Studies on 1,3-diaryltriazene analogues of berenil: molecules with potential GC base-pair selectivity

1,3-Bis(4-acetylphenyl)triazene (II): C16H15N3O2, Mr = 281.32, monoclinic, P2(1)/c, a = 14.002 (5), b = 12.359 (3), c = 8.457 (3) A, beta = 96.35 (2) degrees, V = 1454.5 A3, Z = 4, Dx = 1.287 Mg m-3, Cu K alpha, lambda = 1.54178 A, mu = 0.672 mm-1, F(000) = 592, T = 294 K, final R = 0.089 for 1890 unique observed reflections. 1,3-Bis(4-[2-dimethylamino)ethoxycarbonyl]phenyl)triazene monohydrate (III): C22H29N5O4.H2O, Mr = 445.52, triclinic, P1, a = 9.500 (2), b = 11.753 (3), c = 13.328 (2) A, alpha = 62.84 (1), beta = 66.60 (2), gamma = 77.58 (2) degrees, V = 1214.1 A3, Z = 2, Dx = 1.172 Mg m-3, Cu K alpha, lambda = 1.54178 A, mu = 0.640 mm-1, F(000) = 476, T = 294 K, final R = 0.063 for 1100 unique observed reflections. Both crystal structures have extended conformations for the 1,3-diaryltriazene groups, with a cisoid arrangement of phenyl rings. The terminal N--N bonds of each triazene are non-equivalent, and a hydrogen atom has been located in the N==N--NH moiety. Extensive molecular-orbital (MNDO) calculations on the model core 1,3-diphenyltriazene system have confirmed that this geometry is energetically favoured, and have revealed the shape of the energy surface for rotation about the N--NH bond in the triazene linkage.