Similar Unit Cell Research Articles

High-pressure/high-temperature synthesis of Ln 2CdB5O11(OH) (Ln = Tm, Lu)

Abstract This report presents work on the orthorhombic phases Ln 2CdB5O11(OH) (Ln = Tm, Lu). The title compounds were synthesized in a Walker-type multianvil device at 7 GPa and 650 °C, and the resulting samples were thoroughly investigated through single-crystal and powder X-ray diffraction methods. Lu2CdB5O11(OH) crystallizes in the space group Pmna (no. 53) with the unit cell parameters a = 12.772(2), b = 4.6017(7), and c = 12.481(2) Å. Similar unit cell parameters are observed for the isotypic Tm analogue compound. The crystals have a layered crystal structure built up by four-, five-, and eight-membered rings of corner-sharing [BO4] tetrahedra. The structural data are accompanied by attenuated total reflection (ATR) infrared spectra and energy-dispersive X-ray spectroscopy (EDX).

Crystal structures of two formamidinium hexa-fluorido-phosphate salts, one with batch-dependent disorder.

Syntheses of the acyclic amidinium salts, morpholino-formamidinium hexa-fluorido-phosphate [OC4H8N-CH=NH2]PF6 or C5H11N2O+·PF6 -, 1, and pyrrolidinoformamidinium hexa-fluorido-phosphate [C4H8N-CH= NH2]PF6 or C5H11N2 +·PF6 -, 2, were carried out by heating either morpholine or pyrrolidine with triethyl orthoformate and ammonium hexa-fluorido-phosphate. Crystals of 1 obtained directly from the reaction mixture contain one cation and one anion in the asymmetric unit. The structure involves cations linked in chains parallel to the b axis by N-H⋯O hydrogen bonds in space group Pbca, with glide-related chains pointing in opposite directions. Crystals of 1 obtained by recrystallization from ethanol, however, showed a similar unit cell and the same basic structure, but unexpectedly, there was positional disorder [occupancy ratio 0.639 (4):0.361 (4)] in one of the cation chains, which lowered the crystal symmetry to the non-centrosymmetric space group Pca21, with two cations and anions in the asymmetric unit. In the pyrrolidino compound, 2, cations and anions are ordered and are stacked separately, with zigzag N-H⋯F hydrogen-bonding between stacks, forming ribbons parallel to (101), extended along the b-axis direction. Slight differences in the delocalized C=N distances between the two cations may reflect the inductive effect of the oxygen atom in the morpholino compound.

The synthesis, spectroscopic characterization, and crystallographic study of the tetra-phenylimido-diphosphinates of Sc, Y, La, and Lu

In the present study, we report the synthesis, spectroscopic characterization, and X-ray single crystal structural determination of four rare earth complexes, M[Ph2P(O)NP(O)PPh2]3, M = Sc, Y, La, and Lu. The structural study reveals that the Sc, Y, and Lu complexes have coordination numbers of six, while the La complex shows a coordination number of seven, through the presence of the additional coordination of a water molecule with a square-face-capped geometry, where the water molecule enables the formation of a dimeric structure through OH…O hydrogen bond interactions. The metal ions M3+, Sc, Y, La, and Lu are coordinated to the [Ph2P(O)NP(O)Ph2]− ligand with a delocalized phosphazenic PNP system in an O,O isobidentate manner, generating carbon-free metallo-inorganic six-membered rings, of which one acquires the a (anti-parallel) conformation and the other two the twist-boat conformation. The Y and Lu complexes crystallized with similar unit cells, M…O distances, and O…M…O angles that are consequences of their similar crystal radii related to the lanthanide contraction in Lu, while the La complex has a coordination number of seven through the coordination of a water molecule and a square-face-capped geometry. The O-M-O angles in the complexes suggest that the bite of the ligand depends on the size of the metal ion, the flexibility, and the steric effects of the tetra-phenyl-imidodiphosphinate ligand.

Conformally graded metamaterials for elastic wave guidance

Although metamaterials have been widely used for controlling elastic waves through bandgap engineering, the directed guidance of stress waves in non-periodic structures has remained a challenge. This work demonstrates that spatially graded metamaterials based on conformal mappings present a rich design space for controlling and attenuating wave motion — without the need for bandgaps. Conformal mappings transform an elementary unit cell by scaling and rotation into graded lattices with approximately geometrically similar unit cells. This self-similarity allows for control over the local wave dispersion throughout the metamaterial. As a key mechanism, it is shown that elastic waves cannot propagate through graded unit cells with significant size differences, except at low frequencies. This is exploited to create low-pass elastic wave guides, extending beyond classical bandgap engineering, since bandgaps are not required to achieve wave guiding and attenuation. Experiments confirm the low-pass elastic wave filtering capability of a planar truss metamaterial with conformal grading. Finally, a systematic design of curved metamaterial surfaces is presented, providing a flexible framework for programming low-pass attenuation and wave guiding in three dimensions.

Crystal structure of heteroepitaxial BaTiO3–KNbO3 core–shell nanocomposite particles studied by synchrotron radiation X-ray diffraction

Abstract We investigated the temperature-dependent crystal structure of a BaTiO3−KNbO3 (BT−KN) nanocomposite particle in which the KN shell epitaxially covers the BT core. Synchrotron radiation X-ray diffraction experiments were performed over a temperature range of 300–800 K. Near the interface, BT and KN were found to be bonded in a pseudo-cubic crystal structure with similar lattice constants across all temperatures. As the temperature decreased, strain-gradient regions (SGRs) near the interface, caused by lattice mismatch, enlarged significantly owing to phase transitions. The largest SGRs with a tetragonal BT core and an orthorhombic KN shell were observed at 300 K. However, SGRs were minimal at 800 K, where both BT and KN possessed cubic crystal structures. Engineering interfaces such as SGRs can enhance the dielectric constant; therefore, it is crucial to consider material combinations with different crystal symmetries but similar unit cell volumes, such as BT−KN at RT.

Layered 3D Covalent Organic Framework Films Based on Carbon-Carbon Bonds.

The development of covalent organic frameworks (COFs) during the past decades has led to a variety of promising applications within gas storage, catalysis, drug delivery, and sensing. Even though most described synthesis methods result in powdery COFs with uncontrolled grain size, several approaches to grow COF films have recently been explored. However, in all COFs so far presented, the isolated materials are chemically homogeneous, with all functionalities homogeneously distributed throughout the entire material. Strategies to synthetically manipulate the spatial distribution of functionalities in a single film would be game changing. Specifically, this would allow for the introduction of local functionalities and even consecutive functions in single frameworks, thus broadening their synthetic versatility and application potential. Here, we synthesize two 3D crystalline COF films. The frameworks, the ionic B-based and neutral C-based COFs, have similar unit cell parameters, which enables their epitaxial stacking in a layered 3D COF film. The film growth was monitored in real time using a quartz crystal microbalance, showing linear growth with respect to reaction time. The high degree of polymerization was confirmed by chemical analysis and vibrational spectroscopy. Their polycrystalline and anisotropic natures were confirmed with grazing incidence X-ray diffraction. We further expand the scope of the concept by making layered films from COF-300 and its iodinated derivative. Finally, the work presented here will pave the path for multifunctional COF films where concurrent functionalities are embedded in the same crystalline material.

Improved Birefringence Activated by Tetrahedra Decorated with a Single Linear Unit

AbstractPerformance enhancement induced by structural modification has long been the target in materials science fields. Direct evidence to witness the effectivity of one strategy is challenging and necessary. In this work, a tetrahedra‐decoration strategy was proposed to improve the birefringent performance sharply, namely decorating the tetrahedra with a single linear [S2] unit. The strategy was verified by comprehensive characterization of two thiogermanates K2BaGeS4 and K2BaGeS5, which crystallize in the same space group, have similar unit cells and the same units arrangements. Theoretical characterization verified that the [GeS5] group has much larger polarization anisotropy than [GeS4], further demonstrated that the linear [S2] led to the sharp birefringence enlargement of K2BaGeS5 (0.19 vs 0.03 of K2BaGeS4). This work provides a new guiding thought to improve the birefringence performance.

Improved Birefringence Activated by Tetrahedra Decorated with Single Linear Unit.

Performance enhancement induced by structural modification has long been the target in materials science fields. Direct evidence to witness the effectivity of one strategy is challenging and necessary. In this work, a tetrahedra-decoration strategy was proposed to improve the birefringent performance sharply, namely decorating the tetrahedra with single linear [S2] unit. The strategy was verified by comprehensive characterization of two thiogermanates K2BaGeS4 and K2BaGeS5, which crystallize in the same space group, have similar unit cells and the same units arrangements. Theoretical characterization verified that the [GeS5] group has much larger polarization anisotropy than [GeS4], further demonstrated that the linear [S2] lead to the sharp birefringence enlargement of K2BaGeS5 (0.19 vs 0.03 of K2BaGeS4). This work provides a new guiding thought to improve the birefringence performance.

MOF-derived crystalline carbon with graphite-like crystal: A high initial coulombic efficiency, low potential and large capacity anode for Na-ion batteries

Carbonaceous materials, such as hard carbon and porous carbon, have gained great attentions as the anode materials for Na-ion batteries (NIBs). However, their defects and disordered structure cause the low initial coulombic efficiency (ICE), high-potential slope region and small charge capacity below 0.5 V. Herein, a structurally stable MOF contained 1,3,5-triazine-2,4,6-triamine moieties, belonging to the tetragonal space group I 4/m, is synthesized. On this basis, MOF-derived crystalline carbon with graphite-like crystal, instead of amorphous porous carbon, can be obtained due to slow pyrolysis of MOF framework along with timely and sufficient reassembly of the pyrolyzed carbon atoms into graphite-like crystal under graphite-induced condition. The graphite-like crystal has a geometrically similar unit cell to graphite crystal but with a magnification ratio of 1.25, yielding proportionally expanded d-spacing of (002) plane (4.2 Å), which enables the reversible Na+ intercalation/de-intercalation. When applied in NIBs, it exhibits a very high ICE of 96.0% and reversible charge capacity of 356.2 mAh g−1, reaching the advanced level of graphite applied in LIBs. More importantly, its charge capacity below 0.5 V can account for 90% of the total charge capacity, which is also the key parameter to effectively increase the energy density of full batteries.

High-throughput phase elucidation of polycrystalline materials using serial rotation electron diffraction

Rapid phase elucidation of polycrystalline materials is essential for developing new materials of chemical, pharmaceutical and industrial interest. Yet, the size and quantity of many crystalline phases are too small for routine X-ray diffraction analysis. This has become a workflow bottleneck in materials development, especially in high-throughput synthesis screening. Here we demonstrate the application of serial rotation electron diffraction (SerialRED) for high-throughput phase identification of complex polycrystalline zeolite products. The products were prepared from a combination of multiple framework T atoms ([Si,Ge,Al] or [Si,Ge,B]) and a simple organic structure-directing agent. We show that using SerialRED, five zeolite phases can be identified from a highly complex mixture. This includes phases with ultra-low contents undetectable using X-ray diffraction and phases with identical crystal morphology and similar unit cell parameters. By automatically and rapidly examining hundreds of crystals, SerialRED enables high-throughput phase analysis and allows the exploration of complex synthesis systems. It provides new opportunities for rapid development of polycrystalline materials.

Noncentrosymmetric Supramolecular Hydrogen-Bonded Assemblies Based on Achiral Pyrazine-Bridged Zinc(II) Coordination Polymers with Pyrazinedione Derivatives

Reaction of M(OAc)2·xH2O (M, x = Zn, 2 and Co, 4), 1,4-dihydro-5,6-dicyano-2,3-pyrazinedione (H2CN2pyzdione), and pyrazine (pyz) affords two compounds of the same molecular formula {[M(H2O)6][M(CN2pyzdione)2(pyz)]·6H2O}n (M = Zn for 1 and Co for 2) in which discrete units of [M(H2O)6]2+ are linked to one-dimensional chains of [M(CN2pyzdione)2(pyz)]2– via multiple O–H···O hydrogen-bonding interactions and M2+-bound H2O molecules in [M(H2O)6]2+ also serve as linkers of hydrogen-bonded interstitial H2O molecules. Remarkably, 1 crystallizes in the monoclinic crystal system, the similar crystal system and unit cell parameters as 2, but with a space group distinct from 1 and 2, i.e., 1 is the noncentrosymmetric space group C2, whereas 2 is the centrosymmetric space group C2/m. This polar structure for 1 is induced by the presence of alternating arrangements of distinguishable two axial Zn–N bonds within [Zn(CN2pyzdione)2(pyz)]2– chains. Indeed, solid-state circular dichroism spectra of 1 exhibit significant Cotton effects, as evidenced by the polar space group C2. Moreover, these Cotton effects show clear temperature-dependence depending on contents of H2O molecules of 1.

Influence of the deposition process on the Cr2AlC phase formation during heat treatment of Cr-Al-C thin films

This paper focuses on the Cr2AlC phase formation during annealing post-treatment, with amorphous Cr-Al-C and (Cr,Al)2C as initial phases in the as-deposited state. The influence of the deposition process on the Cr2AlC formation, texture, and phase composition is investigated and an in-depth discussion of the intermediate phase is carried out. Cr-Al-C thin films were deposited by Direct Current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering with the variation of the deposition temperature. To investigate the microstructure, phase composition, and texture, in situ synchrotron and high-temperature X-ray diffraction experiments were conducted and accompanied by electron microscopy. The Cr2AlC formation can be described as a temperature and time-dependent process with one intermediate state characterized by the formation of the disordered-Cr2AlC phase. Disordered-Cr2AlC shows a similar unit cell to Cr2AlC with an increased c/a ratio. The ratio decreases during the phase formation resulting from an ordering process. Formation temperatures depend on the initial phase, with a decreased formation temperature for (Cr,Al)2C, and the deposition process. While the (002) fiber texture of (Cr,Al)2C inherited to Cr2AlC, Cr2AlC originated from amorphous Cr-Al-C showed no preferred orientation. The coatings contained Cr7C3 as an additional phase, dependent on the deposition process and initial phases.

Zn(II) halide coordination compounds with imidazole and 2-methylimidazole. Structural and computational characterization of intermolecular interactions and disorder

Novel zinc(II) coordination compounds with imidazole (Im) and 2-methylimidazole (2-MeIm) were prepared and characterized: [ZnX2(Im)2] (X = Cl (1a), Br (1b), I (1c)) and [ZnX2(2-MeIm)2] (X = Cl (2a), Br (2b), I (2c)). Coordination compounds 1a–c were prepared mechanochemically by neat grinding while 2a–c were prepared by solution synthesis. The complexes were characterized by FT-IR and NMR spectroscopy and by powder X-ray diffraction. Crystal and molecular structures were determined by the single crystal X-ray diffraction. The characteristic of all structures is a distorted tetrahedral coordination of zinc consisting of two halide atoms and two nitrogen atoms from the imidazole (or 2-methylimidazole) ligand. Molecules in 1a–c are interconnected by hydrogen bonds into 3D structures. Structures of 1b and 1c were found to have similar unit cells and similar crystal packing and hydrogen bonding. Introduction of the 2-methylimidazole substituent introduced disorder in the crystal structures of 2a–c. Because of the very small size of the crystals data were collected by synchrotron radiation. For the disordered 2a,2b and 2c fixed geometry was used in refining of the structures. Crystal structures of 2a–c are characterized by chains of molecules connected by hydrogen bonds of the type N–H⋅⋅⋅X, with weak π⋅⋅⋅π and van der Waals interactions between the chains. The QTAIM, RDG and NCI computational analysis of 1a and 2a–c confirmed the presence of weak attractive intermolecular interactions that can be attributed to weak N–H⋅⋅⋅X and van der Waals interactions.

MICROEMULSION-BASED METHOD OF SYNTHESIS OF ZINC-NICKEL FERRITE AND THEIR MAGNETIC PROPERTIES

Solid solutions of nickel-zinc ferrites ZnxNi1-xFe2O4 were synthesized by two different methods: synthesis in microemulsions and by stepwise precipitation. The properties of the resulted nano-sized particles synthesized by two different methods were compared. It was found that the increase in zinc content leads to an increase in the lattice parameters. During the synthesis by the method of microemulsions, the temperature of a single-phase product formation is 400 °C, while by the method of precipitation, a single-phase product formation begins at 600 °C. It was shown that the materials synthesized by both methods have similar unit cell parameters. The average size of ferrite nanoparticles synthesized in microemulsions is smaller, lattice strain is higher compared to ferrites synthesized by stepwise precipitation. Also, lower treatment temperatures provide higher stoichiometry, and homogeneity of materials while magnetization difference is negligible. The particles of the obtained powders have high saturation magnetization Ms = 45.6 Am2/kg for synthesis from microemulsions and Ms = 44.8 Am2/kg for co-precipitated samples, the low coercive force Hc = 1.3 kA/m and Hc = 3 kA/m, respectively. Changes made make synthesized particles more applicable in film deposition, and manufacturing of high-quality magnetic coatings.

Thermal-hydraulic performance of additively manufactured lattices for gas turbine blade trailing edge cooling

• Thermal-hydraulic performance of four lattice frame materials, namely, Octet, Tetrakaidecahedron, Face diagonal-cube, and Cube is studied for turbine edge cooling application. • Face diagonal-cube provided the highest heat transfer coefficient and pressure drop values amongst the investigated samples at similar porosity values and unit cell size. • Cube topology yielded the lowest flow losses and consequently highest thermal–hydraulic performance of ∼ 2.78 at the lowest investigated Reynolds number. Gas turbine blade trailing edge cooling is challenging because of the stringent geometrical constraints driven by aerodynamics and thermal stresses. The blade topology becomes significantly thin towards the trailing edge which leaves a narrow room for the construction of internal cooling channels and also makes this section susceptible to failure due to thermal stresses. Conventionally, pin-fins are employed in the internal cooling channels of the trailing edge because they provide high levels of heat transfer coefficient values and also structural integrity. Much of the past studies on pin fins have focused on their relative arrangements, heights, crossflow scheme, etc., with an aim to enhance the endwall heat transfer coefficient as well as leverage the conjugate heat dissipation capabilities of these “extended surfaces”. Lattices on the other hand, have been investigated to a lesser degree, and some studies can be found for blade mid-chord region, however, with their manufacturability challenges at that time, the concepts did not gain traction. Lattices are far more complex topologies with superior local heat transfer characteristics as well as high conjugate heat dissipation capabilities due to large wetted surface area. With the recent advancements in metal additive manufacturing, complex topologies such as lattices can be revisited due to high chances of their realization now. To this end, we are presenting our study on lattices additively manufactured in 420 Stainless Steel (thermal conductivity nearly twice of Inconel 718), where four different unit cell topologies, (a) Octet, (b) Tetrakaidecahedron, (c) Face diagonal-cube, and (d) Cube, were printed using Binder Jetting technology. The aim of this study is to characterize the conjugate heat transfer capabilities of these lattices manufactured in 420 Stainless Steel prior to conduct similar study with Inconel 718, due to relatively simpler additive manufacturing route of Binder jetting (420 stainless steel) compared to Direct Metal Laser Sintering (Inconel 718). The intended design porosity of the samples was 0.886 and the coupons had single unit cell (edge size of 10 mm) in the thickness. The steady-state experiments were conducted to evaluate the effective thermal conductivity and forced convective heat transfer performance. For forced convection, the experiments were conducted for a wide range of Reynolds numbers with air as the working fluid. Overall heat transfer coefficient, pressure drop, Nusselt number and friction factor enhancement level and pumping power requirements of these structures are presented. The implications of the porosity variation due to manufacturing process on the interpretation of relative performance trends is discussed. The effective thermal conductivity was independent of the topology for considered porosity value. Face diagonal-cube yielded the highest heat transfer and pressure drop for the investigated Reynolds number range. However, Cube provided the best overall thermal hydraulic performance value of 1.94 to 2.78 for the investigated range of Reynolds number. At fixed pumping power conditions, Cube was capable of providing the highest heat transfer coefficient.

Iron(II) Complexes of 4-(Alkyldisulfanyl)-2,6-di(pyrazolyl)pyridine Derivatives. Correlation of Spin-Crossover Cooperativity with Molecular Structure Following Single-Crystal-to-Single-Crystal Desolvation.

The complex salts [Fe(L1)2]X2 (1X2; L1 = 4-(isopropyldisulfanyl)-2,6-bis(pyrazolyl)pyridine; X– = BF4–, ClO4–) form solvated crystals from common organic solvents. Crystals of 1X2·Me2CO show abrupt spin transitions near 160 K, with up to 22 K thermal hysteresis. 1X2·Me2CO cocrystallizes with other, less cooperative acetone solvates, which all transform into the same solvent-free materials 1X2·sf upon exposure to air, or mild heating. Conversion of 1X2·Me2CO to 1X2·sf proceeds in a single-crystal to single-crystal fashion. 1X2·sf are not isomorphous with the acetone solvates, and exhibit abrupt spin transitions at low temperature with hysteresis loops of 30–38 K (X– = BF4–) and 10–20 K (X– = ClO4–), depending on the measurement method. Interestingly, the desolvation has an opposite effect on the SCO temperature and hysteresis in the two salts. The hysteretic spin transitions in 1X2·Me2CO and 1X2·sf do not involve a crystallographic phase change but are accompanied by a significant rearrangement of the metal coordination sphere. Other solvates 1X2·MeNO2, 1X2·MeCN, and 1X2·H2O are mostly isomorphous with each other and show more gradual spin-crossover equilibria near room temperature. All three of these lattice types have similar unit cell dimensions and contain cations associated into chains through pairwise, intermolecular S···π interactions. Polycrystalline [Fe(L2)2][BF4]2·MeNO2 (2[BF4]2·MeNO2; L2 = 4-(methyldisulfanyl)-2,6-bis(pyrazolyl)pyridine) shows an abrupt spin transition just above room temperature, with an unsymmetrical and structured hysteresis loop, whose main features are reversible upon repeated thermal scanning.

Structure, thermal stability and transport properties of heat-resistant high-entropy ZrTiHfNb alloy

The problem of phase stability is one of the key problems in the study of high-entropy alloys. Here we address this issue for a heat-resistant high-entropy TiZrHfNb alloy with a bcc structure. The evolution of the structure of this alloy is studied during isothermal annealing at T=400oC. It was found that the as-cast alloy consists of two coexisting bcc phases with similar unit cell parameters. This state is homogenized during annealing. Still, the highly stressed nanostructured state is retained and the texture is enhanced. The thermal conductivity of the alloy in the temperature range of 20-400oC changes in the range of 8-16 W/m·K, which is comparable in order of magnitude with the thermal conductivity of steels. Keywords: high-entropy alloys, heat-resistant alloys, phase stability.

Crystal Structure of Na2V2(PO4)3, an Intriguing Phase Spotted in the Na3V2(PO4)3–Na1V2(PO4)3 System

The Na superionic conductor (NASICON) Na3V2(PO4)3 is an important positive electrode material for Na-ion batteries. Here, we investigate the mechanisms of phase transition in NaxV2(PO4)3 (1 ≤ x ≤ 4) upon nonequilibrium battery cycling. Unlike the widely believed two-phase reaction in a Na3V2(PO4)3–Na1V2(PO4)3 system, we determine, for the first time, the structure of a recently reported intermediate Na2V2(PO4)3 phase using operando synchrotron X-ray diffraction. Density functional theory calculations further support the existence of the Na2V2(PO4)3 phase. We propose two possible crystal structures of Na2V2(PO4)3 analyzed by Rietveld refinement. The two structure models with the space groups P21/c or P2/c for the new intermediate Na2V2(PO4)3 phase show similar unit cell parameters but different atomic arrangements, including vanadium charge ordering. As the appearance of the intermediate Na2V2(PO4)3 phase is accompanied by symmetry reduction, Na(1) and Na(2) sites split into several positions in Na2V2(PO4)3, in which one of the splitting Na(2) position is found to be a vacancy, whereas the Na(1) positions are almost fully filled. The intermediate Na2V2(PO4)3 phase reduces the lattice mismatch between Na3V2(PO4)3 and Na1V2(PO4)3 phases, facilitating a fast phase transition. This work paves the way for a better understanding of great rate capabilities of Na3V2(PO4)3.

A numerical homogenization technique for unidirectional composites using polygonal generalized finite elements

The present study proposes a computational methodology to obtain the homogenized effective elastic properties of unidirectional fibrous composite materials by using the generalized finite-element method and penalization techniques to impose periodic boundary conditions on non-uniform polygonal unit cells. Each unit cell is described by a single polygonal finite element using Wachspress functions as base shape functions and different families of enrichment functions to account for the internal fiber influence on stresses and strains fields. The periodic boundary conditions are imposed using reflection laws between two parallel opposing faces using a Lagrange multiplier approach; this reflection law creates a distributed reaction force over the edges of the [Formula: see text]-gon from the direct application of a given deformation gradient, which simulates different macroscopic load cases on the macroscopic body the unit cell is part of. The methodology is validated through a comparison with results for similar unit cells found in the literature and its computational efficiency is compared to simple cases solved using a classic finite-element approach. This methodology showed computational advantages over the classic finite elements in both computational efficiency and total number of degrees of freedom for convergence and flexibility on the shape of the unit cell used. Finally, the methodology provides an efficient way to introduce non-circular fiber shapes and voids.

Zwitterion coordination to configurationally flexibled10cations: synthesis and characterization of tetrakis(betaine) complexes of divalent Zn, Cd, and Hg

AbstractThed10ions MII(M = Zn, Cd, Hg) and four equivalents of the neutral zwitterion trimethylglycine (betaine, bet) aggregate to discrete six-coordinated cationic complexes. With nitrate as counter anions, solids of the composition [M(bet)4](NO3)2·H2O are obtained. Their structural characterization reveals close relationship: they crystallize in metrically similar unit cells adopting three different subgroups of a hypothetical aristotype. In all cases, the divalent cations exhibit a strongly distorted coordination sphere in which two betaine ligands bind with both carboxylato O atoms and the other two with only one oxygen to the cation. Non-coordinating O atoms of different betaine ligands act as hydrogen bond acceptors towards co-crystallized water molecules. At least for the Pearson-soft HgIIcations, this coordination is unexpected: to the best of our knowledge, HgIIcomplexes with four carboxylato ligands have not yet been characterized. Without the necessity for charge balancing, the composition of zwitterion complexes is dominated by steric requirements and possibly by competition with alternative dipole molecules such as solvent water.