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Crystals, Volume 3, Issue 2 (June 2013) – 8 articles , Pages 275-390

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Review
Soft Elasticity in Main Chain Liquid Crystal Elastomers
Crystals 2013, 3(2), 363-390; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020363 - 07 Jun 2013
Cited by 36 | Viewed by 8467
Abstract
Main chain liquid crystal elastomers exhibit several interesting phenomena, such as three different regimes of elastic response, unconventional stress-strain relationship in one of these regimes, and the shape memory effect. Investigations are beginning to reveal relationships between their macroscopic behavior and the nature [...] Read more.
Main chain liquid crystal elastomers exhibit several interesting phenomena, such as three different regimes of elastic response, unconventional stress-strain relationship in one of these regimes, and the shape memory effect. Investigations are beginning to reveal relationships between their macroscopic behavior and the nature of domain structure, microscopic smectic phase structure, relaxation mechanism, and sample history. These aspects of liquid crystal elastomers are briefly reviewed followed by a summary of the results of recent elastic and high-resolution X-ray diffraction studies of the shape memory effect and the dynamics of the formation of the smectic-C chevron-like layer structure. A possible route to realizing auxetic effect at molecular level is also discussed. Full article
(This article belongs to the Special Issue Advances in Liquid Crystals)
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Article
Synthesis, Structure and Spectroscopy of Two Structurally Related Hydrogen Bonded Compounds in the dpma/HClO4 System; dpma (dimethylphosphoryl)methanamine
Crystals 2013, 3(2), 350-362; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020350 - 05 Jun 2013
Cited by 11 | Viewed by 5058
Abstract
The new phosphine oxide compound, (dimethylphosphoryl)methanaminium perchlorate, dpmaHClO4 (1), was synthesized by the reaction of (dimethylphosphoryl) methanamine (dpma) with concentrated perchloric acid. (Dimethylphosphoryl)methanaminium perchlorate (dimethylphosphoryl)methanamine solvate, dpmaHClO4dpma (2) was obtained by [...] Read more.
The new phosphine oxide compound, (dimethylphosphoryl)methanaminium perchlorate, dpmaHClO4 (1), was synthesized by the reaction of (dimethylphosphoryl) methanamine (dpma) with concentrated perchloric acid. (Dimethylphosphoryl)methanaminium perchlorate (dimethylphosphoryl)methanamine solvate, dpmaHClO4dpma (2) was obtained by the slow evaporation of an equimolar methanolic solution of 1 and dpma at room temperature. For both compounds, single-crystal X-ray structures, IR and Raman spectra are reported. The assignment of the spectroscopic data were supported by quantum chemical calculations at the B3LYP/6-311G(2d,p) level of theory. In 1, the dpmaH cations form polymeric, polar double-strands along [010] by head to tail connections via N–H∙∙∙O hydrogen bonds. The perchlorate anions are located between these strands attached by one medium strong and two weaker un-bifurcated hydrogen bonds (monoclinic, centrosymmetric space group C2/c, a = 17.8796(5) Å, b = 5.66867(14) Å, c = 17.0106(5) Å, β = 104.788(3)°, V = 1666.9(1) Å3, Z = 8, T = 293 K, R(F) [I > 2σ(I)] = 0.0391, wR(F2) [all] = 0.1113). In 2, besides the N–H∙∙∙O hydrogen bonds, medium strong N–H∙∙∙N hydrogen bonds are present. One dpmaH cation and the neutral dpma molecule are connected head to tail by two N–H∙∙∙O hydrogen bonds forming a monocationic cyclic unit. These cyclic units are further connected by N–H∙∙∙O and N–H∙∙∙N hydrogen bonds forming polymeric, polar double-strands along [001]. The perchlorate anions fill the gaps between these strands, and each [ClO4] anion is weakly connected to the NH2 group by one N–H∙∙∙O hydrogen bond (orthorhombic, non-centrosymmetric space group Pca21 (No. 29), a = 18.5821(5) Å, b = 11.4320(3) Å, c = 6.89400(17) Å, V = 1464.50(6) Å3, Z = 4, T = 100 K, R(F) [I > 2σ(I)] = 0.0234, wR(F2) [all] = 0.0575). Both structures are structurally related, and their commonalities are discussed in terms of a graph-set analysis. Full article
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Article
Influence of Mesogenic Properties of Cruciform-Shaped Liquid Crystals by Incorporating Side-Arms with a Laterally-Substituted-Fluorine
Crystals 2013, 3(2), 339-349; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020339 - 30 May 2013
Cited by 2 | Viewed by 3826
Abstract
Fluoro substitution in thermotropic liquid crystals provides a general way of modifying the properties of a parent system. Transition temperatures, mesophase types and other physical properties can be affected by fluoro substitution, so that frequently the behaviors of the parent compound can be [...] Read more.
Fluoro substitution in thermotropic liquid crystals provides a general way of modifying the properties of a parent system. Transition temperatures, mesophase types and other physical properties can be affected by fluoro substitution, so that frequently the behaviors of the parent compound can be manipulated and improved in a predictable manner. This paper discusses the effects of a fluoro substitution in each side-arm of 1,2,4,5-tetrakis((4-(alkoxy)phenyl)ethynyl)benzenes on the resulting mesomorphic properties characterized by optical polarizing microscopy and differential scanning calorimetry. Without any fluoro-substituted side-arms, longer chain-length leads to a wider nematic temperature range on cooling. Incorporation of a fluoro substitution in each side-arm induces the formation of a lamellar suprastructure, lowers transition temperatures and results in a wider mesophase temperature range on cooling. Full article
(This article belongs to the Special Issue Advances in Liquid Crystals)
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Short Note
The Synthesis and Molecular Structure of 1-(3,4-Dihydroxyphenethyl)-3-hydroxy-2-methylpyridin-4(1H)-one Hydrochloride Methanol Solvate
Crystals 2013, 3(2), 333-338; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020333 - 17 May 2013
Cited by 2 | Viewed by 3894
Abstract
A 3-hydro-4-pyridinone compound derived from maltol and dopamine has been prepared using a microwave reactor. The molecular structure of the protonated product was confirmed by single crystal X-ray diffraction. Crystals were obtained from a saturated solution of methanol and belong to the triclinic [...] Read more.
A 3-hydro-4-pyridinone compound derived from maltol and dopamine has been prepared using a microwave reactor. The molecular structure of the protonated product was confirmed by single crystal X-ray diffraction. Crystals were obtained from a saturated solution of methanol and belong to the triclinic space group P-1 with unit cell parameters a = 8.3801(11) Å; b = 9.2583(12) Å; c = 11.5671(15) Å; α = 73.566(2)°; β = 84.514(2)°; γ = 66.578(2)°. The asymmetric unit contains two molecules. Full article
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Review
One-, Two-, and Three-Dimensional Hopping Dynamics
Crystals 2013, 3(2), 315-332; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020315 - 29 Apr 2013
Cited by 9 | Viewed by 3992
Abstract
Hopping dynamics in glass has been known for quite a long time. In contrast, hopping dynamics in smectic-A (SmA) and hexatic smectic-B (HexB) liquid crystals (LC) has been observed only recently. The hopping in SmA phase occurs among the smectic layers (one-dimensionally), while [...] Read more.
Hopping dynamics in glass has been known for quite a long time. In contrast, hopping dynamics in smectic-A (SmA) and hexatic smectic-B (HexB) liquid crystals (LC) has been observed only recently. The hopping in SmA phase occurs among the smectic layers (one-dimensionally), while hopping in HexB phase occurs inside the layers (two-dimensionally). The hopping dynamics in SmA and HexB liquid crystal phases is investigated by parallel soft-core spherocylinders, while three-dimensional hopping dynamics in inherent glassy states is investigated by systems of Weeks–Chandler–Andersen (WCA) spheres. The temperature dependence of diffusion coefficients of hopping in SmA phase can be described by the Arrhenius equation characteristic of activation process. In HexB LC phase, the diffusion coefficients saturate at higher temperatures. In a system of WCA spheres, the values and temperature dependence of diffusion coefficients depend on the observed states. Full article
(This article belongs to the Special Issue Advances in Liquid Crystals)
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Article
Glycine Betaine Recognition through Cation−π Interactions in Crystal Structures of Glycine Betaine Complexes with C-Ethyl-pyrogallol[4]arene and C-Ethyl-resorcin[4]arene as Receptors
Crystals 2013, 3(2), 306-314; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020306 - 16 Apr 2013
Cited by 7 | Viewed by 3672
Abstract
The glycine betaine (betaine), interacts with several types of proteins with diverse structures in vivo, and in the contact regions, the aromatic rings of protein residues are frequently found beside the trimethylammonium group of betaine, implying the importance of the cation−π interactions [...] Read more.
The glycine betaine (betaine), interacts with several types of proteins with diverse structures in vivo, and in the contact regions, the aromatic rings of protein residues are frequently found beside the trimethylammonium group of betaine, implying the importance of the cation−π interactions in recognition of this molecule. The crystal structures determined by X-ray crystallography of the complexes of betaine and C-ethyl-pyrogallol[4]arene (pyrogallol cyclic tetramer: PCT) and betaine and C-ethyl-resorcin[4]arene (resorcinol cyclic tetramer: RCT) mimic the conformations of betaine and protein complexes and show that the clathrate conformations are retained by the cation−π interactions. The difference of the conformation feature of betaine in the Protein Data Bank and in the Cambridge Structural Database was found by chance during the research and analyzed with the torsion angles. Full article
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Article
Impact of Vacancies on Diffusive and Pseudodiffusive Electronic Transport in Graphene
Crystals 2013, 3(2), 289-305; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020289 - 08 Apr 2013
Cited by 5 | Viewed by 4514
Abstract
We present a survey of the effect of vacancies on quantum transport in graphene, exploring conduction regimes ranging from tunnelling to intrinsic transport phenomena. Vacancies, with density up to 2%, are distributed at random either in a balanced manner between the two sublattices [...] Read more.
We present a survey of the effect of vacancies on quantum transport in graphene, exploring conduction regimes ranging from tunnelling to intrinsic transport phenomena. Vacancies, with density up to 2%, are distributed at random either in a balanced manner between the two sublattices or in a totally unbalanced configuration where only atoms sitting on a given sublattice are randomly removed. Quantum transmission shows a variety of different behaviours, which depend on the specific system geometry and disorder distribution. The investigation of the scaling laws of the most significant quantities allows a deep physical insight and the accurate prediction of their trend over a large energy region around the Dirac point. Full article
(This article belongs to the Special Issue Graphenes)
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Article
Hydrogen-Bonding in Two Pyridinium Salts of [Mo2O4Cl4(μ2-dmsH)]3−Complex (dmsH = a Half-Neutralized Form of 2,2-Dimethylsuccinic Acid)
Crystals 2013, 3(2), 275-288; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst3020275 - 03 Apr 2013
Cited by 2 | Viewed by 4128
Abstract
Reactions of a mononuclear molybdenum(V) starting material, (PyH)5[MoOCl4(H2O)]3Cl2, with 2,2-dimethylsuccinic acid in the presence of base afforded two products, (PyH)3[Mo2O4Cl42-dmsH)]·1/2CH3CN ( [...] Read more.
Reactions of a mononuclear molybdenum(V) starting material, (PyH)5[MoOCl4(H2O)]3Cl2, with 2,2-dimethylsuccinic acid in the presence of base afforded two products, (PyH)3[Mo2O4Cl42-dmsH)]·1/2CH3CN (1) and (PyH)4[Mo2O4Cl42-dmsH)]Cl (2). As revealed by the X-ray structure analysis, the half-neutralized form of the dicarboxylic acid, the dmsH ion, coordinated to the well-known {Mo2O4}2+ core in the syn-syn bidentate bridging manner. In both compounds, the non-ionized terminus of the ligand, the COOH function, participated in hydrogen-bonding interactions. The incorporation of the chloride counteranion in 2, prevented the formation of the common “carboxylic acid dimer” which was observed for 1. Instead, a hydrogen-bonded linkage of the COOH function with the chloride occurred. Full article
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