Hydrogen-bonded molecular salts of reduced benzothiazole derivatives with carboxylates: a robust R_2^2(8) supramolecular motif (even when disordered)

The syntheses and structures of five mol­ecular salts of protonated 4,4,7,7-tetra­methyl-3a,5,6,7a-tetra­hydro­benzo­thia­zol-2-yl­amine (C₁₁H₁₉N₂S⁺) with different deprotonated carb­oxy­lic acids (4-methyl­benzoic acid, 4-bromo­benzoic acid, 3,5-di­nitro­benzoic acid, fumaric acid and succinic acid) are reported, namely 2-amino-4,4,7,7-tetra­methyl-4,5,6,7-tetra­hydro-1,3-benzo­thia­zol-3-ium 4-methyl­benzoate, C₁₁H₁₉N₂S⁺·C₈H₇O₂−, (I), 2-amino-4,4,7,7-tetra­methyl-4,5,6,7-tetra­hydro-1,3-benzo­thia­zol-3-ium 4-bromo­benzoate, C₁₁H₁₉N₂S⁺·C₇H₄BrO2⁻, (II), 2-amino-4,4,7,7-tetra­methyl-4,5,6,7-tetra­hydro-1,3-benzo­thia­zol-3-ium 3,5-di­nitro­benzoate, C₁₁H₁₉N₂S⁺·C₇H₃N₂O6⁻, (III), bis­(2-amino-4,4,7,7-tetra­methyl-4,5,6,7-tetra­hydro-1,3-benzo­thia­zol-3-ium) fumarate, 2C₁₁H₁₉N₂S⁺·C₄H₂O₄²⁻,(IV), and the 1:1 co-crystal of bis­(2-amino-4,4,7,7-tetra­methyl-4,5,6,7-tetra­hydro-1,3-benzo­thia­zol-3-ium) succinate and 2-amino-4,4,7,7-tetra­methyl-4,5,6,7-tetra­hydro-1,3-benzo­thia­zol-3-ium hydrogen succin­ate 4,4,7,7-tetra­methyl-3a,5,6,7a-tetra­hydro­benzo­thia­zol-2-yl­amine, 1.5C₁₁H₁₉N₂S⁺·0.5C₄H₄O₄²⁻·0.5C₄H₅O₄⁻. 0.5C₁₁H₁₈N₂S, (V). In every case, the cation protonation occurs at the N atom of the thia­zole ring and the six-membered ring adopts a half-chair conformation (in some cases, the deviating methyl­ene groups are disordered over two sets of sites). The C—N bond lengths of the nominal –NH⁺=C—NH₂ fragment of the cation are indistinguishable, indicating a significant contribution of the –NH—C=N⁺H₂ resonance form to the structure. The packing for (I)–(V) features a robust local R₂²(8) loop motif in which the cation forms two near-linear N—H⋯O hydrogen bonds from the N⁺—H group and syn H atom of the amine group to the carboxyl­ate group of an adjacent anion [(V) shows disorder of one of these bonds over N—H⋯O and N⋯H—O contributors but the same R₂²(8) loop results for both disorder components]. The anti H atom of the –NH₂ group also forms an N—H⋯O hydrogen bond, which results in [001] chains in (I) and (II), isolated centrosymmetric tetra­mers in (III) and [100] chains in (IV) and (V). Hirshfeld fingerprint plots and contact percentages for the different types of contacts of the cations are discussed.