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The syntheses and crystal structure studies of four organic salts of trihexyphenidyl, viz., trihexyphenidylium [1-(3-cyclohexyl-3-hydroxy-3-phenylpropyl)piperidin-1-ium] 4-nitrobenzoate, C20H32NO+·C7H4NO4− (I), trihexyphenidylium 4-hydroxybenzoate, C20H32NO+·C7H5O− (II), trihexyphenidylium 4-bromobenzoate, C20H32NO+·C7H4BrO2− (III), and trihexyphenidylium thiophene-2-carboxylate hemihydrate, 2C20H32NO+·2C5H3O2S−·H2O (IV), conducted at 90 K are described. Structures I, II, and III are solvent free with one cation–anion pair per asymmetric unit, while IV crystallizes as a hemihydrate, having two cation–anion pairs and one water of crystallization in its asymmetric unit. Structures I and III exhibit configurational disorder of the cation. Structure IV also exhibits disorder, but only of the thiophene-2-carboxylate anions. Structure II is a non-merohedric twin by a twofold rotation about [403]. The main supramolecular motifs in I, II, and III are similar R22(10) rings between cation–anion pairs, although their packing within the crystals is distinct. As a consequence of having two cation–anion pairs and a water molecule in its asymmetric unit, the packing in IV is by far the most complex of the four structures, its hydrogen-bonding patterns being quite different from I, II, or III. In all the crystals studied, N—H...O, O—H...O, and C—H...O interactions are observed, plus C—H...Br close contacts for III.

The synthesis and crystal structure of C3HF3N2OS, systematic name 5-(trifluoromethyl)-1,3,4-thiadiazol-2(3H)-one (5-TMD-2-one), a compound containing the pharmacologically important heterocycle 1,3,4-thiadiazole, is presented. The asymmetric unit comprises six independent molecules (Z′ = 6), all of which are planar. The r.m.s. deviations from each mean plane range from 0.0063 to 0.0381 Å, not including the CF3 fluorine atoms. Within the crystal, two of the molecules form hydrogen-bonded dimers that in turn combine with inversion-related copies to form tetrameric constructs. Similar tetramers, but lacking inversion symmetry, are formed by the remaining four molecules. The tetramers are linked into tape-like motifs by S...O and O...O close contacts. The environments of each symmetry-independent molecule were compared via a Hirshfeld surface analysis. The most abundant atom–atom contacts are between fluorine atoms, while the strongest result from N—H...O hydrogen bonds.

The syntheses and crystal structures of four salts of amitriptynol (C20H25NO) with different carboxylic acids are described. The salts formed directly from solutions of amitriptyline (which first hydrolysed to amitriptynol) and the corresponding acid in acetonitrile to form amitriptynolium [systematic name: (3-{2-hydroxytricyclo[9.4.0.03,8]pentadeca-1(11),3,5,7,12,14-hexaen-2-yl}propyl)dimethylazanium] 4-methoxybenzoate monohydrate, C20H26NO+·C8H7O3−·H2O, (I), amitriptynolium 3,4-dimethoxybenzoate trihydrate, C20H26NO+·C9H9O4−·3H2O, (II), amitriptynolium 2-chlorobenzoate, C20H26NO+·C7H4ClO2−, (III), and amitriptynolium thiophene-2-carboxylate monohydrate, C20H26NO+·C5H3O2S−·H2O, (IV). Compound (III) crystallizes with two cations, two anions and six water molecules in the asymmetric unit. The different conformations of the amitriptynolium cations are determined by the torsion angles in the dimethylamino-propyl chains and the –CH2–CH2- bridge between the benzene rings in the tricyclic ring system, and are complicated by disorder of the bridging unit in II and III. The packing in all four salts is dominated by N—H...O and O—H...O hydrogen bonds. Hirshfeld surface analyses show that the amitriptynolium cations make similar inter-species contacts, despite the distinctly different packing in each salt.

Syntheses and X-ray crystal structures of four 4-(4-methoxyphenyl)piperazin-1-ium (MeOPP) salts, with 2,2,2-trifluoroacetate, C11H17N2O+·C2F3O2− (I), 2,3,4,5,6-pentafluorobenzoate, C11H17N2O+·C7F5O2−·H2O (II), 4-iodobenzoate C11H17N2O+·C7H4IO2−·H2O (III), and 4-methylbenzoate, C11H17N2O+·C8H7O2−·H2O (IV) anions are presented. The salts form directly from equimolar quantities of N-(4-methoxyphenyl)piperazine and the corresponding organic acid in methanol and crystallize from 1:1 methanol/ethyl acetate. Salt I is anhydrous whereas II, III, and IV are all monohydrates. In all cases, the MeOPP cation conformation is determined by the torsion about the N—C bond between the piperazinium and 4-methoxybenzene rings. Crystal packing in each structure is largely dictated by N—H...O and (in II, III, and IV) O—H...O hydrogen bonds, although each also features weak C—H...O-type hydrogen bonds. Salt II also has π–π-stacking interactions between cation and anion arene rings, and III exhibits I...I close contacts.

The crystal structures of three salts, namely N-(4-methoxyphenyl)piperazin-1-ium ethoxybenzoate monohydrate (I), N-(4-methoxyphenyl)piperazin-1-ium methoxybenzoate monohydrate (II) and N-(4-methoxyphenyl)piperazin-1-ium hydroxybenzoate monohydrate (III), have been determined and compared. In each of them, the ionic components and the water molecules are linked by a combination of N—H···O and O—H···O hydrogen bonds to form infinite chains of edge-fused centrosymmetric rings running parallel to the [100] direction. The C—H···O, C—H···π(arene) interactions and O—H···O in (III) are responsible for the further propagation of the aforementioned chains into di-periodic layers or tri-periodic networks. From an energetic point of view, all structures are primarily di-periodic; the very strong ionic interactions determine the periodicity. For comparison purposes, quantum chemical calculations were performed to show the difference between the ionic and neutral components. The energy of the hydrogen-bonded ring motifs was also estimated.