MOLECULAR AND CRYSTAL-STRUCTURES OF YDRO-1,2,4-TRIAZOLO[5,1-B]NAPHTHO[1,2-D]PYRIMIDINE - THE NATURE OF DISORDER IN THE DIHYDRONAPHTHALENE FRAGMENT

The crystal structure of ydro-1,2,4-triazolo[5,1-b]naphtho[1,2-d]pyrim idine has been studied by X-ray diffraction analysis at 293 and 153 K, The crystal data are as follows. Ar T = 293 K: monoclinic, a = 10.588 (3), b = 18.196(6), and c = 7.939(2) Angstrom; beta = 98.55(1)degrees; sp, gr. P2(1)/c; Z = 4; number of reflections = 1780; wR2 = 0.139; an d R1 = 0.067 for 1130 reflections with F > 4 sigma(F). At T = 153 K: m onoclinic, a = 10.414(9), b = 18.11(2), and c = 7.952(6) Angstrom; bet a = 97.95(2)degrees; sp. gr, P2(1)/c; Z = -4; number of reflections = 2384; wR2 = 0.161, and R1 = 0.078 for 1456 reflections with F > 4 sigm a(F). It is demonstrated that annelation of the dihydropyrimidine cycl e with a carbocycle at the C=C double bond brings about a substantial flattening of the boat conformation of the dihydroheterocycle. The dih ydronaphthalene fragment is disordered between two equally probable co nformations. The presence of the forbidden intermolecular contact C .. . C (2.83 Angstrom) indicates that the disorder is statistic in nature , which is corroborated by the low-temperature (T = 153 K) in investig ation, In the crystal, the molecules are linked by hydrogen bonds that give rise to the centrosymmetric dimers that, in turn, form the ribbo ns. Each ribbon contains molecules in which the dihydronaphthalene fra gments adopt only one of two conformations found.