Hydrogen-bonded molecular salts of reduced benzothiazole derivatives with carboxylates: a robust R2² (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+·C4H2O4 2-,(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+·0.5C4H4O4 2-·0.5C4H5O4 -. 0.5C11H18N2S, (V). In every case, the cation protonation occurs at the N atom of the thiazole ring and the sixmembered 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 R2 ²(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 R2 2(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. [ABSTRACT FROM AUTHOR]