Molecular co-crystals of 2-aminothiazole derivatives

A series of molecular adducts of 2-aminothiazole derivatives - 2-aminothiaz ole, 2-amino-2-thiazoline and 2-aminobenzothiazole with the carboxylic-acid -substituted heterocyclics indole-2-carboxylic acid, N-methylpyrrole-2-carb oxylic acid and thiophene-2-carboxylic acid - have been prepared and charac terized 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-me thylpyrrole-2-carboxylate [(C3H7N2S)(+) (C6H6NO2)(-)], 2-aminobenzothiazoli um with indole-2-carboxylate [(C7H7N2S)(+)(C9H6NO2)(-)], N-methylpyrrole-2- carboxylate [(C7H7N2S)(+)(C6H6NO2)(-)] and thiophene-2-carboxylate [(C7H7N2 S)(+)(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 R-2(2)(8) graph se t dimer association between carboxylate groups and the amine/heterocyclic n itrogen sites. Futhermore, in each case a subsiduary interaction between an amino proton and a carboxylate oxygen completes a linear hydrogen-bonded c hain. In addition to this, the indole-2-carboxylate molecules in the adduct structure with 2-amino-2-thiazolium form associated dimers which add to th e hydrogen-bonding network.