A structural systematic study of four isomers of difluoro‐N‐(3‐pyridyl)benzamide

The four isomers 2,4‐, (I), 2,5‐, (II), 3,4‐, (III), and 3,5‐difluoro‐N‐(3‐pyridyl)benzamide, (IV), all with formula C₁₂H₈F₂N₂O, display molecular similarity, with interplanar angles between the C₆/C₅N rings ranging from 2.94 (11)° in (IV) to 4.48 (18)° in (I), although the amide group is twisted from either plane by 18.0 (2)–27.3 (3)°. Compounds (I) and (II) are isostructural but are not isomorphous. Intermolecular N—H...O=C interactions form one‐dimensional C(4) chains along [010]. The only other significant interaction is C—H...F. The pyridyl (py) N atom does not participate in hydrogen bonding; the closest H...N_py contact is 2.71 Å in (I) and 2.69 Å in (II). Packing of pairs of one‐dimensional chains in a herring‐bone fashion occurs viaπ‐stacking interactions. Compounds (III) and (IV) are essentially isomorphous (their a and b unit‐cell lengths differ by 9%, due mainly to 3,4‐F₂ and 3,5‐F₂ substitution patterns in the arene ring) and are quasi‐isostructural. In (III), benzene rotational disorder is present, with the meta F atom occupying both 3‐ and 5‐F positions with site occupancies of 0.809 (4) and 0.191 (4), respectively. The N—H...N_py intermolecular interactions dominate as C(5) chains in tandem with C—H...N_py interactions. C—H...O=C interactions form R₂²(8) rings about inversion centres, and there are π–π stacks about inversion centres, all combining to form a three‐dimensional network. By contrast, (IV) has no strong hydrogen bonds; the N—H...N_py interaction is 0.3 Å longer than in (III). The carbonyl O atom participates only in weak interactions and is surrounded in a square‐pyramidal contact geometry with two intramolecular and three intermolecular C—H...O=C interactions. Compounds (III) and (IV) are interesting examples of two isomers with similar unit‐cell parameters and gross packing but which display quite different intermolecular interactions at the primary level due to subtle packing differences at the atom/group/ring level arising from differences in the peripheral ring‐substitution patterns.     

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.     

N‐(4‐Methoxy­benzyl­idene)‐N′‐(2‐pyridyl)­hydrazine

Molecules of the title compound (alternative name p‐methoxybenzaldehyde 2‐pyridyl­hydrazone), C₁₃H₁₃N₃O, adopt an E configuration about the azomethine C=N double bond. Molecules are almost planar, the dihedral angle between the pyridine and methoxy­phenyl rings being only 6.19 (12)°. Pairwise N—H⃛N hydrogen bonds [R(8) in graph‐set notation] link centrosymmetrically related mol­ecules into discrete pairs.     

Phenyl‐(2‐pyridyl)‐(3‐pyridyl)‐(4‐pyridyl)methane: Synthesis,Chiroptical Properties,and Theoretical Calculation of Its Absolute Configuration

The title compound, a prototypical chiral molecule based on a tetraarylmethane framework, has been synthesized in five steps from (2‐pyridyl)‐(3‐pyridyl)ketone. X‐ray crystallographic analysis revealed the tetraarylmethane framework of the molecule but did not determine the positions of the nitrogen atoms because the crystal is a racemic compound and the aryl groups are disordered in the crystal. The optical resolution of the title compound was achieved by chiral HPLC with a Chiralcel OD column. The CD spectra of the two fractions in acetonitrile exhibited opposite signs as expected for a pair of enantiomers. Their CD spectra are changed in 2 M HCl due to protonation. The calculated CD curve for the target molecule based on time‐dependent density functional theory (TDDFT) reproduces the experimental result very well, thus suggesting that the first eluted fraction is the R isomer in terms of absolute configuration.     

N‐(4‐Methyl­phenyl)‐N‐(5‐nitro­furfuryl)‐N‐prop‐2‐ynyl­amine

The title compound, C₁₅H₁₄N₂O₃, is the first example of a structurally determined tertiary amine with both N‐5‐nitro­furfuryl and N‐prop‐2‐ynyl moieties. The mol­ecule is not planar, i.e. the furan ring is inclined at an angle of 84.35 (4)° to the phenyl ring. The crystal structure is dominated by van der Waals forces. The terminal alkynyl group as the strongest C—H hydrogen‐bond donor is not involved in hydrogen‐bond formation.     

(E)‐N′‐(4‐Chlorobenzylidene)‐, (E)‐N′‐(4‐bromobenzylidene)‐ and (E)‐N′‐[4‐(diethylamino)benzylidene]‐ derivatives of 4‐hydroxybenzohydrazide

The 4‐chloro‐ [C₁₄H₁₁ClN₂O₂, (I)], 4‐bromo‐ [C₁₄H₁₀BrN₂O₂, (II)] and 4‐diethylamino‐ [C₁₈H₂₁N₃O₂, (III)] derivatives of benzylidene‐4‐hydroxybenzohydrazide, all crystallize in the same space group (P2₁/c), (I) and (II) also being isomorphous. In all three compounds, the conformation about the C=N bond is E. The molecules of (I) and (II) are relatively planar, with dihedral angles between the two benzene rings of 5.75 (12) and 9.81 (17)°, respectively. In (III), however, the same angle is 77.27 (9)°. In the crystal structures of (I) and (II), two‐dimensional slab‐like networks extending in the a and c directions are formed via N—H...O and O—H...O hydrogen bonds. The molecules stack head‐to‐tail viaπ–π interactions involving the aromatic rings [centroid–centroid distance = 3.7622 (14) Å in (I) and 3.8021 (19) Å in (II)]. In (III), undulating two‐dimensional networks extending in the b and c directions are formed via N—H...O and O—H...O hydrogen bonds. The molecules stack head‐to‐head viaπ–π interactions involving inversion‐related benzene rings [centroid–centroid distances = 3.6977 (12) and 3.8368 (11) Å].     

Assembling an isomer grid: the isomorphous 4‐, 3‐ and 2‐fluoro‐N′‐(4‐pyridyl)benzamides

The three title isomers, 4‐, (I), 3‐, (II), and 2‐fluoro‐N′‐(4‐pyridyl)benzamide, (III), all C₁₂H₉FN₂O, crystallize in the P2₁/c space group (No. 14) with similar unit‐cell parameters and are isomorphous and isostructural at the primary hydrogen‐bonding level. An intramolecular C—H...O=C interaction is present in all three isomers [C...O = 2.8681 (17)–2.884 (2) Å and C—H...O117–118°], with an additional N—H...F [N...F = 2.7544 (15) Å] interaction in (III). Intermolecular amide–pyridine N—H...N hydrogen bonds link molecules into one‐dimensional zigzag chains [graph set C(6)] along the [010] direction as the primary hydrogen bond [N...N = 3.022 (2), 3.049 (2) and 3.0213 (17) Å]. These are augmented in (I) by C—H...π(arene) and cyclic C—F...π(arene) contacts about inversion centres, in (II) by C—F...F—C interactions [C...F = 3.037 (2) Å] and weaker C—H...π(arene)/C—H...F contacts, and in (III) by C—H...π(arene) and C=O...O=C interactions, linking the alternating chains into two‐dimensional sheets. Typical amide N—H...O=C hydrogen bonds [as C(4) chains] are not present [N...O = 3.438 (2) Å in (I), 3.562 (2) Å in (II) and 3.7854 (16) Å in (III)]; the C=O group is effectively shielded and only participates in weaker interactions/contacts. This series is unusual as the three isomers are isomorphous (having similar unit‐cell parameters, packing and alignment), but they differ in their interactions and contacts at the secondary level.     

Interaction of Bovine Serum Albumin with N‐(4‐Ethoxyphenyl)‐N′‐(4‐Antipyrinyl)Thiourea (EPAT) Using Spectroscopies

The interaction between N‐(4‐ethoxyphenyl)‐N′‐(4‐antipyrinyl)thiourea (EPAT) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy in combination with UV absorption spectroscopy. The intrinsic fluorescence of bovine serum albumin was quenched by EPAT through a static quenching procedure. The binding constants of EPAT with BSA were estimated according to the fluorescence quenching results at different temperatures. The thermodynamic parameters: enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?10.69 kJ/mol and 42.64 J·mol^?1·K^?1 according to thermodynamic equations, respectively, and indicating that the binding force was suggested to be mainly a hydrophobic force. The effect of common ions on the binding constant was also investigated. A new fluorescence spectroscopy assay of the proteins was presented in this paper. The determination results of the proteins in bovine serum by means of this method were very close to those obtained using Coomassie Brilliant Blue G‐250 colorimetry.     

N‐(3‐Phenoxy‐4‐pyridinio)methanesulfonamidate

The title compound, C₁₂H₁₂N₂O₃S, is a strict pyridine analogue of nimesulide, a selective inhibitor of cyclooxygen­ase‐2. The structure is characterized by a pyridinium ring with a deprotonated sulfon­amide group. An intermolecular charge‐assisted hydrogen bond between these two groups is observed within the crystal packing, linking the mol­ecules into an infinite chain running along the b‐axis direction.     

N‐(Ferrocenecarbonyl)‐N′‐(quinolin‐8‐yl)thio­urea

In the title compound, [Fe(C₅H₅)(C₁₆H₁₂N₃OS)], the 8‐am­inoquinoline and acyl­thio­urea moieties are almost planar. There are two perpendicular arrangements of the mol­ecules in the crystal with slightly different conformations. The two cyclo­penta­dienyl rings in each mol­ecule are parallel and eclipsed.     

Two hydration products of 3,4,5,6‐tetrachloro‐N‐(methyl‐2‐pyridyl)phthalmic acids

In 2‐amino‐6‐methylpyridin‐1‐ium 2‐carboxy‐3,4,5,6‐tetrachlorobenzoate, C₆H₉N₂⁺·C₈HCl₄O₄⁻, there are two perpendicular chains of hydrogen‐bonded ions, one arising from the interaction between 2‐carboxy‐3,4,5,6‐tetrachlorobenzoate ions and the other from the interaction between the 2‐amino‐6‐methylpyridin‐1‐ium and 2‐carboxy‐3,4,5,6‐tetrachlorobenzoate ions. These chains combine to form a two‐dimensional network of hydrogen‐bonded ions. Cocrystals of bis(2‐amino‐3‐methylpyridin‐1‐ium) 3,4,5,6‐tetrachlorophthalate–3,4,5,6‐tetrachlorophthalic acid (1/1), 2C₆H₉N₂⁺·C₈Cl₄O₄²⁻·C₈H₂Cl₄O₄, form finite aggregates of hydrogen‐bonded ions. π–π interactions are observed between 2‐amino‐3‐methylpyridin‐1‐ium cations. Both structures exhibit the characteristic R₂²(8) motif as a result of the hydrogen bonding between the 2‐aminopyridinium and carboxylate units.     

N‐(2‐Bromoethyl)‐4‐piperidino‐1,8‐naphthalimide and N‐(3‐bromopropyl)‐4‐piperidino‐1,8‐naphthalimide

N‐(2‐Bromoethyl)‐4‐piperidino‐1,8‐naphthalimide, C₁₉H₁₉BrN₂O₂, (I), and N‐(3‐bromopropyl)‐4‐piperidino‐1,8‐naphthalimide, C₂₀H₂₁BrN₂O₂, (II), are an homologous pair of 1,8‐naphthalimide derivatives. The naphthalimide units are planar and each piperidine substituent adopts a chair conformation. This study emphasizes the importance of π‐stacking interactions, often augmented by other contacts, in determining the crystal structures of 1,8‐naphthalimide derivatives.     

N‐(4‐Nitro­benzyl­idene)‐N′‐phenyl­hydrazine

Molecules of the title compound (alternative name: p‐nitro­benz­aldehyde phenyl­hydrazone), C₁₃H₁₁N₃O₂, adopt an E configuration about the azomethine C=N double bond. Molecules are approximately planar and the dihedral angle between the planes of the phenyl rings is 11.62 (9)°. Hydro­gen bonding links mol­ecules related by 4₂ screw axes to form helices with a pitch of 7.7186 (8) Å.     

N‐Cyclo­hexyl‐2‐[5‐(4‐pyridyl)‐4‐(p‐tolyl)‐4H‐1,2,4‐triazol‐3‐yl­sulfanyl]­acetamide dihydrate

In the title compound, C₂₂H₂₅N₅OS·2H₂O, the mol­ecules are stacked in columns running along the b axis. In this arrangemant, the mol­ecules are linked to each other by a combination of one two‐centre N—H⋯O hydrogen bond and four two‐centre O—H⋯O hydrogen bonds containing two types of ring motif, viz.R₄⁴(10) and R₃³(11). In the crystal structure, centrosymmetric π–π inter­actions between the triazole rings, with a distance of 3.691 (2) Å between the ring centroids, also affect the packing of the mol­ecules.     

N‐(4‐Cyano­phenyl)‐α‐(4‐methoxy­phenyl)­nitro­ne

In the crystal structure of the title compound, 4‐cyano‐N‐(4‐methoxy­benzyl­idene)­phenyl­amine N‐oxide, C₁₅H₁₂N₂O₂, the 4‐methoxy­phenyl is approximately coplanar with the nitrone moiety but significantly rotated with respect to the 4‐cyano­phenyl moiety. The extent of this rotation is significantly different for the two crystallographically independent mol­ecules of the asymmetric unit [dihedral angles of 19.4 (1) and 26.5 (1)°]. The geometry about the C=N bond is Z. The two mol­ecules are related to one another by a pseudo inversion centre.     

Reactions of 1‐(3‐aryl‐3‐oxopropenyl)azulenes and 1‐cinnamoylazulenes with malononitrile: Synthesis of 1‐(2‐aryl‐4‐pyridyl)azulenes and 1‐(4‐aryl‐2‐pyridyl)azulenes

The reactions of 1‐formyl‐3‐methoxycarbonylazulene ( 1 ) with acetophenones 3a‐e gave 1‐(3‐aryl‐3‐oxopropenyl)‐3‐methoxycarbonylazulenes 4a‐e which reacted with malononitrile in the presence of sodium methoxide to afford 1‐(2‐aryl‐4‐pyridyl)‐3‐methoxycarbonylazulenes 9a‐d , except for 4′‐nitro‐substituted compounds. Heating of the compounds 9a‐d in 100% phosphoric acid yielded 1‐(2‐aryl‐4‐pyridyl)azulenes 10a‐d . In a similar manner, 1‐(4‐aryl‐2‐pyridyl)azulenes 12a‐1 and 1‐[4‐(2‐furyl)‐ and 4‐(2‐thienyl)‐2‐pyridyl)]azulenes 14a,b were obtained.     

4‐[2‐(4‐Methoxyphenyl)ethenyl]‐N‐methylpyridinium tetraphenylborate

In the cation of the title compound, C₁₅H₁₆NO⁺·C₂₄H₂₀B^?, the pyridyl ring makes a dihedral angle of 14.03° with the phenyl ring. The anion has a slightly distorted tetrahedral geometry and forms honeycomb‐like sheets which extend along the b axis, forming channels containing the cations. A comparison of packing energies reveals a difference between the title compound and a similar material which has non‐linear optical properties.     

Hexanuclear Wheel‐Shaped Lithium N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidinate

Lithiation of N‐(2,6‐diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidine ( 1 ) with LiN(SiMe₃)₂ in a solvent mixture of toluene and TMEDA yields hexameric lithium N‐(2,6‐diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidinate ( 2 ), which can be purified by recrystallization from a solvent mixture of toluene and THF. The three‐coordinate lithium ions have T‐shaped coordination spheres. The negative charge is delocalized within the 1,3‐diazaallylic system, which adopts a (syn‐Z)‐arrangement.     

1‐(1H‐Indol‐3‐ylcarbonyl)‐N‐(4‐methoxy­benzyl)formamide

In the title compound, C₁₈H₁₆N₂O₃, the indole ring is planar and the two adjacent carbonyl groups are mutually trans oriented with a torsion angle of 144.8 (3)°. The single C—C bond linking the two carbonyl functionalities is 1.539 (4) Å. Mol­ecules are linked into a two‐dimensional network by inter­molecular N—H⋯O hydrogen bonds.