[1,2,5]Selenadiazolo[3,4-c][1,2,5]thiadiazole and[1,2,5]Selenadiazolo-[3,4-c][1,2,5]thiadiazolidyl-A Synthetic,Structural,and Theoretical Study

摘要

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 SeCl4 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]selenadia-zolo[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.