P. Tollin

Structure of 2-Amino-5-bromopyrimidine

C4H4BrN3, M r = 174.01, orthorhombic, Cmca, a -- 7.702 (3), b = 8.215 (3), c = 17.733 (12) A, u = 1122.0 A 3, z = 8, D x = 2.06 gcm -3, Mo Ka radiation, /l = 0.71069 A, /1 = 71.4 cm -~, F(000) = 672, T= 293 K, R = 0.060 for 578 unique observed (F > 5a(F)) reflections. Atoms Br, C5, C2 and N2 lie on the mirror plane at x = 0; atoms N3 and C4 are therefore symmetry equivalents of N1 and C6. The numbering system conforms to that for pyrimidine nucleobases. The molecules of the title compound form self-base-paired ribbons which run parallel to the a axis. The hydrogen bond involved in the base-pairing between symmetry related molecules is N2...N1 (-0.5-x, 1.5-y,-z) 3.10 (3)/~. Experimental. Crystals were obtained from aqueous solution as very thin micaceous plates. Space group and initial cell dimensions were obtained from Weissenberg photographs. Data were collected on a Nicolet P3 (four-circle) diffractometer in Aberdeen by RAH. The crystal had dimensions 0.04 × 0.4 × 0.6 mm. Cell parameters were measured on the diffractometer using 14 reflections in the 20 range 17-21 o. Range of indices: 0_ 5tT(F)l reflections Table 1. Coordinates (× 10 4) and Ueq values (A 2 × 10 3) for non-hydrogen atoms with e.s.d. s in parentheses Ueq - ~EiEjUija i aj ai.a i.