Interdigitation Of Alkyl Chains Research Articles

On the Mesophase Formation of 1,3-Dialkylimidazolium Ionic Liquids

A series of seven different 1,3-dialkylimidazolium-based ion-pair salts with the same molecular weight and size but different symmetries was synthesized. For all salts, bromide was chosen as the counterion, giving the series ([CnIMCm][Br]), where IM = imidazolium and Cn and Cm are varying N-alkyl substituents with n + m = 13. Thus, the effect of symmetry on the physicochemical properties, such as thermal transitions, densities and viscosities and particularly mesophase formation, is investigated herein. All salts are fully characterized by NMR spectroscopy and mass spectrometry, and their physicochemical properties such as thermal transitions, densities, and viscosities are reported. Single crystal X-ray structure analysis is reported for 1-tridecylimidazolium bromide ([C0IMC13][Br]) and 1-ethyl-3-undecylimidazolium bromide ([C2IMC11][Br]). Salts 1-tridecylimidazolium bromide ([C0IMC13][Br]) and 1-dodecyl-3-methylimidazolium bromide ([C1IMC12][Br]) exhibit thermotropic liquid crystal behavior, confirmed by differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray diffraction to be the SmA mesophase. A structure with interdigitation of alkyl chains is observed for all of [C0IMC13][Br], [C1IMC12][Br], and [C2IMC11][Br], despite the absence of thermotropic liquid crystalline behavior for the latter (and all other isomers with an alkyl chain length less than 12 carbon atoms). This allows us to draw the conclusion that for the liquid crystal phase of an ionic liquid to exist, not only are the calamitic shape and integral length of a molecule important but a minimal alkyl chain length of n = 12 is also required. Therefore, a dodecyl group could be considered as the functional group responsible for liquid crystalline behavior.

Monolayer and bilayer structures in ionic liquids and their mixtures confined to nano-films

The confinement of liquids to thin films can lead to dramatic changes in their structural arrangement and dynamic properties. Ionic liquids display nano-structures in the bulk of the liquid, consisting of polar and non-polar domains, whereas a solid surface can induce layered structures in the near-surface liquid. Here we compare and contrast the layer structures in a series of imidazolium and pyrrolidinium-based ionic liquids upon confinement of the liquids to films of approximately 0-20 nm between two negatively charged mica surfaces. Using a surface force balance (SFB) we measured the force between the two atomically smooth mica surfaces with ionic liquid between, directly revealing the ion packing and dimensions of layered structures for each liquid. The ionic liquids with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement, whilst a longer alkyl chain leads to alignment of the cations in bilayer formation. The crossover from monolayers to bilayers, however, occurs at different alkyl chain lengths for imidazolium- and pyrrolidinium-based ionic liquids with a common anion. In addition, we find that imidazolium cation bilayers are arranged in toe-to-toe orientation, whereas pyrrolidinium cations form bilayers consisting of fully interdigitated alkyl chains. Results for a mixture of monolayer-preferring (i.e. short alkyl chain) and bilayer-preferring (i.e. long alkyl chain) liquids indicate alkyl chain segregation and bilayer-like structures. We discuss the driving forces for these self-assembly effects, and the contrasting behaviour of the imidazolium and pyrrolidinium-type ionic liquids.

Organic Crystal Engineering with 1,4-Piperazine-2,5-diones. 8. Synthesis, Crystal Packing, and Thermochemistry of Piperazinediones Derived from 2-Amino-4,7-dialkoxyindan-2-carboxylic Acids

1,4-Piperazine-2,5-diones possessing C2hmolecular symmetry and bearing four methoxy, ethoxy, butoxy, hexyloxy, octyloxy, nonyloxy, dodecyloxy, or octadecyloxy groups weresynthesized from 2-amino-4,7-dialkoxyindan-2-carboxylic acids. Where possible, the piperazinediones were crystallized from appropriate solvents and the supramolecular organizations were determined by X-ray crystallography. In each case so studied, crystal assembly via three mutually orthogonal interactions, namely, R22(8) hydrogen bonding, arene perpendicular edge-to-center interactions, and alkyl chain interdigitation, was observed. The thermochemical properties of these compounds were studied by modulated differential scanning calorimetry. In most cases, one or more reversible thermal events were observed between room temperature and melting to an isotropic liquid. In the cooling cycle, freezing point temperatures were observed to decrease with increasing hydrocarbon chain length. This may be due to greater entropic penalties for hydrogen-bond association of molecules with longer hydrocarbon chains.

固液界面における多孔性二次元分子集合体の形成と制御

Two-dimensional (2D) architectures, particularly porous molecular networks, on solid surfaces formed via self-assembly have received a great deal of interest because of the prospective applications in optoelectronics and tailor-made catalysis. We found that porous 2D molecular networks were formed at liquid-solid interfaces, typically an organic solvent/graphite or Au(111), by triangle-shaped phenylene-ethynylene macrocycles, dehydrobenzo[12]annulenes (DBAs), via their self-assembly by van der Waals interactions between the interdigitated alkyl chains attached to the periphery of the macrocyclic core. Factors that led to the preferential formation of porous, honeycomb-shaped networks were elucidated including the size of the π-conjugated cores, alkyl chain length, solvent, concentration, temperature, and solid substrates. Not only homochiral molecular networks were achieved by self-assembly of DBAs with chiral side chains, but also network homochirality was induced by addition of a small amount of a chiral DBA into an achiral DBA as a chirality inducer. Co-adsorption of guest molecules in the pores occurred through recognition of the size and shape, leading to selective inclusion of homo-molecular as well as hetero-molecular clusters into the nanowells. Moreover, the interior of the pores was functionalized for tailored molecular recognition toward advanced use of 2D molecular networks on surfaces.

Structural and vibrational characteristics of amphiphilic phosphonate salts

► We reported X-ray studies of NH 4 C 10 H 21 PO 3 H and enH 2 C 10 H 21 PO 3 ·1.5H 2 O. ► Strong hydrogen bonds generate the layered structures. ► The vibrational spectra of phosphonate salts are discussed. 1-Decylphosphonic acid ( 1 ), ammonium 1-decylphosphonate (NH 4 C 10 H 21 PO 3 H) ( 2 ), ethylenediaminium 1-decylphosphonate 1,5 hydrate (enH 2 C 10 H 21 PO 3 ·1.5H 2 O) ( 3 ) and calcium 1-decylphosphonate (Ca(C 10 H 21 PO 3 H) 2 ) ( 4 ) were prepared and characterized by IR and Raman spectroscopy. The structures of 2 and 3 were determined by single crystal X-ray diffraction analysis. Compound 2 crystallizes in the P 1 ¯ space group of triclinic system with two molecules in the asymmetric unit cell whereas compound 3 crystallizes in C 2/ c space group of monoclinic system with four molecules in the unit cell and both exhibit layered supramolecular structures generated by ionic interaction, H-bonding and alkyl chain interdigitation in the case of 3 . The FT-IR and Raman spectra have been assigned in the range 4000–500 cm −1 for all compounds, and reveal the trans conformation of alkane chain in all compounds.

A matter of greasy tails: Interdigitation of alkyl chains in free and coordinated 4′-(4-dodecyloxyphenyl)-4,2′:6′,4″-terpyridines

Abstract The syntheses and single crystal structures of 4′-(4-dodecyloxyphenyl)-4,2′:6′,4″-terpyridine, 2, and [Zn2(μ-OAc)4(2)2] are reported. Crystal packing is dominated by van der Waals interactions between fully extended alkyl chains producing lamellar structures in both compounds, and appears to be the reason for the formation of crystalline [Zn2(μ-OAc)4(2)2] rather than a one-dimensional coordination polymer as observed for related compounds.

Linear and branched alkyl substituted octakis(dimethylsiloxy)octasilsesquioxanes: WAXS and thermal properties

A series of octakis(dimethylsiloxy)octasilsesquioxanes bearing linear and branched alkyl substituents has been prepared in high yield by Pt-catalyzed hydrosilylation of alkenes with octakis(hydrodimethylsiloxy)octasilsesquioxane, chain length varying between C3 and C8 for the straight-chain derivatives and between C5 and C7 for the branched-chain derivatives. On the basis of a WAXS study, we showed that the linear derivatives are amorphous and that the interdigitation of alkyl chains between neighboring POSS molecules increases as the alkyl chain length increases from propyl to octyl. The thermal behavior of these compounds was studied by DSC, polarized optical microscopy and TGA in nitrogen and air atmosphere. The derivatives with shorter n-alkyl chains from C3 to C6 crystallize below 0 °C whereas the derivatives with longer n-alkyl chains (C7 and C8) can be regarded as amorphous glasses with a T g around –100 °C. The morphology and thermal properties change considerably with branching of the alkyl chain. Melting points above ambient temperature were found for the iso-hexyl and iso-heptyl POSS derivatives whereas the iso-pentyl POSS derivative is liquid at 25 °C. From the values of the heat of fusion as well as entropy of fusion, it was concluded that packing of the side groups in the crystal structure increases as the size of the branched alkyl group increases. TGA evidenced a negative effect of the branching of the alkyl chain on the thermal stability in air.

ChemInform Abstract: Supramolecular Surface‐Confined Architectures Created by Self‐Assembly of Triangular Phenylene—Ethynylene Macrocycles via van der Waals Interaction.

AbstractReview: 77 refs.

Molecular pentagonal tiling: self-assemblies of pentagonal-shaped macrocycles at liquid/solid interfaces

We present a systematic scanning tunneling microscopy study on the 2D self-assembly of pentagonal shaped macrocycles at the liquid/solid interface to gain insight about 2D pentagonal molecular crystallization. Macrocycles with alkyl ester groups form an anti-parallel type linear pattern mainly via favorable intermolecular interactions between the interdigitated alkyl chains at the 1,2,4-trichlorobenzene (TCB)/graphite interface. On the other hand, at the TCB/Au(111) interface, they showed a random pattern and an anti-parallel type linear pattern. The selection between both motifs is ascribed to the balance between the intermolecular and molecule–substrate interactions. Most interestingly, the parent molecule forms dense anti-parallel and parallel linear patterns reflecting the intrinsic pentagonal core shape. Moreover, bright and mobile spots were often observed in the networks to occupy free spaces, including the cavity of the macrocycles, which we attribute to a co-adsorbed solvent molecule or Au ion.

Two- and three-dimensional packing diagrams of M(salophen) complexes

For better understanding of two- (2D) and three-dimensional (3D) crystal engineering of metal complexes, the 2D and 3D packing diagrams of metal salophen (=N,N′-o-phenylene-bis(salicylideneimine)) complexes are compared in detail. According to the 3D structures, determined by X-ray crystallography, N,N′-(o-phenylene)bis(4-hexyloxysalicylideneiminato)Cu(II) (1) and N,N′-(o-phenylene)bis(4-decyloxysalicylidene-iminato)Ni(II) (2) have a square-planar coordination geometry. 1 forms a host–guest complex with CH2Cl2 solvent molecule via intermolecular hydrogen bonds. In 2 the interdigitating alkyl chains allow the molecules to be packed in parallel sheets with a zigzag-type pattern while in 1 the molecules are packed in coplanar layers. In both structures the layers are connected by short {M}⋯H contacts (3.07 A in 1, 3.15 A in 2). The molecular packings in planes of the 3D structures are compared with previously determined 2D surface patterns of five equivalent Cu(II), Ni(II) and Co(II) complexes formed at the liquid–solid interface. The structures were studied at the interface by means of scanning tunneling microscopy. It is shown that in the case of 2 the 2D structures observed in the plane of a bulk crystal and at the liquid–solid interface are not comparable. As shown, even the metal ion and the alkyl chain length affect differently on the 2D and 3D packing. The role of molecular planarity on the packing diagrams is addressed by comparing the nearly planar single crystal structures of salophen complexes 1 and 2 to the structure of N,N′-ethylene-bis(4-octyloxysalicylideneiminato)Cu(II) which has a twisted salen moiety.

Synthesis, characterization and coordination properties of bis(alkyl)selenosalen ligands

New bis (alkyl) selenosalen podand ligands having Se2N2 donor sites have been synthesized by the condensation of unsymmetrical o-formylphenyl alkyl selenide (1-3) with ethylenediamine. The reaction of bis(alkyl)selenosalen podands with Pd(II) and Pt(II) afforded selenoether-selenolate coordination complexes 7-10via cleavage of one of the two Se-C(alkyl) bonds of bis(alkyl)selenosalen podands upon complexation. DFT calculations revealed that the cleavage of Se-C(alkyl) bonds occurred possibly via S(N)2 mechanism instead of a sequence of oxidative addition and reductive elimination reactions. The spectral data and elemental analyses confirmed the formation of selenoether-selenolate complexes. The structures of the podands N,N'-bis[(2-methylseleno)phenylmethylene]-1,2-ethanediamine (4), N,N'-bis[(2-decylseleno)phenylmethylene]-1,2-ethanediamine (5) and the selenoether-selenolate complex 8 have been determined by single crystal X-ray diffraction analysis. The crystal structure of 5 showed SeH interaction with a ladder like 3D supramolecular arrangement via interdigitation of long alkyl chains. Comparison of crystal packing of podands 4 and 5 indicates that the alkyl chain length has significant impact on the crystal packing. The platinum selenolate complex 8 shows a square planar arrangement around the Pt centre, where the Se atoms in the selenolate and the selenoether have nearly equal Pt-Se bond length.

Pronounced sponge-like nanostructure in propylammonium nitrate

The bulk structure of the ionic liquid propylammonium nitrate (PAN) has been determined using neutron diffraction. Empirical potential structure refinement (EPSR) fits to the data show that PAN self-assembles into a quasi-periodic bicontinuous nanostructure reminiscent of an amphiphile L(3)-sponge phase. Atomic detail on the ion arrangements around the propylammonium cation and nitrate anion yields evidence of hydrogen bonding between ammonium and nitrate groups and of strong alkyl chain aggregation and interdigitation. The resultant amphiphilic PAN nanostructure is more pronounced than that previously determined for ethylammonium nitrate (EAN) or ethanolammonium nitrate (EtAN).

A Luminescent Ionic Liquid Crystal: [C12mim]4[EuBr6]Br

Abstract[C12mim]4[EuBr6]Br·CH3CN (2) was obtained at –15 °C by reacting europium bromide with [C12mim]Br (1‐dodecyl‐3‐methylimidazolium bromide) in acetonitrile. 2 crystallizes in the triclinic space group P$\bar {1}$ (No. 2) with two formula units in the unit cell. The structure is characterized by double layers of [C12mim] cations with interdigitated alkyl chains which are separated by anion layers formed by [EuBr6] octahedra and Br···CH3CN units. Upon warming to room temperature 2 looses acetonitrile to form the room temperature ionic liquid crystal [C12mim]4[EuBr6]Br (1). The temperature dependent structural behavior has been characterized by differential scanning calorimentry and hot‐stage polarizing optical microscopy. In the temperature range of –3 to 98 °C 1 adopts a smectic liquid crystal phase. At 77 K 1 shows a strong red emission with a lifetime of 2.6 ms. Analysis of the emission spectrum yields a quantum efficiency of 0.45.

Synthesis and solid state structure of fluorous probe molecules for fluorous separation applications

A series of colored hydrocarbon and fluorocarbon tagged 1-fluoro-4-alkylamino-anthraquinones and 1,4-bis-alkylamino-anthraquinone probe molecules were synthesized from a (fluorinated) alkyl amine and 1,4-difluoroanthraquinone to aid in the development of fluorous separation applications. The anthraquinones displayed stacking of the anthraquinone tricycle and interdigitation of the (fluorinated) alkyl chains in the solid state. Furthermore, intramolecular N–H⋯O hydrogen bonds forced the hydrocarbon and fluorocarbon tags into a conformation pointing away from the anthraquinone tricycle, with the angle of the tricycle plane normal and the main (fluorinated) alkyl vector ranging from 1° to 39°. Separation of the probe molecules on fluorous silica gel showed that the degree of fluorination of the probe molecules plays only a minor role with most eluents (e.g., hexane/ethyl acetate and methyl nonafluorobutyl ethers/ethyl acetate). However, toluene as eluent caused a pronounced separation by degree of fluorination for fluorocarbon, but not hydrocarbon tagged probe molecules on both silica gel and fluorous silica gel. These studies suggest that hydrocarbon and fluorocarbon tagged anthraquinones are useful probe molecules for the development of laboratory scale fluorous separation applications.

A feasibly synthesized ladder-type conjugated molecule as the novel high mobility n-type organic semiconductor

Two ladder-type conjugated molecules, i.e., 2,2′-(2,7-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diylidene) dimalononitrile (1) and 2,7-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (2) were synthesized in high yields, and their electrochemical properties, single crystal structures, thin-film morphology and field-effect mobility were investigated. The LUMO/HOMO levels of 1 and 2 are −4.07/−6.00 and −3.62/−5.82 eV, respectively, as estimated from the thin-film cyclic voltammetry measurements. In the single crystals, both compounds exhibit one dimensional π–π stacking of molecules, and 1 shows the larger π-electron overlap between the neighboring molecules than 2, along with interdigitation of alkyl chains. Thin-film X-ray diffraction (XRD) and atomic force microscopy (AFM) characterizations indicate that 1 can form films with higher molecular order than 2. Field-effect electron mobility up to 0.33 cm2 V−1 s−1 in air for 1 and hole mobility up to 0.05 cm2 V−1 s−1 for 2 have been demonstrated with the top-contact organic thin-film transistor (OTFT) device structure. Electron mobility of 1 is among the highest value for n-type organic semiconductors.

Supramolecular surface-confined architectures created by self-assembly of triangular phenylene–ethynylene macrocycles via van der Waals interaction

At the liquid/graphite interface triangular and rhombic phenylene-ethynylene macrocycles substituted by alkyl chains self-assemble to form porous two-dimensional (2D) molecular networks of honeycomb and Kagomé types, respectively, or close-packed non-porous structures via alkyl chain interdigitation as the directional intermolecular linkages. Factors that affect the formation of the 2D molecular networks, such as alkyl chain length, solvent, solute concentration, and co-adsorption of guest molecules, were elucidated through a systematic study. For the porous networks, various molecules and molecular clusters were adsorbed in the pores reflecting the size and shape complementarity, exploring a new field of 2D host-guest chemistry.

Structure and Epitaxial Registry on Graphite of a Series of Nanoporous Self-Assembled Molecular Monolayers

We have analyzed by STM the detailed structures of a series of nanoporous honeycomb networks stabilized by alkyl chain interdigitation on graphite at the liquid−solid interface, that is, clip-like noncovalent bonding. The variations observed as a function of the length of the peripheral aliphatic chains show that the assembly is directed not only by lateral intermolecular interactions but also by the adsorption site on the substrate. We derive an atomically accurate model for the registry with graphite of our nanoporous model series of systems. In full agreement with the quantitative model, the pore areas vary step-by-step by more than one order of magnitude along the whole series while preserving the detailed features of the graphite-induced alkyl chain interdigitation. The largest pores observed correspond to a ratio of uncovered substrate area as large as 35%.

Bipyridine Derivatives at a Solid/Liquid Interface: Effects of the Number and Length of Peripheral Alkyl Chains

Bipyridine derivatives (bpys) with various number and length of peripheral alkyl chains (with carbon numbers of n = 11-17) were synthesized, and their self-assembled monolayers were observed by scanning tunneling microscopy (STM) at a 1-phenyloctane/highly oriented pyrolytic graphite (HOPG) interface. The effects of the number, the substitution position, and the length of alkyl chains on the two-dimensional structures were systematically studied. Bpys substituted by a single alkyl chain in the p-position on each side adopted an almost linear form with zigzag-type alignment of the pi-conjugated unit, whereas, in the case of m-substitution, the bpys showed Z-shaped morphology with interdigitated alkyl chains. In both cases, no odd-even alkyl chain length effects were observed. The bpys with double alkyl chains at m- and p-positions displayed odd-even alkyl chain effects, suggesting that the formation of two-dimensional structure is dominated by the interactions between alkyl chains. Bpys with triple alkyl chains at o-, m-, and p-positions also showed odd-even alkyl chain effects, but only for the higher number of carbon atoms in the alkyl chain unit (n = 14-17). These results indicate that concerted intermolecular interactions of the alkyl chain unit introduce the odd-even chain length effect on the self-assembled two-dimensional structure. After coordination of PdCl(2), odd-even effects were quenched, and bpys were converged into the same lamellar structure, in which the molecules are almost linear. All the structural differences due to the odd-even alkyl chain length effect were explained in terms of intermolecular and molecule-substrate interactions.

Reversible Thermochromic Nanocomposites Based on Thiolate-Capped Silver Nanoparticles Embedded in Amorphous Polystyrene

Technologically useful reversible thermochromic materials can be prepared using very simple polymer-embedded nanostructures. In particular, silver nanoparticles capped by long-chain alkyl-thiolate molecules (i.e., Agx(SCnH2n+1)y, with n > 10) spontaneously organize in aggregates because of the interdigitation phenomenon involving the linear alkyl chains bonded at surfaces of neighboring nanoparticles. Owing to the alkyl-chain interdigitation, nanoparticles very close to each other result and an interaction among their surface plasmon resonances may take place. Surface plasmon interaction causes a splitting of the absorption band whose characteristics depend on the aggregate shape. Since shape-less aggregates are generated, a multiple-splitting of the silver surface plasmon absorption band is observed, which causes a broad absorption spreading on the whole visible spectral region. Amorphous polystyrene containing interdigitated silver nanoparticles has a dark-brown or black coloration, depending on the nanoparticle numerical density, but since the inter-particle distance slightly increases at melting point of interdigitation crystallites a reversible termochromic effect is observed at this special temperature. In particular, the material coloration changes from dark-brown to yellow which is the coloration produced by the surface plasmon absorption of isolated silver nanoparticles. This reversible thermochromism can be finely controlled by modifying the structure of thiolate groups, and precisely, the strength of interactions acting inside the interdigitation crystallites.

Molecular Structure of Self-Assembled Chiral Nanoribbons and Nanotubules Revealed in the Hydrated State

A detailed molecular organization of racemic 16-2-16 tartrate self-assembled multi-bilayer ribbons in the hydrated state is proposed where 16-2-16 amphiphiles, tartrate ions, and water molecules are all accurately positioned by comparing experimental X-ray powder diffraction and diffraction patterns derived from modeling studies. X-ray diffuse scattering studies show that molecular organization is not fundamentally altered when comparing the flat ribbons of the racemate to chirally twisted or helical ribbons of the pure tartrate enantiomer. Essential features of the three-dimensional molecular organizations of these structures include interdigitation of alkyl chains within each bilayer and well-defined networks of ionic and hydrogen bonds between cations, anions, and water molecules between bilayers. The detailed study of diffraction patterns also indicated that the gemini headgroups are oriented parallel to the long edge of the ribbons. The structure thus possesses a high cohesion and good crystallinity, and for the first time, we could relate the packing of the chiral molecules to the expression of the chirality at a mesoscopic scale. The organization of the ribbons at the molecular level sheds light on a number of their macroscopic features. Among these are the reason why enantiomerically pure 16-2-16 tartrate forms ribbons that consist of exactly two bilayers, and a plausible mechanism by which a chirally twisted or helical shape may emerge from the packing of chiral tartrate ions. Importantly, the distinction between commonly observed helical and twisted morphologies could be related to a subtle symmetry breaking. These results demonstrate that accurately solving the molecular structure of self-assembled soft materials--a process rarely achieved--is within reach, that it is a valid approach to correlate molecular parameters to macroscopic properties, and thus that it offers opportunities to modulate properties through molecular design.