Three anilides of 2,2′‐thiodibenzoic acid

The structures of N,N′‐bis(2‐methylphenyl)‐2,2′‐thiodibenzamide, C₂₈H₂₄N₂O₂S, (Ia), N,N′‐bis(2‐ethylphenyl)‐2,2′‐thiodibenzamide, C₃₀H₂₈N₂O₂S, (Ib), and N,N′‐bis(2‐bromophenyl)‐2,2′‐thiodibenzamide, C₂₆H₁₈Br₂N₂O₂S, (Ic), are compared with each other. For the 19 atoms of the consistent thiodibenzamide core, the r.m.s. deviations of the molecules in pairs are 0.29, 0.90 and 0.80 Å for (Ia)/(Ib), (Ia)/(Ic) and (Ib)/(Ic), respectively. The conformations of the central parts of molecules (Ia) and (Ib) are similar due to an intramolecular N—H...O hydrogen‐bonding interaction. The molecules of (Ia) are further linked into infinite chains along the c axis by intermolecular N—H...O interactions, whereas the molecules of (Ib) are linked into chains along b by an intermolecular N—H...π contact. The conformation of (Ic) is quite different from those of (Ia) and (Ib), since there is no intramolecular N—H...O hydrogen bond, but instead there is a possible intramolecular N—H...Br hydrogen bond. The molecules are linked into chains along c by intermolecular N—H...O hydrogen bonds.     

Three structures containing (E)‐1,2‐bis­(benzimidazol‐2‐yl)ethene groups

Two of the title compounds, namely (E)‐1,2‐bis­(1‐methyl­benzimidazol‐2‐yl)ethene, C₁₈H₁₆N₄, (Ib), and (E)‐1,2‐bis­(1‐ethyl­benzimidazol‐2‐yl)ethene, C₂₀H₂₀N₄, (Ic), consist of centrosymmetric trans‐bis­(1‐alkyl­benzimidazol‐2‐yl)ethene mol­ecules, while 3‐eth­yl‐2‐[(E)‐2‐(1‐ethyl­benzimidazol‐2‐yl)­ethen­yl]benzimidazol‐1‐ium perchlorate, C₂₀H₂₁N₄⁺·ClO₄⁻, (II), contains the monoprotonated analogue of compound (Ic). In the three structures, the benzimidazole and benzimidazolium moieties are essentially planar; the geometric parameters for the ethene linkages and their bonds to the aromatic groups are consistent with double and single bonds, respectively, implying little, if any, conjugation of the central C=C bonds with the nitro­gen‐containing rings. The C—N bond lengths in the N=C—N part of the benzimidazole groups differ and are consistent with localized imine C=N and amine C—N linkages in (Ib) and (Ic); in contrast, the corresponding distances in the benzimidazolium cation are equal in (II), consistent with electron delocalization resulting from protonation of the amine N atom. Crystals of (Ib) and (Ic) contain columns of parallel mol­ecules, which are linked by edge‐over‐edge C—H⋯π overlap. The columns are linked to one another by C—H⋯π inter­actions and, in the case of (Ib), C—H⋯N hydrogen bonds. Crystals of (II) contain layers of monocations linked by π–π inter­actions and separated by both perchlorate anions and the protruding eth­yl groups; the cations and anions are linked by N—H⋯O hydrogen bonds.     

Comparison of the structure of (E)‐2‐(2‐benzylidenehydrazinylidene)quinoxaline with those of its chloro‐ and bromobenzylidene analogues

(E)‐2‐(2‐Benzylidenehydrazinylidene)quinoxaline, C₁₅H₁₂N₄, crystallized with two molecules in the asymmetric unit. The structures of six halogen derivatives of this compound were also investigated: (E)‐2‐[2‐(2‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(3‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(4‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(2‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(3‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(4‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄. The 3‐Cl and 3‐Br compounds are isomorphous, as are the 4‐Cl and 4‐Br compounds. In all of these compounds, it was found that the supramolecular structures are governed by similar predominant patterns, viz. strong intermolecular N—H...N(pyrazine) hydrogen bonds supplemented by weak C—H...N(pyrazine) hydrogen‐bond interactions in the 2‐ and 3‐halo compounds and by C—H...Cl/Br interactions in the 4‐halo compounds. In all compounds, there are π–π stacking interactions.     

Conformations and resulting hydrogen‐bonded networks of hydrogen {phosphono[(pyridin‐1‐ium‐3‐yl)amino]methyl}phosphonate and related 2‐chloro and 6‐chloro derivatives

In the crystal structures of the conformational isomers hydrogen {phosphono[(pyridin‐1‐ium‐3‐yl)amino]methyl}phosphonate monohydrate (pro‐E), C₆H₁₀N₂O₆P₂·H₂O, (Ia), and hydrogen {phosphono[(pyridin‐1‐ium‐3‐yl)amino]methyl}phosphonate (pro‐Z), C₆H₁₀N₂O₆P₂, (Ib), the related hydrogen {[(2‐chloropyridin‐1‐ium‐3‐yl)amino](phosphono)methyl}phosphonate (pro‐E), C₆H₉ClN₂O₆P₂, (II), and the salt bis(6‐chloropyridin‐3‐aminium) [hydrogen bis({[2‐chloropyridin‐1‐ium‐3‐yl(0.5+)]amino}methylenediphosphonate)] (pro‐Z), 2C₅H₆ClN₂⁺·C₁₂H₁₆Cl₂N₄O₁₂P₄²⁻, (III), chain–chain interactions involving phosphono (–PO₃H₂) and phosphonate (–PO₃H⁻) groups are dominant in determining the crystal packing. The crystals of (Ia) and (III) comprise similar ribbons, which are held together by N—H...O interactions, by water‐ or cation‐mediated contacts, and by π–π interactions between the aromatic rings of adjacent zwitterions in (Ia), and those of the cations and anions in (III). The crystals of (Ib) and (II) have a layered architecture: the former exhibits highly corrugated monolayers perpendicular to the [100] direction, while in the latter, flat bilayers parallel to the (001) plane are formed. In both (Ib) and (II), the interlayer contacts are realised through N—H...O hydrogen bonds and weak C—H...O interactions involving aromatic C atoms.     

Pseudopolymorphs of chelidamic acid and its dimethyl ester

Different tautomeric and zwitterionic forms of chelidamic acid (4‐hydroxypyridine‐2,6‐dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C₇H₅NO₅·CH₄O, (Ia), dimethylammonium chelidamate (dimethylammonium 6‐carboxy‐4‐hydroxypyridine‐2‐carboxylate), C₂H₈N⁺·C₇H₄NO₅⁻, (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C₇H₅NO₅·C₂H₆OS, (Ic). While the zwitterionic pyridinium carboxylate in (Ia) can be explained from the pK_a values, a (partially) deprotonated hydroxy group in the presence of a neutral carboxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O—H...O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4‐hydroxypyridine‐2,6‐dicarboxylate) were obtained as a monohydrate, C₉H₉NO₅·H₂O, (IIa), and as a solvent‐free modification, in which both ester molecules adopt the hydroxypyridine form. In (IIa), the solvent water molecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O—H...O hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water‐free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.     

Two polymorphs,with Z′ = 1 and 2, of 2‐amino‐4‐chloro‐6‐morpholino­pyrimidine in P21/c,and 2‐amino‐4‐chloro‐6‐piperidino­pyrimidine,which is isomorphous and almost isostructural with the Z′ = 2 polymorph

Crystallization of 2‐amino‐4‐chloro‐6‐morpholino­pyrimidine, C₈H₁₁ClN₄O, (I), yields two polymorphs, both with space group P2₁/c, having Z′ = 1 (from diethyl ether solution) and Z′ = 2 (from di­chloro­methane solution), denoted (Ia) and (Ib), respectively. In polymorph (Ia), the mol­ecules are linked by an N—H⋯O and an N—H⋯N hydrogen bond into sheets built from alternating R(8) and R(40) rings. In polymorph (Ib), one mol­ecule acts as a triple acceptor of hydrogen bonds and the other acts as a single acceptor; one N—H⋯O and three N—H⋯N hydrogen bonds link the mol­ecules in a complex chain containing two types of R(8) and one type of R(18) ring. 2‐Amino‐4‐chloro‐6‐piperidino­pyrimidine, C₉H₁₃ClN₄, (II), which is isomorphous with polymorph (Ib), also has Z′ = 2 in P2₁/c, and the mol­ecules are linked by three N—­H⋯N hydrogen bonds into a centrosymmetric four‐mol­ecule aggregate containing three R(8) rings.     

Structures of 1‐hydrophenanthroimidazoles: building blocks in the synthesis of expanded‐ring bis(imidazoles)

The structures of 1H‐phenanthro[9,10‐d]imidazole, C₁₅H₁₀N₂, (I), and 3,6‐dibromo‐1H‐phenanthro[9,10‐d]imidazole hemihydrate, C₁₅H₈Br₂N₂·0.5H₂O, (II), contain hydrogen‐bonded polymeric chains linked by columns of π–π stacked essentially planar phenanthroimidazole monomers. In the structure of (I), the asymmetric unit consists of two independent molecules, denoted (Ia) and (Ib), of 1H‐phenanthro[9,10‐d]imidazole. Alternating molecules of (Ia) and (Ib), canted by 79.07 (3)°, form hydrogen‐bonded zigzag polymer chains along the a‐cell direction. The chains are linked by π–π stacking of molecules of (Ia) and (Ib) along the b‐cell direction. In the structure of (II), the asymmetric unit consists of two independent molecules of 3,6‐dibromo‐1H‐phenanthro[9,10‐d]imidazole, denoted (IIa) and (IIb), along with a molecule of water. Alternating molecules of (IIa), (IIb) and water form hydrogen‐bonded polymer chains along the [110] direction. The donor–acceptor distances in these N(imine)...H—O(water)...H—N(amine) hydrogen bonds are the shortest thus far reported for imidazole amine and imine hydrogen‐bond interactions with water. Centrosymmetrically related molecules of (IIa) and (IIb) alternate in columns along the a‐cell direction and are canted by 48.27 (3)°. The present study provides the first examples of structurally characterized 1H‐phenanthroimidazoles.     

Seven 3‐methylidene‐1H‐indol‐2(3H)‐ones related to the multiple‐receptor tyrosine kinase inhibitor sunitinib

The solid‐state structures of a series of seven substituted 3‐methylidene‐1H‐indol‐2(3H)‐one derivatives have been determined by single‐crystal X‐ray diffraction and are compared in detail. Six of the structures {(3Z)‐3‐(1H‐pyrrol‐2‐ylmethylidene)‐1H‐indol‐2(3H)‐one, C₁₃H₁₀N₂O, (2a); (3Z)‐3‐(2‐thienylmethylidene)‐1H‐indol‐2(3H)‐one, C₁₃H₉NOS, (2b); (3E)‐3‐(2‐furylmethylidene)‐1H‐indol‐2(3H)‐one monohydrate, C₁₃H₉NO₂·H₂O, (3a); 3‐(1‐methylethylidene)‐1H‐indol‐2(3H)‐one, C₁₁H₁₁NO, (4a); 3‐cyclohexylidene‐1H‐indol‐2(3H)‐one, C₁₄H₁₅NO, (4c); and spiro[1,3‐dioxane‐2,3′‐indolin]‐2′‐one, C₁₁H₁₁NO₃, (5)} display, as expected, intermolecular hydrogen bonding (N—H...O=C) between the 1H‐indol‐2(3H)‐one units. However, methyl 3‐(1‐methylethylidene)‐2‐oxo‐2,3‐dihydro‐1H‐indole‐1‐carboxylate, C₁₃H₁₃NO₃, (4b), a carbamate analogue of (4a) lacking an N—H bond, displays no intermolecular hydrogen bonding. The structure of (4a) contains three molecules in the asymmetric unit, while (4b) and (4c) both contain two independent molecules.     

A new polymorph and two pseudopolymorphs of pyrimethamine

Due to its donor–acceptor–donor site, the antimalarial drug pyrimethamine [systematic name: 5‐(4‐chlorophenyl)‐6‐ethylpyrimidine‐2,4‐diamine] is a potential component of a supramolecular synthon. During a cocrystallization screen, one new polymorph of solvent‐free pyrimethamine, C₁₂H₁₃ClN₄, (I), and two pseudopolymorphs, pyrimethamine dimethyl sulfoxide monosolvate, C₁₂H₁₃ClN₄·C₂H₆OS, (Ia), and pyrimethamine N‐methylpyrrolidin‐2‐one monosolvate, C₁₂H₁₃ClN₄·C₅H₉NO, (Ib), were obtained. In (I), (Ia), (Ib) and the previously reported polymorph, the pyrimethamine molecules exhibit similar conformations and form R²₂(8) dimers stabilized by a pair of N—H...N hydrogen bonds. However, the packing arrangements are completely different. In (I), the dimers are connected by two additional N—H...N hydrogen bonds to form ribbons and further connected into a two‐dimensional network parallel to (100), while layers containing N—H...Cl hydrogen‐bonded pyrimethamine ribbons are observed in the packing of the known polymorph. In the two pseudopolymorphs, two pyrimethamine molecules are linked to form R²₂(8) dimers and the solvent molecules are connected to the dimers by R²₃(8) interactions involving two N—H...O hydrogen bonds. These arrangements are connected to form zigzag chains by N—H...Cl interactions in (Ia) and to form ribbons by N—H...N interactions in (Ib). Unexpectedly, a reaction between pyrimethamine and N‐methylpyrrolidin‐2‐one occurred during another cocrystallization experiment from a solvent mixture of N‐methylpyrrolidin‐2‐one and dimethyl sulfoxide, yielding solvent‐free 5,5′‐{[5‐(4‐chlorophenyl)‐6‐ethylpyrimidine‐2,4‐diyl]bis(azanediyl)}bis(1‐methylpyrrolidin‐2‐one), C₂₂H₂₇ClN₆O₂, (II). In the packing of (II), the pyrimethamine derivatives are N—H...O hydrogen bonded to form ribbons. A database study was carried out to compare the molecular conformations and hydrogen‐bonding interactions of pyrimethamine.     

Conformational studies of hydantoin‐5‐acetic acid and orotic acid

Hydantoin‐5‐acetic acid [2‐(2,5‐dioxoimidazolidin‐4‐yl)acetic acid] and orotic acid (2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidine‐4‐carboxylic acid) each contain one rigid acceptor–donor–acceptor hydrogen‐bonding site and a flexible side chain, which can adopt different conformations. Since both compounds may be used as coformers for supramolecular complexes, they have been crystallized in order to examine their conformational preferences, giving solvent‐free hydantoin‐5‐acetic acid, C₅H₆N₂O₄, (I), and three crystals containing orotic acid, namely, orotic acid dimethyl sulfoxide monosolvate, C₅H₄N₂O₄·C₂H₆OS, (IIa), dimethylammonium orotate–orotic acid (1/1), C₂H₈N⁺·C₅H₃N₂O₄⁻·C₅H₄N₂O₄, (IIb), and dimethylammonium orotate–orotic acid (3/1), 3C₂H₈N⁺·3C₅H₃N₂O₄⁻·C₅H₄N₂O₄, (IIc). The crystal structure of (I) shows a three‐dimensional network, with the acid function located perpendicular to the ring. Interestingly, the hydroxy O atom acts as an acceptor, even though the carbonyl O atom is not involved in any hydrogen bonds. However, in (IIa), (IIb) and (IIc), the acid functions are only slightly twisted out of the ring planes. All H atoms of the acidic functions are directed away from the rings and, with respect to the carbonyl O atoms, they show an antiperiplanar conformation in (I) and synperiplanar conformations in (IIa), (IIb) and (IIc). Furthermore, in (IIa), (IIb) and (IIc), different conformations of the acid O=C—C—N torsion angle are observed, leading to different hydrogen‐bonding arrangements depending on their conformation and composition.     

2,5‐Diaryl‐1,3,4‐selenadiazoles prepared from Woollins' reagent

Two polymorphs of 2,5‐diphenyl‐1,3,4‐selenadiazole, C₁₄H₁₀N₂Se, denoted (Ia) and (Ib), and a new polymorph of 2,5‐bis(thiophen‐2‐yl)‐1,3,4‐selenadiazole, C₁₀H₆N₂S₂Se, (IIb), form on crystallization of the compounds, prepared using Woollins' reagent (2,4‐diphenyl‐1,3‐diselenadiphosphetane 2,4‐diselenide). These compounds, along with 2‐(4‐chlorophenyl)‐5‐phenyl‐1,3,4‐selenadiazole, C₁₄H₉ClN₂Se, (III), and 2‐(furan‐2‐yl)‐5‐(p‐tolyl)‐1,3,4‐selenadiazole, C₁₃H₁₀N₂OSe, (IV), show similar intermolecular interactions, with π–π stacking, C—H...π interactions and weak hydrogen bonds typically giving rise to molecular chains. However, the combination of interactions differs in each case, giving rise to different packing arrangements. In polymorph (Ib), the molecule lies across a crystallographic twofold rotation axis, and (IV) has two independent molecules in the asymmetric unit.     

Five pseudopolymorphs and a cocrystal of nitrofurantoin

The antibiotic nitrofurantoin {systematic name: (E)‐1‐[(5‐nitro‐2‐furyl)methylideneamino]imidazolidine‐2,4‐dione} is not only used for the treatment of urinary tract infections, but also illegally applied as an animal food additive. Since derivatives of 2,6‐diaminopyridine might serve as artificial receptors for its recognition, we crystallized one potential drug–receptor complex, nitrofurantoin–2,6‐diacetamidopyridine (1/1), C₈H₆N₄O₅·C₉H₁₁N₃O₂, (I·II). It is characterized by one N—H...N and two N—H...O hydrogen bonds and confirms a previous NMR study. During the crystallization screening, several new pseudopolymorphs of both components were obtained, namely a nitrofurantoin dimethyl sulfoxide monosolvate, C₈H₆N₄O₅·C₂H₆OS, (Ia), a nitrofurantoin dimethyl sulfoxide hemisolvate, C₈H₆N₄O₅·0.5C₂H₆OS, (Ib), two nitrofurantoin dimethylacetamide monosolvates, C₈H₆N₄O₅·C₄H₉NO, (Ic) and (Id), and a nitrofurantoin dimethylacetamide disolvate, C₈H₆N₄O₅·2C₄H₉NO, (Ie), as well as a 2,6‐diacetamidopyridine dimethylformamide monosolvate, C₉H₁₁N₃O₂·C₃H₇NO, (IIa). Of these, (Ia), (Ic) and (Id) were formed during cocrystallization attempts with 1‐(4‐fluorophenyl)biguanide hydrochloride. Obviously nitrofurantoin prefers the higher‐energy conformation in the crystal structures, which all exhibit N—H...O and C—H...O hydrogen‐bond interactions. The latter are especially important for the crystal packing. 2,6‐Diacetamidopyridine shows some conformational flexibility depending on the hydrogen‐bond pattern.     

Four (2,2′‐bipyridyl)(ferrocenyl)boronium derivatives

Crystal structures are reported for four (2,2′‐bipyridyl)(ferrocenyl)boronium derivatives, namely (2,2′‐bipyridyl)(ethenyl)(ferrocenyl)boronium hexafluoridophosphate, [Fe(C₅H₅)(C₁₇H₁₅BN₂)]PF₆, (Ib), (2,2′‐bipyridyl)(tert‐butylamino)(ferrocenyl)boronium bromide, [Fe(C₅H₅)(C₁₉H₂₂BN₃)]Br, (IIa), (2,2′‐bipyridyl)(ferrocenyl)(4‐methoxyphenylamino)boronium hexafluoridophosphate acetonitrile hemisolvate, [Fe(C₅H₅)(C₂₂H₂₀BN₃O)]PF₆·0.5CH₃CN, (IIIb), and 1,1′‐bis[(2,2′‐bipyridyl)(cyanomethyl)boronium]ferrocene bis(hexafluoridophosphate), [Fe(C₁₇H₁₄BN₃)₂](PF₆)₂, (IVb). The asymmetric unit of (IIIb) contains two independent cations with very similar conformations. The B atom has a distorted tetrahedral coordination in all four structures. The cyclopentadienyl rings of (Ib), (IIa) and (IIIb) are approximately eclipsed, while a bisecting conformation is found for (IVb). The N—H groups of (IIa) and (IIIb) are shielded by the ferrocenyl and tert‐butyl or phenyl groups and are therefore not involved in hydrogen bonding. The B—N(amine) bond lengths are shortened by delocalization of π‐electrons. In the cations with an amine substituent at boron, the B—N(bipyridyl) bonds are 0.035 (3) Å longer than in the cations with a methylene C atom bonded to boron. A similar lengthening of the B—N(bipyridyl) bonds is found in a survey of related cations with an oxy group attached to the B atom.     

Three new fluorinated N‐phenyl‐substituted pentacyclic ethanoanthracenedicarboximides

Diels–Alder reaction between maleimides featuring 3,5‐di‐, 2,4,6‐tri‐ and pentafluorinated N‐phenyl substituents and anthracene yields the corresponding pentacyclic ethanoanthracenedicarboximide compounds, namely N‐(3,5‐difluorophenyl)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximide, C₂₄H₁₅F₂NO₂, (IIa), N‐(2,4,6‐trifluorophenyl)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximide, C₂₄H₁₄F₃NO₂, (IIb), N‐(2,3,4,5,6‐pentafluorophenyl)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximide, C₂₄H₁₂F₅NO₂, (IIc). The crystal structures of (IIa)–(IIc) reveal an expected molecular geometry with a `V'‐shape of the anthracene‐derived tricyclic moiety. The crystal packings of (IIa) and (IIb) are dominated by π–π and C—H...O/F interactions, while F...F and C—H...π contacts are absent. In contrast, (IIc) shows F...F and C—H...O/F contacts, but no π‐involved contacts of relevance.     

Hydrogen‐bonded assembly in six closely related pyrazolo[3,4‐b]pyridine derivatives; a simple chain,three types of chains of rings and a complex sheet structure

Six closely related pyrazolo[3,4‐b]pyridine derivatives, namely 6‐chloro‐3‐methyl‐1,4‐diphenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₄ClN₃O, (I), 6‐chloro‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O, (II), 6‐chloro‐4‐(4‐chlorophenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃Cl₂N₃O, (III), 4‐(4‐bromophenyl)‐6‐chloro‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃BrClN₃O, (IV), 6‐chloro‐4‐(4‐methoxyphenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O₂, (V), and 6‐chloro‐3‐methyl‐4‐(4‐nitrophenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃ClN₄O₃, (VI), which differ only in the identity of a single small substituent on one of the aryl rings, crystallize in four different space groups spanning three crystal systems. The molecules of (I) are linked into a chain of rings by a combination of C—H...N and C—H...π(arene) hydrogen bonds; those of (II), (IV) and (V), which all crystallize in the space group P, are each linked by two independent C—H...O hydrogen bonds to form chains of edge‐fused rings running in different directions through the three unit cells; the molecules of (III) are linked into complex sheets by a combination of two C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond; finally, the molecules of (VI) are linked by a single C—H...O hydrogen bond to form a simple chain.     

A series of (E)‐5‐(arylideneamino)‐1‐tert‐butyl‐1H‐pyrrole‐3‐carbonitriles and their reduction products to secondary amines: syntheses and X‐ray structural studies

An efficent access to a series of N‐(pyrrol‐2‐yl)amines, namely (E)‐1‐tert‐butyl‐5‐[(4‐chlorobenzylidene)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₆ClN₃, (7a), (E)‐1‐tert‐butyl‐5‐[(2,4‐dichlorobenzylidene)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₅Cl₂N₃, (7b), (E)‐1‐tert‐butyl‐5‐[(pyridin‐4‐ylmethylene)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₅H₁₆N₄, (7c), 1‐tert‐butyl‐5‐[(4‐chlorobenzyl)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₈ClN₃, (8a), and 1‐tert‐butyl‐5‐[(2,4‐dichlorobenzyl)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₇Cl₂N₃, (8b), by a two‐step synthesis sequence (solvent‐free condensation and reduction) starting from 5‐amino‐1‐tert‐butyl‐1H‐pyrrole‐3‐carbonitrile is described. The syntheses proceed via isolated N‐(pyrrol‐2‐yl)imines, which are also key synthetic intermediates of other valuable compounds. The crystal structures of the reduced compounds showed a reduction in the symmetry compared with the corresponding precursors, viz. Pbcm to P from compound (7a) to (8a) and P2₁/c to P from compound (7b) to (8b), probably due to a severe change in the molecular conformations, resulting in the loss of planarity observed in the nonreduced compounds. In all of the crystals, the supramolecular assembly is controlled mainly by strong (N,C)—H…N hydrogen bonds. However, in the case of (7a)–(7c), C—H…Cl interactions are strong enough to help in the three‐dimensional architecture, as observed in Hirshfeld surface maps.     

Two polymorphs and the diethylammonium salt of the barbiturate eldoral

Polymorph (Ia) of eldoral [5‐ethyl‐5‐(piperidin‐1‐yl)barbituric acid or 5‐ethyl‐5‐(piperidin‐1‐yl)‐1,3‐diazinane‐2,4,6‐trione], C₁₁H₁₇N₃O₃, displays a hydrogen‐bonded layer structure parallel to (100). The piperidine N atom and the barbiturate carbonyl group in the 2‐position are utilized in N—H...N and N—H...O=C hydrogen bonds, respectively. The structure of polymorph (Ib) contains pseudosymmetry elements. The two independent molecules of (Ib) are connected via N—H...O=C(4/6‐position) and N—H...N(piperidine) hydrogen bonds to give a chain structure in the [100] direction. The hydrogen‐bonded layers, parallel to (010), formed in the salt diethylammonium 5‐ethyl‐5‐(piperidin‐1‐yl)barbiturate [or diethylammonium 5‐ethyl‐2,4,6‐trioxo‐5‐(piperidin‐1‐yl)‐1,3‐diazinan‐1‐ide], C₄H₁₂N⁺·C₁₁H₁₆N₃O₃⁻, (II), closely resemble the corresponding hydrogen‐bonded structure in polymorph (Ia). Like many other 5,5‐disubstituted derivatives of barbituric acid, polymorphs (Ia) and (Ib) contain the R₂²(8) N—H...O=C hydrogen‐bond motif. However, the overall hydrogen‐bonded chain and layer structures of (Ia) and (Ib) are unique because of the involvement of the hydrogen‐bond acceptor function in the piperidine group.     

Synthesis and crystal structures of some bis(3‐methyl‐1H‐indol‐2‐yl)(salicyl)methanes

Four 2,2′‐bisindolylmethanes (BIMs), a useful class of polyindolyl species joined to a central carbon, were synthesized using salicylaldehyde derivatives and simple acid catalysis; these are 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐6‐methylphenol, (IIa), 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4,6‐dichlorophenol, (IIb), 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4‐nitrophenol, (IIc), and 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4,6‐di‐tert‐butylphenol, (IId). BIMs (IIa) and (IIb) were characterized crystallographically as the dimethyl sulfoxide (DMSO) disolvates, i.e. C₂₆H₂₄N₂O·2C₂H₆OS and C₂₅H₂₀Cl₂N₂O·2C₂H₆OS, respectively. Both form strikingly similar one‐dimensional hydrogen‐bonding chain motifs with the DMSO solvent molecules. BIM (IIa) packs into double layers of chains whose orientations alternate every double layer, while (IIb) forms more simply packed chains along the a axis. BIM (IIa) has a remarkably long c axis.     

Polymorphism of 2,5‐[(diphenylphosphanyl)methyl]‐1,1,2,4,4,5‐hexaphenyl‐1,4‐diphospha‐2,5‐diboracyclohexane

2,5‐[(Diphenylphosphanyl)methyl]‐1,1,2,4,4,5‐hexaphenyl‐1,4‐diphospha‐2,5‐diboracyclohexane shows polymorphism as two tetrahydrofuran (THF) disolvates [C₆₄H₅₈B₂P₄·2C₄H₈O, (Ia) and (Ib)] and pseudo‐polymorphism as its toluene monosolvate [C₆₄H₅₈B₂P₄·C₇H₈, (Ic)]. In each of polymorphs (Ia) and (Ib), the diphosphadiboracyclohexane molecule is located on a centre of inversion. The THF molecule of (Ib) is disordered over two sites, with a site‐occupation factor of 0.612 (8) for the major‐occupied site. Both structures crystallize in the same space group (P2₁/n), but they display a different crystal packing. For pseudo‐polymorph (Ic), although the space group is P2₁/c, which is just a different setting of the P2₁/n space group of (Ia) and (Ib), the crystal packing is completely different. Although the crystal packing in these three structures is significantly different, their molecular conformations are surprisingly the same.     

6‐Chloroisocytosine and 5‐bromo‐6‐methylisocytosine: again,one or two tautomers present in the same crystal?

It is well known that pyrimidin‐4‐one derivatives are able to adopt either the 1H‐ or the 3H‐tautomeric form in (co)crystals, depending on the coformer. As part of ongoing research to investigate the preferred hydrogen‐bonding patterns of active pharmaceutical ingredients and their model systems, 2‐amino‐6‐chloropyrimidin‐4‐one and 2‐amino‐5‐bromo‐6‐methylpyrimidin‐4‐one have been cocrystallized with several coformers and with each other. Since Cl and Br atoms both have versatile possibilities to interact with the coformers, such as via hydrogen or halogen bonds, their behaviour within the crystal packing was also of interest. The experiments yielded five crystal structures, namely 2‐aminopyridin‐1‐ium 2‐amino‐6‐chloro‐4‐oxo‐4H‐pyrimidin‐3‐ide–2‐amino‐6‐chloropyrimidin‐4(3H)‐one (1/3), C₅H₇N₂⁺·C₄H₃ClN₃O⁻·3C₄H₄ClN₃O, (Ia), 2‐aminopyridin‐1‐ium 2‐amino‐6‐chloro‐4‐oxo‐4H‐pyrimidin‐3‐ide–2‐amino‐6‐chloropyrimidin‐4(3H)‐one–2‐aminopyridine (2/10/1), 2C₅H₇N₂⁺·2C₄H₃ClN₃O⁻·10C₄H₄ClN₃O·C₅H₆N₂, (Ib), the solvent‐free cocrystal 2‐amino‐5‐bromo‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐5‐bromo‐6‐methylpyrimidin‐4(1H)‐one (1/1), C₅H₆BrN₃O·C₅H₆BrN₃O, (II), the solvate 2‐amino‐5‐bromo‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐5‐bromo‐6‐methylpyrimidin‐4(1H)‐one–N‐methylpyrrolidin‐2‐one (1/1/1), C₅H₆BrN₃O·C₅H₆BrN₃O·C₅H₉NO, (III), and the partial cocrystal 2‐amino‐5‐bromo‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐5‐bromo‐6‐methylpyrimidin‐4(1H)‐one–2‐amino‐6‐chloropyrimidin‐4(3H)‐one (0.635/1/0.365), C₅H₆BrN₃O·C₅H₆BrN₃O·C₄H₄ClN₃O, (IV). All five structures show R₂²(8) hydrogen‐bond‐based patterns, either by synthon 2 or by synthon 3, which are related to the Watson–Crick base pairs.