The conformational analyses of 2‐amino‐N‐[2‐(dimethylphenoxy)ethyl]propan‐1‐ol derivatives in different environments

Four crystal structures of 2‐amino‐N‐(dimethylphenoxyethyl)propan‐1‐ol derivatives, characterized by X‐ray diffraction analysis, are reported. The free base (R,S)‐2‐amino‐N‐[2‐(2,3‐dimethylphenoxy)ethyl]propan‐1‐ol, C₁₃H₂₁NO₂, 1 , crystallizes in the space group P2₁/n, with two independent molecules in the asymmetric unit. The hydrochloride, (S)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium chloride, C₁₃H₂₂NO₂⁺·Cl^?, 2c , crystallizes in the space group P2₁, with one cation and one chloride anion in the asymmetric unit. The asymmetric unit of two salts of 2‐picolinic acid, namely, (R,S)‐N‐[2‐(2,3‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium pyridine‐2‐carboxylate, C₁₃H₂₂NO₂⁺·C₆H₄NO₂^?, 1p , and (R)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium pyridine‐2‐carboxylate, C₁₃H₂₂NO₂⁺·C₆H₄NO₂^?, 2p , consists of one cation and one 2‐picolinate anion. Salt 1p crystallizes in the triclinic centrosymmetric space group P, while salt 2p crystallizes in the space group P4₁2₁2. The conformations of the amine fragments are contrasted and that of 2p is found to have an unusual antiperiplanar arrangement about the ether group. The crystal packing of 1 and 2c is dominated by hydrogen‐bonded chains, while the structures of the 2‐picolinate salts have hydrogen‐bonded rings as the major features. In both salts with 2‐picolinic acid, the specific R₁²(5) hydrogen‐bonding motif is observed. Structural studies have been enriched by the generation of fingerprint plots derived from Hirshfeld surfaces.     

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.     

Ethyl N‐[2‐(hydroxy­acetyl)­phenyl]­carbamate,ethyl N‐[2‐(hydroxy­acetyl)‐4‐iodo­phenyl]­carbamate and ethyl N‐[2‐(hydroxy­acetyl)‐4‐methyl­phenyl]­carbamate

In ethyl N‐[2‐(hydroxy­acetyl)phenyl]carbamate, C₁₁H₁₃NO₄, all of the non‐H atoms lie on a mirror plane in the space group Pnma; the mol­ecules are linked into simple chains by a single C—H⋯O hydrogen bond. The mol­ecules of ethyl N‐[2‐(hydroxy­acetyl)‐4‐iodo­phenyl]carbamate, C₁₁H₁₂INO₄, are linked into sheets by a combination of O—H⋯I and C—H⋯O hydrogen bonds and a dipolar I⋯O contact. Ethyl N‐­[2‐(hydroxy­acetyl)‐4‐methyl­phenyl]carbamate, C₁₂H₁₅NO₄, crystallizes with Z′ = 2 in the space group P; pairs of mol­ecules are weakly linked by an O—H⋯O hydrogen bond and these aggregates are linked into chains by two independent aromatic π–π stacking inter­actions.     

Two succinic acid derivatives of 2‐ethyl‐6‐methylpyridin‐3‐ol

Crystals of bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate–succinic acid (1/1), C₈H₁₂NO⁺·0.5C₄H₄O₄²⁻·0.5C₄H₆O₄, (I), and 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium hydrogen succinate, C₈H₁₂NO⁺·C₄H₅O₄⁻, (II), were obtained by reaction of 2‐ethyl‐6‐methylpyridin‐3‐ol with succinic acid. The succinate anion and succinic acid molecule in (I) are located about centres of inversion. Intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds are responsible for the formation of a three‐dimensional network in the crystal structure of (I) and a two‐dimensional network in the crystal structure of (II). Both structures are additionally stabilized by π–π interactions between symmetry‐related pyridine rings, forming a rod‐like cationic arrangement for (I) and cationic dimers for (II).     

catena‐Poly[[[aqua[3‐(2‐pyridylsulfanyl)propionato N‐oxide‐κO1]copper(II)]‐μ‐[3‐(2‐pyridylsulfanyl)propionato N‐oxide‐κ3O3:O1,O1′] dihydrate]

In the title complex, {[Cu(C₈H₈NO₃S)₂(H₂O)]·2H₂O}_n, the Cu^II cation has a distorted square‐pyramidal coordination environment consisting of five O atoms, one from a water molecule, one from an N—O group and the other three from the carboxylate groups of two 3‐(2‐pyridylsulfanyl)propionate N‐oxide anions. The aqua[3‐(2‐pyridylsulfanyl)propionato N‐oxide]copper(II) moieties are bridged by 3‐(2‐pyridylsulfanyl)propionate N‐oxide anions to form an infinite three‐dimensional coordination polymer with a zigzag chain structure. The crystal structure is stabilized by hydrogen bonds.     

cis‐(6RS,13RS)‐3,3,10,10‐Tetra­methyl‐6,13‐diphenyl‐1,8‐dioxa‐4,11‐diaza­cyclo­tetra­decane‐2,5,9,12‐tetra­one and two of its precursors

The title macrocycle, C₂₆H₃₀N₂O₆, (VI), was obtained by `direct amide cyclization' from the linear precursor 3‐hydr­oxy‐N‐[1‐methyl‐1‐(N‐methyl‐N‐phenyl­carbamoyl)ethyl]‐2‐phenylpropanamide, the N‐methyl­anilide of rac‐2‐methyl‐2‐[(3‐hydroxy‐2‐phenyl­propanoyl)­amino]­propanoic acid, C₁₃H₁₇NO₄, (IV). The reaction proceeds via the inter­mediate rac‐2‐(2‐hydroxy‐1‐phenyl­ethyl)‐4,4‐dimethyl‐1,3‐oxazol‐5(4H)‐one, C₁₃H₁₅NO₃, (V), which was synthesized independently and whose structure was also established. Unlike all previously described analogues, the title macrocycle has the cis‐diphenyl configuration. The 14‐membered ring has a distorted rect­angular diamond‐based [3434] configuration and inter­molecular N—H⋯O hydrogen bonds link the mol­ecules into a three‐dimensional framework. The propanoic acid precursor forms a complex series of inter­molecular hydrogen bonds, each of which involves pairwise association of mol­ecules and which together result in the formation of extended two‐dimensional sheets. The oxazole inter­mediate forms centrosymmetric hydrogen‐bonded dimers in the solid state.     

Six closely related 4,6‐disubstituted 2‐amino‐5‐formylpyrimidines: different ring conformations,polarized electronic structures,and hydrogen‐bonded assembly in zero,one, two and three dimensions

In each of ethyl N‐{2‐amino‐5‐formyl‐6‐[methyl(phenyl)amino]pyrimidin‐4‐yl}glycinate, C₁₆H₁₉N₅O₃, (I), N‐{2‐amino‐5‐formyl‐6‐[methyl(phenyl)amino]pyrimidin‐4‐yl}glycinamide, C₁₄H₁₆N₆O₂, (II), and ethyl 3‐amino‐N‐{2‐amino‐5‐formyl‐6‐[methyl(phenyl)amino]pyrimidin‐4‐yl}propionate, C₁₇H₂₁N₅O₃, (III), the pyrimidine ring is effectively planar, but in each of methyl N‐{2‐amino‐6‐[benzyl(methyl)amino]‐5‐formylpyrimidin‐4‐yl}glycinate, C₁₆H₁₉N₅O₃, (IV), ethyl 3‐amino‐N‐{2‐amino‐6‐[benzyl(methyl)amino]‐5‐formylpyrimidin‐4‐yl}propionate, C₁₈H₂₃N₅O₃, (V), and ethyl 3‐amino‐N‐[2‐amino‐5‐formyl‐6‐(piperidin‐4‐yl)pyrimidin‐4‐yl]propionate, C₁₅H₂₃N₅O₃, (VI), the pyrimidine ring is folded into a boat conformation. The bond lengths in each of (I)–(VI) provide evidence for significant polarization of the electronic structure. The molecules of (I) are linked by paired N—H...N hydrogen bonds to form isolated dimeric aggregates, and those of (III) are linked by a combination of N—H...N and N—H...O hydrogen bonds into a chain of edge‐fused rings. In the structure of (IV), molecules are linked into sheets by means of two hydrogen bonds, both of N—H...O type, in the structure of (V) by three hydrogen bonds, two of N—H...N type and one of C—H...O type, and in the structure of (VI) by four hydrogen bonds, all of N—H...O type. Molecules of (II) are linked into a three‐dimensional framework structure by a combination of three N—H...O hydrogen bonds and one C—H...O hydrogen bond.     

A new [(1R,2R)‐1,2‐diaminocyclohexane]platinum(II) complex: formation by nitrate–acetonitrile ligand exchange

The title compound, cis‐diacetonitrile[(1R,2R)‐1,2‐diaminocyclohexane‐κ²N,N′]platinum(II) dinitrate monohydrate, [Pt(C₂H₃N)₂(C₆H₁₄N₂)](NO₃)₂·H₂O, is a molecular salt of the diaminocyclohexane–Pt complex cation. There are two formula units in the asymmetric unit. Apart from the two charge‐balancing nitrate anions, one neutral molecule of water is present. The components interact via N—H...O and O—H...O hydrogen bonds, resulting in supramolecular chains. The title compound crystallizes only from acetonitrile with residual water, with the acetonitrile coordinating to the molecule of cis‐[Pt(NO₃)₂(DACH)] (DACH is 1,2‐diaminocyclohexane) and the water forming a monohydrate.     

Hydrogen‐bonding patterns in 3‐alkyl‐3‐hydroxyindolin‐2‐ones

The molecules of racemic 3‐benzoylmethyl‐3‐hydroxyindolin‐2‐one, C₁₆H₁₃NO₃, (I), are linked by a combination of N—H...O and O—H...O hydrogen bonds into a chain of centrosymmetric edge‐fused R₂²(10) and R₄⁴(12) rings. Five monosubstituted analogues of (I), namely racemic 3‐hydroxy‐3‐[(4‐methylbenzoyl)methyl]indolin‐2‐one, C₁₇H₁₅NO₃, (II), racemic 3‐[(4‐fluorobenzoyl)methyl]‐3‐hydroxyindolin‐2‐one, C₁₆H₁₂FNO₃, (III), racemic 3‐[(4‐chlorobenzoyl)methyl]‐3‐hydroxyindolin‐2‐one, C₁₆H₁₂ClNO₃, (IV), racemic 3‐[(4‐bromobenzoyl)methyl]‐3‐hydroxyindolin‐2‐one, C₁₆H₁₂BrNO₃, (V), and racemic 3‐hydroxy‐3‐[(4‐nitrobenzoyl)methyl]indolin‐2‐one, C₁₆H₁₂N₂O₅, (VI), are isomorphous in space group P. In each of compounds (II)–(VI), a combination of N—H...O and O—H...O hydrogen bonds generates a chain of centrosymmetric edge‐fused R₂²(8) and R₂²(10) rings, and these chains are linked into sheets by an aromatic π–π stacking interaction. No two of the structures of (II)–(VI) exhibit the same combination of weak hydrogen bonds of C—H...O and C—H...π(arene) types. The molecules of racemic 3‐hydroxy‐3‐(2‐thienylcarbonylmethyl)indolin‐2‐one, C₁₄H₁₁NO₃S, (VII), form hydrogen‐bonded chains very similar to those in (II)–(VI), but here the sheet formation depends upon a weak π–π stacking interaction between thienyl rings. Comparisons are drawn between the crystal structures of compounds (I)–(VII) and those of some recently reported analogues having no aromatic group in the side chain.     

A structural study of 4‐aminoantipyrine and six of its Schiff base derivatives

Six derivatives of 4‐amino‐1,5‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐3‐one (4‐aminoantipyrine), C₁₁H₁₃N₃O, (I), have been synthesized and structurally characterized to investigate the changes in the observed hydrogen‐bonding motifs compared to the original 4‐aminoantipyrine. The derivatives were synthesized from the reactions of 4‐aminoantipyrine with various aldehyde‐, ketone‐ and ester‐containing molecules, producing (Z)‐methyl 3‐[(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)amino]but‐2‐enoate, C₁₆H₁₉N₃O₃, (II), (Z)‐ethyl 3‐[(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)amino]but‐2‐enoate, C₁₇H₂₁N₃O₃, (III), ethyl 2‐[(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)amino]cyclohex‐1‐enecarboxylate, C₂₀H₂₅N₃O₃, (IV), (Z)‐ethyl 3‐[(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)amino]‐3‐phenylacrylate, C₂₂H₂₃N₃O₃, (V), 2‐cyano‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamide, C₁₄H₁₄N₄O₂, (VI), and (E)‐methyl 4‐{[(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)amino]methyl}benzoate, C₂₀H₁₉N₃O₃, (VII). The asymmetric units of all these compounds have one molecule on a general position. The hydrogen bonding in (I) forms chains of molecules via intermolecular N—H...O hydrogen bonds around a crystallographic sixfold screw axis. In contrast, the formation of enamines for all derived compounds except (VII) favours the formation of a six‐membered intramolecular N—H...O hydrogen‐bonded ring in (II)–(V) and an intermolecular N—H...O hydrogen bond in (VI), whereas there is an intramolecular C—H...O hydrogen bond in the structure of imine (VII). All the reported compounds, except for (II), feature π–π interactions, while C—H...π interactions are observed in (II), C—H...O interactions are observed in (I), (III), (V) and (VI), and a C—O...π interaction is observed in (II).     

Three new olanzapine structures: the acetic acid monosolvate,and the propan‐2‐ol and propan‐2‐one hemisolvate monohydrates

The crystal structures of three new solvates of olanzapine [systematic name: 2‐methyl‐4‐(4‐methylpiperazin‐1‐yl)‐10H‐thieno[2,3‐b][1,5]benzodiazepine], namely olanzapine acetic acid monosolvate, C₁₇H₂₀N₄S·C₂H₄O₂, (I), olanzapine propan‐2‐ol hemisolvate monohydrate, C₁₇H₂₀N₄S·0.5C₃H₈O·H₂O, (II), and olanzapine propan‐2‐one hemisolvate monohydrate, C₁₇H₂₀N₄S·0.5C₃H₆O·H₂O, (III), are presented and compared with other known olanzapine forms. There is a fairly close resemblance of the molecular conformation for all studied analogues. The crystal structures are built up through olanzapine dimers, which are characterized via C—H...π interactions between the aliphatic fragment (1‐methylpiperazin‐4‐yl) and the aromatic fragment (benzene system). All solvent (guest) molecules participate in hydrogen‐bonding networks. The crystal packing is sustained via intermolecular N_host—H...O_guest, O_guest—H...N_host, O_guest—H...O_guest and C_host—H...O_guest hydrogen bonds. It should be noted that the solvent propan‐2‐ol in (II) and propan‐2‐one in (III) show orientational disorder. The propan‐2‐ol molecule lies close to a twofold axis, while the propan‐2‐one molecule resides strictly on a twofold axis through the carbonyl C atom. In both cases, the water molecules present positional disorder of the H atoms.     

3,5‐Di­fluoro‐4‐nitro­pyridine N‐oxide and 3,5‐di­amino‐4‐nitro­pyridine N‐oxide monohydrate

The mol­ecule of 3,5‐di­fluoro‐4‐nitro­pyridine N‐oxide, C₅H₂F₂N₂O₃, is twisted around the C—NO₂ bond by 38.5 (1)°, while the 3,5‐di­amino analogue, 3,5‐di­amino‐4‐nitro­pyridine N‐oxide monohydrate, C₅H₆N₄O₃·H₂O, adopts a planar conformation stabilized by intramolecular hydrogen bonds, with a significant redistribution of π electrons.     

2‐Oxo‐2‐phenyl‐N‐[(R)‐1‐phenylethyl]acetamide and N,N‐dimethyl‐2‐(1‐naphthyl)‐2‐oxoacetamide: possibility of Yang photocyclization in a crystal

The crystal structures of 2‐oxo‐2‐phenyl‐N‐[(R)‐1‐phenylethyl]acetamide, C₁₆H₁₅NO₂, (I), and N,N‐dimethyl‐2‐(1‐naphthyl)‐2‐oxoacetamide, C₁₄H₁₃NO₂, (II), were determined in an attempt to understand the reason for the lack of Yang photocyclization in their respective crystals. In the case of (I), the long distance between the O atom of the carbonyl group and the γ‐H atom, and between the C atom of the carbonyl group and the γ‐C atom, preclude Yang photocyclization. For (II), the deviation of the γ‐H atom from the plane of the carbonyl group and interactions between the naphthalene rings are regarded as possible reasons for the chemical inertia. The two independent molecules of (I) differ in their conformation. N—H...O hydrogen bonds link molecules of (I) into chains extended along the b axis.     

Crystal structures of four δ‐keto esters and a Cambridge Structural Database analysis of cyano–halogen interactions

The revived interest in halogen bonding as a tool in pharmaceutical cocrystals and drug design has indicated that cyano–halogen interactions could play an important role. The crystal structures of four closely related δ‐keto esters, which differ only in the substitution at a single C atom (by H, OMe, Cl and Br), are compared, namely ethyl 2‐cyano‐5‐oxo‐5‐phenyl‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₂N₂O₃, (1), ethyl 2‐cyano‐5‐(4‐methoxyphenyl)‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₂₀H₂₄N₂O₄, (2), ethyl 5‐(4‐chlorophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁ClN₂O₃, (3), and the previously published ethyl 5‐(4‐bromophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁BrN₂O₃, (4) [Maurya, Vasudev & Gupta (2013). RSC Adv. 3 , 12955–12962]. The molecular conformations are very similar, while there are differences in the molecular assemblies. Intermolecular C—H...O hydrogen bonds are found to be the primary interactions in the crystal packing and are present in all four structures. The halogenated derivatives have additional aromatic–aromatic interactions and cyano–halogen interactions, further stabilizing the molecular packing. A database analysis of cyano–halogen interactions using the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53 , 662–671] revealed that about 13% of the organic molecular crystals containing both cyano and halogen groups have cyano–halogen interactions in their packing. Three geometric parameters for the C—X...N[triple‐bond]C interaction (X = F, Cl, Br or I), viz. the N...X distance and the C—X...N and C—N...X angles, were analysed. The results indicate that all the short cyano–halogen contacts in the CSD can be classified as halogen bonds, which are directional noncovalent interactions.     

Methyl 2‐benzamido‐4‐(3,4‐dimethoxyphenyl)‐5‐methylbenzoate and N‐{5‐benzoyl‐2‐[(Z)‐2‐methoxyethenyl]‐4‐methylphenyl}benzamide

Methyl 2‐benzamido‐4‐(3,4‐dimethoxyphenyl)‐5‐methylbenzoate, C₂₄H₂₃NO₅, (Ia), and N‐{5‐benzoyl‐2‐[(Z)‐2‐methoxyethenyl]‐4‐methylphenyl}benzamide, C₂₄H₂₁NO₃, (IIa), were formed via a Diels–Alder reaction of appropriately substituted 2H‐pyran‐2‐ones and methyl propiolate or (Z)‐1‐methoxybut‐1‐en‐3‐yne, respectively. Each of these cycloadditions might yield two different regioisomers, but just one was obtained in each case. In (Ia), an intramolecular N—H...O hydrogen bond closes a six‐membered ring. A chain is formed due to aromatic π–π interactions, and a three‐dimensional framework structure is formed by a combination of C—H...O and C—H...π(arene) hydrogen bonds. Compound (IIa) was formed not only regioselectively but also chemoselectively, with just the triple bond reacting and the double bond remaining unchanged. Compound (IIa) crystallizes as N—H...O hydrogen‐bonded dimers stabilized by aromatic π–π interactions. Dimers of (IIa) are connected into a chain by weak C—H...π(arene) interactions.     

Polymorph of {2‐[(2‐hydroxyethyl)iminiomethyl]phenolato‐κO}dioxido{2‐[(2‐oxidoethyl)iminomethyl]phenolato‐κ3O,N,O′}molybdenum(VI)

A second polymorphic form (form I) of the previously reported compound {2‐[(2‐hydroxyethyl)iminiomethyl]phenolato‐κO}dioxido{2‐[(2‐oxidoethyl)iminomethyl]phenolato‐κ³O,N,O′}molybdenum(VI) (form II), [Mo(C₉H₉NO₂)O₂(C₉H₁₁NO₂)], is presented. The title structure differs from the previously reported polymorph [Głowiak, Jerzykiewicz, Sobczak & Ziółkowski (2003). Inorg. Chim. Acta, 356 , 387–392] by the fact that the asymmetric unit contains three molecules linked by O—H...O hydrogen bonds. These trimeric units are further linked through O—H...O hydrogen bonds to form a chain parallel to the [11] direction. As in the previous polymorph, each molecule is built up from an MoO₂²⁺ cation surrounded by an O,N,O′‐tridentate ligand (O⁻C₆H₄CH=NCH₂CH₂O⁻) and weakly coordinated by a second zwitterionic ligand (O⁻C₆H₄CH=N⁺HC₂H₄OH). All complexes are chiral with the absolute configuration at Mo being C or A. The main difference between the two polymorphs results from the alternation of the chirality at Mo within the chain.     

Weak C—H...O and C—H...π hydrogen bonds and π–π stacking interactions in a series of four N′‐[(E)‐(aryl)methylidene]‐N‐methyl‐2‐oxo‐1,3‐oxazolidine‐4‐carbohydrazides

Oxazolidin‐2‐ones are widely used as protective groups for 1,2‐amino alcohols and chiral derivatives are employed as chiral auxiliaries. The crystal structures of four differently substituted oxazolidinecarbohydrazides, namely N′‐[(E)‐benzylidene]‐N‐methyl‐2‐oxo‐1,3‐oxazolidine‐4‐carbohydrazide, C₁₂H₁₂N₃O₃, (I), N′‐[(E)‐2‐chlorobenzylidene]‐N‐methyl‐2‐oxo‐1,3‐oxazolidine‐4‐carbohydrazide, C₁₂H₁₂ClN₃O₃, (II), (4S)‐N′‐[(E)‐4‐chlorobenzylidene]‐N‐methyl‐2‐oxo‐1,3‐oxazolidine‐4‐carbohydrazide, C₁₂H₁₂ClN₃O₃, (III), and (4S)‐N′‐[(E)‐2,6‐dichlorobenzylidene]‐N,3‐dimethyl‐2‐oxo‐1,3‐oxazolidine‐4‐carbohydrazide, C₁₃H₁₃Cl₂N₃O₃, (IV), show that an unexpected mild‐condition racemization from the chiral starting materials has occurred in (I) and (II). In the extended structures, the centrosymmetric phases, which each crystallize with two molecules (A and B) in the asymmetric unit, form A+B dimers linked by pairs of N—H...O hydrogen bonds, albeit with different O‐atom acceptors. One dimer is composed of one molecule with an S configuration for its stereogenic centre and the other with an R configuration, and possesses approximate local inversion symmetry. The other dimer consists of either R,R or S,S pairs and possesses approximate local twofold symmetry. In the chiral structure, N—H...O hydrogen bonds link the molecules into C(5) chains, with adjacent molecules related by a 2₁ screw axis. A wide variety of weak interactions, including C—H...O, C—H...Cl, C—H...π and π–π stacking interactions, occur in these structures, but there is little conformity between them.     

Strong intramolecular O—H⋯O hydrogen bonds in quinaldic acid N‐oxide and picolinic acid N‐oxide

The title compounds contain very short intramolecular hydrogen bonds of the type C—O—H?O—N. The O?O distances are 2.425 (2) Å in picolinic acid N‐oxide (2‐carboxy­pyridine N‐oxide), C₆H₅NO₃, (I), and 2.435 (2) Å in quinaldic acid N‐oxide (2‐carboxy­quinoline N‐oxide), C₁₀H₇NO₃, (II). In (II), this is associated with slight molecular distortion from planarity, while in (I), such an effect cannot be observed because the mol­ecule crystallizes on a mirror plane.     

The 1:1 proton‐transfer compounds of 4‐(phenyldiazenyl)aniline (aniline yellow) with 3‐nitrophthalic, 4‐nitrophthalic and 5‐nitroisophthalic acids

The structures of the anhydrous 1:1 proton‐transfer compounds of the dye precursor aniline yellow [4‐(phenyldiazenyl)aniline], namely isomeric 4‐(phenyldiazenyl)anilinium 2‐carboxy‐6‐nitrobenzoate, C₁₂H₁₂N₃⁺·C₈H₄NO₆⁻, (I), and 4‐(phenyldiazenyl)anilinium 2‐carboxy‐4‐nitrobenzoate, C₁₂H₁₂N₃⁺·C₈H₄NO₆⁻, (II), and 4‐(phenyldiazenyl)anilinium 3‐carboxy‐5‐nitrobenzoate monohydrate, C₁₂H₁₂N₃⁺·C₈H₄NO₆⁻·H₂O, (III), have been determined at 130 K. In (I) the cation has longitudinal rotational disorder. All three compounds have substructures comprising backbones formed through strong head‐to‐tail carboxyl–carboxylate hydrogen‐bond interactions [graph set C(7) in (I) and (II), and C(8) in (III)]. Two‐dimensional sheet structures are formed in all three compounds by the incorporation of the 4‐(phenyldiazenyl)anilinium cations into the substructures, including, in the cases of (I) and (II), infinite H—N—H to carboxylate O—C—O group interactions [graph set C(6)], and in the case of (III), bridging through the water molecule of solvation. The peripheral alternating aromatic ring residues of both cations and anions give only weakly π‐interactive step features which lie between the sheets.     

Hydrogen‐bonded supramolecular networks of N,N′‐bis(4‐pyridylmethyl)oxalamide and 4,4′‐{[oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate

The molecule of N,N′‐bis(4‐pyridylmethyl)oxalamide, C₁₄H₁₄N₄O₂, (I) or 4py‐ox, has an inversion center in the middle of the oxalamide group. Adjacent molecules are then linked through intermolecular N—H...N and C—H...O hydrogen bonds, forming an extended supramolecular network. 4,4′‐{[Oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate, C₁₄H₁₆N₄O₂²⁺·2NO₃⁻, (II), contains a diprotonated 4py‐ox cation and two nitrate counter‐anions. Each nitrate ion is hydrogen bonded to four 4py‐ox cations via intermolecular N—H...O and C—H...O interactions. Adjacent 4py‐ox cations are linked through weak C—H...O hydrogen bonding between an α‐pyridinium C atom and an oxalamide O atom, forming a two‐dimensional extended supramolecular network.