CLAIRE WILSON AND JUDITH A. K. HOWARD 547 Triclinic PT a = 7.0543 (7) ,A o b = 8.8125 (9) A c = 15.016 (1) A a = 72.980 (3) ° = 77.562 (3) ° 7 = 69.707 (3) ° V 830.4(1) A 3 Z=2 Dx = 1.592 Mg m -3 D,, not measured Data collection Siemens SMART CCD diffractometer to rotation scans with narrow frames Absorption correction: empirical via ~b scans (SHELXTL; Sheldrick, 1994) Train = 0.65, Tmax = 0.89 Refinement Refinement on F 2 R[F 2 > 20.(F2)] = 0.039 wR(F 2) = 0.099 S - 1.118 2554 reflections 266 parameters Only coordinates of H atoms refined w = 1/[0.2(F2) + (0.0414P) 2 + 1.0763P] where P = (F 2 + 2F~)/3 Cell parameters from 510 reflections 0 = 7.0-24.1 ° # = 0.711 mm -~ T = 150 (2) K Rectangular 0.50 x 0.42 x 0.16 mm Colourless 3487 measured reflections 2560 independent reflections 2429 reflections with I > 20(/) Rint = 0.032 0max = 25.14 ° h = - 8 ----~ 7 k= -10 ---~ 7 1 = - 17 ~ 17 (m/o')max -- 0.001 Apmax = 0.295 e ~-3 Apmin = -0.390 e ~-3 Extinction correction: SHELXL Extinction coefficient: 0.072 (5) Scattering factors from International Tables for Crystallography (Vol. C) References Geich, H., Grimme, W. & Proske, K. (1992). J. Am. Chem. Soc. 114, 1492-1493. Hagenbuch, J.-P., Stampfli, B. & Vogel, P. (1981). J. Am. Chem. Sac. 103, 3934-3935. Mackenzie, K., Howard, J. A. K., Mason, S. A., Gravett, E. C., Astin, K. B., Shi-Xiong, L., Batsanov, A. B., Vlaovic, D., Maher, J. P., Murray, M., Kendrew, D., Wilson, C., Johnson, R. E., PreiB, T. & Gregory, R. J. (1993). J. Chem. Sac. Perkin Trans. 2, pp. 1211- 1228. Mackenzie, K., Howard, J. A. K., Siedlecka, R., Astin, K. B., Gravett, E. C., Wilson, C., Cole, J., Gregory, R. G. & Tomlins, A. S. (1996). J. Chem. Soc. Perkin Trans. 2, pp. 1749-1760. Mackenzie, K., Proctor, G. & Woodnutt, D. J. (1987). Tetrahedron, 43, 5981-5993. Molecular Structure Corporation (1991). MSCIAFC Diffractometer Control Software. MSC, 3200 Research Forest Drive, The Wood- lands, TX 77381, USA. Molecular Structure Corporation (1992). TEXSAN. TEXRAY Structure Analysis Package. MSC, 3200 Research Forest Drive, The Wood- lands, TX 77381, USA. O'Doherty, G. A., Rogers, R. D. & Paquette, L. A. (1994). J. Am. Chem. Soc. 116, 10883-10894. Paquette, L. A., Kesselmayer, M. A. & Rogers, R. D. (1990). J. Am. Chem. Soc. 112, 284-291. Paquette, L. A., O'Doherty, G. A. & Rogers, R. D. (1991). J. Am. Chem. Soc. 113, 7761-7762. Sheldrick, G. M. (1994). SHELXTL. Structure Determination Pro- grams. Version 5.03. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. Siemens (1995). SMART and SAINT. Area Detector Control and Integration Software. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. Wilson, C. (1995). PhD thesis, University of Durham, England. Table 2. Selected bond lengths (,~)for (2D) c2--c7 1.395 (3) Cl2--Cll 1.530 (4) Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1991) for (1D); SMART (Siemens, 1995) for (2D). Cell refinement: TEXSAN (Molec- ular Structure Corporation, 1992) for (1D); SMART for (2D). Data reduction: TEXSAN for (1D); SA/NT (Siemens, 1995) for (2D). For both compounds, program(s) used to solve struc- tures: SHELXTL (Sheldrick, 1994); program(s) used to refine structures: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. We thank Dr K. Mackenzie who conceived the research programme, executed preparative and kinetic work, and provided excellent quality crystals. Dr R. Siedlecka is thanked for the preparation of compound (2D). CW thanks the Institut Laue-Langevin for a studentship. Supplementary data for this paper are available from the IUCr electronic archives (Reference: CF1209). Services for accessing these data are described at the back of the journal. Acta Cryst. (1998). C54, 547-550 Two New Structures of 5-Nitrouracil ALAN R. KENNEDY, /~AURICE O. OKOTH,t DAVID B. SHEEN, JOHN N. SHERWOOD AND RANKO M. VRCELJ Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL Scotland. E-mail: a. r. kennedy @ ccsun, strath, ac. uk (Received 17 July 1997; accepted 12 November 1997) Abstract The structure of monoclinic anhydrous 5-nitrouracil, C4H3N304, and of the solvate 5-nitrouracil dimethyl sulfoxide, C4H3N304.C2H6OS, are presented and com- pared with the previously known structures of the orthorhombic anhydrous form and the monohydrate. f Present address: Department of Chemistry, Moi University, PO Box 1125, Eldoret, Kenya. © 1998 Intemational Union of Crystallography Printed in Great Britain - all fights reserved Acta Crystallographica Section C ISSN 0108-2701 ©1998