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

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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)A for (1) and a=b= 13.262(1), c= 17.713(4)A for (2). The crystal structures have been determined by X-ray diffraction from Mo-Kα 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)A; 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.