Synthesis of dimorpholino-di-, -tri-, and -tetra-selane, and dipiperidinotetraselane. Crystal and molecular structures of the two tetraselanes

Abstract

The title compounds have been prepared by heating black selenium powder with morpholine or piperidine in the presence of Pb₃O₄. Dimorpholino- and dipiperidino-tetraselane, Se₄(NC₄H₈O)₂(1) and Se₄(NC₅H₁₀)₂(2), form isomorphous tetragonal crystals, space group l4₁/a(no. 88), Z= 8, with a=b= 13.074(1), c= 16.798(3)Å for (1) and a=b= 13.262(1), c= 17.713(4)Å for (2). The crystal structures have been determined by X-ray diffraction from Mo-K_α diffractometer data and refined by full-matrix least squares to R 0.037 and 0.035 for 803 and 871 observed reflections respectively. The molecules lie across crystallographic two-fold axes. The N–Se – Se–Se–Se–N chains occur in the trans-trans form, with the dimensions in (1) and (2) respectively: N–Se 1.836(6) and 1.824(6), Se–Se (terminal) 2.336(2) and 2.327(2), Se–Se (central) 2.356(2) and 2.347(2)Å; N–Se–Se 106.8(2) and 106.9(2), Se–Se–Se 102.1(1) and 104.1(1), NSeSe–SeSeSe 90.2 and 88.5, SeSeSe–SeSeSe 75.7 and 76.4°. The organic groups occur in the chair form, with N–Se equatorial. The shortest intermolecular Se ⋯ Se contact occurs in (1) and is 3.658(2) A.