Six piperazinium salts, namely 4-(4-nitrophenyl)piperazin-1-ium 4-bromobenzoate dihydrate, C10H14N3O2 +·C7H4BrO2 −·2H2O, (I), 4-(4-nitrophenyl)piperazin-1-ium 4-iodobenzoate dihydrate, C10H14N3O2 +·C7H4IO2 −·2H2O, (II), 4-(4-nitrophenyl)piperazin-1-ium 4-hydroxybenzoate monohydrate, C10H14N3O2 +·C7H5O3 −·H2O, (III), 4-(4-nitrophenyl)piperazin-1-ium 4-methylbenzoate monohydrate, C10H14N3O2 +·C8H7O2 −·H2O, (IV), 4-(4-nitrophenyl)piperazin-1-ium 4-methoxybenzoate hemihydrate, 2C10H14N3O2 +·2C8H7O3 −·H2O, (V), and 4-(4-nitrophenyl)piperazin-1-ium 4-ethoxybenzoate, 2C10H14N3O2 +·2C9H9O3 −, (VI), have been synthesized and their crystal structures solved by single-crystal X-ray diffraction, revealing that all of them crystallize in the triclinic space group P\overline{1} except for (V), which crystallizes in the monoclinic space group P21/c and has a disordered nitro group. Compounds (I) and (II) are isostructural. The crystal packing of (I)–(V) is constructed from organic chains formed by a combination of hydrogen bonds of type N—H...O and/or O—H...O and other weak interactions of type C—H...O and/or C—H...π, forming sheets, whereas (VI) shows a cationic and anionic-based layer structure.

Three 1-[(1,3-benzodioxol-5-yl)methyl]-4-(halobenzo­yl)piperazines adopt very similar mol­ecular conformations but, while the mol­ecules of the 3-fluoro­benzoyl are linked by hydrogen bonds into a three-dimensional structure, there are no hydrogen bonds in either of the 2,6-di­fluoro­benzoyl and 2,4-di­chloro­benzoyl analogues.

Two new 1-(thiazol-2-yl)-4,5-dihydropyrazoles have been synthesized from simple precursors, and characterized both spectroscopically and structurally. In addition, two intermediates in the reaction pathway have been isolated and characterized, one of them structurally. The molecules of the intermediate (E)-1-(4-methoxyphenyl)-3-[4-(prop-2-ynyloxy)phenyl]prop-2-en-1-one, C19H16O3 (I), are linked by a combination of C—H...O and C—H...π(arene) hydrogen bonds to form ribbons. The products (RS)-5-(4-methoxyphenyl)-1-(4-phenythiazol-2-yl)-3-[4-(prop-2-ynyloxy)phenyl]-4,5-dihydro-1H-pyrazole, C28H23N3O2S (II), and (RS)-5-(4-methoxyphenyl)-1-[4-(4-methylphenyl)thiazol-2-yl]-3-[4-(prop-2-ynyloxy)phenyl]-4,5-dihydro-1H-pyrazole, C29H25N3O2S (III), are closely related – differing only by presence or absence of a methyl group at the arylthiazolyl substituent – and crystallize in an isomorphous setting. Both molecules contain an effectively planar dihydro-pyrazole ring, and possess an overall T-shaped structure, which is a characteristic of triaryl-substituted 4,5-dihydro-1-(thiazol-2-yl)pyrazole compounds. The crystal packing is characterized by intermolecular C—H...S and C—H...π (aryl/alkyne) interactions. A combination of two C—H...π(arene) hydrogen bonds links the product molecules into sheets.

Crystal structures are reported for three amides containing N-benzo[d]thiazole substituents. In N-(benzo[d]thiazol-6-yl)-3-bromobenzamide, C14H9BrN2OS, where the two ring systems are nearly parallel to one another [dihedral angle = 5.8 (2)°], the molecules are linked by N—H...O and C—H...N hydrogen bonds to form ribbons of R 3 3(19) rings, which are linked into sheets by short Br...Br interactions [3.5812 (6) Å]. N-(6-Methoxybenzo[d]thiazol-2-yl)-2-nitrobenzamide, C15H11N3O4S, crystallizes with Z′ = 2 in space group Pna21: the dihedral angles between the ring systems [46.43 (15) and 66.35 (13)°] are significantly different in the independent molecules and a combination of two N—H...N and five C—H...O hydrogen bonds links the molecules into a three-dimensional network. The molecules of 5-cyclopropyl-N-(6-methoxybenzo[d]thiazol-2-yl)isoxazole-3-carboxamide, C15H13N3O3S, exhibit two forms of disorder, in the methoxy group and in the cyclopropylisoxazole unit; symmetry-related pairs of molecules are linked into dimers by pairwise N—H...N hydrogen bonds. Comparisons are made with the structures of some related compounds.

In this study, four new piperazinium salts, namely, 4-phenylpiperazin-1-ium 4-ethoxybenzoate monohydrate, C9H9O3·C10H15N2·H2O (I); 4-phenylpiperazin-1-ium 4-methoxybenzoate monohydrate, C10H15N2·C8H7O3·H2O (II); 4-phenylpiperazin-1-ium 4-methylbenzoate monohydrate, C10H15N2·C8H7O2·H2O (III); and 4-phenylpiperazin-1-ium trifluoroacetate 0.12 hydrate, C10H15N2·C2F3O2·0.12H2O (IV), have been synthesized. The single-crystal structures of these compounds reveal that all of them crystallize in the triclinic P\overline{1} space group and the crystal packing of (I)–(III) is built up of ribbons formed by a combination of hydrogen bonds of type N—H...O, O—H...O and other weak interactions of type C—H...O and C—H...π, leading to a three-dimensional network. In the crystal of (IV), the cations and the anions are connected by C—H...O, N—H...O and C—H...F hydrogen bonds and by C—H...π interactions, forming sheets which in turn interact to maintain the crystal structure by linking through the oxygen atoms of water molecules and van der Waals interactions, giving the whole structure.