Triclinic Crystals Research Articles

Multifunctional Bilayer Template for Near-Infrared-Sensitive Organic Solar Cells.

For organic solar cells (OSCs) based on nonplanar phthalocyanines, it has previously been reported that a thin film composed of triclinic crystals with face-on (or flat-lying)-oriented molecules, typically obtained with a CuI template layer, is desired for optical absorption in the near-infrared (NIR) spectral region. However, this work demonstrates that for a PbPc-C60 donor-acceptor pair, less face-on orientation with a broader orientation distribution obtained with a new template layer consisting of a ZnPc/CuI bilayer is more desirable in terms of solar cell efficiency than the face-on orientation. A NIR-sensitive PbPc-C60 OSC employing this bilayer-templated PbPc film is found to increase the internal quantum efficiency (IQE) by 36% on average in the NIR spectral region compared to a device using a CuI-templated PbPc film. Analyses of the change in IQE using the exciton diffusion model and the entropy- and disorder-driven charge-separation model suggest that the improved IQE is attributed to the facilitated dissociation of charge-transfer excitons as well as the reduction in exciton quenching near the indium tin oxide surface.

Manganese Oxides for Environmental Assessment

Core Ideas Synthesis of birnessite that forms a durable coating requires both high lactate and high Na to K ratios. A high lactate to permanganate ratio facilitates a rapid (<10 min) nucleation of birnessite crystals. The high Na/K ratio facilitates crystal growth along the c axis because Na+ ions fit well within the triclinic structure. Early‐formed birnessite is initially poorly ordered, but ordering along the c axis occurs over 2 to 3 d. Differences in durability of birnessites are likely related to crystal morphology. Following on earlier work that has shown the value of iron‐based IRIS (Indicator of Reduction In Soils) technology, recent efforts have focused on developing a manganese‐based IRIS coating. A synthesis procedure developed utilizing a high Na lactate to KMnO4 molar ratio followed by 3 d of dialysis, forms a crystalline birnessite that can be easily applied to PVC tubing and which forms a durable manganese oxide coating. In this study, a series of experiments were run to evaluate the impact of the following parameters on the synthesis of the birnessite: Na/K ratio; lactate/permanganate ratio; lactate source; reaction time; centrifuge washing; dialysis and ageing of the samples. Results confirm that to synthesize birnessite that forms a durable coating both high lactate and high Na/K ratios are required. The high lactate/permanganate ratio (6.7) facilitates a rapid nucleation of triclinic birnessite crystals within 10 min during which time the initial structural template is established, and where some of the manganese (approximately 38%) is reduced to Mn3+. The high Na/K facilitates the ordering of the triclinic birnessite along the c axis following synthesis, and based on analyses of x‐ray diffraction (XRD) patterns, the crystallites grow from 2 to 12 nm in direction of c axis over the course of several days. Scanning electron microscopy (SEM) analyses show that oriented structured particles up to 1 μm form. X‐ray photoelectron spectroscopy (XPS) analyses demonstrate that there is no difference in the charge structure of the Mn between birnessites that will, or will not, form a durable coating. We conclude that the differences in durability are related primarily to physical interaction and/or interlocking of crystals.

Self-Assembly of Protein Crystals with Different Crystal Structures Using Tobacco Mosaic Virus Coat Protein as a Building Block.

In this work, a typical cylinder-shaped tobacco mosaic virus coat protein (TMVCP) is employed as an anisotropic building block to assemble into triclinic and hexagonal close-packed (HCP) protein crystals by introducing cysteine residues at the 1 and 3 sites and four histidine residues at the C-terminal, respectively. The engineered functional groups of cysteine and histidine in the TMVCP and the self-assembly conditions determine the thermodynamics and kinetics in the self-assembly process for forming different crystal structures. The results show that the TMVCPs are thermodynamically driven to form triclinic crystals due to the formation of disulfide bonds between neighboring TMVCPs. On the other hand, the self-assembly of HCP crystals is kinetically directed by the strong metal-histidine chelation. This work not only greatly expands TMVCP for fabricating promising nanomaterials but also represents an approach to adjusting the protein crystal structures by tuning the thermodynamics and kinetics during crystallization.

Synthesis of a Series of Monophthalocyaninato Cyclen Heavy Lanthanide(III) Complexes with Tetragonal Symmetry.

A series of the new monophthalocyaninato lanthanide complexes, [Ln(Pc)(cyclen)]Cl (Ln = Y, Tb, Dy, Ho, Er, Tm, and Yb; Pc = phthalocyaninato; cyclen = 1,4,7,10-tetraazacyclododecane) was synthesized and characterized. The crystallographic study of monophthalocyaninato complexes with a capping macrocyclic ligand having no π-conjugation while keeping the 4-fold symmetry is presented for the first time. All the six complexes were crystallized in a tetragonal structure of the I4mm space group. In addition to this, the Tb complex exhibited a triclinic crystal structure of the P1̅ space group. All of the complexes are isostructural, where both Pc and cyclen are coordinated to an Ln3+ ion giving an eight-coordinate square-antiprismatic geometry. The skew angle between the Pc and cyclen ligands was 45° in the tetragonal crystals and 41.5° in the triclinic crystal. The metal-nitrogen bond lengths were shorter on the Pc ligand side than cyclen side, presumably due to the difference in the charges of the ligands and the steric factor.

Dyeing performance of the azo dyes containing trifluoromethyl group for polyester fabrics and its single crystal structure

The structures of disperse dyes and their intermolecular interactions have important impacts on dyeing and printing performances for polyester fabrics. The fluorine dyes show some unique molecular stability and photochemical properties. The dyeing property of the azo dye containing trifluoromethyl group for polyester fabrics, 4'-(N-acetoxyethyl-Nethyl)- amino-2-bromine-4-nitro-6-trifluoromethylazo- benzene (D1), was investigated and compared with the similar structure disperse dye. The results show that the high color yield and good exhaustion of the dyed PET fabrics could be obtained. The polyester fabrics dyed with D1 had excellent light fastness. Its single crystal was prepared and the supramolecular interactions were solved by X-ray diffraction. Dye D1 formed triclinic crystals in a trimeric packing mode. The C-F bond distances of CF3 are 1.2730 A, 1.2240 A and 1.2900 A, respectively. The two benzene rings linked azo unit (-N=N-) are obviously twist. The dihedral angle of the two benzene rings is 50.23 o. There are six weak hydrogen bonds around trifluoromethyl group in the intramolecule and intermolecule. The excellent light stability of the dye should be attributed to its unique supramolecular structure.

Anomalous Polarized Raman Scattering and Large Circular Intensity Differential in Layered Triclinic ReS2.

The Raman tensor of a crystal is the derivative of its polarizability tensor and is dependent on the symmetries of the crystal and the Raman-active vibrational mode. The intensity of a particular mode is determined by the Raman selection rule, which involves the Raman tensor and the polarization configurations. For anisotropic two-dimensional (2D) layered crystals, polarized Raman scattering has been used to reveal the crystalline orientations. However, due to its complicated Raman tensors and optical birefringence, the polarized Raman scattering of triclinic 2D crystals has not been well studied yet. Herein, we report the anomalous polarized Raman scattering of 2D layered triclinic rhenium disulfide (ReS2) and show a large circular intensity differential (CID) of Raman scattering in ReS2 of different thicknesses. The origin of CID and the anomalous behavior in polarized Raman scattering were attributed to the appearance of nonzero off-diagonal Raman tensor elements and the phase factor owing to optical birefringence. This can provide a method to identify the vertical orientation of triclinic layered materials. These findings may help to further understand the Raman scattering process in 2D materials of low symmetry and may indicate important applications in chiral recognition by using 2D materials.

Synthesis and molecular structure of catena((μ2-4,4,10,10-tetramethyl-1,3,7,9-tetraazaspiro[5.5]undecane-2,8-dione-O,O')- aquadinitratocadmium(II))

A coordination polymer, catena((μ2-4,4,10,10-tetramethyl-1,3,7,9-tetraazaspiro[5.5]undecane- 2,8-dione-O,O')-aquadinitratocadmium(II) {[Cd(C11H20N4O2)(H2O)(NO3)2]} n } (I), has been prepared for the first time from cadmium(II) nitrate and the bicyclic bisurea 4,4,10,10-tetramethyl-1,3,7,9-tetraazaspiro[5.5]undecane-2,8-dione (TTSU). Its molecular structure has been determined (CIF file CCDC no. 903387). Triclinic crystals: space group P1, a = 8.9967(4) A, b = 9.6011(4) A, c = 12.5131(7) A, α = 76.307(4)°, β = 73.465(5)°, γ = 63.310(5)°, V = 918.26(8) A3, ρcalc = 1.789 g/cm3, Z = 2. The Rietveld refinement was carried out at 293 K to confirm the single-phase constitution of the obtained powder sample of I: a = 8.9972(4) A, b = 9.6104(4) A, c = 12.5203(4) A, α = 76.373(3)°, β = 73.485(3)°, γ = 73.485(3)°, V = 919.80(6) A3. A number of lines not corresponding to the main phase and not identified from PDF-2 database are observed on the powder X-ray diffraction pattern. The Rietveld refinement showed that the sample contains 91.4 wt % of the main compound I and 8.6 wt % of the TTSU nitrate admixture. The cadmium atom is coordinated by the O(1) and O(1)i atoms of two molecules of the organic ligand (L) generated by the symmetry operation (i1–x,–y,–z), the O(2)ii atom of the third ligand L molecule bound with the supporting one with the symmetry operation (ii–x,–y,–z), a water molecule, and a bidentate and a monodentate nitrate anions. The coordination number of the cadmium atom is 7, the coordination polyhedron is a distorted pentagonal bipyramid. The Cd···Cd distance is 4.0208 (3) A.

2‐Pyridylmetallocenes, Part VI. Double Cycloplatination of 1,1′‐Dipyridylferrocene. Synthesis and Molecular Structure of σ‐{Pt2Cl2(DMSO)2[Fe[η5‐(C5H3(2‐C5H4N)2]2

The reaction of 1,1′‐dipyridylferrocene with [PtCl2(DMSO)2] yields the doubly cyclometalated complex σ‐{Pt2Cl2(DMSO)2[Fe[η5‐(C5H3(2‐C5H4N)2]2]} as a mixture of meso‐and d,l‐diastereomers. An X‐ray structure determination of the obtained triclinic crystals (space group P1) shows, however, only the chiral d,l form as a racemic mixture.

Synthesis and Characterization of [Rb([18]crown‐6)]3As15Zn·4NH3 and [Rb([2.2.2]crypt)]4Sb14Zn·8NH3

The new compound [Rb([18]crown‐6)]3As15Zn·4NH3 was obtained by the reaction of Rb3As7, ZnPh2, [18]crown‐6, and [2.2.2]crypt in liquid ammonia. The black monoclinic crystals contain the (As15Zn)3– anion, in which two As73– cages are linked by an As–Zn unit. The anionic units are separated by cationic [Rb([18]crown‐6)]+ units. The analogous reaction of Rb3Sb7, ZnPh2, [18]crown‐6, and [2.2.2]crypt yielded black triclinic crystals of the compound [Rb([2.2.2]crypt)]4Sb14Zn·8NH3. This is the first antimony derivative with the (E14Zn)4– anionic motif, which consists of two nortricyclane like cages linked by a Zn atom. Quantum chemical calculations on the anionic units confirm that the electron density is mainly found at the periphery of the cluster system. This phenomenon is in accord with the observations already reported for the 1,2,3‐tripnicolides.

Synthesis, NMR Spectral and DFT Studies of Styryl Imidazole Derivatives—Nano-SiO2 as an Efficient Catalyst

A series of novel styryl imidazole derivatives has been designed and synthesized using nano-SiO2 as an efficient catalyst. Synthesized compounds have been characterized by 1H and 13C-NMR spectral studies. The significant features of this nanocatalyst are high product yield, short reaction times and a vast range of substrates usage. Proton and 13C chemical shifts of the synthesized compounds were calculated. Single crystal XRD analysis has been carried out to confirm the structure of MDPI (1-(3-methoxyphenyl)-4, 5-dimethyl-2-phenyl-1H-imidazole) and it shows the imidazole ring is essentially planar and triclinic crystal. Optimization of compound MDPI was performed by DFT at B3LYP/6-31G (d, p) using Gaussian-03. Imidazole derivatives were used to construct highly sensitive fluorescent chemosensors for sensing of metal ions.

Discontinuous transition from insulator to semiconductor induced by phase change of the new organic- inorganic hybrid [(CH2)7(NH3)2]CoBr4

[(CH2)7(NH3)2]CoBr4, triclinic crystal has a space group P1¯ with two molecules per asymmetric unit cell (Z = 2). Unit cell dimensions are: a = 7.6588 (3) Å, b = 10.5160 (3) Å, c = 11.3319 (5) Å, α = 66.745 (2) °, β = 77.2258 (13) °, γ = 88.001 (2) °, volume = 816.37(5) Å3 and calculated density = 2.078 Mgm−3. The structure consists of [CoBr4]2−tetrahdera separated by heptane diammonium layers. The organic hydrocarbon layers' pack in a stacked herring-bone manner hydrogen bonded to the halide ions. Lattice potential energy is Upot = 1827.7 kJ/mol, and molecular volume Vm = 0.408 nm3. Calorimetric (DSC) measurements indicate phase transitions at T1 = 350 ± 1 K (ΔS = 22.7 J/K-mol) and 335 K (ΔS = 10.5 J/K-mol). Dielectric and conductivity as a function of temperature (300 < T K < 420) and frequency (0.21 < f (kHz) < 60) were investigated. Abrupt change from an insulator to semiconductor behavior takes place around T1. At low temperatures, thermally activated Arrhenius behavior is observed with frequency dependent, temperature independent activation energy. At high temperatures conductivity and activation energy are frequency and temperature dependent implying non-Arrhenius type behavior where the charged particles experience different potentials for local and long distance movements. Conduction takes place via correlated barrier hopping with maximum barrier height WM = 0.015 eV.

A molecular dynamics calculation of solid phase of malonic acid: role of hydrogen-bond chains and the elastic constants

Recent studies suggest that hydrogen bonds, in particular, hydrogen bond chains play an important role in determining the properties of a substance. We report an investigation into the triclinic phase of crystalline malonic acid. One of two intermolecular interaction potentials proposed here is seen to predict the lattice parameters as well as the enthalpy of the triclinic phase in good agreement with experimental data. Structural and dynamic properties are reported. Also reported are the lifetime of the hydrogen bond and hydrogen bond chains of length l along [011] direction where l = 1 to 5. From the temperature dependence of the lifetime we have obtained the activation energies of the chains. We also report the elements of elastic constant tensor. The results show that the presence of the hydrogen bond chain along [011] direction leads to higher value for elastic tensor $$\hbox {C}_{yyzz}$$ suggesting a strong correlation between hydrogen bond chains and the elastic constant along that direction. This is consistent with the recent report of Azuri I et al. 2015 Angew. Chem. Int. Ed. Engl. 54 13566 who reported that rather large Young’s modulus for certain amino acid crystals. The calculation reports the lifetime and activation energies of hydrogen bond chains and demonstrates that there is a relation between direction of the hydrogen bond chains and elastic constants along that direction. Presence of hydrogen bonds along a given crystallographic direction leads to larger elastic constants. A view down the a direction. Cyan dots represent centre of mass of malonic acid molecule in the triclinic crystal phase and red lines indicate hydrogen bond between them. Note the existence of hydrogen bond chains along [011] direction.

Water-carbon dioxide solid phase equilibria at pressures above 4 GPa

A solid phase in the mixed water-carbon dioxide system, previously identified as carbonic acid, was observed in the high-pressure diamond-anvil cell. The pressure-temperature paths of both its melting and peritectic curves were measured, beginning at 4.4 GPa and 165 °C (where it exists in a quadruple equilibrium, together with an aqueous fluid and the ices H2O(VII) and CO2(I)) and proceeding to higher pressures and temperatures. Single-crystal X-ray diffraction revealed a triclinic crystal with unit cell parameters (at 6.5 GPa and 20 °C) of a = 5.88 Å, b = 6.59 Å, c = 6.99 Å, α = 88.7°, β = 79.7°, and γ = 67.7°. Raman spectra exhibit a major line at ~1080 cm−1 and lattice modes below 300 cm−1.

Dispersion analysis of arbitrarily cut orthorhombic crystals

We developed a measurement and evaluation scheme to perform dispersion analysis on arbitrarily cut orthorhombic crystals based on the schemes developed for triclinic and uniaxial crystals. As byproduct of dispersion analysis the orientations of the crystal axes are found.In contrast to the spectra of arbitrarily cut uniaxial crystals, where the fit routine has to separate two independent principal spectra, the spectra of arbitrarily cut orthorhombic crystals are a combination of three independent spectra and the evaluation scheme gets more complex. Dispersion analysis is exemplary performed on two different crystals, which show different spectral features and different levels of difficulties to evaluate. Neodymium gallate (NdGaO3) has broad overlapping reflections bands while topaz (Al2SiO4 [F, OH]2) has a quite high total number of infrared active bands.

Quantitative analysis of H-species in anisotropic minerals by polarized infrared spectroscopy along three orthogonal directions

Infrared spectroscopy is a powerful technique for probing H-species in nominally anhydrous minerals, and a particular goal of considerable efforts has been providing a simple yet accurate method for the quantification. The available methods, with either polarized or unpolarized analyses, are usually time-consuming or, in some cases, subjected to larger uncertainty than theoretically expected. It is shown here that an empirical approach for measuring the concentration, by determining three polarized infrared spectra along any three mutually perpendicular directions, is theoretically and in particular experimentally correct. The theoretical background is established by considering the integrated absorbance, and the experimental measurements are based on a careful evaluation of the species and content of H in a series of gem-quality orthogonal, monoclinic and triclinic crystals, including olivine, orthopyroxene, clinopyroxene, orthoclase and albite (natural and H-annealed). The results demonstrate that the sum of the integrated absorbance from two polarized spectra along two perpendicular directions in any given plane is a constant, and that the sum of the integrated absorbance from three polarized spectra along any three orthogonal directions is of essentially the same accuracy as that along the principal axes. It is also shown that this method works well, with a relative accuracy within 10%, even at some extreme cases where the sample absorption bands are both intense and strongly anisotropic.

Peculiarities of crystallization in the multiblock copolymers of norbornene and cyclooctene

Crystallinity of statistical multiblock copolymers of norbornene and cyclooctene with nearly equimolar composition and different degrees of blockiness is studied by differential scanning calorimetry including thermal fractionation by successive self-nucleation and annealing and by X-ray diffraction. The copolymers are synthesized via recently invented reaction of polymer cross-metathesis, as a result of interchain exchange between polynorbornene and polyoctenamer in the presence of Grubbs’ catalyst of the first generation. This catalyst raises the fraction of trans-octenylene units up to more than 80% promoting formation of triclinic crystals. The copolymer degree of crystallinity and melting peak temperature decrease with the cross-metathesis conversion. At the same time the equilibrium melting temperature predicted by the Flory theory of copolymer crystallization is not much affected by the interchange reaction. Compared with the pure polyoctenamer or its equimolar blend with polynorbornene, the norborene-cyclooctene copolymers form considerably smaller crystallites. Thermal fractionation makes it possible to find their size distribution, which correlates with the average length of trans-octenylene blocks. Short annealing the multiblock copolymers above their melting points gives rise to a small but persistent endotherm 5–10 degrees above the annealing temperature, which is absent in polyoctenamer and, therefore, may indicate mixing of segregated norbornene and cyclooctene blocks.

A generalized crystal-cutting method for modeling arbitrarily oriented crystals in 3D periodic simulation cells with applications to crystal–crystal interfaces

A Generalized Crystal-Cutting Method (GCCM) is developed that automates construction of three-dimensionally periodic simulation cells containing arbitrarily oriented single crystals and thin films, two-dimensionally (2D) infinite crystal–crystal homophase and heterophase interfaces, and nanostructures with intrinsic N-fold interfaces. The GCCM is based on a simple mathematical formalism that facilitates easy definition of constraints on cut crystal geometries. The method preserves the translational symmetry of all Bravais lattices and thus can be applied to any crystal described by such a lattice including complicated, low-symmetry molecular crystals. Implementations are presented with carefully articulated combinations of loop searches and constraints that drastically reduce computational complexity compared to simple loop searches. Orthorhombic representations of monoclinic and triclinic crystals found using the GCCM overcome some limitations in standard distributions of popular molecular dynamics software packages. Stability of grain boundaries in β-HMX was investigated using molecular dynamics and molecular statics simulations with 2D infinite crystal–crystal homophase interfaces created using the GCCM. The order of stabilities for the four grain boundaries studied is predicted to correlate with the relative prominence of particular crystal faces in lab-grown β-HMX crystals. We demonstrate how nanostructures can be constructed through simple constraints applied in the GCCM framework. Example GCCM constructions are shown that are relevant to some current problems in materials science, including shock sensitivity of explosives, layered electronic devices, and pharmaceuticals.

Two tautomeric forms of 2-amino-5,6-dimethylpyrimidin-4-one.

Derivatives of 4-hydroxypyrimidine are an important class of biomolecules. These compounds can undergo keto-enol tautomerization in solution, though a search of the Cambridge Structural Database shows a strong bias toward the 3H-keto tautomer in the solid state. Recrystallization of 2-amino-5,6-dimethyl-4-hydroxypyrimidine, C6H9N3O, from aqueous solution yielded triclinic crystals of the 1H-keto tautomer, denoted form (I). Though not apparent in the X-ray data, the IR spectrum suggests that small amounts of the 4-hydroxy tautomer are also present in the crystal. Monoclinic crystals of form (II), comprised of a 1:1 ratio of both the 1H-keto and the 3H-keto tautomers, were obtained from aqueous solutions containing uric acid. Forms (I) and (II) exhibit one-dimensional and three-dimensional hydrogen-bonding motifs, respectively.

A novel approach to study the isothermal and non-isothermal crystallization kinetics of Poly(Ethylene Terephthalate) by Raman spectroscopy

This paper focuses on the study of the crystallization kinetics of an initially quasi-amorphous Poly(Ethylene Terephthalate) (PET) during controlled heating treatments using Raman Spectroscopy. Characteristic vibrational bands of both crystalline and amorphous phases are then investigated in terms of wavenumber values, full widths at half maximum and integrated intensities variations which led to the establishment of a more accurate crystallinity ratio criterion than the one obtained by standard differential scanning calorimetry (DSC) analysis too much dependent on the low polymer thermal conductivity. Applying this last criterion, isothermal and non-isothermal crystallization kinetics were investigated following the Avrami’s and Ozawa’s theories in order to identify the germination and growth modes of the triclinic crystals of PET as a function of thermal treatment. Moreover, all the specific microstructural transitions such as cold crystallization, crystallization from the melt, melting and glass transition are detected and characterized. Similar thermal behaviors were obtained from Raman results and conventional differential scanning calorimetry measurements.

Triclinic nematic colloidal crystals from competing elastic and electrostatic interactions.

The self-assembly of nanoparticles can enable the generation of composites with predesigned properties, but reproducing the structural diversity of atomic and molecular crystals remains a challenge. We combined anisotropic elastic and weakly screened electrostatic interactions to guide both orientational and triclinic positional self-ordering of inorganic nanocrystals in a nematic fluid host. The lattice periodicity of these low-symmetry colloidal crystals is more than an order of magnitude larger than the nanoparticle size. The orientations of the nanocrystals, as well as the crystallographic axes of the ensuing triclinic colloidal crystals, are coupled to the uniform alignment direction of the nematic host, which can be readily controlled on large scales. We examine colloidal pair and many-body interactions and show how triclinic crystals with orientational ordering of the semiconductor nanorods emerge from competing long-range elastic and electrostatic forces.