organic papers o1790 A. Moghimi et al.  C 4 H 8 N 3 O + C 7 H 4 NO 4  H 2 O DOI: 10.1107/S1600536804022482 Acta Cryst. (2004). E60, o1790±o1792 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 Creatininium dipicolinate monohydrate Abolghasem Moghimi, a * Mahboubeh A. Sharif b and Hossein Aghabozorg c a Department of Chemistry, Imam Hossein University, PO Box 16575-347, Tehran, Iran, b Department of Chemistry, Islamic Azad University, Science and Research Campus, Tehran, Iran, and c Department of Chemistry, Teacher Training University, PO Box 15614, Tehran, Iran Correspondence e-mail: samoghimi@yahoo.com Key indicators Single-crystal X-ray study T = 293 K Mean (C±C) = 0.003 A Ê Disorder in main residue R factor = 0.048 wR factor = 0.162 Data-to-parameter ratio = 22.3 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. # 2004 International Union of Crystallography Printed in Great Britain ± all rights reserved The title compound, (creatH) + (pydcH)  H 2 O or C 4 H 8 N 3 O + - C 7 H 4 NO 4  H 2 O, was obtained by the reaction of 2,6-pyridine- dicarboxylic acid (dipicolinic acid, pydcH 2 ) with creatinine (creat). A single proton from the dicarboxylic acid is transferred to the endocyclic imine N atom of creatinine. The cations and anions lie on a crystallographic mirror plane, across which the water molecule is disordered. The interac- tions among cations, anions and water molecules consist of ion-pairing, hydrogen bonding and ± stacking. Comment Proton transfer in molecular associations between carboxylic acids and Lewis bases confers considerable stability in the structure-forming process, resulting generally in more hydrogen-bonding associations, particularly involving the protonated amine groups (Smith et al., 1999). In order to study the role of the proton-acceptor compounds in the construction of the three-dimensional structure of the resulting proton- transfer compounds, we have already reported a number of novel proton-transfer compounds, using 2,6-pyridinedi- carboxylic acid (pydcH 2 ) and 1,10-phenanthroline-2,9-di- carboxylic acid (phendcH 2 ) as proton donors and 2,6- pyridinediamine (pyda) and guanidine (G) as proton accep- tors (Moghimi, Ranjbar, Aghabozorg, Jalali, Shamsipur, Yap & Rahbarnoohi, 2002; Moghimi et al., 2003, 2004). The di- carboxylic acids in all of these cases are suitable ligands in the synthesis of metal complexes (Moghimi et al., 2002a,b; Ranjbar, Moghimi et al., 2001; Ranjbar, Aghabozorg & Moghimi, 2002; Ranjbar, Taghavipur et al., 2002; Ranjbar, Moghimi et al., 2002; Ranjbar, Aghabozorg et al., 2001, Ranjbar et al., 2003), leaving protonated acceptors as cationic counter-ions in the complexes. Reasoning that similar phenomena could be observed with biologically important acceptors having a number of functional groups suitable for hydrogen bonding, we undertook the synthesis of a novel creatinine-containing proton-transfer compound. Creatinine as a proton acceptor has previously been used in the synthesis of some proton-transfer compounds such as those with nitrobenzoic acids, 3,5-dinitrobenzoic acid, 5- nitrosalicyclic acid, 3,5-dinitrosalicyclic acid and pyrazine-2,3- Received 11 June 2004 Accepted 9 September 2004 Online 18 September 2004