Molecular co-crystals of 2-aminothiazole derivatives

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 [(C(3)H(7)N(2)S)(+)(C(9)H(6)NO(2))(-)], and N-methylpyrrole-2-carboxylate [(C(3)H(7)N(2)S)(+)-(C(6)H(6)NO(2))(-)], 2-aminobenzothiazolium with indole-2-carboxylate [(C(7)H(7)N(2)S)(+)(C(9)H(6)NO(2))(-)], N-methylpyrrole-2-carboxylate [(C(7)H(7)N(2)S)(+)(C(6)H(6)NO(2))(-)] and thiophene-2-carboxylate [(C(7)H(7)N(2)S)(+)(C(5)H(3)O(2)S)(-)]. 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 R(2)(2)(8) 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.