ORIGINAL PAPER Low Temperature Crystal Structures of Two Rhodanine Derivatives, 3-Amino Rhodanine and 3-Methyl Rhodanine: Geometry of the Rhodanine Ring Saima Jabeen Æ Rex A. Palmer Æ Brian S. Potter Æ Madeleine Helliwell Æ Trevor J. Dines Æ Babur Z. Chowdhry Received: 17 March 2008 / Accepted: 4 June 2008 / Published online: 2 July 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Rhodanines (2-thio-4-oxothiazolidines) are synthetic small molecular weight organic molecules with diverse applications in biochemistry, medicinal chemistry, photochemistry, coordination chemistry and industry. The X-ray crystal structure determination of two rhodanine derivatives, namely (I), 3-aminorhodanine [3-amino-2-thio- 4-oxothiazolidine], C 3 H 4 N 2 OS 2, and (II) 3-methylrhodanine [3-methyl-2-thio-4-oxothiazolidine], C 4 H 5 NOS 2 , have been conducted at 100 K. I crystallizes in the monoclinic space group P2 1 /n with unit cell parameters a = 9.662(2), b = 9.234(2), c = 13.384(2) A ˚ , b = 105.425(3)°,V = 1151.1(3) A ˚ 3 ,Z = 8 (2 independent molecules per asymmetric unit), density (calculated) = 1.710 mg/m 3 , absorption coefficient = 0.815 mm -1 . II crystallizes in the orthorhombic space group Iba2 with unit cell a = 20.117(4), b = 23.449(5), c = 7.852(2) A ˚ ,V = 3703.9(12) A ˚ 3 ,Z = 24 (three inde- pendent molecules per asymmetric unit), density (calculated) = 1.584 mg/m 3 , absorption coefficient 0.755 mm -1 . For I in the final refinement cycle the data/restraints /parameter ratios were 2639/0/161, goodness-of-fit on F 2 = 0.934, final R indices [I [ 2sigma(I)] were R1 = 0.0299, wR2 = 0.0545 and R indices (all data) R1 = 0.0399, wR2 = 0.0568. The largest difference peak and hole were 0.402 and -0.259 eA ˚ -3 . For II in the final refinement cycle the data/restraints/ parameter ratios were 3372/1/221, goodness-of-fit on F 2 = 0.950, final R indices [I [ 2sigma(I)] were R1 = 0.0407, wR2 = 0.1048 and R indices (all data) R1 = 0.0450, wR2 = 0.1088. The absolute structure parameter = 0.19(9) and largest difference peak and hole 0.934 and -0.301 e A ˚ -3 . Details of the geometry of the five molecules (two for I and three for II) and the crystal structures are fully discussed. Corresponding features of the molecular geometry are highly consistent and firmly establish the geometry of the rhodanine ring. Keywords Rhodanine derivative Á Crystal structure Á Low temperature Á Ring geometry Á Rhodanine Á 3-Aminorhodanine Á 3-Methylrhodanine Á Accurate crystal structures Á Geometry of the rhodanine ring Introduction Rhodanine [2-thio-4-oxothiazolidine (Rd)] and its derivatives, 3-aminorhodanine (I) [3-amino-2-thio-4-oxothiazolidine (H 2 NRd)] and 3-methylrhodanine (II) [3-methyl-2-thio-4-oxo- thiazolidine (MeRd)], are five-membered ring heterocyclic systems (Fig. 1) with diverse applications particularly in biochemistry, medicinal chemistry, photochemistry, industry, and coordination chemistry. Intriguingly the parent Rd struc- ture is not prevalent in natural molecules, but the Rd moiety can be synthesized by various methods. The classification of Rd derivatives is based solely on whether the 2-thioxo-4- oxothiazolidine ring is linked to the rest of the molecule S. Jabeen Á B. Z. Chowdhry (&) School of Science, University of Greenwich, (Medway Campus), Chatham Maritime, Kent ME4 4TB, UK e-mail: b.z.chowdhry@gre.ac.uk R. A. Palmer (&) Á B. S. Potter School of Crystallography, Birkbeck College, University of London, Malet Street, London WC1E7HX, UK e-mail: rex.palmer@btinternet.com M. Helliwell School of Chemistry, University of Manchester, Brunswick Street, Manchester M13 9PL, UK T. J. Dines Division of Electronic Engineering & Physics, University of Dundee, Dundee DD1 4HN, UK 123 J Chem Crystallogr (2009) 39:151–156 DOI 10.1007/s10870-008-9427-6