Ropinirole hydro­chloride,a dopamine agonist

Ropinirole hydro­chloride, or diethyl[2‐(2‐oxo‐2,3‐dihydro‐1H‐indol‐4‐yl)ethyl]ammonium chloride, C₁₆H₂₅N₂O⁺·Cl⁻, belongs to a class of new non‐ergoline dopamine agonists which bind specifically to D2‐like receptors with a selectivity similar to that of dopamine (D3 > D2 > D4). The N atom in the ethyl­amine side chain is protonated and there is a hydrogen bond between it and the Cl⁻ ion. In the crystal structure, two cations and two anions form inversion‐related cyclic dimers via N—H⋯Cl hydrogen bonds.     

Dorzolamide hydro­chloride: an anti­glaucoma agent

Dorzolamide hydro­chloride [systematic name: (4S)‐trans‐4‐ethyl­ammonio‐6‐methyl‐5,6‐dihydro‐4H‐thieno[2,3‐b]thio­pyran‐2‐sulfonamide 7,7‐dioxide chloride], C₁₀H₁₇N₂O₄S₂⁺·Cl⁻, belongs to a class of drugs called carbonic anhydrase inhibitors. The ethyl­ammonio side chain is in an extended conformation and is protonated at the N atom, which is hydrogen bonded to the Cl⁻ anion. The dihedral angle between the planes of the thio­phene ring and the sulfonamide group is 80.7 (1)°. A comparison is made with the dorzolamide bound in human carbonic anhydrase in the solid state. Hydrogen bonding is mediated by Cl⁻ anions, resulting in indirect connectivity between the mol­ecules.     

Hydrogen‐bonded and π‐interaction assembly in two 8‐alkoxycarbonyl‐1,8‐diazabicyclo[5.4.0]undec‐7‐enium chloride salts

The crystal structures of 8‐phenoxycarbonyl‐1,8‐diazabicyclo[5.4.0]undec‐7‐enium chloride, C₁₆H₂₁N₂O₂⁺·Cl⁻, (I), and 8‐methoxycarbonyl‐1,8‐diazabicyclo[5.4.0]undec‐7‐enium chloride monohydrate, C₁₁H₁₉N₂O₂⁺·Cl⁻·H₂O, (II), recently reported by Carafa, Mesto & Quaranta [Eur. J. Org. Chem. (2011), pp. 2458–2465], are analysed and discussed with a focus on crystal interaction assembly. Both compounds crystallize in the space group P2₁/c. The crystal packings are characterized by dimers linked through π–π stacking interactions and intermolecular nonclassical hydrogen bonds, respectively. Additional intermolecular C—H...Cl interactions [in (I) and (II)] and classical O—H...Cl hydrogen bonds [in (II)] are also evident and contribute to generating three‐dimensional hydrogen‐bonded networks.     

l‐Methioninium chloride and l‐seleno­methioninium chloride at 103 K

The crystal structures of the title compounds, (S)‐1‐carboxy‐3‐(methyl­sulfanyl)­propanaminium chloride, C₅H₁₂NO₂S⁺·Cl⁻, and (S)‐1‐carboxy‐3‐(methyl­selanyl)­propanaminium chloride, C₅H₁₂NO₂Se⁺·Cl⁻, are isomorphous. The proton­ated l ‐methionine and l ‐seleno­methionine mol­ecules have almost identical conformations and create very similar contacts with the Cl⁻ anions in the crystal structures of both compounds. The amino acid cations and the Cl⁻ anions are linked viaN—H⋯Cl⁻ and O—H⋯Cl⁻ hydrogen bonds.     

Lamotrigine,an antiepileptic drug,and its chloride and nitrate salts

In lamotrigine [systematic name: 6‐(2,3‐dichlorophenyl)‐1,2,4‐triazine‐3,5‐diamine], C₉H₇Cl₂N₅, (I), the asymmetric unit contains one lamotrigine base molecule. In lamotriginium chloride [systematic name: 3,5‐diamino‐6‐(2,3‐dichlorophenyl)‐1,2,4‐triazin‐2‐ium chloride], C₉H₈Cl₂N₅⁺·Cl⁻, (II), the asymmetric unit contains one lamotriginium cation and one chloride anion, while in lamotriginium nitrate, C₉H₈Cl₂N₅⁺·NO₃⁻, (III), the asymmetric unit contains two crystallographically independent lamotriginium cations and two nitrate anions. In all three structures, N—H...N hydrogen bonds form an R₂²(8) dimer. In (I) and (II), hydrophilic layers are sandwiched between hydrophobic layers in the crystal packing. In all three structures, hydrogen bonds lead to the formation of a supramolecular hydrogen‐bonded network. The significance of this study lies in its illustration of the differences between the supramolecular aggregation in the lamotrigine base and in its chloride and nitrate salts.     

The anilinium chloride adduct of 4‐bromo‐N‐phenylbenzene­sulfonamide

The title compound anilinium chloride–4‐bromo‐N‐phenyl­benzene­sulfonamide (1/1), C₆H₈N⁺·Cl⁻·C₁₂H₁₀BrNO₂S, displays a hydrogen‐bonded ladder motif with four independent N—H⋯Cl bonds in which both the NH group of the sulfonamide molecule and the NH₃ group of the anilinium ion [N⋯Cl = 3.135 (3)–3.196 (2) Å and N—H⋯Cl = 151–167°] are involved. This hydrogen‐bonded chain contains two independent R₄²(8) rings and each chloride ion acts as an acceptor of four hydrogen bonds.     

Nimustine hydrochloride: the first crystal structure determination of a 2‐chloroethyl‐N‐nitrosourea hydrochloride derivative by X‐ray powder diffraction and solid‐state NMR

Nimustine hydrochloride [systematic name: 4‐amino‐5‐({[N‐(2‐chloroethyl)‐N‐nitrosocarbamoyl]amino}methyl)‐2‐methylpyrimidin‐1‐ium chloride], C₉H₁₄ClN₆O₂⁺·Cl⁻, is a prodrug of CENU (chloroethylnitrosourea) and is used as a cytostatic agent in cancer therapy. Its crystal structure was determined from laboratory X‐ray powder diffraction data. The protonation at an N atom of the pyrimidine ring was established by solid‐state NMR spectroscopy.     

Isomorphism in 1‐(2‐halidobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium halide hemihydrates (halide = Cl,Br)

The crystal structures of two (E)‐stilbazolium salts, namely 1‐(2‐chlorobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium chloride hemihydrate, C₂₀H₁₇ClNO⁺·Cl⁻·0.5H₂O, (I), and 1‐(2‐bromobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium bromide hemihydrate, C₂₀H₁₇BrNO⁺·Br⁻·0.5H₂O, (II), are isomorphous; the isostructurality index is 99.3%. In both salts, the azastyryl fragments are almost planar, while the rings of the benzyl groups are almost perpendicular to the azastyryl planes. The building blocks of the structures are twofold symmetric hydrogen‐bonded systems of two cations, two halide anions and one water molecule, which lies on a twofold axis. In the crystal structure, these blocks are connected by means of weaker interactions, viz. van der Waals, weak hydrogen bonding and stacking. This study illustrates the robustness of certain supramolecular motifs created by a spectrum of intermolecular interactions in generating these isomorphous crystal structures.     

Eight salt forms of sulfadiazine

Proton transfer to the sulfa drug sulfadiazine [systematic name: 4‐amino‐N‐(pyrimidin‐2‐yl)benzenesulfonamide] gave eight salt forms. These are the monohydrate and methanol hemisolvate forms of the chloride (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium chloride monohydrate, C₁₀H₁₁N₄O₂S⁺·Cl⁻·H₂O, (I), and 2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium chloride methanol hemisolvate, C₁₀H₁₁N₄O₂S⁺·Cl⁻·0.5CH₃OH, (II)); a bromide monohydrate (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium bromide monohydrate, C₁₀H₁₁N₄O₂S⁺·Br⁻·H₂O, (III)), which has a disordered water channel; a species containing the unusual tetraiodide dianion [bis(2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium) tetraiodide, 2C₁₀H₁₁N₄O₂S⁺·I₄²⁻, (IV)], where the [I₄]²⁻ ion is located at a crystallographic inversion centre; a tetrafluoroborate monohydrate (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium tetrafluoroborate monohydrate, C₁₀H₁₁N₄O₂S⁺·BF₄⁻·H₂O, (V)); a nitrate (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium nitrate, C₁₀H₁₁N₄O₂S⁺·NO₃⁻, (VI)); an ethanesulfonate {4‐[(pyrimidin‐2‐yl)sulfamoyl]anilinium ethanesulfonate, C₁₀H₁₁N₄O₂S⁺·C₂H₅SO₃⁻, (VII)}; and a dihydrate of the 4‐hydroxybenzenesulfonate {4‐[(pyrimidin‐2‐yl)sulfamoyl]anilinium 4‐hydroxybenzenesulfonate dihydrate, C₁₀H₁₁N₄O₂S⁺·HOC₆H₄SO₃⁻·2H₂O, (VIII)}. All these structures feature alternate layers of cations and of anions where any solvent is associated with the anion layers. The two sulfonate salts are protonated at the aniline N atom and the amide N atom of sulfadiazine, a tautomeric form of the sulfadiazine cation that has not been crystallographically described before. All the other salt forms are instead protonated at the aniline group and on one N atom of the pyrimidine ring. Whilst all eight species are based upon hydrogen‐bonded centrosymetric dimers with graph set R₂²(8), the two sulfonate structures also differ in that these dimers do not link into one‐dimensional chains of cations through NH₃‐to‐SO₂ hydrogen‐bonding interactions, whilst the other six species do. The chloride methanol hemisolvate and the tetraiodide are isostructural and a packing analysis of the cation positions shows that the chloride monohydrate structure is also closely related to these.     

Two polymorphs of afobazole from powder diffraction data

Afobazole {systematic name: 2‐[2‐(morpholin‐4‐yl)ethylsulfanyl]‐1H‐benzimidazole} is a new anxiolytic drug and Actins, Auzins & Petkune [(2012). Eur. Patent EP10163962] described four polymorphic modifications. In the present study, the crystal structures of two monoclinic polymorphs, 5‐ethoxy‐2‐[2‐(morpholin‐4‐ium‐4‐yl)ethylsulfanyl]‐1H‐benzimidazol‐3‐ium dichloride, C₁₅H₂₃N₃O₂S²⁺·2Cl⁻, (II) and (IV), have been established from laboratory powder diffraction data. The crystal packing and conformation of the dications in (II) and (IV) are different. In (II), there are channels in the [001] direction, which offer atmospheric water molecules an easy way of penetrating into the crystal structure, thus explaining the higher hygroscopicity of (II) compared with (IV).     

Chlorido(dimethyl 2,2′‐bipyridine‐4,4′‐dicarboxylate‐κ2N,N′)(η5‐pentamethylcyclopentadienyl)rhodium(III) chloride 1‐hydroxypyrrolidine‐2,5‐dione disolvate

The title complex, [Rh(C₁₀H₁₅)Cl(C₁₄H₁₂N₂O₄)]Cl·2C₄H₅NO₃, has been synthesized by a substitution reaction of the precursor [bis(2,5‐dioxopyrrolidin‐1‐yl) 2,2′‐bipyridine‐4,4′‐dicarboxylate]chlorido(pentamethylcyclopentadienyl)rhodium(III) chloride with NaOCH₃. The Rh^III cation is located in an RhC₅N₂Cl eight‐coordinated environment. In the crystal, 1‐hydroxypyrrolidine‐2,5‐dione (NHS) solvent molecules form strong hydrogen bonds with the Cl⁻ counter‐anions in the lattice and weak hydrogen bonds with the pentamethylcyclopentadienyl (Cp*) ligands. Hydrogen bonding between the Cp* ligands, the NHS solvent molecules and the Cl⁻ counter‐anions form links in a V‐shaped chain of Rh^III complex cations along the c axis. Weak hydrogen bonds between the dimethyl 2,2′‐bipyridine‐4,4′‐dicarboxylate ligands and the Cl⁻ counter‐anions connect the components into a supramolecular three‐dimensional network. The synthetic route to the dimethyl 2,2′‐bipyridine‐4,4′‐dicarboxylate‐containing rhodium complex from the [bis(2,5‐dioxopyrrolidin‐1‐yl) 2,2′‐bipyridine‐4,4′‐dicarboxylate]rhodium(III) precursor may be applied to link Rh catalysts to the surface of electrodes.     

Three new quinuclidine‐based structures: second harmonic generation response for 1,2‐bis(1‐azoniabicyclo[2.2.2]octan‐3‐ylidene)hydrazine dichloride

The crystal structures of three quinuclidine‐based compounds, namely (1‐azabicyclo[2.2.2]octan‐3‐ylidene)hydrazine monohydrate, C₇H₁₃N₃·H₂O ( 1 ), 1,2‐bis(1‐azabicyclo[2.2.2]octan‐3‐ylidene)hydrazine, C₁₄H₂₂N₄ ( 2 ), and 1,2‐bis(1‐azoniabicyclo[2.2.2]octan‐3‐ylidene)hydrazine dichloride, C₁₄H₂₄N₄²⁺·2Cl^? ( 3 ), are reported. In the crystal structure of 1 , the quinuclidine‐substituted hydrazine and water molecules are linked through N—H…O and O—H…N hydrogen bonds, forming a two‐dimensional array. The compound crystallizes in the centrosymmetric space group P2₁/c. Compound 2 was refined in the space group Pccn and exhibits no hydrogen bonding. However, its hydrochloride form 3 crystallizes in the noncentrosymmetric space group Pc. It shows a three‐dimensional network structure via intermolecular hydrogen bonding (N—H…C and N/C—H…Cl). Compound 3 , with its acentric structure, shows strong second harmonic activity.     

Understanding the microcrystal tests of three related phenethylamines: the ortho‐metallated (±)‐amphetamine formed with gold(III) chloride,and the tetrachloridoaurate(III) salts of (+)‐methamphetamine and (±)‐ephedrine

The ortho‐metallation product of the reaction of (±)‐amphetamine with gold(III) chloride, [D,L‐2‐(2‐aminopropyl)phenyl‐κ²N,C¹]dichloridogold(III), [Au(C₉H₁₂N)Cl₂], and the two salts resulting from crystallization of (+)‐methamphetamine with gold(III) chloride, D‐methyl(1‐phenylpropan‐2‐yl)azanium tetrachloridoaurate(III), (C₁₀H₁₆N)[AuCl₄], and of (±)‐ephedrine with gold(III) chloride, D,L‐(1‐hydroxy‐1‐phenylpropan‐2‐yl)(methyl)azanium tetrachloridoaurate(III), (C₁₀H₁₆NO)[AuCl₄], have different structures. The first makes a bidentate complex directly with a dichloridogold(III) group, forming a six‐membered ring structure; the second and third each form a salt with [AuCl₄]⁻ (each has two formula units in the asymmetric unit). The organic components are all members of the same class of stimulants that are prevalent in illicit drug use. These structures are important contributions to the understanding of the microcrystal tests for these drugs that have been employed for well over 100 years.     

Unusual hydrate stabilization in the two‐dimensional layered structure of quinacrinium bis(2‐carboxy‐4,5‐dichlorobenzoate) tetrahydrate,a proton‐transfer compound of the drug quinacrine

The crystal structure of the hydrated proton‐transfer compound of the drug quinacrine [rac‐N′‐(6‐chloro‐2‐methoxyacridin‐9‐yl)‐N,N‐diethylpentane‐1,4‐diamine] with 4,5‐dichlorophthalic acid, C₂₃H₃₂ClN₃O²⁺·2C₈H₃Cl₂O₄⁻·4H₂O, has been determined at 200 K. The four labile water molecules of solvation in the structure form discrete ...O—H...O—H... hydrogen‐bonded chains parallel to the quinacrine side chain, the two N—H groups of which act as hydrogen‐bond donors for two of the water acceptor molecules. The other water molecules, as well as the acridinium H atom, also form hydrogen bonds with the two anion species and extend the structure into two‐dimensional sheets. Between these sheets there are also weak cation–anion and anion–anion π–π aromatic ring interactions. This structure represents the third example of a simple quinacrine derivative for which structural data are available but differs from the other two in that it is unstable in the X‐ray beam due to efflorescence, probably associated with the destruction of the unusual four‐membered water chain structures.     

Salt forms of the pharmaceutical amide dihydrocarbamazepine

Carbamazepine (CBZ) is well known as a model active pharmaceutical ingredient used in the study of polymorphism and the generation and comparison of cocrystal forms. The pharmaceutical amide dihydrocarbamazepine (DCBZ) is a less well known material and is largely of interest here as a structural congener of CBZ. Reaction of DCBZ with strong acids results in protonation of the amide functionality at the O atom and gives the salt forms dihydrocarbamazepine hydrochloride {systematic name: [(10,11‐dihydro‐5H‐dibenzo[b,f]azepin‐5‐yl)(hydroxy)methylidene]azanium chloride, C₁₅H₁₅N₂O⁺·Cl⁻}, dihydrocarbamazepine hydrochloride monohydrate {systematic name: [(10,11‐dihydro‐5H‐dibenzo[b,f]azepin‐5‐yl)(hydroxy)methylidene]azanium chloride monohydrate, C₁₅H₁₅N₂O⁺·Cl⁻·H₂O} and dihydrocarbamazepine hydrobromide monohydrate {systematic name: [(10,11‐dihydro‐5H‐dibenzo[b,f]azepin‐5‐yl)(hydroxy)methylidene]azanium bromide monohydrate, C₁₅H₁₅N₂O⁺·Br⁻·H₂O}. The anhydrous hydrochloride has a structure with two crystallographically independent ion pairs (Z′ = 2), wherein both cations adopt syn conformations, whilst the two hydrated species are mutually isostructural and have cations with anti conformations. Compared to neutral dihydrocarbamazepine structures, protonation of the amide group is shown to cause changes to both the molecular (C=O bond lengthening and C—N bond shortening) and the supramolecular structures. The amide‐to‐amide and dimeric hydrogen‐bonding motifs seen for neutral polymorphs and cocrystalline species are replaced here by one‐dimensional polymeric constructs with no direct amide‐to‐amide bonds. The structures are also compared with, and shown to be closely related to, those of the salt forms of the structurally similar pharmaceutical carbamazepine.     

Structural diversity in imidazolidinone organocatalysts: a synchrotron and computational study

(S)‐1‐(Methylaminocarbonyl)‐3‐phenylpropanaminium chloride (S2·HCl), C₁₀H₁₅N₂O⁺·Cl⁻, crystallizes in the orthorhombic space group P2₁2₁2₁ with a single formula unit per asymmetric unit. (5R/S)‐5‐Benzyl‐2,2,3‐trimethyl‐4‐oxoimidazolidin‐1‐ium chloride (R3 and S3), C₁₃H₁₉N₂O⁺·Cl⁻, crystallize in the same space group as S2·HCl but contain three symmetry‐independent formula units. (R/S)‐5‐Benzyl‐2,2,3‐trimethyl‐4‐oxoimidazolidin‐1‐ium chloride monohydrate (R4 and S4), C₁₃H₁₉N₂O⁺·Cl⁻·H₂O, crystallize in the space group P2₁ with a single formula unit per asymmetric unit. Calculations at the B3LYP/6–31G(d,p) and B3LYP/6–311G(d,p) levels of the conformational energies of the cation in R3, S3, R4 and S4 indicate that the ideal gas‐phase global energy minimum conformation is not observed in the solid state. Rather, the effects of hydrogen‐bonding and van der Waals interactions in the crystal structure cause the molecules to adopt higher‐energy conformations, which correspond to local minima in the molecular potential energy surface.     

Structural comparison of three N‐(4‐halogenophenyl)‐N′‐[1‐(2‐pyridyl)ethylidene]hydrazine hydrochlorides

2‐{1‐[(4‐Chloroanilino)methylidene]ethyl}pyridinium chloride methanol solvate, C₁₃H₁₃ClN₃⁺·Cl⁻·CH₃OH, (I), crystallizes as discrete cations and anions, with one molecule of methanol as solvent in the asymmetric unit. The N—C—C—N torsion angle in the cation indicates a cis conformation. The cations are located parallel to the (02) plane and are connected through hydrogen bonds by a methanol solvent molecule and a chloride anion, forming zigzag chains in the direction of the b axis. The crystal structure of 2‐{1‐[(4‐fluoroanilino)methylidene]ethyl}pyridinium chloride, C₁₃H₁₃FN₃⁺·Cl⁻, (II), contains just one anion and one cation in the asymmetric unit but no solvent. In contrast with (I), the N—C—C—N torsion angle in the cation corresponds with a trans conformation. The cations are located parallel to the (100) plane and are connected by hydrogen bonds to the chloride anions, forming zigzag chains in the direction of the b axis. In addition, the crystal packing is stabilized by weak π–π interactions between the pyridinium and benzene rings. The crystal of (II) is a nonmerohedral monoclinic twin which emulates an orthorhombic diffraction pattern. Twinning occurs via a twofold rotation about the c axis and the fractional contribution of the minor twin component refined to 0.324 (3). 2‐{1‐[(4‐Fluoroanilino)methylidene]ethyl}pyridinium chloride methanol disolvate, C₁₃H₁₃FN₃⁺·Cl⁻·2CH₃OH, (III), is a pseudopolymorph of (II). It crystallizes with two anions, two cations and four molecules of methanol in the asymmetric unit. Two symmetry‐equivalent cations are connected by hydrogen bonds to a chloride anion and a methanol solvent molecule, forming a centrosymmetric dimer. A further methanol molecule is hydrogen bonded to each chloride anion. These aggregates are connected by C—H...O contacts to form infinite chains. It is remarkable that the geometric structures of two compounds having two different formula units in their asymmetric units are essentially the same.     

catena‐Poly­[[tri‐n‐butyl­tin]‐μ‐N‐(1‐naphthyl)­maleamato]

The crystal structure of catena‐poly­[[tri‐n‐butyl­tin]‐μ‐3‐(1‐naph­thyl­amino­carbonyl)­acrylato‐κ²O¹:O³], [Sn(C₄H₉)₃(C₁₄H₁₀NO₃)]_n, is composed of polymeric chains wherein the metal center exhibits a distorted trigonal‐bipyramidal geometry, with three n‐butyl groups defining the trigonal plane [mean Sn—C 2.133 (7) Å] and the axial positions being occupied by the carboxyl­ate O atoms of two different N‐(1‐naphthyl)­maleamate ligands with inequivalent Sn—O distances [2.167 (4) and 2.457 (4) Å]. The N‐(1‐naphthyl)­maleamate fragment forms an essentially planar seven‐membered ring involving an intramolecular N—H?O hydrogen bond.     

A structural study of Si6‐ring‐containing [Si6Cl14]2− chlorosilicates

The crystal structures of four substituted‐ammonium dichloride dodecachlorohexasilanes are presented. Each is crystallized with a different cation and one of the structures contains a benzene solvent molecule: bis(tetraethylammonium) dichloride dodecachlorohexasilane, 2C₈H₂₀N⁺·2Cl⁻·Cl₁₂Si₆, (I), tetrabutylammonium tributylmethylammonium dichloride dodecachlorohexasilane, C₁₆H₃₆N⁺·C₁₃H₃₀N⁺·2Cl⁻·Cl₁₂Si₆, (II), bis(tetrabutylammonium) dichloride dodecachlorohexasilane benzene disolvate, 2C₁₆H₃₆N⁺·2Cl⁻·Cl₁₂Si₆·2C₆H₆, (III), and bis(benzyltriphenylphosphonium) dichloride dodecachlorohexasilane, 2C₂₅H₂₂P⁺·2Cl⁻·Cl₁₂Si₆, (IV). In all four structures, the dodecachlorohexasilane ring is located on a crystallographic centre of inversion. The geometry of the dichloride dodecachlorohexasilanes in the different structures is almost the same, irrespective of the cocrystallized cation and solvent. However, the crystal structure of the parent dodecachlorohexasilane molecule shows that this molecule adopts a chair conformation. In (IV), the P atom and the benzyl group of the cation are disordered over two sites, with a site‐occupation factor of 0.560 (5) for the major‐occupied site.     

Hydrogen‐bonding motifs and thermotropic polymorphism in redetermined halide salts of hexamethylenediamine

The redetermined crystal structures of hexane‐1,6‐diammonium dichloride, C₆H₁₈N₂²⁺·2Cl⁻, (I), hexane‐1,6‐diammonium dibromide, C₆H₁₈N₂²⁺·2Br⁻, (II), and hexane‐1,6‐diammonium diiodide, C₆H₁₈N₂²⁺·2I⁻, (III), are described, focusing on their hydrogen‐bonding motifs. The chloride and bromide salts are isomorphous, with both demonstrating a small deviation from planarity [173.89 (10) and 173.0 (2)°, respectively] in the central C—C—C—C torsion angle of the hydrocarbon backbone. The chloride and bromide salts also show marked similarities in their hydrogen‐bonding interactions, with subtle differences evident in the hydrogen‐bond lengths reported. Bifurcated interactions are exhibited between the N‐donor atoms and the halide acceptors in the chloride and bromide salts. The iodide salt is very different in molecular structure, packing and intermolecular interactions. The hydrocarbon chain of the iodide straddles an inversion centre and the ammonium groups on the diammonium cation of the iodide salt are offset from the planar hydrocarbon backbone by a torsion angle of 69.6 (4)°. All three salts exhibit thermotropic polymorphism, as is evident from differential scanning calorimetry analysis and variable‐temperature powder X‐ray diffraction studies.