiazolo[3,4‐<i>c</i>][1,2,5]thiadiazolidyl – A Synthetic, Structural, and Theoretical Study

Abstract

Abstract A new heterocyclic system, namely [1,2,5]selenadiazolo[3,4‐ c ][1,2,5]thiadiazole ( 1 ), has been prepared in 60 % yield by the 1:1 condensation of 3,4‐diamino‐1,2,5‐thiadiazole ( 4 ) with SeCl 4 in the presence of pyridine. The structures of 1 and its 1:1 complex with pyridinium chloride ( 5 ) have been elucidated by X‐ray diffraction (XRD). The reversible electrochemical reduction of 1 , as well as its chemical reduction with PhS – anion, provide the long‐lived [1,2,5]selenadiazolo[3,4‐ c ][1,2,5]thiadiazolidyl radical anion ( 2 ), which has been isolated in the form of the thermally stable salt [K(18‐crown‐6)][ 2 ] ( 3 ) in 75 % yield. The experimental structural and spectral characteristics of 1 and 2 agree fairly well with those obtained from density functional (DFT) calculations. The salt 3 has been characterized by ESR spectroscopy (in the solid state and in solution) and XRD. The radical anion 2 acts as a bridging ligand in crystalline 3 . Magnetic measurements on salt 3 reveal weak antiferromagnetic interactions ( J = –1.65 cm –1 ). The magnetic structures of 3 and its disulfur congener 11 have been analyzed in terms of dimeric exchange integrals calculated by spin‐unrestricted broken‐symmetry DFT and post‐HF methods.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)