Acta Cryst. (2002). E58, o865±o866 DOI: 10.1107/S1600536802012473 V. S. Senthil Kumar et al.  C 7 H 4 N 2 O 7 C 12 H 8 N 2 o865 organic papers Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 3,5-Dinitrosalicylic acid-phenazine (1/1) V. S. Senthil Kumar, Srinivasan S. Kuduva and Gautam R. Desiraju* School of Chemistry, University of Hyderabad, Hyderabad 500 046, India Correspondence e-mail: desiraju@uohyd.ernet.in Key indicators Single-crystal X-ray study T = 293 K Mean (C±C) = 0.004 A Ê R factor = 0.059 wR factor = 0.132 Data-to-parameter ratio = 15.4 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. # 2002 International Union of Crystallography Printed in Great Britain ± all rights reserved In the 1:1 molecular complex of 3,5-dinitrosalicylic acid and phenazine, C 7 H 4 N 2 O 7 C 12 H 8 N 2 , the carboxylic acid group forms an OÐHN hydrogen bond to only one of the two heterocyclic N atoms. The structure is also stabilized extensively by CÐHO hydrogen bonds. Comment The carboxylic acid functionality is well known to form molecular complexes with compounds having strong acceptor groups, such as N and O (Palmore et al. , 1999). Recently, this concept was invoked in the cocrystallization experiment of simple alkane dicarboxylic acids with phenazine (Batchelor et al., 2000), where both N atoms of the phenazine molecule are involved in OÐHN hydrogen bonds. Here, we have cocrystallized phenazine with 3,5-dinitrosalicylic acid. The molecular geometry of the title compound, (I), is shown in Fig. 1 (ORTEPII; Johnson, 1976). The carboxylic acid group forms OÐHN hydrogen bonds on one side of the phen- azine molecule, while the other N atom was found to be inactive. The emphasis of this crystal structure is on the structural attributes of CÐHO hydrogen bonding (Desiraju & Steiner, 1999). In the crystal structure, each 3,5- dinitrosalicylic acid molecule is connected to the phenazine molecule by CÐHO interactions and forms 2 1 -screw- related ribbons parallel to [044] and [0 44]. These two ribbons are connected by an OÐHN (1.76 A Ê and 161  ) and an auxiliary CÐHO (2.78 A Ê and 143  ) hydrogen bond to make a two-dimensional grid structure. These grids are further connected by CÐHO hydrogen bonds, forming another such grid. The packing diagram of the molecular complex is shown in Fig. 2. The occurrence of CÐHO hydrogen bonds follows from the presence of activated CÐH groups in the constituent molecules. Experimental Yellow crystals of the 1:1 molecular complex of 3,5-dinitrosalicylic acid and phenazine were obtained when a 2:1 mixture of 3,5-di- nitrosalicylic acid and phenazine was kept for crystallization in acetonitrile solvent. Received 9 July 2002 Accepted 11 July 2002 Online 19 July 2002