A pair of diastereomeric 1:2 salts of (R)‐ and (S)‐2‐methylpiperazine with (2S,3S)‐tartaric acid

The crystal structures of a pair of diastereomeric 1:2 salts of (R)‐ and (S)‐2‐methylpiperazine with (2S,3S)‐tartaric acid, namely (R)‐2‐methylpiperazinediium bis[hydrogen (2S,3S)‐tartrate] monohydrate, (I), and (S)‐2‐methylpiperazinediium bis[hydrogen (2S,3S)‐tartrate] monohydrate, (II), both C₅H₁₄N₂²⁺·2C₄H₅O₆⁻·H₂O, each reveal the formation of well‐defined head‐to‐tail‐connected hydrogen tartrate chains; these chains are linked into a two‐dimensional sheet via intermolecular hydrogen bonds involving hydroxy groups and water molecules, resulting in a layer structure. The (R)‐2‐methylpiperazinediium ions lie between the hydrogen tartrate layers in the most stable equatorial conformation in (I), whereas in (II), these ions are in an unstable axial position inside the more interconnected layers and form a larger number of intermolecular hydrogen bonds than are observed in (I).     

Brucine salts of l‐α‐hydr­oxy acids: brucinium hydrogen (S)‐malate penta­hydrate and anhydrous brucinium hydrogen (2R,3R)‐tartrate at 130 K

The structures of two brucinium (2,3‐dimeth­oxy‐10‐oxostrychnidinium) salts of the α‐hydr­oxy acids l ‐malic acid and l ‐tartaric acid, namely brucinium hydrogen (S)‐malate penta­hydrate, C₂₃H₂₇N₂O₄⁺·C₄H₅O₅⁻·5H₂O, (I), and anhydrous brucinium hydrogen (2R,3R)‐tartrate, C₂₃H₂₇N₂O₄⁺·C₄H₅O₆⁻,(II), have been determined at 130 K. Compound (I) has two brucinium cations, two hydrogen malate anions and ten water mol­ecules of solvation in the asymmetric unit, and forms an extensively hydrogen‐bonded three‐dimensional framework structure. In compound (II), the brucinium cations form the common undulating brucine sheet substructures, which accommodate parallel chains of head‐to‐tail hydrogen‐bonded tartrate anion species in the inter­stitial cavities.     

Three‐dimensional hydrogen‐bonded structures in the 1:1 proton‐transfer compounds of l‐tartaric acid with the associative‐group monosubstituted pyridines 3‐aminopyridine, 3‐carboxypyridine (nicotinic acid) and 2‐carboxypyridine (picolinic acid)

The 1:1 proton‐transfer compounds of l ‐tartaric acid with 3‐aminopyridine [3‐aminopyridinium hydrogen (2R,3R)‐tartrate dihydrate, C₅H₇N₂⁺·C₄H₅O₆⁻·2H₂O, (I)], pyridine‐3‐carboxylic acid (nicotinic acid) [anhydrous 3‐carboxypyridinium hydrogen (2R,3R)‐tartrate, C₆H₆NO₂⁺·C₄H₅O₆⁻, (II)] and pyridine‐2‐carboxylic acid [2‐carboxypyridinium hydrogen (2R,3R)‐tartrate monohydrate, C₆H₆NO₂⁺·C₄H₅O₆⁻·H₂O, (III)] have been determined. In (I) and (II), there is a direct pyridinium–carboxyl N⁺—H...O hydrogen‐bonding interaction, four‐centred in (II), giving conjoint cyclic R₁²(5) associations. In contrast, the N—H...O association in (III) is with a water O‐atom acceptor, which provides links to separate tartrate anions through O_hydroxy acceptors. All three compounds have the head‐to‐tail C(7) hydrogen‐bonded chain substructures commonly associated with 1:1 proton‐transfer hydrogen tartrate salts. These chains are extended into two‐dimensional sheets which, in hydrates (I) and (III) additionally involve the solvent water molecules. Three‐dimensional hydrogen‐bonded structures are generated via crosslinking through the associative functional groups of the substituted pyridinium cations. In the sheet struture of (I), both water molecules act as donors and acceptors in interactions with separate carboxyl and hydroxy O‐atom acceptors of the primary tartrate chains, closing conjoint cyclic R₄⁴(8), R₃⁴(11) and R₃³(12) associations. Also, in (II) and (III) there are strong cation carboxyl–carboxyl O—H...O hydrogen bonds [O...O = 2.5387 (17) Å in (II) and 2.441 (3) Å in (III)], which in (II) form part of a cyclic R₂²(6) inter‐sheet association. This series of heteroaromatic Lewis base–hydrogen l ‐tartrate salts provides further examples of molecular assembly facilitated by the presence of the classical two‐dimensional hydrogen‐bonded hydrogen tartrate or hydrogen tartrate–water sheet substructures which are expanded into three‐dimensional frameworks via peripheral cation bifunctional substituent‐group crosslinking interactions.     

Three salts from the reactions of cysteamine and cystamine with L‐(+)‐tartaric acid

Reaction between cysteamine (systematic name: 2‐aminoethanethiol, C₂H₇NS) and L‐(+)‐tartaric acid [systematic name: (2R,3R)‐2,3‐dihydroxybutanedioic acid, C₄H₆O₆] results in a mixture of cysteamine tartrate(1−) monohydrate, C₂H₈NS⁺·C₄H₅O₆⁻·H₂O, (I), and cystamine bis[tartrate(1−)] dihydrate, C₄H₁₄N₂S₂²⁺·2C₄H₅O₆⁻·2H₂O, (III). Cystamine [systematic name: 2,2′‐dithiobis(ethylamine), C₄H₁₂N₂S₂], reacts with L‐(+)‐tartaric acid to produce a mixture of cystamine tartrate(2−), C₄H₁₄N₂S₂²⁺·C₄H₄O₆²⁻, (II), and (III). In each crystal structure, the anions are linked by O—H...O hydrogen bonds that run parallel to the a axis. In addition, hydrogen bonding involving protonated amino groups in all three salts, and water molecules in (I) and (III), leads to extensive three‐dimensional hydrogen‐bonding networks. All three salts crystallize in the orthorhombic space group P2₁2₁2₁.     

Supramolecular motifs in the first structures of organic carboxylate salts of 1‐(diaminomethylene)thiourea (HATU)

The structures of the first two organic carboxylate salts of 1‐(diaminomethylene)thiourea (HATU), namely 1‐(diaminomethylene)thiouron‐1‐ium formate, C₂H₇N₄S⁺·HCOO⁻, (I), and bis[1‐(diaminomethylene)thiouron‐1‐ium] oxalate dihydrate, 2C₂H₇N₄S⁺·C₂O₄²⁻·2H₂O, (II), in which the oxalate lies on a symmetry centre, possess different extended hydrogen‐bonding networks with different graph‐set motifs. The R₂²(8) motif present in (I) does not appear in (II), but an R₂¹(6) motif is present in both (I) and (II). Compound (I) has a three‐dimensional hydrogen‐bonding network, whereas (II) has a layered structure with layers joined by hydrogen‐bonding motifs that form R₄²(8) patterns. This work extends the known supramolecular structural data for HATU to include these organic carboxylates in addition to the previously characterized salts with inorganic acids.     

Bis(diisopropylammonium) thiosulfate and bis(tert‐butylammonium) thiosulfate

Two new dialkylammonium thiosulfates, namely bis(diisopropylammonium) thiosulfate, 2C₆H₁₆N⁺·S₂O₃²⁻, (I), and bis(tert‐butylammonium) thiosulfate, 2C₄H₁₂N⁺·S₂O₃²⁻, (II), have been characterized. The secondary ammonium salt (I) crystallizes with Z = 4, while the primary ammonium salt (II), with more hydrogen‐bond donors, crystallizes with Z = 8 and a noncrystallographic centre of inversion. In both salts, the organic cations and thiosulfate anions are linked within extensive N—H...O and N—H...S hydrogen‐bond networks, forming extended two‐dimensional layers. Layers are parallel to (10) in (I) and to (002) in (II), and have a polar interior and a nonpolar hydrocarbon exterior. The layered structure and hydrogen‐bond motifs observed in (I) and (II) are similar to those in related ammonium sulfates.     

The effect of amino acid backbone length on molecular packing: crystalline tartrates of glycine, β‐alanine, γ‐aminobutyric acid (GABA) and dl‐α‐aminobutyric acid (AABA)

We report a novel 1:1 cocrystal of β‐alanine with dl ‐tartaric acid, C₃H₇NO₂·C₄H₆O₆, (II), and three new molecular salts of dl ‐tartaric acid with β‐alanine {3‐azaniumylpropanoic acid–3‐azaniumylpropanoate dl ‐tartaric acid–dl ‐tartrate, [H(C₃H₇NO₂)₂]⁺·[H(C₄H₅O₆)₂]⁻, (III)}, γ‐aminobutyric acid [3‐carboxypropanaminium dl ‐tartrate, C₄H₁₀NO₂⁺·C₄H₅O₆⁻, (IV)] and dl ‐α‐aminobutyric acid {dl ‐2‐azaniumylbutanoic acid–dl ‐2‐azaniumylbutanoate dl ‐tartaric acid–dl ‐tartrate, [H(C₄H₉NO₂)₂]⁺·[H(C₄H₅O₆)₂]⁻, (V)}. The crystal structures of binary crystals of dl ‐tartaric acid with glycine, (I), β‐alanine, (II) and (III), GABA, (IV), and dl ‐AABA, (V), have similar molecular packing and crystallographic motifs. The shortest amino acid (i.e. glycine) forms a cocrystal, (I), with dl ‐tartaric acid, whereas the larger amino acids form molecular salts, viz. (IV) and (V). β‐Alanine is the only amino acid capable of forming both a cocrystal [i.e. (II)] and a molecular salt [i.e. (III)] with dl ‐tartaric acid. The cocrystals of glycine and β‐alanine with dl ‐tartaric acid, i.e. (I) and (II), respectively, contain chains of amino acid zwitterions, similar to the structure of pure glycine. In the structures of the molecular salts of amino acids, the amino acid cations form isolated dimers [of β‐alanine in (III), GABA in (IV) and dl ‐AABA in (V)], which are linked by strong O—H…O hydrogen bonds. Moreover, the three crystal structures comprise different types of dimeric cations, i.e. (A…A)⁺ in (III) and (V), and A⁺…A⁺ in (IV). Molecular salts (IV) and (V) are the first examples of molecular salts of GABA and dl ‐AABA that contain dimers of amino acid cations. The geometry of each investigated amino acid (except dl ‐AABA) correlates with the melting point of its mixed crystal.     

Three‐dimensional networks in bis(imidazolium) 2,2′‐dithiodibenzoate and 4‐methylimidazolium 2‐[(2‐carboxyphenyl)disulfanyl]benzoate

Cocrystallization of imidazole or 4‐methylimidazole with 2,2′‐dithiodibenzoic acid from methanol solution yields the title 2:1 and 1:1 organic salts, 2C₃H₅N₂⁺·C₁₄H₁₀O₄S₂²⁻, (I), and C₄H₇N₂⁺·C₁₄H₁₀O₄S₂⁻, (II), respectively. Compound (I) crystallizes in the monoclinic C2/c space group with the mid‐point of the S—S bond lying on a twofold axis. The component ions in (I) are linked by intermolecular N—H...O hydrogen bonds to form a two‐dimensional network, which is further linked by C—H...O hydrogen bonds into a three‐dimensional network. In contrast, by means of N—H...O, N—H...S and O—H...O hydrogen bonds, the component ions in (II) are linked into a tape and adjacent tapes are further linked by π–π, C—H...O and C—H...π interactions, resulting in a three‐dimensional network.     

Products of the interaction of (1‐diaminomethylene)thiourea with hydrofluoric acid

The salts 1‐(diaminomethylene)thiouron‐1‐ium hydrogen difluoride, C₂H₇N₄S⁺·HF₂⁻, (I), and bis[1‐(diaminomethylene)thiouron‐1‐ium] hexafluoridosilicate, 2C₂H₇N₄S⁺·SiF₆²⁻, (II), have both been obtained from the reaction of (1‐diaminomethylene)thiourea (HATU) with hydrofluoric acid. Both compounds contain extensive networks of N—H...F hydrogen bonds. The hydrogen difluoride salt contains four independent asymmetric [HF₂]⁻ anions. In the hexafluoridosilicate salt, the centrosymmetric [SiF₆]²⁻ anion is distorted, although this distortion is not clearly correlated with the N—H...F hydrogen‐bonding network.     

Hexaaquacobalt(II) and hexaaquanickel(II) bis(μ‐pyridine‐2,6‐dicarboxylato)bis[(pyridine‐2,6‐dicarboxylato)bismuthate(III)] dihydrate

The title complexes, hexaaquacobalt(II) bis(μ‐pyridine‐2,6‐dicarboxylato)bis[(pyridine‐2,6‐dicarboxylato)bismuthate(III)] dihydrate, [Co(H₂O)₆][Bi₂(C₇H₄NO₄)₄]·2H₂O, (I), and hexaaquanickel(II) bis(μ‐pyridine‐2,6‐dicarboxylato)bis[(pyridine‐2,6‐dicarboxylato)bismuthate(III)] dihydrate, [Ni(H₂O)₆][Bi₂(C₇H₄NO₄)₄]·2H₂O, (II), are isomorphous and crystallize in the triclinic space group P. The transition metal ions are located on the inversion centre and adopt slightly distorted MO₆ (M = Co or Ni) octahedral geometries. Two [Bi(pydc)₂]⁻ units (pydc is pyridine‐2,6‐dicarboxylate) are linked via bridging carboxylate groups into centrosymmetric [Bi₂(pydc)₄]²⁻ dianions. The crystal packing reveals that the [M(H₂O)₆]²⁺ cations, [Bi₂(pydc)₄]²⁻ anions and solvent water molecules form multiple hydrogen bonds to generate a supramolecular three‐dimensional network. The formation of secondary Bi...O bonds between adjacent [Bi₂(pydc)₄]²⁻ dimers provides an additional supramolecular synthon that directs and facilitates the crystal packing of both (I) and (II).     

Luminescence properties of three structures built from 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate and alkaline metals (Na,K and Rb)

The structures of three salts of 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate with alkali metals (Na, K and Rb) are related to their luminescence properties. The Rb salt, rubidium(I) 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate, Rb⁺·C₈HN₄O₂⁻, is isomorphous with the previously reported potassium salt. For the Na compound, sodium(I) 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate dihydrate, Na⁺·C₈HN₄O₂⁻·2H₂O, two independent sodium ions, located on inversion centers, are coordinated by four water molecules each and additionally by two cyano groups for one and two carbonyl groups for the other. The luminescence spectra in solution are unaffected by the nature of the cation but vary strongly with the dielectric constant of the solvent. In the solid state, the emission maxima vary with structural features; the redshift of the maximum luminescence varies inversely with the distance between the stacked anions.     

Hydrogen‐bonded frameworks of bis(2‐carboxypyridinium) hexafluorosilicate and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate

In bis(2‐carboxypyridinium) hexafluorosilicate, 2C₆H₆NO₂⁺·SiF₆²⁻, (I), and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate, 2C₁₀H₈NO₂⁺·SiF₆²⁻·2H₂O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter‐ion interactions in (I) occur via strong N—H...F and O—H...F hydrogen bonds, generating corrugated layers incorporating [SiF₆]²⁻ anions as four‐connected net nodes and organic cations as simple links in between. In (II), a set of strong N—H...F, O—H...O and O—H...F hydrogen bonds, involving water molecules, gives a three‐dimensional heterocoordinated rutile‐like framework that integrates [SiF₆]²⁻ anions as six‐connected and water molecules as three‐connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) Å], while the N—H group supports direct bonding to the anion [N...F = 2.7061 (12) Å].     

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.     

Two salts of di‐p‐toluoyltartaric acid with aromatic amines

The structures of bis­[(R)‐(+)‐1‐phenyl­ethyl­ammonium] (2R,3R)‐(−)‐2,3‐di‐p‐toluoyloxybutane­dioate methanol disolvate monohydrate, 2C₈H₁₂N⁺·C₂₀H₁₆O₈²⁻·2CH₄O·H₂O, (I), and bis­(benzyl­ammonium) (2R,3R)‐(−)‐2,3‐di‐p‐toluoyl­oxy­butane­­dioate dihydrate, 2C₇H₁₀N⁺·C₂₀H₁₆O₈²⁻·2H₂O, (II), exhibit extensive hydrogen bonding, with (N—)H⋯O and (O—)H⋯O distances in the ranges 2.716 (2)–2.929 (3) and 2.687 (2)–2.767 (2) Å, respectively, in (I), and 2.673 (2)–2.888 (2) and 2.785 (2)–2.931 (2) Å, respectively, in (II). The amine groups are protonated and the carboxyl­ate groups of the tartrate anions are fully deprotonated. The conformation of the toluoyltartrate anion and its mol­ecular parameters are similar in both structures.     

(Z)‐2‐Methylbuten‐1‐yl(aryl)iodonium trifluoromethanesulfonates containing electron‐withdrawing groups on the aryl moiety

The crystal structures of [(Z)‐2‐methyl­but‐1‐en‐1‐yl]­[4‐(tri­fluoro­methyl)­phenyl]­iodo­nium tri­fluoro­methane­sulfonate, C₁₂H₁₃F₃I⁺·CF₃O₃S^?, (I), (3,5‐di­chloro­phenyl)­[(Z)‐2‐methyl­but‐1‐en‐1‐yl]­iodo­nium tri­fluoro­methane­sulfonate, C₁₁H₁₂­Cl₂I⁺·CF₃O₃S^?, (II), and bis{[3,5‐bis­(tri­fluoro­methyl)­phenyl][(Z)‐2‐methyl­but‐1‐en‐1‐yl]­iodo­nium} bis­(tri­fluoro­methane­sulfonate) di­chloro­methane solvate, 2C₁₃H₁₂F₆I⁺·­2CF₃­O₃S^?·CH₂Cl₂, (III), are described. Neither simple acyclic β,β‐di­alkyl‐substituted alkenyl­(aryl)­idonium salts nor a series containing electron‐deficient aryl rings have been described prior to this work. Compounds (I)–(III) were found to have distorted square‐planar geometries, with each I atom interacting with two tri­fluoro­methane­sulfonate counter‐ions.     

Three‐dimensional networks in the 1:2 organic salts 2,2′‐biimidazolium bis(3‐carboxy‐4‐hydroxybenzenesulfonate) and 2,2′‐bibenzimidazolium bis(3‐carboxy‐4‐hydroxybenzenesulfonate) trihydrate

The two title compounds of 2,2′‐biimidazole (Bim) with 5‐sulfosalicylic acid (5‐H₂SSA) and 2,2′‐bibenzimidazole (Bbim) with 5‐H₂SSA are 1:2 organic salts, viz. C₆H₈N₄²⁺·2C₇H₅O₆S⁻, (I), and C₁₄H₁₂N₄²⁺·2C₇H₅O₆S⁻·3H₂O, (II). The cation of compound (I) lies on a centre of inversion, whereas that of (II) lies on a twofold axis. Whilst compound (I) is anhydrous, three water molecules are incorporated into the crystal structure of (II). The substitution of imidazole H atoms by other chemical groups may favour the incorporation of water molecules into the crystal structure. In both compounds, the component cations and anions adopt a homogeneous arrangement, forming alternating cation and anion layers which run parallel to the (001) plane in (I) and to the (100) plane in (II). By a combination of N—H...O, O—H...O and C—H...O hydrogen bonds, the ions in both compounds are linked into three‐dimensional networks. In addition, π–π interactions are observed between symmetry‐related benzene rings of Bbim²⁺ cations in (II).     

Supramolecular architectures of succinates of 1‐hydroxypropan‐2‐aminium derivatives

Aminoalkanol and aroxyalkyl derivatives are known as potential anticonvulsants. Two new salts, namely bis{(R,S)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium} succinate ( 1s ), C₁₃H₂₂NO₂⁺·0.5C₄H₄O₄²⁻, and bis{(S)‐(+)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium} succinate ( 2s ), C₁₃H₂₂NO₂⁺·0.5C₄H₄O₄²⁻, have been prepared and characterized by single‐crystal X‐ray diffraction. The N atoms are protonated by proton transfer from succinic acid. Salt 1s crystallizes in the space group P2₁/n with one cation and half an anion in the asymmetric unit across an inversion centre, while ( 2s ) crystallizes in the space group P2₁ with four cations and two anions in the asymmetric unit. The hydroxy group of the cation of 1s is observed in two R/S disorder positions. The crystals of these two salts display similar supramolecular architectures (i.e. two‐dimensional networks), built mainly by intermolecular N⁺—H…O^δ− and O—H…O^δ− hydrogen bonds, where `δ−' represents a partial charge. The succinate anions are engaged in hydrogen bonds, not only with protonated N atoms, but also with hydroxy groups.     

Ammonium 1‐hydroxy‐2‐(2‐pyridinio)ethane‐1,1‐diyldiphosphonate dihydrate and potassium 1‐hydroxy‐2‐(2‐pyridinio)ethane‐1,1‐diyldiphosphonate dihydrate

The crystal structures of the title compounds, ammonium risedronate dihydrate, NH₄⁺·C₇H₁₀NO₇P₂⁻·2H₂O, (I), and potassium risedronate dihydrate, K⁺·C₇H₁₀NO₇P₂⁻·2H₂O, (II), have been determined from single‐crystal X‐ray data collected at 120 K. Compound (I) forms a three‐dimensional hydrogen‐bonded network which connects the ammonium and risedronate ions and the water mol­ecules. In compound (II), the K⁺ ions are seven‐coordinated in a capped distorted trigonal prism. The coordination polyhedra form chains by corner‐sharing, and these chains are connected by phosphon­ate groups into layers in the ac plane. The layers are stacked and connected by hydrogen bonds in the b direction. The risedronate conformation is determined by intra­molecular inter­actions fine‐tuned by crystal packing effects. All H‐atom donors in both structures are involved in hydrogen bonding, with D⋯A distances between 2.510 (2) and 3.009 (2) Å.     

Solvatomorphism in (E)‐2‐(2,6‐dichloro‐4‐hydroxybenzylidene)hydrazinecarboximidamide

The structures of orthorhombic (E)‐4‐(2‐{[amino(iminio)methyl]amino}vinyl)‐3,5‐dichlorophenolate dihydrate, C₈H₈Cl₂N₄O·2H₂O, (I), triclinic (E)‐4‐(2‐{[amino(iminio)methyl]amino}vinyl)‐3,5‐dichlorophenolate methanol disolvate, C₈H₈Cl₂N₄O·2CH₄O, (II), and orthorhombic (E)‐amino[(2,6‐dichloro‐4‐hydroxystyryl)amino]methaniminium acetate, C₈H₉Cl₂N₄O⁺·C₂H₃O₂⁻, (III), all crystallize with one formula unit in the asymmetric unit, with the molecule in an E configuration and the phenol H atom transferred to the guanidine N atom. Although the molecules of the title compounds form extended chains via hydrogen bonding in all three forms, owing to the presence of different solvent molecules, those chains are connected differently in the individual forms. In (II), the molecules are all coplanar, while in (I) and (III), adjacent molecules are tilted relative to one another to varying degrees. Also, because of the variation in hydrogen‐bond‐formation ability of the solvents, the hydrogen‐bonding arrangements vary in the three forms.     

Neutral 4‐phenyl‐1‐[phenyl(pyridin‐2‐yl)methylidene]semicarbazide and its salt forms with inorganic anions

Semicarbazones can exist in two tautomeric forms. In the solid state, they are found in the keto form. This work presents the synthesis, structures and spectroscopic characterization (IR and NMR spectroscopy) of four such compounds, namely the neutral molecule 4‐phenyl‐1‐[phenyl(pyridin‐2‐yl)methylidene]semicarbazide, C₁₉H₁₆N₄O, (I), abbreviated as HBzPyS, and three different hydrated salts, namely the chloride dihydrate, C₁₉H₁₇N₄O⁺·Cl^?·2H₂O, (II), the nitrate dihydrate, C₁₉H₁₇N₄O⁺·NO₃^?·2H₂O, (III), and the thiocyanate 2.5‐hydrate, C₁₉H₁₇N₄O⁺·SCN^?·2.5H₂O, (IV), of 2‐[phenyl({[(phenylcarbamoyl)amino]imino})methyl]pyridinium, abbreviated as [H₂BzPyS]⁺·X^?·nH₂O, with X = Cl^? and n = 2 for (II), X = NO₃^? and n = 2 for (III), and X = SCN^? and n = 2.5 for (IV), showing the influence of the anionic form in the intermolecular interactions. Water molecules and counter‐ions (chloride or nitrate) are involved in the formation of a two‐dimensional arrangement by the establishment of hydrogen bonds with the N—H groups of the cation, stabilizing the E isomers in the solid state. The neutral HBzPyS molecule crystallized as the E isomer due to the existence of weak π–π interactions between pairs of molecules. The calculated IR spectrum of the hydrated [H₂BzPyS]⁺ cation is in good agreement with the experimental results.