STRUCTURES OF 6A-THIA SELENA-1,3,4,6-TETRAAZAPENTALENE DERIVATIVES - HYPERVALENT S/SE-N BONDS

2,3,4,5-Tetrahydro-1,6-diphenyl-3,4-propano-6a-thia-1,3,4,6-tetraazapentalene-2,5-dione, (I), C18H16N4O2S, M(r) = 352.42, orthorhombic, Iba2, a = 20.490 (10), b = 21.420 (5), c = 7.575 (2) angstrom, V = 3324 (2) angstrom 3, Z = 8, D(x) = 1.408 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 0.204 mm-1, F(000) = 1472, T = 293 K, R = 0.051 for 1014 observed reflections. 1,6-Diethyl-2,3,4,5-tetrahydro-3,4-propano-6a-thia-1,3,4,6-tetraazapentalene-2,5-dione, (II), C10H16N4O2S, M(r) = 256.33, monoclinic, P2(1)/n, a = 23.888 (3), b = 4.8422 (6), c = 22.518 (4) angstrom, beta = 102.62 (1)degrees, V = 2541.8 (6) angstrom 3, Z = 8, D(x) = 1.340 Mg m-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu = 2.214 mm-1, F(000) = 1088, T = 293 K, R = 0.073 for 2615 observed reflections. 1,6-Diethyl-2,3,4,5-tetrahydro-3,4-propano-6a-selena-1,3,4,6-tetraazapentalene-2,5-dithione, (III), C10H16N4S2Se, M(r) = 335.36, monoclinic, P2(1), a = 13.025 (4), b = 10.233 (1), c = 5.2535 (7) angstrom, beta = 98.36 (2)degrees, V = 692.7 (2) angstrom 3, Z = 2, D(x) = 1.611 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 2.956 mm-1, F(000) = 340, T = 293 K, R = 0.043 for 1382 observed reflections. Each molecule has approximate mirror symmetry except phenyl or ethyl groups with equidistant S-N/Se-N bonds. The mean distances of S-N bonds are 1.959 (6) and 1.927 (6) angstrom in (I) and (II), respectively, and that of the Se-N bonds in (III) is 2.034 (6) angstrom. These values are longer than those of the normal S/Se-N single bonds by 9-12%. The S-C distances, 1.717 (7) for (I), 1.717 (6) angstrom (mean value) for (II), and the Se-C distance, 1.852 angstrom for (III), are intermediate between those for single and double bonds. The pentalene framework and O or S atoms of carbonyl or thiocarbonyl groups are almost coplanar. The structural features show the pi-hypervalency of the 12-pi-system.