Acta Crystallographica Section B

Structural Science

Volume 55, Part 5 (October 1999)

research papers

Acta Cryst. (1999). B55, 758-766 [ doi:10.1107/S0108768199003146 ]

Molecular co-crystals of 2-aminothiazole derivatives

D. E. Lynch, L. J. Nicholls, G. Smith, K. A. Byriel and C. H. L. Kennard

Abstract: A series of molecular adducts of 2-aminothiazole derivatives - 2-aminothiazole, 2-amino-2-thiazoline and 2-aminobenzothiazole with the carboxylic-acid-substituted heterocyclics indole-2-carboxylic acid, N-methylpyrrole-2-carboxylic acid and thiophene-2-carboxylic acid - have been prepared and characterized using X-ray powder diffraction and in five cases by single-crystal X-ray diffraction methods. These five compounds are the adducts of 2-amino-2-thiazolium with indole-2-carboxylate [(C₃H₇N₂S)⁺(C₉H₆NO₂)^-], and N-methylpyrrole-2-carboxylate [(C₃H₇N₂S)⁺-(C₆H₆NO₂)^-], 2-aminobenzothiazolium with indole-2-carboxylate [(C₇H₇N₂S)⁺(C₉H₆NO₂)^-], N-methylpyrrole-2-carboxylate [(C₇H₇N₂S)⁺(C₆H₆NO₂)^-] and thiophene-2-carboxylate [(C₇H₇N₂S)⁺(C₅H₃O₂S)^-]. All complexes involve proton transfer, as indicated by IR spectroscopy, while the five crystal structures display similar hydrogen-bonding patterns with the dominant interaction being an graph set dimer association between carboxylate groups and the amine/heterocyclic nitrogen sites. Futhermore, in each case a subsiduary interaction between an amino proton and a carboxylate oxygen completes a linear hydrogen-bonded chain. In addition to this, the indole-2-carboxylate molecules in the adduct structure with 2-amino-2-thiazolium form associated dimers which add to the hydrogen-bonding network.

Keywords: 2-Aminothiazole derivatives; Proton transfer.