Abstract

<h2>Acta Crystallographica Section B</h2><h3>Structural Crystallography and Crystal Chemistry</h3><h3>0567-7408</h3> <h2>research papers</h2> Volume 32 Part 8 Pages 2361-2367 August 1976 <h2>The X-ray structure of the molecular complex 9-ethyladenine-parabanic acid</h2> H.-S. Shieh and D. Voet 2361 Acta Cryst. (1976). B32, 2361 The X-ray Structure of the Molecular Complex 9-Ethyladenine-Parabanic Acid BY HUEY-SHENG SHIEH* AND DONALD VOET Department of Chemistry and the Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19174, U.S.A. (Received 17 November 1975; accepted 24 February 1976) The hydrogen-bonded complex 9-ethyladenine-parabanic acid, Cx0H11NTO3, crystallizes in the space group Pbcn with unit-cell parameters a=21.386 (8), b= 7.119 (5) and c= 16.288 (6)/~, with eight com- plexes per unit cell. Intensity data were measured with monochromated Mo K0c radiation. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R = 0"059 based on 1137 observed unique reflections. The adenine and parabanic acid molecules associate through a Hoogsteen pairing that includes an extremely long N-H.-.O hydrogen bond. The parabanic acid accepts no other hydrogen bonds. In contrast, through two additional hydrogen bonds, each with unusual features, all three of the adenine hydrogen-bond acceptor sites are utilized. The structure exhibits