Pseudo-hexagonal Lattice Research Articles

Nb2O5 Microcolumns for Ethanol Sensing.

Pseudohexagonal Nb2O5 microcolumns spanning a size range of 50 to 610 nm were synthesized utilizing a cost-effective hydrothermal process (maintained at 180 °C for 30 min), followed by a subsequent calcination step at 500 °C for 3 h. Raman spectroscopy analysis unveiled three distinct reflection peaks at 220.04 cm-1, 602.01 cm-1, and 735.3 cm-1, indicative of the pseudohexagonal crystal lattice of Nb2O5. The HRTEM characterization confirmed the inter-lattice distance of 1.8 Å for the 110 plain and 3.17 Å for the 100 plain. The conductometry sensors were fabricated by drop-casting a dispersion of Nb2O5 microcolumns, in ethanol, on Pt electrodes. The fabricated sensors exhibited excellent selectivity in detecting C2H5OH (ΔG/G = 2.51 for 10 ppm C2H5OH) when compared to a variety of tested gases, including CO, CO2, NO2, H2, H2S, and C3H6O. The optimal operating temperature for this selective detection was determined to be 500 °C in a dry air environment. Moreover, the sensors demonstrated exceptional repeatability over the course of three testing cycles and displayed strong humidity resistance, even when exposed to 90% relative humidity. This excellent humidity resistance gas sensing property can be attributed to their nanoporous nature and elevated operating temperature.

A succession of two viral lattices drives vaccinia virus assembly.

During its cytoplasmic replication, vaccinia virus assembles non-infectious spherical immature virions (IV) coated by a viral D13 lattice. Subsequently, IV mature into infectious brick-shaped intracellular mature virions (IMV) that lack D13. Here, we performed cryo-electron tomography (cryo-ET) of frozen-hydrated vaccinia-infected cells to structurally characterise the maturation process in situ. During IMV formation, a new viral core forms inside IV with a wall consisting of trimeric pillars arranged in a new pseudohexagonal lattice. This lattice appears as a palisade in cross-section. As maturation occurs, which involves a 50% reduction in particle volume, the viral membrane becomes corrugated as it adapts to the newly formed viral core in a process that does not appear to require membrane removal. Our study suggests that the length of this core is determined by the D13 lattice and that the consecutive D13 and palisade lattices control virion shape and dimensions during vaccinia assembly and maturation.

A Novel Hexagonal Psuedo framework for Edge Detection Operators on Hexagonal Framework

Edge detection using a gradient-based detector is a gold-standard method for identifying and analyzing different edge points in an image. A hexagonal grid structure is a powerful architecture dominant for intelligent human-computer vision. This structure provides the best angle resolution, good packing density, high sampling efficiency, equidistant pixels, and consistent connectivity. Edge detection application on hexagonal framework provides more accurate and efficient computations. All the real-time hardware devices available capture and display images in rectangular-shaped pixels. So, an alternative approach to mimic hexagonal pixels using software approaches is modeled in this paper. In this research work, an innovative method to create a pseudo hexagonal lattice has been simulated and the performance is compared with various edge detection operators on the hexagonal framework by comparing the quantitative and qualitative metrics of the grayscale image in both square and hexagonal lattice. The quantitative performance of the edge detection on the hexagonal framework is compared based on the experimental facts. The pseudo-hexagonal lattice structure assures to be aligned toward the human vision.

Objective Point Symmetry Classifications/Quantifications of an Electron Diffraction Spot Pattern with Pseudo-Hexagonal Lattice Metric

The recently developed information-theoretic approach to crystallographic symmetry classifications and quantifications in two dimensions (2D) from digital transmission electron and scanning probe microscope images is adapted for the analysis of an experimental electron diffraction spot pattern, for the first time. Digital input data are considered in this approach to consist of the pixel-wise sums of approximately Gaussian distributed noise and an unknown underlying signal that is strictly 2D periodic. Structural defects within the crystals or on the crystal surfaces, instrumental image recording noise, slight deviations from zero-crystal-tilt conditions in transmission electron microscopy, inhomogeneous staining in structural biology studies of intrinsic membrane protein complexes in lipid bilayers, and small inaccuracies in the algorithmic processing of the digital data all contribute to a single generalized noise term. The plane symmetry group and projected Laue class(or 2D Bravais lattice type) that is anchored to the least broken symmetries are identified as genuine in the presence of generalized noise. More severely broken symmetries that are not anchored to the least broken symmetries are identified as pseudo-symmetries. Our point symmetry quantification study of an electron diffraction spot pattern is highly topical because a new contrast mechanism for 4D scanning transmission electron microscopy was recently demonstrated by other authors. The usage of objective symmetry quantifications is bound to become the preeminent condition of the establishment of that contrast mode as an industry-wide standard.

(Invited) Structural Chemistry of Battery Materials: Metal Oxide Open Frameworks and Li Salts

For several decades, since the discovery of the lithium batteries, the search for novel and improving existing cathode materials and other components of the rechargeable batteries became one of the top priorities of modern technology. In order to develop novel materials, establish structure-property relationship, and find more effective synthetic routes, the knowledge of the crystal structure and comprehensive understanding of the structural changes during battery performance are of the utmost importance.This presentation is based on our more than decade long research on crystallography and structural chemistry of battery materials [1], as well as Li salts and their solvates, conducted in the Institute for Materials Research at Binghamton University. The crystal structure of several dozens of novel compounds has been determined from the powder and single crystal diffraction data. The obtained structural information was used: to analyze the relationship between different structure types for vanadium oxide open frameworks [2]; to establish structural changes or the phase transition during the intercalation and deintercalation processes for an electrochemical cell in Li-VOPO4 systems [3]; to study the role of pH in the synthesis of the vanadium oxide frameworks and their structure types [4,5]; and to link the red-ox properties with the coordination of the transition metal [2]. Theoretical crystal-chemical analysis of open framework structures allowed us not only to understand known structures and establish a relationship between them but also to deduct and predict new structures. For example, it was possible to deduct 4 possible types of V3O7 layers, only 2 of which were known (tmaV3O7 [4] and [en 2Ni]V6O14 [6], tma – tetramethylammonium, en – ethylenediamine), and to predict ordered version (V5O11) of disordered “VO2” layer discovered in LixV1-yO2-y.nH2O (y = ~1/6) compound [7]. When new lithium bis-oxalatoborate (BOB) salt Li[(C2O4)B(C2O4)] was considered for use in the batteries, we have determined its crystal structure from powder diffraction data along with structure of sodium and potassium BOB salts that was quite challenging due to pseudo-hexagonal LiBOB lattice [8]. Recrystallization of LiBOB from the solvent used in the electrochemical cell resulted in solvates with water, acetonitrile, acetone, dimethoxyethylene, 1,3-dioxolane, ethylenecarbonate which crystal structures were determined and are discussed in [9].Recently the crystal structure determination was successfully performed for several important Li salts: lithium ethylene mono-carbonate (EMC), lithium methyl carbonate (MC) [10], and lithium acetylacetone oxalate borate Li[(acac)B(C2O4)] [11]. Interestingly LiEMC structure resulted from the compound that was for quite a while claimed to be Li salt with ethylene dicarbonate (EDC). M.S. Whittingham, Solid State Ionics, 134(1-2), 169-178 (2000); M.S. Whittingham, Chemical reviews, 104(10), 4271-4302 (2004).P.Y. Zavalij and M.S. Whittingham, Acta Cryst., B55, 627-663 (1999).Y. Song, P.Y. Zavalij, and M.S. Whittingham, J. Electrochem. Soc., 152, A721-A728 (2005).T.G. Chirayil, E.A. Boylan, M. Mamak, P.Y. Zavalij, and M.S. Whittingham, Chem. Comm., 33-34 (1997).T. Chirayil, P.Y. Zavalij, and M.S. Whittingham, Chem. Mater., 10, 2629-2640 (1998).P.Y. Zavalij, F. Zhang, and M.S. Whittingham, Acta Cryst., B55, 953-962 (1999).T. Chirayil, P. Zavalij, and M.S. Whittingham, Solid State Ionics, 84, 163-168 (1996).P.Y. Zavalij, S. Yang, and M.S. Whittingham, Acta Cryst., B59, 753–759 (2003).P.Y. Zavalij, S. Yang, and M.S. Whittingham, Acta Cryst., B60, 716-724 (2004).L. Wang, A. Menakath, F. Han, Y. Wang, P.Y. Zavalij, D. Iuga, S.P. Brown, C. Wang, K. Xu, and B.W. Eichhorn, Nature Chem., 11(9), 789-796 (2019).P.Y. Zavalij, L. Wang, and B.W. Eichhorn, CCDC (2019), doi: 10.5517/ccdc.csd.cc22h53w.

Evidence for Orientational Order in Nanothreads Derived from Thiophene.

Nanothreads are one-dimensional sp3 hydrocarbons that pack within pseudohexagonal crystalline lattices. They are believed to lack long-range order along the thread axis and also lack interthread registry. Here we investigate the phase behavior of thiophene up to 35 GPa and establish a pressure-induced phase transition sequence that mirrors previous observations in low-temperature studies. Slow compression to 35 GPa results in the formation of a recoverable saturated product with a 2D monoclinic diffraction pattern along (0001) that agrees closely with atomistic simulations for single crystals of thiophene-derived nanothreads. Paradoxically, this lower-symmetry packing signals a higher degree of structural order since it must arise from constituents with a consistent azimuthal orientation about their shared axis. The simplicity of thiophene reaction pathways (with only four carbon atoms per ring) apparently yields the first nanothreads with orientational order, a striking outcome considering that a single point defect in a 1D system can disrupt long-range structural order.

Membrane organization of photosystem I complexes in the most abundant phototroph on Earth.

Prochlorococcus is a major contributor to primary production, and globally the most abundant photosynthetic genus of picocyanobacteria because it can adapt to highly stratified low-nutrient conditions that are characteristic of the surface ocean. Here, we examine the structural adaptations of the photosynthetic thylakoid membrane that enable different Prochlorococcus ecotypes to occupy high-light (HL), low-light (LL) and nutrient-poor ecological niches. We used atomic force microscopy (AFM) to image the different photosystem I (PSI) membrane architectures of the MED4 (HL) Prochlorococcus ecotype grown under high-light and low-light conditions in addition to the MIT9313 (LL) and SS120 (LL) Prochlorococcus ecotypes grown under low-light conditions. Mass spectrometry quantified the relative abundance of PSI, photosystem II (PSII) and cytochrome b6f complexes and the various Pcb proteins in the thylakoid membrane. AFM topographs and structural modelling revealed a series of specialised PSI configurations, each adapted to the environmental niche occupied by a particular ecotype. MED4 PSI domains were loosely packed in the thylakoid membrane, whereas PSI in the LL MIT9313 is organised into a tightly-packed pseudo-hexagonal lattice that maximises harvesting and trapping of light. There are approximately equal levels of PSI and PSII in MED4 and MIT9313, but nearly two-fold more PSII than PSI in SS120, which also has a lower content of cytochrome b6f complexes. SS120 has a different tactic to cope with low-light levels, and SS120 thylakoids contained hundreds of closely packed Pcb-PSI supercomplexes that economise on the extra iron and nitrogen required to assemble PSI-only domains. Thus, the abundance and widespread distribution of Prochlorococcus reflect the strategies that various ecotypes employ for adapting to limitations in light and nutrient levels.

Impact of (111)-oriented TiN conductive layers for the growth of vanadium dioxide films and the effect of grain boundary diffusions

We report on advantage of (111)-oriented TiN conductive layers for realizing low temperature crystalline growth of vanadium dioxide (VO2) films with phase transition. Comparison between (111)-oriented TiN and random polycrystalline TiN layers was performed to clarify the effect of oriented TiN for succeeding VO2 growth. Oriented growth of VO2 (010) on (111)-oriented TiN suggests feasibility of most dense TiN (111) surface with pseudo-hexagonal lattice fitted against VO2 (010) surface with monoclinic angle β of 122°. Abrupt resistance change nearly three orders of magnitude was achieved in the films prepared at substrate temperatures of 250 ～ 300 °C. XPS depth profiles clearly showed abrupt interface between VO2 and TiN at deposition temperatures lower than 300 °C. On the other hand, it was found that (111)-oriented TiN layers enhance diffusions of Ti and O atoms through the grain boundaries, which act as direct path for diffusion at temperatures higher than 350 °C. Strictly unchanged composition of TiN layers confirms the superior property as anti-diffusion barrier material, however, grain boundaries arrangements are supposed to be crucial factors for the maintanance of layerd structure. Obtained results tell us the impact of (111)-oriented TiN layers not only for succeeding growth of VO2 films, but also for design of layerd device introducing TiN as electrodes.

Chemically Triggered Formation of Two-Dimensional Epitaxial Quantum Dot Superlattices

Two dimensional superlattices of epitaxially connected quantum dots enable size-quantization effects to be combined with high charge carrier mobilities, an essential prerequisite for highly performing QD devices based on charge transport. Here, we demonstrate that surface active additives known to restore nanocrystal stoichiometry can trigger the formation of epitaxial superlattices of PbSe and PbS quantum dots. More specifically, we show that both chalcogen-adding (sodium sulfide) and lead oleate displacing (amines) additives induce small area epitaxial superlattices of PbSe quantum dots. In the latter case, the amine basicity is a sensitive handle to tune the superlattice symmetry, with strong and weak bases yielding pseudohexagonal or quasi-square lattices, respectively. Through density functional theory calculations and in situ titrations monitored by nuclear magnetic resonance spectroscopy, we link this observation to the concomitantly different coordination enthalpy and ligand displacement potency of the amine. Next to that, an initial ∼10% reduction of the initial ligand density prior to monolayer formation and addition of a mild, lead oleate displacing chemical trigger such as aniline proved key to induce square superlattices with long-range, square micrometer order; an effect that is the more pronounced the larger the quantum dots. Because the approach applies to PbS quantum dots as well, we conclude that it offers a reproducible and rational method for the formation of highly ordered epitaxial quantum dot superlattices.

Atomic resolution structure of a chimeric DNA-RNA Z-type duplex in complex with Ba(2+) ions: a case of complicated multi-domain twinning.

The self-complementary dCrGdCrGdCrG hexanucleotide, in which not only the pyrimidine/purine bases but also the ribo/deoxy sugars alternate along the sequence, was crystallized in the presence of barium cations in the form of a left-handed Z-type duplex. The asymmetric unit of the P21 crystal with a pseudohexagonal lattice contains four chimeric duplexes and 16 partial Ba(2+) sites. The chimeric (DNA-RNA)2 duplexes have novel patterns of hydration and exhibit a high degree of discrete conformational disorder of their sugar-phosphate backbones, which can at least partly be correlated with the fractional occupancies of the barium ions. The crystals of the DNA-RNA chimeric duplex in complex with Ba(2+) ions and also with Sr(2+) ions exhibit complicated twinning, which in combination with structural pseudosymmetry made structure determination difficult. The structure could be successfully solved by molecular replacement in space groups P1 and P21 but not in orthorhombic or higher symmetry and, after scrupulous twinning and packing analysis, was refined in space group P21 to an R and Rfree of 11.36 and 16.91%, respectively, using data extending to 1.09 Å resolution. With the crystal structure having monoclinic symmetry, the sixfold crystal twinning is a combination of threefold and twofold rotations. The paper describes the practical aspects of dealing with cases of complicated twinning and pseudosymmetry, and compares the available software tools for the refinement and analysis of such cases.

WE-F-16A-02: Design, Fabrication, and Validation of a 3D-Printed Proton Filter for Range Spreading

Purpose: To design, fabricate and test a 3D-printed filter for proton range spreading in scanned proton beams. The narrow Bragg peak in lower-energy synchrotron-based scanned proton beams can result in longer treatment times for shallow targets due to energy switching time and plan quality degradation due to minimum monitor unit limitations. A filter with variable thicknesses patterned on the same scale as the beam's lateral spot size will widen the Bragg peak. Methods: The filter consists of pyramids dimensioned to have a Gaussian distribution in thickness. The pyramids are 2.5mm wide at the base, 0.6 mm wide at the peak, 5mm tall, and are repeated in a 2.5mm pseudo-hexagonal lattice. Monte Carlo simulations of the filter in a proton beam were run using TOPAS to assess the change in depth profiles and lateral beam profiles. The prototypes were constrained to a 2.5cm diameter disk to allow for micro-CT imaging of promising prototypes. Three different 3D printers were tested. Depth-doses with and without the prototype filter were then measured in a ~70MeV proton beam using a multilayer ion chamber. Results: The simulation results were consistent with design expectations. Prototypes printed on one printer were clearly unacceptable on visual inspection. Prototypes on a second printer looked acceptable, but the micro-CT image showed unacceptable voids within the pyramids. Prototypes from the third printer appeared acceptable visually and on micro-CT imaging. Depth dose scans using the prototype from the third printer were consistent with simulation results. Bragg peak width increased by about 3x. Conclusions: A prototype 3D printer pyramid filter for range spreading was successfully designed, fabricated and tested. The filter has greater design flexibility and lower prototyping and production costs compared to traditional ridge filters. Printer and material selection played a large role in the successful development of the filter.

Four-Stranded Coiled-Coil Elastic Protein in the Byssus of the Giant Clam, Tridacna maxima

An elastic protein with a secondary structure distinct from all well-known load-bearing proteins is found in the byssus of the giant clam, Tridacna maxima . The byssus consists of a bundle of hundreds of individual threads, each measuring about about 100 μm in diameter, which exhibit a tendon-like mechanical response. The amino acid composition of Tridacna byssus, however, is unlike tendon collagen, lacking high glycine, proline, and hydroxyproline. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) measurements suggest that the constituent nanofibrils of the byssal threads are distinct from known secondary structure motifs previously reported for elastic proteins including the collagen triple-helix, the β-sheet nanocrystalline domains of silks, or the double-stranded coiled-coil regions of intermediate filaments. Instead, X-ray diffraction data indicate a structural organization in which four coiled-coil α-helices form a stable rope-like structure, which then further pack in a pseudohexagonal lattice to form nanofibrils. Amino acid composition analysis shows unusually high concentrations of acidic as well as basic residues, suggesting that the four-helix structure is stabilized by strong ionic interactions between oppositely charged residues in neighboring strands. The composition also suggests additional stabilization by disulfide cross-linking. On a larger scale, scanning and conventional transmission electron microscope (STEM and TEM) observations indicate that the nanofibrils exhibit an alternating periodicity of about 500 nm along the axial direction. A molecular model that combines the mechanical properties with the structural characteristics of the Tridacna byssal threads is proposed.

Modification of terminating species and band alignment at the interface between alumina films and metal single crystals

Thin epitaxial alumina films were grown on Cu(111), Cu–9 at.%Al(111), Ni(111) and NiAl(110) single crystals. The alumina films grew in such a manner that hexagonal or pseudo-hexagonal oxygen lattices were parallel to the surface of the substrates. Photoelectron spectra were obtained either with synchrotron or Al K-alpha radiation. We measured Al 2p spectra and determined the atomic species that terminated the interface between the alumina films and the substrates. The influence of Al in the substrates on the species that terminated the interface has been discussed based on thermodynamics. From valence band spectra, p-type Schottky barrier height (energy difference between the Fermi level of the metallic substrates and the valence band maximum of the alumina films, band offset) was determined. Differences in interface terminating species resulted in variations in p-type Schottky barrier height, or band alignment.

Structural Convergence between Cryo-EM and NMR Reveals Intersubunit Interactions Critical for HIV-1 Capsid Function

Mature HIV-1 particles contain conical-shaped capsids that enclose the viral RNA genome and perform essential functions in the virus life cycle. Previous structural analysis of two- and three-dimensional arrays of the capsid protein (CA) hexamer revealed three interfaces. Here, we present a cryoEM study of a tubular assembly of CA and a high-resolution NMR structure of the CA C-terminal domain (CTD) dimer. In the solution dimer structure, the monomers exhibit different relative orientations compared to previous X-ray structures. The solution structure fits well into the EM density map, suggesting that the dimer interface is retained in the assembled CA. We also identified a CTD-CTD interface at the local three-fold axis in the cryoEM map and confirmed its functional importance by mutagenesis. In the tubular assembly, CA intermolecular interfaces vary slightly, accommodating the asymmetry present in tubes. This provides the necessary plasticity to allow for controlled virus capsid dis/assembly.

Effect of Chain Topology on the Self-Organization and Dynamics of Block Copolypeptides: From Diblock Copolymers to Stars

The effect of chain topology on (i) the peptide secondary structure, (ii) the nanophase self-assembly, and (iii) the local segmental and global peptide relaxations has been studied in a series of model diblock and 3-arm star copolypeptides of poly(epsilon-carbobenzyloxy-L-lysine) (PZLL) and poly(gamma-benzyl-L-glutamate) (PBLG) with PZLL forming the core. Diblock copolypeptides are nanophase separated with PBLG and PZLL domains comprising alpha-helices packed in a hexagonal lattice. Star copolypeptides are only weakly phase separated, comprising PBLG and PZLL alpha-helices in a pseudohexagonal lattice. Phase mixing has profound consequences on the local and global dynamics. The relaxation of the peptide secondary structure speeds up, and the helix persistence length is further reduced in the stars, signifying an increased concentration of helical defects.

Adsorption-induced chirality in highly symmetric hydrocarbon molecules: lattice matching to substrates of lower symmetry

For molecules of high symmetry and lateral interactions dominated by van der Waals' interactions, such as some planar aromatic hydrocarbons, there is a preference for hexagonal close packing on adsorption. Optimization of packing by minimization of the interadsorbate spacing may favour correlated rotations of the molecules, which reduces the symmetry and leads to chiral properties in the two-dimensional overlayer. Independently, mapping of the preferred hexagonal packing on to lower symmetry substrates, which provide pseudo-hexagonal lattices, can lead to alternative mirror image lattices. The interaction of these independent chiral phenomena gives rise to diastereoisomerism in the adsorbed array. Coronene and its substituted, larger derivative hexa-tert-butyl hexabenzocoronene adsorbed on copper surfaces provide examples of these phenomena. A new structure is proposed for coronene on Cu{100} while new STM and LEED data are presented for this molecule adsorbed on Cu{110}. Finally, the adsorption of hexa-tert-butyl hexabenzocoronene on Cu{110} is re-examined and the implications of the competition between two, closely related, pseudo-hexagonal lattices are considered.

Action of α-cyclodextrin on phospholipid assemblies

Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly. Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface: the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact at least a part of the multilamellar assembly.

New potential materials for infrared nonlinear optics. Preparation, characterisation and optical transparency of monometallic and bimetallic iodates

The non-centrosymmetric compounds Mg(IO 3) 2, Mn(IO 3) 2, Co(IO 3) 2 and Zn(IO 3) 2 are isostructural and crystallise in space-group type P 2 1 with a pseudo-hexagonal lattice leading to the formation of a three-individual twin by pseudo-merohedry. Because of this structural analogy, solid solutions are possible between these metallic iodates. Bimetallic iodates Mn 1− x Zn x (IO 3) 2 form a solid solution over the entire domain of composition. Second harmonic generation test and absorption studies carried out on theses materials show high nonlinear activities, high damage thresholds and are transparent up to 12 μm in the IR.

Crystal structure of M(IO3)2 metal iodates, twinned bypseudo-merohedry, with MII: MgII, MnII, CoII, NiII and ZnII

Abstract The non-centrosymmetric materials Zn(IO3)2, Mn(IO3)2, Co(IO3)2, Mg(IO3)2 and β-Ni(IO3)2 have been synthesised by evaporation of nitric acid solutions of metal salts and lithium iodate. All these compounds are isostructural and their structures were characterised both by X-ray diffraction on powder and single crystals. They crystallise in the monoclinic crystal system, space-group type P21 (no. 4) with a pseudo-hexagonal lattice, as shown by the lattice parameters of Mn(IO3)2 for example: a = 11.247(1) Å, b = 5.045(1) Å, c = 11.246(1) Å, β = 120.02(1)°, V = 552.5(1) Å3, Z = 4. This monoclinic symmetry with a ∼ c and β ∼ 120° leads to a three-individual pseudo-hexagonal twin by pseudo-merohedry. The structure reveals a three-dimensional network in which each octahedrally coordinated cation is linked to ten others via iodate bridges. All these metal iodates generate second harmonics.

Different building modes of α-cyclodextrin/monoalkyl amphiphile complexes

In this study, the impact of the length of the guest molecule alkyl chain and the crystallization conditions on the structural parameters of α-cyclodextrin (α-CD)/monoalkyl complexes was determined. Several procedures to crystallize those complexes were developed for different alkylalcohols as model guest molecules, as a function of temperature. Three different crystalline structures were identified depending on the alkyl chain length, using synchrotron X-ray diffraction (LURE, Orsay, France). In all cases, complexes crystallize in channel-type structures, where α-CD molecules are stacked like coins in a roll and the alkyl chain of the guest compound is embedded in the tubular cavity of the α-CDs. However, depending on the length of the chains and the crystallization conditions, the channels are organized differently. C6-C8 chains give rise to a pseudo-hexagonal lattice, a packing mode already observed for polyiodide complexes [1]. C10-C12 chains crystallize in a triclinic pseudo-monoclinic C2 lattice, while longer chains up to C18 form hexagonal crystals with R3 symmetry. These two novel crystal structures are described. Understanding these structures opens new routes to nanotube formation through amphiphile-driven crystallization of cyclodextrin templates.