Low Temperature Crystal Structures of Two Rhodanine Derivatives, 3-Amino Rhodanine and 3-Methyl Rhodanine: Geometry of the Rhodanine Ring

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], C₃H₄N₂OS_2, and (II) 3-methylrhodanine [3-methyl-2-thio-4-oxothiazolidine], C₄H₅NOS₂, have been conducted at 100 K. I crystallizes in the monoclinic space group P2₁/n with unit cell parameters a = 9.662(2), b = 9.234(2), c = 13.384(2) Å, β = 105.425(3)°, V = 1151.1(3) ų, Z = 8 (2 independent molecules per asymmetric unit), density (calculated) = 1.710 mg/m³, 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) Å, V = 3703.9(12) ų, Z = 24 (three independent molecules per asymmetric unit), density (calculated) = 1.584 mg/m³, 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 F² = 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 e Å⁻³. For II in the final refinement cycle the data/restraints/parameter ratios were 3372/1/221, goodness-of-fit on F² = 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 Å⁻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.

Index Abstract

Low temperature X-ray structures of (I) 3-aminorhodanine [3-amino-2-thio-4-oxothiazolidine] and (II) 3-methylrhodanine3-methyl-2-thio-4-oxothiazolidine are presented. Crystals of I are monoclinic and occupy space group P2₁/n with eight molecules (2 per asymmetric unit cell) and (II) is orthorhombic in space group Iba2 with 24 molecules (3 per asymmetric unit). This study has provided five highly consistent copies of the rhodanine ring at high resolution thus enabling its geometry to be established with confidence.