Reinvestigation of the structure of 2-hydroxyquinoxaline

Abstract

$C_8H_6N_20$, M r= 146.15, orthorhombic, $P2_12_12_1$, a = 4.354 (1), b = 7.348 (1), c = 21.320 (1) \AA, V= 682.13 $\AA^ 3$, Z = 4, $D_x = 1.43, D _m = 1.41 Mg m ^{-3}$, \lambda(CuKa) = 1.5418 \AA, \mu = 7.6 $mm ^{-1}$, F(000) = 304, room temperature, R =0.041 for 771 observed reflections [I > 3\rho(I)]. A reinvestigation of the structure of 2-hydroxyquinoxaline based on diffractometer data has yielded more precise structural parameters (bond-length and angle e.s.d.'s of 0.004 \AA, 0.2 °) than the photographic results of Stepien, Grabowski, Cygler & Wajsman [(1976). Acta Cryst. B32, 2048-2050] (R = 0. 110, bond-length and angle e.s.d.'s 0.01 \AA, 0.7°). The compound exists in the keto form in the crystal with C=O = 1.239 (3)A. The quinoxaline rings are essentially planar (inter-ring dihedral angle = 1.6 °) including the exocyclic atoms. The large deviation of H(5) from the ring plane (0.59 \AA) reported earlier is not observed here. The crystal structure is stabilized by strong intermolecular hydrogen bonds: N...O = 2.782 (6) \AA, N--H...O = 162 ° .