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1.
We report CH/π hydrogen‐bond‐driven self‐assembly in π‐conjugated skeletons based on oligophenylenevinylenes (OPVs) and trace the origin of interactions at the molecular level by using single‐crystal structures. OPVs were designed with appropriate pendants in the aromatic core and varied by hydrocarbon or fluorocarbon tails along the molecular axis. The roles of aromatic π‐stack, van der Waals forces, fluorophobic effect and CH/π interactions were investigated on the theromotropic liquid crystallinity of OPV molecules. Single‐crystal structures of hydrocarbon OPVs provided direct evidence for the existence of CH/π interactions between the π‐ring (H‐bond acceptor) and alkyl C? H (H‐bond donor). The four important crystallographic parameters, dc?x=3.79 Å, θ=21.49°, φ=150.25° and dHp?x=0.73 Å, matched in accordance with typical CH/π interactions. The CH/π interactions facilitate the close‐packing of mesogens in xy planes, which were further protruded along the c axis producing a lamellar structure. In the absence of CH/π interactions, van der Waals interactions drove the assembly towards a Schlieren nematic texture. Fluorocarbon OPVs exhibited smectic liquid‐crystalline textures that further underwent Smectic A (SmA) to Smectic C (SmC) phase transitions with shrinkage up to 11 %. The orientation and translational ordering of mesogens in the liquid‐crystalline (LC) phases induced H‐ and J‐type molecular arrangements in fluorocarbon and hydrocarbon OPVs, respectively. Upon photoexcitation, the H‐ and J‐type molecular arrangements were found to emit a blue or yellowish/green colour. Time‐resolved fluorescence decay measurements confirmed longer lifetimes for H‐type smectic OPVs relative to that of loosely packed one‐dimensional nematic hydrocarbon‐tailed OPVs.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
The crystal and molecular structures of 4,4′-disubstituted biphenyls of formula HO(CH2)6 OC6H4C6H4 R with R = cyano and nitro terminal groups have been determined including co-crystallized materials of both of the compounds. The extended molecules arrange in an antiparallel fashion with dipole-dipole interactions, exhibiting a sheet-like structure for the compound with the cyano terminal group, and for the other two materials an extended head to tail string-like structure caused by dipolar interaction, also packed in sheets in an antiparallel fashion by van der Waals interactions. Knowledge of the interaction of the compounds in the crystalline state serves as a prerequisite for the determination of interactions in the liquid crystalline state of the same or similar compounds.  相似文献   

5.
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.  相似文献   

6.
《Chemical physics letters》1985,116(5):415-419
Van der Waals (vdW) volumes (Vw,x) of 117 molecular fragments (X) have been calculated by numerical integration of the van der Waals envelope using the hard-sphere approximation, standard geometries, and effective atomic van der Waals radii which were determined by comparison of their effects on the predicted sterically allowed conformations of peptides with observed crystal structures. vdW volume fragmental constants give accurate estimates of molecular, vdW volume as sum of approximate Vw,xs.  相似文献   

7.
The asymmetric unit of the title polymeric complex, [HgBr(C6H4NO2)]n or HgBr(nic), contains mercury coordinated via two Br atoms [Hg—Br = 2.6528 (9) and 2.6468 (9) Å], two carboxyl­ate O atoms, which form a characteristic four‐membered chelate ring [Hg—O = 2.353 (6) and 2.478 (7) Å], and an N atom [Hg—N = 2.265 (5) Å], in the form of a very irregular (3+2)‐coordination polyhedron. The pronounced irregularity of the effective Hg (3+2)‐coordination is a result of the rigid stereochemistry of the nicotinate ligand. According to the covalent and van der Waals radii criteria, the strongest bonds are Hg—Br and Hg—N. These covalent interactions form a two‐dimensional poly­mer. The puckered planes are connected by van der Waals interactions, and there are only two intermolecular C—H⋯O hydrogen bonds [3.428 (10) and 3.170 (10) Å].  相似文献   

8.
The role of the Mg2+ cation on huperzine molecule binding (drugs used for Alzheimer disease) on human serum albumin (HSA) was studied by affinity chromatography. The thermodynamic data corresponding to this binding were determined for a wide range of Mg2+ concentrations (x). For each solute, the huperzine binding on HSA was divided into two Mg2+ concentration regions. For a low x value, below xc (1.2 mM), the binding decrease with x. For x above xc the hydrophobic effect and van der Waals interactions between the huperzine molecule and the HSA implied a decrease in its binding. These results showed that for patients with Alzheimer disease, an Mg2+ supplementation during treatment with these huperzine molecules can increase the active pharmacological molecule concentration.  相似文献   

9.
The structures of a 2‐oxa‐5‐thia­bi­cyclo­[4.1.0]­heptane derivative, C7H10Cl2O3S, (I), and a 2H,3H,5H‐1,4‐dithiepine derivative, C7H9ClO4S2, (II), are reported. The six‐membered ring in (I) has an envelope conformation and the seven‐membered ring in (II) adopts a chair conformation. There are no untoward intermolecular interactions in (I), but two Cl atoms make a short intermolecular contact across an inversion centre in (II), with a Cl?Cl distance of 3.2784 (9) Å, some 0.22 Å less than the sum of the van der Waals radii.  相似文献   

10.
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.  相似文献   

11.
The title compound, C21H28O4, has a 4‐acetoxy substituent positioned on the steroid α face. The six‐membered ring A assumes a conformation intermediate between 1α,2β‐half chair and 1α‐sofa. A long Csp3—Csp3 bond is observed in ring B and reproduced in quantum‐mechanical ab initio calculations of the isolated molecule using a molecular‐orbital Hartree–Fock method. Cohesion of the crystal can be attributed to van der Waals interactions and weak C—H...O hydrogen bonds.  相似文献   

12.
We calculate the heats of vaporisation for imidazolium‐based ionic liquids [Cnmim][NTf2] with n=1, 2, 4, 6, 8 by means of molecular dynamics (MD) simulations and discuss their behavior with respect to temperature and the alkyl chain length. We use a force field developed recently. The different cohesive energies contributing to the overall heats of vaporisations are discussed in detail. With increasing alkyl chain length, the Coulomb contribution to the heat of vaporisation remains constant at around 80 kJ mol?1, whereas the van der Waals interaction increases continuously. The calculated increase of about 4.7 kJ mol?1 per CH2‐group of the van der Waals contribution in the ionic liquid exactly coincides with the increase in the heats of vaporisation for n‐alcohols and n‐alkanes, respectively. The results support the importance of van der Waals interactions even in systems completely composed of ions.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
A new triclinic polymorph of the title compound, [PdCl2(C18H15P)2], has two independent molecules in the unit cell, with the Pd atoms located on inversion centres. One molecule has an eclipsed conformation, whereas the second molecule adopts a gauche conformation. The molecules with a gauche conformation are involved in weak intermolecular C—H...Cl—Pd interactions with symmetry‐related molecules. It is suggested that C—H...Cl—Pd interactions are mainly responsible for the existence of conformational differences, which contribute to the polymorph formation. In the crystal, there are layers of eclipsed and gauche molecules separated by normal van der Waals interactions.  相似文献   

16.
In 2‐chloro­phenyl 3‐nitro­benzene­sulfonate, C12H8ClNO5S, and 2,4‐di­chloro­phenyl 3‐nitro­benzene­sulfonate, C12H7Cl2NO5S, weak C—H⋯O interactions generate S(5), S(6) and (7) rings. The supramolecular aggregation is completed by the presence of π–π interactions and intermolecular van der Waals short contacts.  相似文献   

17.
Two new metal pnictide halides, (Hg9.75As5.5)(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.  相似文献   

18.
The title compound, C9H11NO3S, has crystallographic mirror symmetry, occurs in the thio­carbamate form and is stabilized in an scisoid,stransoid conformation with respect to the C—N—C group. There are two intramolecular hydrogen bonds, one between the H atom of the N—H group and the O atom of the furan ring, and the other between the H atom of the secondary carbon of the iso­propyl group and the S atom. The packing of the mol­ecules is assumed to be dictated by van der Waals interactions.  相似文献   

19.
The excited electronic origin bands of several DABCO containing van der Waals complexes have been observed via (1+1) resonance enhanced multi-photon ionization. Sharp resonances with widths of about 3 cm–1 are seen for DABCO-Rg n=1,2,3 (Rg is Ar, Kr or Xe), for the DABCO-DABCO dimer and for DABCO-DABCO-Ar. The origins of the rare-gas complexes are blue shifted with respect to the monomer origin. Broad features originating from DABCO-Rg n complexes with highn, appear to higher energies than the complex origins, with widths of 120 cm–1.  相似文献   

20.
The temperature dependence of wetting behavior for pentane on water is analyzed from the standpoint of the Derjaguin-Frumkin theory. The joint action of two mechanisms of surface forces, the van der Waals and the image charge interactions, are considered to calculate the isotherms of the disjoining pressure. To analyze the temperature influence on the magnitude of van der Waals forces, we have used the exact Dzyaloshinsky, Lifshitz, and Pitaevsky equation. It is shown that image forces, arising due to the restricted solubility of water in pentane, decay much faster with increasing the film thickness and can be considered as short ranged in comparison to the van der Waals forces. The competitive action of the image charge and the van der Waals forces provides the plausible explanation of the temperature dependence of wetting in the system under consideration.  相似文献   

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