Crystal structures of four 1-(aryl)-[1,2,4]triazolo[4,3-a]quinoxaline derivatives

The crystal structures of four 1-aryl-[1,2,4]triazolo[4,3-alpha]quinoxaline derivatives, 2, are reported: [aryl = 3-CIC6H4: 2a; 2-HOC6H4:2b;2,3-(HO)(2)C6H3: 2c; and 3,4-(MeO)(2)C6H3: 2d] The compounds, 2, were prepared by oxidation of substituted arenealdehyde quinoxalin-2-ylhydrazones, 1, using ferric chloride in alcohol. In each of the four compounds, the three ring -[1,2,4]triazolo[4,3-alpha]quinoxaline moiety is a near planar moiety, with all ring atoms within 0.1 of the best plane. There are large dihedral angles, 59 +/- 7 degrees, between the [1,2,4]triazolo[4,3-alpha]quinoxaline system and the phenyl ring. The ortho sited hydroxyl groups in 2c are jointly involved in a single O-H center dot center dot center dot O intramolecular hydrogen bond and individually in O-H center dot center dot center dot N intermolecular interactions, while the hydroxyl group in 2b is involved in an intermolecular O-H center dot center dot center dot N hydrogen bond. These and weaker intermolecular interactions, including some of C-H center dot center dot center dot Z (Z = O, N and or pi) and pi center dot center dot center dot pi interactions generate the supramolecular arrangements in 2b and 2c. Intermolecular C-H center dot center dot center dot Z (Z = O, N and or pi) and pi center dot center dot center dot pi interactions are only present in 2a and 2d. (C) 2016 Elsevier B.V. All rights reserved.