Assembly,Thermodynamics, and Structure of a Two‐Wheeled Composite of a Dumbbell‐Shaped Molecule and Cylindrical Molecules with Different Edges

A carbonaceous dumbbell was able to spontaneously glue two tubular receptors to form a unique two‐wheeled composite through van der Waals interactions, thus forcing the wheel components into contact with each other at the edges. In the present study, two tubular receptors with enantiomeric carbon networks were assembled on the dumbbell joint, and the handedness of the receptors was discriminated, thus leading to the self‐sorting of homomeric receptors from a mixture of enantiomeric tubes. The crystal structures of the composites revealed the structural origins of the molecular recognition driven by van der Waals forces as well as the presence of a columnar array of C₁₂₀ molecules in a 1:1 composite.     

Self‐Sorting of Two Hydrocarbon Receptors with One Carbonaceous Ligand

Non‐directional van der Waals forces in biological and synthetic supramolecular systems play important roles in molecular assembly, particularly in determining the distances of the interacting species. The van der Waals forces are normally used in combination with other directional forces and are considered to play a secondary role in achieving specificity and fidelity in molecular recognition. Using an ideal supramolecular system consisting solely of hydrogen and carbon atoms, we found that the van der Waals interactions enable the high‐fidelity sorting of two homomeric receptors during ligand‐induced assembly. The self‐sorting occurred in a narcissistic manner by repulsion of a competing diastereoisomeric receptor from the assembly. The structure–sorting relationship study with enantiomers further revealed the dominant role of the van der Waals forces in shape recognition for high‐fidelity self‐sorting.     

Relative influence of noncovalent interactions on the melting points of a homologous series of 1,2‐dibromo‐4,5‐dialkoxybenzenes

Crystal structures are presented for two members of the homologous series of 1,2‐dibromo‐4,5‐dialkoxybenzenes, viz. those with decyloxy and hexadecyloxy substituents, namely 1,2‐dibromo‐4,5‐bis(decyloxy)benzene, C₂₆H₄₄Br₂O₂, (II), and 1,2‐dibromo‐4,5‐bis(hexadecyloxy)benzene, C₃₈H₆₈Br₂O₂, (III). The relative influences which halogen bonding, π–π stacking and van der Waals interactions have on these structures are analysed and the results compared with those already found for the lightest homologue, 1,2‐dibromo‐4,5‐dimethoxybenzene, (I) [Cukiernik, Zelcer, Garland & Baggio (2008). Acta Cryst. C 64 , o604–o608]. The results confirm that the prevalent interactions stabilizing the structures of (II) and (III) are van der Waals contacts between the aliphatic chains. In the case of (II), weak halogen C—Br...(Br—C)′ interactions are also present and contribute to the stability of the structure. In the case of (III), van der Waals interactions between the aliphatic chains are almost exclusive, weaker C—Br...π interactions being the only additional interactions detected. The results are in line with commonly accepted models concerning trends in crystal stability along a homologous series (as measured by their melting points), but the earlier report for n = 1, and the present report for n = 10 and 16, are among the few providing single‐crystal information validating the hypothesis.     

1,7,8‐Tri‐O‐acetyl‐6‐O‐benzoyl­castanospermine

The title compound (alternatively 1,7,8‐tri­acetoxy­per­hydro­indolizin‐6‐yl benzoate), C₂₁H₂₅NO₈, was obtained during studies of castanospermine derivatives. The crystal structure consists of independent mol­ecules with only van der Waals contacts. The fused six‐ and five‐membered rings adopt chair and twist conformations, respectively.     

α‐Haloketal (1′R,4S,5S)‐dimethyl 2‐(1′‐bromoethyl)‐2‐(3,4‐dimethoxyphenyl)‐1,3‐dioxolane‐4,5‐dicarboxylate

The crystal structure and absolute configuration of the title compound, C₁₇H₂₁BrO₈, have been determined by X‐ray analysis. They confirmed the 1′R absolute configuration at the 1′‐bromoethyl moiety which has been assigned previously on the basis of chemical and spectroscopic data. Cohesion of the crystal can be attributed to weak intermolecular C—H?O and van der Waals interactions.     

Viox,a COX‐II inhibitor

Viox {2,5‐di­hydro‐4‐[4‐(methyl­sulfonyl)­phenyl]‐3‐phenyl‐2‐furan­one, C₁₇H₁₄O₄S, (I)} is one of the selective COX‐II inhibitors with anti‐arthritic activity. The absolute structure of viox has been determined on the basis of anomalous scattering effects. Molecules are held together in the crystal structure only by normal van der Waals interactions.     

Micro‐ and Nanometer‐Scale Porous,Fibrous, and Sheet Architectures Constructed by Supramolecular Assemblies of Dipyrrolyldiketones

X‐ray analysis of some 1,3‐dipyrrolyl‐1,3‐propanediones synthesized from pyrroles and malonyl chloride derivatives revealed 1D supramolecular networks formed by N? H???O?C interactions in the solid state. Micro‐ and nanometer‐scale morphologies of porous, fibrous, and sheet structures were fabricated by hydrogen‐bonding interactions and determined by fine‐tuning the substituents and the solvents used. Of the unique polymorphs, ordered 2D lamellar sheet structures of the derivatives with long alkyl chains (C₁₆H₃₃, C₁₄H₂₉, and so on) were constructed by van der Waals hydrophobic effects between aliphatic chains as well as hydrogen bonding.     

p‐Quaterphenylene as an Aggregation‐Induced Emission Fluorogen in Supramolecular Organogels and Fluorescent Sensors

Two dumbbell‐shaped organogelators with a p ‐quaterphenylene core were synthesized, and their self‐assembly properties were investigated. These low‐molecular‐weight gelators could form self‐supporting gels in many apolar organic solvents with an H‐type aggregation form through a synergic effect of π–π stacking, intermolecular translation‐related hydrogen bonding, and van der Waals forces. In comparison to the p ‐terphenylene‐cored gelator, the extended π‐conjugated segment improved the gelation efficiency significantly with enhanced gelation rate. Additionally, these p ‐quaterphenylene‐centered gelators exhibited strong fluorescence emission induced by aggregation, which not only provided an in situ method to optically monitor the gelation process, but also endowed these self‐assemblies with substantial applications in sensing explosives.     

Large and Fast Single‐Crystal Resistive Humidity Sensitivity of Metal Pnictide Halides Containing van der Waals Host–Guest Interactions

Two new metal pnictide halides, (Hg_9.75As_5.5)(GaCl₄)₃ and (Hg₁₃Sb₈)(ZnBr₄)₄, have been prepared by solid‐state reactions. Their structures feature 3D cationic host frameworks built of mercury pnictide polyhedra and form 1D tunnels filled with discrete guest halide polyanions; the guests and hosts are assembled by van der Waals interactions. Both complexes exhibit good single‐crystal humidity sensitivity, with a humidity sensitivity factor as big as three orders of magnitude, a quick resistance response, fast recovery, and good reproducibility. This study provide a new way to design promising resistive humidity detectors by introducing van der Waals host–guest interactions into their structures.     

Halogen‐bonded adduct of 1,2‐dibromo‐1,1,2,2‐tetrafluoroethane and 1,4‐diazabicyclo[2.2.2]octane

Halogen bonding is an intermolecular interaction capable of being used to direct extended structures. Typical halogen‐bonding systems involve a noncovalent interaction between a Lewis base, such as an amine, as an acceptor and a halogen atom of a halofluorocarbon as a donor. Vapour‐phase diffusion of 1,4‐diazabicyclo[2.2.2]octane (DABCO) with 1,2‐dibromotetrafluoroethane results in crystals of the 1:1 adduct, C₂Br₂F₄·C₆H₁₂N₂, which crystallizes as an infinite one‐dimensional polymeric structure linked by intermolecular N...Br halogen bonds [2.829 (3) Å], which are 0.57 Å shorter than the sum of the van der Waals radii.     

cis‐[(4R,5R)‐4,5‐Bis­(amino­methyl)‐2,2‐di­methyl‐1,3‐dioxolane‐N,N′](malonato‐O,O′)­platinum(II), an anticancer agent

In the title compound, [Pt(C₃H₂O₄)(C₇H₁₆N₂O₂)], the Pt atom is coordinated to two O and two N atoms in a square‐planar arrangement. The two independent mol­ecules, which have very similar structures, are approximately related by pseudo‐twofold screw‐axis symmetry. The six‐membered chelate ring in the leaving ligand assumes a conformation intermediate between the half‐chair and boat forms. The seven‐membered ring in the carrier ligand assumes a twist‐chair conformation and the oxolane ring assumes an envelope conformation. The crystal packing consists of extensive hydrogen‐bonding networks which form two‐dimensional molecular layers, and there are weak van der Waals interactions between these layers.     

Oleana‐12(13),15(16)‐diene‐3α,28‐diyl di­acetate

The title compound, C₃₄H₅₂O₄, consists of five six‐membered rings. Barring the two rings, with double bonds, all other rings are in chair conformations. Mean‐plane and ring‐puckering calculations indicate these two rings to be in distorted‐chair conformations, with distortion towards the boat conformation. There are no strong hydrogen bonds and the structure is stabilized by van der Waals interactions only. The structure is compared with those reported for other triterpenes.     

1,1‐Di(9‐fluorenyl)­ethanol,a ­by‐­product from the acetyl­ation of 9‐fluorenyl­lithium

Treatment of 9‐fluorenyl­lithium with acetyl chloride produces 9‐acetyl­fluorene, (I), and several by‐products. Among them is a compound unequivocally identified for the first time as the addition product of (I) with 9‐fluorenyl­lithium, 1,1‐di(9‐fluorenyl)­ethanol, C₂₈H₂₂O, (II). The two fluorene‐ring planes of (II) are essentially perpendicular [89.90 (9)°]. A number of intermolecular non‐bonding distances are well within or close to the sum of their respective van der Waals radii and may be responsible for the rarely observed large bowing of one of the fluorene rings. This bowing apparently arises from two mol­ecules impinging on the convex face of the bowed ring, augmented by hydrogen bonding between the peripheral π electrons of the concave face and the hydroxyl H atom of another mol­ecule adjacent to that face.     

Van der Waals Emulsions: Emulsions Stabilized by Surface‐Inactive,Hydrophilic Particles via van der Waals Attraction

Surface‐inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil‐in‐water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil–water interfaces when repulsive forces between particles and oil droplets are suppressed. The emulsifying efficiency of the highly hydrophilic particles is determined by van der Waals attraction between particle monolayer shells and oil droplets enclosed therein and is inversely proportional to the particle size, while their stabilizing efficiency is determined by van der Waals attraction between single particles and oil droplets, which is proportional to the particle size. This differentiation in mechanism between emulsification and stabilization will significantly advance our knowledge of emulsions, thus enabling better control and design of emulsion‐based technologies in practice.     

Van der Waals Emulsions: Emulsions Stabilized by Surface‐Inactive,Hydrophilic Particles via van der Waals Attraction

Surface‐inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil‐in‐water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil–water interfaces when repulsive forces between particles and oil droplets are suppressed. The emulsifying efficiency of the highly hydrophilic particles is determined by van der Waals attraction between particle monolayer shells and oil droplets enclosed therein and is inversely proportional to the particle size, while their stabilizing efficiency is determined by van der Waals attraction between single particles and oil droplets, which is proportional to the particle size. This differentiation in mechanism between emulsification and stabilization will significantly advance our knowledge of emulsions, thus enabling better control and design of emulsion‐based technologies in practice.     

The molecular conformation of pentan‐3‐one studied in cholic acid pentan‐3‐one solvate

The crystal structure of cholic acid–pentan‐3‐one (1/1), C₅H₁₀O·C₂₄H₄₀O₅, has been determined in order to deduce the molecular conformation of the small volatile ketone. Data were collected at 100 K to a resolution of (sin θ)/λ = 0.91 Å⁻¹. The structure contains a hydrogen‐bonded cholic acid host network, forming only van der Waals interactions with the guest pentan‐3‐one molecules. The ketone molecules are disordered on general positions, with two clearly identifiable conformations. The majority conformer exhibits approximate C₂ symmetry and is similar to that recently observed by microwave spectroscopy in the gas phase.     

7‐Hydroxy‐5‐methoxy‐6,8‐dimethylflavanone: a natural flavonoid

The title flavonoid [systematic name: (2S)‐7‐hydroxy‐5‐methoxy‐6,8‐dimethyl‐2‐phenyl‐3,4‐dihydrochromen‐4(2H)‐one], C₁₈H₁₈O₄, displays statistical conformational disorder, with three conformations of the molecule involving three orientations of the phenyl ring and two orientations of the fused heterocyclic ring. The conformational disorder is correlated with the isomerization equilibrium between the flavanone and chalcone forms. The conformational behaviour has a potential impact on the biological activity of this class of compounds. Moreover, π stacking interactions at van der Waals distances are present between the aromatic rings of chroman‐4‐one groups of symmetry‐related molecules. Apart from these π–π interactions, molecules are linked by strong O—H...O hydrogen bonds between hydroxy and carbonyl groups.     

Dichloro[N,N‐dimethyl‐1‐(1‐methyl‐1H‐tetrazol‐5‐yl‐κN4)methanamine‐κN]copper(II)

The title compound, [CuCl₂(C₅H₁₁N₅)], is the first structurally characterized molecular chelate complex involving an α‐­amino­alkyl­tetrazole. There are two complex mol­ecules in the asymmetric unit. The ligand mol­ecules are bidentate. Both Cu atoms reveal rather distorted square‐planar coordinations. The complex mol­ecules are linked together by van der Waals interactions only.     

Size‐ and Orientation‐Selective Encapsulation of C70 by Cycloparaphenylenes

The size‐ and orientation‐selective formation of the shortest‐possible C₇₀ peapod in solution and in the solid state by using the shortest structural unit of an “armchair” carbon nanotube (CNT), cycloparaphenylene (CPP), has been studied. [10]CPP and [11]CPP exothermically formed 1:1 complexes with C₇₀, thereby giving the resulting peapods. A van′t Hoff plot analysis revealed that the formation of these complexes in 1,2‐dichlorobenzene was mainly driven by entropy, whereas the theoretical calculations suggested that the formation of the complex in the gas phase was predominantly driven by enthalpy. C₇₀ was found to exist in two distinct orientations inside the CPP cavity, namely “lying” and “standing”, depending on the specific size of the CPP. The theoretical calculations and the X‐ray crystallographic analysis revealed that the interactions between [10]CPP and the short axis of C₇₀ in its lying orientation were isotropic and similar to those observed between [10]CPP and C₆₀. However, the interactions between [11]CPP and C₇₀ in its standing orientation were anisotropic, thereby involving the radial deformation of [11]CPP into an ellipsoidal shape. This “induced fit” maximized the van der Waals interactions with the long axis of C₇₀. Theoretical calculations revealed that the deformation occurred readily with low energy loss, thus suggesting that CPPs are highly radially elastic molecules. These results also indicate that the same type of radial deformation should occur in CNT peapods that encapsulate anisotropic fullerenes.     

A Molecular Propeller with Three Nanohoop Blades: Synthesis,Characterization, and Solid‐State Packing

Nanoscale carbon‐rich molecular architectures are not only aesthetically appealing but also of practical importance for energy and biomedical technologies. Herein, we report the synthesis of cyclic‐oligophenylene‐based nanopropeller 1 by using an efficient synthon strategy involving sequential intramolecular bisboronate homocoupling and reductive aromatization by H₂SnCl₄. The nanopropeller molecules pack into a layered hexagonal lattice featuring long‐ranged nano‐sized channels and a total guest‐accessible volume of 48 %, as revealed by X‐ray diffraction studies. We suggest that such a solid‐state arrangement is determined by the interplay between the propeller architecture and the intermolecular van der Waals interactions.