Spectroscopic characterization and molecular structure of 3,14‐dimethyl‐2,6,13,17‐tetraazapentacyclo[16.4.0.12,17.16,13.07,12]tetracosane

Constrained cyclam derivatives have been found to exhibit anti‐HIV effects. The strength of binding to the CXCR4 receptor correlates with anti‐HIV activity. The conformation of the macrocyclic compound is very important for co‐receptor recognition. Therefore, knowledge of the conformation and crystal packing of macrocycles has become important in developing new highly effective anti‐HIV drugs. Structural modifications of N‐functionalized polyaza macrocyclic compounds have been achieved using various methods. A new synthesis affording single crystals of the title tetraazapentacyclo[16.4.0.1^2,17.1^6,13.0^7,12]tetracosane macrocycle, C₂₂H₄₀N₄, is reported. Formaldehyde reacts readily at room temperature with the tetraazatricyclo[16.4.0.0^2,17]docosane precursor to yield a macropolycycle containing two five‐membered rings. Characterization by elemental, spectroscopic and single‐crystal X‐ray diffraction analyses shows that the asymmetric unit contains half of a centrosymmetric molecule. The molecular structure shows a trans conformation for the two methylene bridges owing to molecular symmetry. The crystal structure is stabilized by intramolecular C—H…N hydrogen bonds. NMR and IR spectroscopic properties support the methylene‐bridged macrocyclic structure.     

An unusual conformation of gabapentin (Gpn) in Pyr‐Gpn‐NH‐NH‐Pyr stabilized by weak interactions

The crystal structure of N‐[(1‐{2‐oxo‐2‐[2‐(pyrazin‐2‐ylcarbonyl)hydrazin‐1‐yl]ethyl}cyclohexyl)methyl]pyrazine‐2‐carboxamide monohydrate (Pyr‐Gpn‐NN‐NH‐Pyr·H₂O), C₁₉H₂₃N₇O₃·H₂O, reveals an unusual trans–gauche (tg⁻) conformation for the gabapentin (Gpn) residue around the C^γ—C^β (θ₁) and C^β—C^α (θ₂) bonds. The molecular conformation is stabilized by intramolecular N—H...N hydrogen bonds and weak C—H...O interactions. The packing of the molecules in the crystal lattice shows a network of strong N—H...O and O—H...O hydrogen bonds together with weak C—H...O and π–π inteactions.     

Heteronuclear NMR spectroscopic investigations of hydrogen bonding in 2‐(benzo[d]thiazole‐2′‐yl)‐N‐alkylanilines

The 2‐(benzo[d]thiazole‐2′‐yl)‐N‐alkylanilines have previously revealed the presence of a strong intramolecular hydrogen bond. This in turn gives rise to a more complicated multiplet for the protons attached to the carbon adjacent to the amino group. This intramolecular hydrogen bond was investigated by a deuterium exchange experiment using heteronuclear NMR spectroscopy (¹H, ¹³C, ¹⁵ N and ²H). We observed changes in the multiplet structure and chemical shifts providing further evidence that the deuterium replaces the hydrogen in the intramolecular hydrogen bond. A time course study of the D₂O exchange confirmed the presence of a strong hydrogen bond. The comparison of the structures obtained by X‐ray crystallography showed a very small difference in planarity between the two‐substituted and four‐substituted amino compounds. In both the cases, the phenyl ring is not absolutely coplanar with the thiazole unit. The existence of this intramolecular hydrogen bond in 2‐(benzo[d]thiazole‐2′‐yl)‐N‐alkylanilines was further confirmed by single crystal X‐ray crystallography. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,Spectroscopic Studies,and Crystal Structures of Phenylorganotin Derivatives with [Bis(2,6‐dimethylphenyl)amino]benzoic Acid: Novel Antituberculosis Agents

The novel triphenyl adduct of 2‐[(2,6‐dimethylphenyl)amino]benzoic acid (HDMPA; 1 ), i.e., [SnPh₃(DMPA)] ( 2 ), the dimeric tetraorganostannoxane [Ph₂(DMPA)SnOSn(DMPA)Ph₂]₂ ( 3 ), and the monomeric adduct [SnPh₂(DMPA)₂] ( 4 ), where DMPA is monodeprotonated HDMPA, have been prepared and structurally characterized by means of IR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The structures of 1 and 2 have been determined by X‐ray crystallography. Single‐crystal X‐ray‐diffraction analysis of 1 revealed that there are two molecules in the asymmetric unit, HD1 and HD2 , differing in conformation, both forming centrosymmetric dimers linked by H‐bonds between the carboxylic O‐atoms. X‐Ray analysis of 2 revealed a pentacoordinate structure containing Ph₃Sn coordinated to the carboxylato group. Significant C? H/π interactions and intramolecular H‐bonds stabilize the structures of 1 and 2 , which self‐assembled via C? H/π and π/π‐stacking interactions. The Ph₃Sn adduct 2 was found to be a promising antimycobacterial lead compound, displaying activity against Mycobacterium tuberculosis H37Rv. The cytotoxiciy in the Vero cell line is also reported.     

Synthesis and Structural Characterization of Four Zinc Complexes Containing 3,5‐Dimethylpyrazole and Carboxylate Ligands

Four new zinc(II) complexes Zn₂(μ‐dmpz)₂(Hdmpz)₂(L1)₂ ( 1 ) (Hdmpz = 3,5‐dimethylpyrazole, HL1 = 2‐methyl‐2‐phenoxypropanoic acid), Zn(Hdmpz)₂(L2)₂ ( 2 ) [HL2 = 2‐hydroxy‐5‐(phenyldiazenyl)benzoic acid], Zn₂(μ‐dmpz)₂(Hdmpz)₂(L3)₂ ( 3 ) [HL3 = 3,4‐(methylenedioxy)benzoic acid], and Zn₂(μ‐dmpz)₂(Hdmpz)₂(L4)₂ ( 4 ) [HL4 = 3‐(4‐methoxyphenyl)acrylic acid] were prepared and structurally characterized by different techniques including elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction analysis. The X‐ray studies suggested that all these complexes except compound 2 are centrosymmetric dinuclear complexes with a tetrahedral arrangement around each zinc ion, whereas compound 2 is a mononuclear complex. The pyrazole ligand is coordinated in both terminal as well as a bridging fashion in the dinuclear moiety, whereas the pyrazole ligand in compound 2 is coordinated only in monodentate terminal fashion with its neutral nitrogen group. In all four complexes the carboxylate functions behave as monodentate ligands. All complexes show intramolecular hydrogen bonding of N–H ··· O between N–H of pyrazole and nonbonded oxygen atom of carboxylate. Furthermore, rich intermolecular weak interactions such as classical hydrogen bonds, C–H ··· O, C–H ··· N, C–H ··· π, and CH₃–π interactions exist and complexes 1 – 4 display a set of 3D superamolecular frameworks. In addition, the four compounds are thermally stable below 150 °C.     

Pseudopolyrotaxanes of Cucurbit[6]uril: A Three‐Dimensional Network Self‐assembled by ClO4−(H2O)2 Water Clusters

A pseudorotaxane of cucurbit[6]uril (CB[6]) with guest molecule N,N′‐hexamethylenebis (pyrazinyl perchlorate) (BPHP) was synthesized and characterized by ¹H NMR spectra, IR, single crystal X‐ray diffraction analysis and thermogravimetric analysis. The structure of the pseudorotaxane (CB[6]·BPHP) is stabilized by host‐guest hydrogen bonds. Self‐assembly of the pseudorotaxane produces infinite one‐dimensional and two‐dimensional networks with intermolecular hydrogen bonds. In the molecular packing of the CB[6]·BPHP, ClO₄^?(H₂O)₂ water clusters serve as bridges to associate these pseudorotaxanes and form three‐dimensional networked pseudopolyrotaxane.     

A novel tetraphenylethylene derivative: 4‐methyl‐N‐[3‐(1,2,2‐triphenylethenyl)phenyl]benzenesulfonamide with aggregation‐induced emission

The novel tetraphenylethylene derivative 4‐methyl‐N‐[3‐(1,2,2‐triphenylethenyl)phenyl]benzenesulfonamide (abbreviated as MTBF), C₃₃H₂₇NO₂S, was synthesized successfully and characterized by single‐crystal X‐ray diffraction, high‐resolution mass spectroscopy and ¹H NMR spectroscopy. MTBF crystallizes in the centrosymmetric monoclinic space group P2₁/c. In the crystal structure, the MTBF molecules are connected into a one‐dimensional band and then a two‐dimensional sheet by hydrogen bonds of the N—H…O and C—H…O types. The sheets are further linked to produce a three‐dimensional network via C—H…π interactions. The molecules aggregate via these intermolecular forces, which restrain the intramolecular motions (RIM) and decrease the energy loss in the aggregation state, so as to open the radiative channels, and thus MTBF exhibits excellent fluorescence by aggregation‐induced emission (AIE) enhancement.     

CH–π and CF–π Interactions Lead to Structural Changes of N‐Heterocyclic Carbene Palladium Complexes

The role of CH–π and CF–π interactions in determining the structure of N‐heterocyclic carbene (NHC) palladium complexes were studied using ¹H NMR spectroscopy, X‐ray crystallography, and DFT calculations. The CH–π interactions led to the formation of the cis‐anti isomers in 1‐aryl‐3‐isopropylimidazol‐2‐ylidene‐based [(NHC)₂PdX₂] complexes, while CF–π interactions led to the exclusive formation of the cis‐syn isomer of diiodobis(3‐isopropyl‐1‐pentafluorophenylimidazol‐2‐ylidene) palladium(II).     

Synthesis,characterization and antibacterial activity of 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoic acid and di‐isopropylammonium [3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoato] triphenylstannate(IV). The crystal structure of [HQ][SnPh3(o‐mpspa)]

Reaction of 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoic acid [H₂(o‐mpspa)] with SnPh₃OH in the presence of di‐isopropylamine resulted in the formation of the complex [HQ][SnPh₃(o‐mpspa)] (where HQ = di‐isopropylammonium cation and o‐mpspa = 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoato), which was characterized by mass spectrometry and vibrational spectroscopy, as well as by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The single‐crystal X‐ray structural analysis of the new complex shows a trigonal‐bipyramidal coordination geometry around the Sn atom where o‐mpspa behaves as a bidentate chelating ligand. Dimeric units arise from the existence of N? H…O hydrogen bonds between the NH₂ group of the di‐isopropylammonium cation and the oxygen atoms of the two neighbouring carboxylato groups. The bacteriostatic activity of the complex is also reported. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis,crystal structures and anti‐inflammatory activity of fluorine‐substituted 1,4,5,6‐tetrahydrobenzo[h]quinazolin‐2‐amine derivatives

Two fluorine‐substituted 1,4,5,6‐tetrahydrobenzo[h]quinazolin‐2‐amine (BQA) derivatives, namely 2‐amino‐4‐(2‐fluorophenyl)‐9‐methoxy‐1,4,5,6‐tetrahydrobenzo[h]quinazolin‐3‐ium chloride, ( 8 ), and 2‐amino‐4‐(4‐fluorophenyl)‐9‐methoxy‐1,4,5,6‐tetrahydrobenzo[h]quinazolin‐3‐ium chloride, ( 9 ), both C₁₉H₁₉FN₃O⁺·Cl^?, were generated by Michael addition reactions between guanidine hydrochloride and the α,β‐unsaturated ketones (E)‐2‐(2‐fluorobenzylidene)‐7‐methoxy‐3,4‐dihydronaphthalen‐1(2H)‐one, C₁₈H₁₅FO₂, ( 6 ), and (E)‐2‐(4‐fluorobenzylidene)‐7‐methoxy‐3,4‐dihydronaphthalen‐1(2H)‐one, ( 7 ). Because both sides of α,β‐unsaturated ketones ( 6 ) or ( 7 ) can be attacked by guanidine, we obtained a pair of isomers in ( 8 ) and ( 9 ). Single‐crystal X‐ray diffraction indicates that each isomer has a chiral C atom and both ( 8 ) and ( 9 ) crystallize in the achiral space group P2₁/c. The chloride ion, as a hydrogen‐bond acceptor, plays an important role in the formation of multiple hydrogen bonds. Thus, adjacent molecules are connected through intermolecular hydrogen bonds to generate a banded structure. Furthermore, these bands are linked into an interesting 3D network via hydrogen bonds and π–π interactions. Fortunately, the solubilities of ( 8 ) and ( 9 ) were distinctly improved and can exceed 50 mg ml^?1 in water or PBS buffer system (pH 7.4) at room temperature. In addition, the results of an investigation of anti‐inflammatory activity show that ( 8 ) and ( 9 ), with o‐ and p‐fluoro substituents, respectively, display more potential for inhibitory effects on LPS‐induced NO secretion than starting ketones ( 6 ) and ( 7 ).     

Solid‐state tautomeric structure and invariom refinement of a novel and potent HIV integrase inhibitor

The conformation and tautomeric structure of (Z)‐4‐[5‐(2,6‐difluorobenzyl)‐1‐(2‐fluorobenzyl)‐2‐oxo‐1,2‐dihydropyridin‐3‐yl]‐4‐hydroxy‐2‐oxo‐N‐(2‐oxopyrrolidin‐1‐yl)but‐3‐enamide, C₂₇H₂₂F₃N₃O₅, in the solid state has been resolved by single‐crystal X‐ray crystallography. The electron distribution in the molecule was evaluated by refinements with invarioms, aspherical scattering factors by the method of Dittrich et al. [Acta Cryst. (2005), A 61 , 314–320] that are based on the Hansen–Coppens multipole model [Hansen & Coppens (1978). Acta Cryst. A 34 , 909–921]. The β‐diketo portion of the molecule exists in the enol form. The enol –OH hydrogen forms a strong asymmetric hydrogen bond with the carbonyl O atom on the β‐C atom of the chain. Weak intramolecular hydrogen bonds exist between the weakly acidic α‐CH hydrogen of the keto–enol group and the pyridinone carbonyl O atom, and also between the hydrazine N—H group and the carbonyl group in the β‐position from the hydrazine N—H group. The electrostatic properties of the molecule were derived from the molecular charge density. The molecule is in a lengthened conformation and the rings of the two benzyl groups are nearly orthogonal. Results from a high‐field ¹H and ¹³C NMR correlation spectroscopy study confirm that the same tautomer exists in solution as in the solid state.     

Synthesis,crystal structure and docking studies of tetracyclic 10‐iodo‐1,2‐dihydroisoquinolino[2,1‐b][1,2,4]benzothiadiazine 12,12‐dioxide and its precursors

The title compound, 10‐iodo‐1,2‐dihydroisoquinolino[2,1‐b][1,2,4]benzothiadiazine 12,12‐dioxide, C₁₅H₁₁IN₂O₂S ( 8 ), was synthesized via the metal‐free intramolecular N‐iodosuccinimide (NIS)‐mediated radical oxidative sp³‐C—H aminative cyclization of 2‐(2′‐aminobenzenesulfonyl)‐1,3,4‐trihydroisoquinoline, C₁₅H₁₆N₂O₂S ( 7 ). The amino adduct 7 was prepared via a two‐step reaction, starting from the condensation of 2‐nitrobenzenesulfonyl chloride ( 4 ) with 1,2,3,4‐tetrahydroisoquinoline ( 5 ), to afford 2‐(2′‐nitrobenzenesulfonyl)‐1,3,4‐trihydroisoquinoline, C₁₅H₁₄N₂O₄S ( 6 ), in 82% yield. The catalytic hydrogenation of 6 with hydrogen gas, in the presence of 10% palladium‐on‐charcoal catalyst, furnished 7 . Products 6 – 8 were characterized by their melting points, IR and NMR (¹H and ¹³C) spectroscopy, and single‐crystal X‐ray diffraction. The three compounds crystallized in the monoclinic space group, with 7 exhibiting classical intramolecular hydrogen bonds of 2.16 and 2.26 Å. All three crystal structures exhibit centrosymmetric pairs of intermolecular C—H…π(ring) and/or π–π stacking interactions. The docking studies of molecules 6 , 7 and 8 with deoxyribonucleic acid (PDB id: 1ZEW ) revealed minor‐groove binding behaviours without intercalation, with 7 presenting the most favourable global energy of the three molecules. Nonetheless, molecule 8 interacted strongly with the DNA macromolecule, with an attractive van der Waals energy of ?15.53 kcal mol^?1.     

Structural Studies of Self‐Folding Cavitands

Resorcinarene‐based cavitands 1a – c fold into a deep open‐ended cavity by means of intramolecular hydrogen bonds in both apolar solutions and the solid state. The X‐ray crystal‐structure analysis of cavitand 1a features a seam of secondary amide C=O⋅⋅⋅H−N interactions that bridge adjacent rings and are held in place by intra‐annular hydrogen bonds. This results in a cavity of 9.2×7.0 Å dimensions. The arrangement of the amides in 1a – 1c is cycloenantiomeric, with clock‐ and counterclockwise orientation of the head‐to‐tail amide sequence. Interconversion rates of the two enantiomers are controlled by solvent polarity: the rate is slow on the NMR time‐scale in aromatic solvents and CDCl₃, but fast in (D₆)acetone. The ¹H‐ and ¹³C‐NMR‐spectral analysis is in agreement with the crystallographic data. Chiral cavitand 1b with eight HN−C(O)−C*HMeEt ((+)‐(S)) groups on its upper rim exists as two cyclodiastereoisomers (in a ca. 3 : 1 ratio) in apolar solution. A `library' of 512 diastereoisomeric cavitands 1c is obtained as a mixture by using the corresponding racemic acid chloride.     

Synthesis,structural characterization and luminescence properties of 1‐carboxymethyl‐3‐ethylimidazolium chloride

A microcrystalline carboxyl‐functionalized imidazolium chloride, namely 1‐carboxymethyl‐3‐ethylimidazolium chloride, C₇H₁₁N₂O₂⁺·Cl⁻, has been synthesized and characterized by elemental analysis, attenuated total reflectance Fourier transform IR spectroscopy (ATR‐FT‐IR), single‐crystal X‐ray diffraction, thermal analysis (TGA/DSC), and photoluminescence spectroscopy. In the crystal structure, cations and anions are linked by C—H…Cl and C—H…O hydrogen bonds to create a helix along the [010] direction. Adjacent helical chains are further interconnected through O—H…Cl and C—H…O hydrogen bonds to form a (10) layer. Finally, neighboring layers are joined together via C—H…Cl contacts to generate a three‐dimensional supramolecular architecture. Thermal analyses reveal that the compound melts at 449.7 K and is stable up to 560.0 K under a dynamic air atmosphere. Photoluminescence measurements show that the compound exhibits a blue fluorescence and a green phosphorescence associated with spin‐allowed (¹π←¹π*) and spin‐forbidden (¹π←³π*) transitions, respectively. The average luminescence lifetime was determined to be 1.40 ns for the short‐lived (¹π←¹π*) transition and 105 ms for the long‐lived (¹π←³π*) transition.     

A new antibacterial silver(I) complex incorporating 2,5‐dimethylpyrazine and the anti‐inflammatory diclofenac

Ag^I‐containing coordination complexes have attracted attention because of their photoluminescence properties and antimicrobial activities and, in principle, these properties depend on the nature of the structural topologies. A novel two‐dimensional silver(I) complex with the anti‐inflammatory diclofenac molecule, namely bis{μ‐2‐[2‐(2,6‐dichloroanilino)phenyl]acetato‐κ³O,O′:O}bis(μ‐2,5‐dimethylpyrazine‐κ²N:N′)silver(I), [Ag₂(C₁₄H₁₀Cl₂NO₂)₂(C₆H₈N₂)]_n, (I), has been synthesized and characterized by single‐crystal X‐ray diffraction, revealing that the Ag^I ions are chelated by the carboxylate groups of the anionic 2‐[2‐(2,6‐dichloroanilino)phenyl]acetate (dicl) ligand in a μ₃‐η¹:η² coordination mode. Each dicl ligand links three Ag^I atoms to generate a one‐dimensional infinite chain. Adjacent chains are connected through 2,5‐dimethylpyrazine (dmpyz) ligands to form a two‐dimensional layer structure parallel to the crystallographic bc plane. The layers are further connected by C—H…π interactions to generate a three‐dimensional supramolecular structure. Additionally, the most striking feature is that the structure contains an intramolecular C—H …Ag anagostic interaction. Furthermore, the title complex has been tested for its in vitro antibacterial activity and is determined to be highly effective on the studied microorganisms.     

Interaction between Anions and Cationic Metal Complexes Containing Tridentate Ligands with exo‐CH Groups: Complex Stability and Hydrogen Bonding

[Re(CO)₃([9]aneS₃)][BAr′₄] ( 1 ), prepared by reaction of ReBr(CO)₅, 1,4,7‐trithiacyclononane ([9]aneS₃) and NaBAr′₄, forms stable, soluble supramolecular adducts with chloride ( 2 ), bromide, methanosulfonate ( 3 ) and fluoride ( 4 ) anions. These new species were characterized by IR, NMR spectroscopy and, for 2 and 3 , also by X‐ray diffraction. The results of the solid state structure determinations indicate the formation of CH???X hydrogen bonds between the anion (X) and the exo‐C?H groups of the [9]aneS₃ ligand, in accord with the relatively large shifts found by ¹H NMR spectroscopy in dichloromethane solution for those hydrogens. The stability of the chloride adduct contrasts with the lability of the [9]aneS₃ ligand in allyldicarbonyl molybdenum complexes recently studied by us. With fluoride, in dichloromethane solution, a second, minor neutral dimeric species 5 is formed in addition to 4 . In 4 , the deprotonation of a C?H group of the [9]aneS₃ ligand, accompanied by C?S bond cleavage and dimerization, afforded 5 , featuring bridging thiolates. Compounds [Mo(η³‐methallyl)(CO)₂(TpyN)][BAr′₄] ( 6 ) and [Mo(η³‐methallyl)(CO)₂(TpyCH)][BAr′₄] ( 7 ) were synthesized by the reactions of [MoCl(η³‐methallyl)(CO)₂(NCMe)₂], NaBAr′₄ and tris(2‐pyridyl)amine (TpyN) or tris(2‐pyridyl)methane (TpyCH) respectively, and characterized by IR and ¹H and ¹³C NMR spectroscopy in solution, and by X‐ray diffraction in the solid state. Compound 6 undergoes facile substitution of one of the 2‐pyridyl groups by chloride, bromide, and methanosulfonate anions. Stable supramolecular adducts were formed between 7 and chloride, bromide, iodide, nitrate, and perrhenate anions. The solid state structures of these adducts ( 12 – 16 ) were determined by X‐ray diffraction. Binding constants in dichloromethane were calculated from ¹H NMR titration data for all the new supramolecular adducts. The signal of the bridgehead C?H group is the one that undergoes a more pronounced downfield shift when tetrabutylammonium chloride was added to 7 , whereas smaller shifts were found for the 2‐pyridyl C(3)?H groups. In agreement, both types of C?H groups form hydrogen bonds to the anions in the solid state structures.     

Supramolecular hydrogen‐bonding patterns in two cocrystals of the N(7)–H tautomeric form of N6‐benzoyladenine: N6‐benzoyladenine–3‐hydroxypyridinium‐2‐carboxylate (1/1) and N6‐benzoyladenine–DL‐tartaric acid (1/1)

Two novel cocrystals of the N(7)—H tautomeric form of N⁶‐benzoyladenine (BA), namely N⁶‐benzoyladenine–3‐hydroxypyridinium‐2‐carboxylate (3HPA) (1/1), C₁₂H₉N₅O·C₆H₅NO₃, (I), and N⁶‐benzoyladenine–DL‐tartaric acid (TA) (1/1), C₁₂H₉N₅O·C₄H₆O₆, (II), are reported. In both cocrystals, the N⁶‐benzoyladenine molecule exists as the N(7)—H tautomer, and this tautomeric form is stabilized by intramolecular N—H...O hydrogen bonding between the benzoyl C=O group and the N(7)—H hydrogen on the Hoogsteen site of the purine ring, forming an S(7) motif. The dihedral angle between the adenine and phenyl planes is 0.94 (8)° in (I) and 9.77 (8)° in (II). In (I), the Watson–Crick face of BA (N6—H and N1; purine numbering) interacts with the carboxylate and phenol groups of 3HPA through N—H...O and O—H...N hydrogen bonds, generating a ring‐motif heterosynthon [graph set R₂²(6)]. However, in (II), the Hoogsteen face of BA (benzoyl O atom and N7; purine numbering) interacts with TA (hydroxy and carbonyl O atoms) through N—H...O and O—H...O hydrogen bonds, generating a different heterosynthon [graph set R₂²(4)]. Both crystal structures are further stabilized by π–π stacking interactions.     

Three closely related dibenzazepine carboxylic acids: hydrogen‐bonded aggregation in one,two and three dimensions

In the structure of (6R*,11R*)‐5‐acetyl‐11‐ethyl‐6,11‐dihydro‐5H‐dibenzo[b,e]azepine‐6‐carboxylic acid, C₁₉H₁₉NO₃, (I), the molecules are linked into sheets by a combination of O—H...O and C—H...O hydrogen bonds; in the structure of the monomethyl analogue (6RS,11SR)‐5‐acetyl‐11‐ethyl‐2‐methyl‐6,11‐dihydro‐5H‐dibenzo[b,e]azepine‐6‐carboxylic acid, C₂₀H₂₁NO₃, (II), the molecules are linked into simple C(7) chains by O—H...O hydrogen bonds; and in the structure of the dimethyl analogue (6RS,11SR)‐5‐acetyl‐11‐ethyl‐1,3‐dimethyl‐6,11‐dihydro‐5H‐dibenzo[b,e]azepine‐6‐carboxylic acid, C₂₁H₂₃NO₃, (III), a combination of O—H...O, C—H...O and C—H...π(arene) hydrogen bonds links the molecules into a three‐dimensional framework structure. None of these structures exhibits the R₂²(8) dimer motif characteristic of simple carboxylic acids.     

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).     

Two Fe3(μ3‐S)2(CO)8 clusters with terminal N‐heterocyclic carbenes

The title compounds with terminal N‐heterocyclic carbenes, namely octacarbonyl(imidazolidinylidene‐κC²)di‐μ₃‐sulfido‐triiron(II)(2 Fe—Fe), [Fe₃(C₃H₆N₂)(μ₃‐S)₂(CO)₈], (I), and octacarbonyl(1‐methylimidazo[1,5‐a]pyridin‐3‐ylidene‐κC³)di‐μ₃‐sulfido‐triiron(II)(2 Fe—Fe), [Fe₃(C₈H₈N₂)(μ₃‐S)₂(CO)₈], (II), have been synthesized. Each compound contains two Fe—Fe bonds and two S atoms above and below a triiron triangle. One of the eight carbonyl ligands deviates significantly from linearity. In (I), dimers generated by an N—H...S hydrogen bond are linked into [001] double chains by a second N—H...S hydrogen bond. These chains are packed by a C—H...O hydrogen bond to yield [101] sheets. In (II), dimers generated by an N—H...S hydrogen bond are linked by C—H...O hydrogen bonds to form [111] double chains.