Similar Unit Cell Research Articles

Two closely related polymorphs of ammonium trifluorooxovanadate

Two polymorphs of ammonium trifluorooxovanadate (NH4VOF3) were synthesized as single crystals by the reaction of ammonium metavanadate with vanadium in hydrofluoric acid. The two phases crystalize in the same space group (Pbam), have similar unit cell volumes (α-NH4VOF3:371 Å3, β-NH4VOF3:375 Å3 at 100 K), and similar total energies (difference of ∼2.2 meV per formula unit at 0 K). Both structures contain the [VOF3]nn− ladder motif that has been reported in phases such as KVOF3 and RbVOF3. The polymorphs are differentiated by the angle between two neighboring ladder motifs. Although the two polymorphs are structurally similar, selective synthesis is possible as longer reaction times favor β-NH4VOF3.

Modular Pressure and Flow Rate-Balanced Microfluidic Serial Dilution Networks for Miniaturised Point-of-Care Diagnostic Platforms.

Fast, efficient and more importantly accurate serial dilution is a necessary requirement for most biochemical microfluidic-based quantitative diagnostic applications. Over the last two decades, a multitude of microfluidic devices has been proposed, each one demonstrating either a different type of dilution technique or complex system architecture based on various flow source and valving combinations. In this work, a novel serial dilution network architecture is demonstrated, implemented on two entirely different substrates for validation and performance characterisation. The single layer, stepwise serial diluter comprises an optimised microfluidic network, where identical dilution ratios per stage are ensured, either by applying equal pressure or equal flow rates at both inlets. The advantages of this serial diluter are twofold: Firstly, it is structured as a modular unit cell, simplifying the required fluid driving mechanism to a single source for both sample and buffer solution. Thus, this unit cell can be used as a fundamental microfluidic building block, forming multistage serial dilution cascades, once combined appropriately with itself or other similar unit cells. Secondly, the serial diluter can tolerate the inevitable flow source fluctuations, ensuring constant dilution ratios without the need to employ damping mechanisms, making it ideal for Point of Care (PoC) platforms. Proof-of-concept experiments with glucose have demonstrated good agreement between simulations and measurements, highlighting the validity of our serial diluter.

Opencage radio frequency coil for magnetic resonance imaging

We present a volume radio frequency coil for Magnetic Resonance Imaging that provides access to the region of interest. While the conventional birdcage coil is composed of a periodic array of similar unit cells making a cylindrical structure, the proposed coil, called “opencage,” is made of an aperiodic array of metamaterial based unit cells presenting different geometries and characteristics. We develop here a dedicated approach based on Bloch impedance matching and phase balance for the design of the opencage coil. We perform full-wave numerical simulations to validate this concept. An experimental demonstration of the opencage coil for small animal imaging at 7 Tesla is presented. The results of the in-vitro, in-vivo imaging and B1+ map reconstruction achieved with a preclinical MRI scanner are presented. We show that B1+ field homogeneity and amplitude generated by the opencage coil are comparable to those of a conventional birdcage coil of the same size.

Reduced order derivation of the two-dimensional band structure of a mixed-mode resonator array

In this paper, the 2D band structure of a mixed-mode metamaterial resonator array for in-plane waves is investigated. The band structure in the interior and on the boundary of the irreducible Brillouin zone and 1D dispersion diagrams for different propagation angles are calculated numerically and presented. Additionally, a reduced order analytical method is established to compare and approximate the band structure. The studied metamaterial, with a T-shaped cantilever beam as the resonator in its square array repeating unit cells, exhibits branches with mixed P and SV waves except at exactly one angle of propagation. This paper also reports on the occurrence of avoided level crossings, which are related to the existence of exceptional points in the complex domain. A reduced order analytical approach is used that can generate partial (low branches) band structure with relatively little computational effort. The reduced order model agrees well with the numerical results for these low branches and can provide support in mode identification and band sorting. With proper adjustments in parameters, this analytical method will be applicable to other metamaterials that have a similar unit cell structure.

Ionic‐Liquid‐Based Synthesis of the Bromine‐Rich Bromidoplatinates [NBu3Me]2[Pt2Br10](Br2)2 and [NBu3Me]2[Pt2Br10](Br2)3

The bromine‐rich bromidoplatinates(IV) [NBu3Me]2[Pt2Br10](Br2)2 (1) and [NBu3Me]2[Pt2Br10](Br2)3 (2) were prepared by reaction of PtBr4 and elemental bromine in the ionic liquid [MeBu3N][N(Tf)2] [N(Tf)2 = bis(trifluoromethylsulfonyl)amide]. Both bromine‐rich bromidoplatinates(IV) contain [Pt2Br10]2– anions and [NBu3Me]+ cations as voluminous building units with an almost identical structural arrangement and very similar unit cells. The difference of the title compounds is related to the specific number of Br2 molecules that link the [Pt2Br10]2– anions to three‐dimensional networks. Whereas 1 is relatively stable under inert conditions, 2 releases bromine even at ambient pressure. The title compounds are characterized by single‐crystal structure analysis and Raman spectroscopy.

Spin-charge transport properties for graphene/graphyne zigzag-edged nanoribbon heterojunctions: A first-principles study

Graphene and graphyne hold great potential for spintronic device applications due to their exceptionally good electrical and mechanical properties in the pristine form. Recently, considering these 2D carbon allotropes have similar bond lengths and unit cell shapes, ensuring a perfectly matched interface between them and construction of graphene/graphyne heterojunctions feasible. To this end, we study the spin-charge transport properties for monolayer graphene/graphyne zigzag-edged nanoribbon heterojunctions by employing the ab initio calculations, where two types of γ- and (6,6,12)-graphynes are considered, respectively. Our important result here is that these heterojunctions can exhibit an interesting variation of magnetoresistane by applying ferromagnetic stripes or external magnetic fields onto the ribbons to initially orient their spin configuration. Specifically, the magnetoresistance ratio can be up to 104% for graphene/γ-graphyne heterojunction, but only 300% for the graphene/(6,6,12)-graphyne one. In addition, the effects of spin-filtering and negative differential resistance are also observed in those heterojunctions. The maximum of spin filtering efficiency can be up to 99%. The mechanisms are revealed and analyzed by the connection of these effects to the evolution of the spin-resolved electron transmission spectra and pathways around the Fermi level at zero bias.

Synthesis and Structural, Electrical, and Magnetic Properties of New Iron-Aluminum Alluaudite Phases β-Na2Ni2M(PO4)3 (M = Fe and Al).

Herein we report the studies of different physical properties (structural, magnetic, thermal, morphologic, electrical, and electrochemical) of two new allotropic β-Na2Ni2M(PO4)3 (NNMP) phosphates, with M = Fe and Al. Pure orthorhombic single-phase powders were prepared under air, using an autocombustion synthesis method. They crystallize in the orthorhombic Imma space group with similar unit cell parameters [a = 10.1592(2), b = 13.0321(3), c = 6.4864(2) Å] and [a = 10.3993(1), b = 13.1966(1), c = 6.4955(1) Å] for β-Na2Ni2M(PO4)3 (NNAP) and β-Na2Ni2Fe(PO4)3 (NNFP), respectively. Crystal structures of both compounds were determined using X-ray powder diffraction and Rietveld method refinements, which indicate the occurrence of Ni2+ in the 8g site, and of M3+ in the 4a site of the structure. The structure consists of a three-dimensional anionic framework obtained by the association on MO6, NiO6, and PO4 polyhedra, sharing edges and corners. The resulting three-dimensional structure creates monodimensional channels along the [100] and [010] directions formed by face-shared oxygen polyhedra and occupied by Na+ cations. This nondisordered cationic distribution is confirmed by a significant change of magnetic properties. Thus, both NNAP and NNFP samples show paramagnetic to ferromagnetic transition at 14 and 19 K, respectively. For the two compounds, thermal stability, electrical conductivity, and electrochemical properties have been also investigated. The intercalation/desintercalation properties of NNMP compounds as positive electrode were tested in sodium-ion batteries. The first cycling curves exhibit a significant polarization for both prepared samples.

Phase transitions of Cu3+xSi observed by temperature-dependent x-ray powder diffraction

Phases in the system Cu3+xSi were analyzed by temperature-dependent x-ray powder diffraction and differential scanning calorimetry on samples with nominal composition Cu74Si26 and Cu78Si22 in the temperature range between 30 °C and 700 °C. Contrary to previous works, which report three phases in the system, we identified six distinct phases, labeled, in order of increasing temperature, η‴, η″, η′, η3, η2, η1. All these phases can be indexed with a similar basic unit cell. However, each phase has a different superstructure or modulation vectors.

Canted Antiferromagnetism on Rectangular Layers of Fe2+ in Polymorphic CaFeSeO.

From stoichiometric amounts of CaO, Fe, and Se, pure powders and single crystals of quaternary [Formula: see text] can be obtained by solid-state reaction and self-flux growth, respectively. The as-synthesized compound exhibits a polymorphic crystal structure, where the two modifications have different stacking sequences of [Formula: see text] layers. The two polymorphs have similar unit cells but different crystal symmetries (Cmc21 and Pnma), of which the former is non-centrosymmetric. Fe is divalent (d6) and high-spin, as proven by X-ray spectroscopy, Mössbauer spectroscopy, and powder neutron diffraction data. The latter two, in combination with magnetic susceptibility and specific heat data, reveal a long-range antiferromagnetic spin order (TN = 160 K) with a minor spin canting. CaFeSeO is an electronic insulator, as confirmed by resistivity measurements and density functional theory calculations. The latter also suggest a relatively small energy difference between the two polymorphs, explaining their intimate intergrowth.

New tetrahedral zinc halide Schiff base complexes: Synthesis, crystal structure, theoretical, 3D Hirshfeld surface analyses, antimicrobial and thermal studies

A new bidentate Schiff base ligand named as N,N′-bis((E)-3-phenylallylidene)butane-1,4-diamine (L) and three its zinc halide complexes were synthesized and characterized by FT-IR, 1H NMR, 13C NMR and UV–Vis spectroscopy. The crystal structure of zinc bromide and iodide complexes were characterized using single crystal X-ray diffraction. The two structures are isomorphous, crystallizing in the monoclinic crystal system with space group C2/c with closely similar unit cell dimensions. In these complexes, the Zn(II) ion is in the center of a distorted tetrahedral environment completed by two iminic nitrogen atoms of Schiff base ligand and two halide anions. The analysis of crystal structures shows that intermolecular interactions such as CH⋯halogen, π⋯π and CH⋯π interactions have effective role in stabilization of complexes structure. Intermolecular interactions were more analyzed using 3D Hirshfeld surface analysis and corresponding 2D fingerprint plots. Furthermore, structural optimization by DFT calculations at the B3LYP/LANL2DZ level have been performed and then compared with the experimental data. Time-dependent density functional theory (TDDFT) has been also used to calculate the electronic transitions of molecules at B3LYP/LANL2DZ level using the optimized ground-state geometries. NBO analysis was applied for investigation of intra and inter-molecular bonding and conjugative interaction in molecular systems. Schiff base ligand and their zinc complexes have been screened for their antibacterial and antifungal activities by disc diffusion method. Thermal behaviors of all compounds were studied by TG/DTG analysis data. Also, nanostructures of zinc complexes were synthesized by sonochemical method and characterized by FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). ZnO nanoparticles were simply prepared by calcination of zinc iodide complex as new precursor at 600°C.

Thermal characterization of tetrabasic lead sulfate used in the lead acid battery technology

The thermal production of 4PbO·PbSO4 was comprehensively studied and characterized for two syntheses routes, i.e. either heating 3PbO·PbSO4·H2O, or a mixture of 4PbO:PbSO4, in air to about 700 °C. In the 3PbO·PbSO4·H2O approach, the formation of an intermediate amorphous phase occurred at around 210 °C with the loss of H2O from the hydrated structure. Formation of 4PbO·PbSO4 initiated at around 270 °C with predominantly 4PbO·PbSO4 and 13% residual PbO·PbSO4 existing at 700 °C. With the synthesis route of mixing a stoichiometric ratio of 4PbO with PbSO4, an intermediate phase of PbO·PbSO4 formed at around 300 °C, before the 4PbO·PbSO4 phase started to form at around 500 °C. Upon further heating, 4PbO·PbSO4 was the predominant phase with 8% of PbO·PbSO4 remaining. Both samples decomposed upon further heating to 850 °C. Powder neutron diffraction studies of the final 4PbO·PbSO4 products from the two different synthesis routes showed similar crystallographic unit cell lattice parameters with slight differences in the PbO:PbSO4 contents. This could possibly be linked to differences observed in the microscopic crystallite shapes from the two synthesis routes.

An Efficient Approach towards the Synthesis, Crystal Structures, DFT and Cytotoxic Activity of Highly Congested 11-Aryl-10,12-Dihydrodiindino[1,2-b‘,2′,1′-e]Pyridine

An efficient and novel method for the synthesis of a series of 11-aryl-10,12-dihydrodiindino[1,2- b‘,2′,1′- e]pyridine via one-pot multi-component reactions of aldehydes, indan-1-one and ammonium acetate has been delineated. All prepared compounds were structurally elucidated by IR, UV-Vis, 1H and 13C NMR and X-ray diffraction techniques. The molecules adopted monoclinic crystal system with P21/ c space group and almost similar unit cell dimensions. The X-ray molecular geometries of the studied compounds were in excellent agreement with those computed by B3LYP/6-311++G(d,p) level of theory. The energies of the frontier orbitals calculated by B3LYP/6-311++G(d,p) level of theory enabled monitoring the reactivity and stability of the title molecules. The non-linear optical properties (NLO) and pNA were also computed and discussed. Compounds have shown broad spectrum cytotoxic activity against some human tumour cell lines; two of them rendering the most profound effect.

Time Evolution of an Aluminogermanate Zeolite Synthesis: Segregation of Two Closely Similar Phases with the Same Structure Type

A synthesis of zeolite-like aluminogermanates using N,N,N-trimethyl-terc-butylammonium (TMTBA) and fluoride evolved from an initially crystallized zeolite with the AST Zeolite Framework Type and very little Al in it into an Al-free GeO2 phase with the same structure but a slightly smaller unit cell. In spite of both zeolites having the same framework type, same symmetry, a much similar unit cell size and almost the same framework composition, phase segregation occurred at intermediate crystallization times as the initial AST phase was gradually replaced by the new one. For reaction mixtures with a high Al content complete replacement of the large cell by the smaller cell phase was accomplished. The solids have been characterized by powder X-ray diffraction (XRD), Rietveld refinement from synchrotron diffraction data, multinuclear Nuclear Magnetic Resonance (NMR) of both intact and disolved solids and infrarred spectroscopy. The study reveals TMTBA can degrade under the crystallization conditions to initia...

The Identification and Synthesis of Lead Apatite Minerals Formed in Lead Water Pipes

Phosphate is added to drinking water in the UK to minimise the release of lead from lead water pipes. The phosphate encourages the formation of insoluble lead apatites on the walls of the pipe. Hydroxylpyromorphite Pb5(PO4)3OH is the lead apatite that is most often used to model lead levels in tap water; however, its presence has not been confirmed. Our aims were to identify the lead pipe apatite and synthesise it. The synthetic mineral would then be used in future solubility studies to produce better predictions of lead levels in tap water. XRD and FTIR were used to characterise the minerals on a range of lead pipes. Pyromorphite and hydroxylpyromorphite were absent and instead a range of mixed calcium lead apatites were present. For every five lead ions in the general formula Pb5(PO4)3X between one and two ions were replaced with calcium and there was evidence of substitution ofPO43-by eitherCO32-orHPO42-. Calcium lead apatites with similar unit cell dimensions to those found on lead water pipes were then synthesised. The calcium : lead ratio in these reaction mixtures was in excess of 500 : 1 and the resulting crystals were shown by TEM to be nanosized rods and flakes. The synthetic apatites that most closely resembled the unit cell dimensions of the apatites on lead water pipes were shown to be Pb3.4Ca1.3(PO4)3Cl0.03OH0.97, Pb3.6Ca1.2(PO4)3Cl0.07OH0.93, and Pb3.6Ca1.2(PO4)3Cl0.27OH0.73.

Low temperature mechanism of adsorption of methane: Comparison between homogenous and heterogeneous pores

Abstract The mechanisms of methane adsorption in (i) homogeneous carbon slit pores of widths between 1 nm and 2 nm and (ii) heterogeneous MOF pores of similar unit cell sizes have been compared. We discuss the mechanism of layering transition in subcritical conditions, for temperatures between 80 K and 180 K. The layer formation is strongly temperature-dependent. In slit pores it varies from a sharp adsorption at low temperatures to a more continuous uptake at higher temperatures. The pore size defines the number of adsorbed layers: the 1 nm pore allows adsorption of 2 layers while the 2 nm pore allows adsorption of 5 layers of methane molecules. We compare this behavior with the mechanism of adsorption in two MOFs, IRMOF-1 and IRMOF-16, with strongly heterogeneous walls (both structurally and energetically). This comparison allows us to discuss separately the influence of wall topology and intermolecular interactions on the mechanism of layering.

Chiral Resolution of RS-Praziquantel via Diastereomeric Co-Crystal Pair Formation with l-Malic Acid

Praziquantel (PZQ) is an important chiral active pharmaceutical ingredient for the treatment of gastrointestinal parasites, which is commercially available only in the form of its racemate. In this article, on the basis of co-crystallization experiments a convenient two-step protocol for the chiral resolution of RS-PZQ is described. Screening experiments with RS-PZQ using the liquid-assisted grinding technique revealed the formation of a diastereomeric co-crystal pair with l-malic acid (l-MA) of the compositions R-PZA:l-MA and S-PZQ:l-MA. Both co-crystals have been examined by single-crystal X-ray diffraction analysis, revealing similar unit cell parameters but differences in the supramolecular organization. Particularly the analysis of the hydrogen bonding patterns indicated overall stronger intermolecular interactions in the case of R-PZA:l-MA, which was confirmed by thermogravimetric–differential scanning calorimetry analysis giving a substantial difference in the melting point when compared to S-PZA:l...

An experimental and theoretical approach to investigate the effect of chain length on aminothiol adsorption and assembly on gold.

Despite the numerous studies on the self-assembled monolayers (SAMs) of alkylthiols on gold, the mechanisms involved, especially the nature and influence of the thiol-gold interface are still under debate. In this work the adsorption of aminothiols on Au(111) surfaces has been studied by using surface IR and X-ray photoelectron spectroscopy (XPS) as well as by density functional theory (DFT) modeling. Two aminothiols were used, cysteamine (CEA) and mercaptoundecylamine (MUAM), which contain two and eleven carbon atoms, respectively. By combining experimental and theoretical methods, it was possible to draw a molecular picture of the thiol-gold interface. The long-chain aminothiol produced better ordered SAMs, but, interestingly, the XPS data showed different sulfur binding environments depending on the alkyl chain length; an additional peak at low binding energy was observed upon CEA adsorption, which indicates the presence of sulfur in a different environment. DFT modeling showed that the positions of the sulfur atoms in the SAMs on gold with similar unit cells [(2√3×2√3)R30°] depended on the length of the alkyl chain. Short-chain alkylthiol SAMs were adsorbed more strongly than long-chain thiol SAMs and were shown to induce surface reconstruction by extracting atoms from the surface, possibly forming adatom/vacancy combinations that lead to the additional XPS peak. In the case of short alkylthiols, the thiol-gold interface governs the layer, CEA adsorbs strongly, and the mechanism is closer to single-molecule adsorption than self-assembly, whereas for long chains, interactions between alkyl chains drive the system to self-assembly, leading to a higher level of SAM organization and restricting the influence of the sulfur-gold interface.

Cyanato- and thiocyanato-substituted triangular clusters of molybdenum, [Mo3S4(dppe)3X3]+ (X = NCO−, NCS−; dppe = 1,2-bis(diphenylphosphino)ethane)

Two pseudohalido-substituted cluster complexes, [Mo3S4(dppe)3(NCS)3]NCS (1) and [Mo3S4(dppe)3(NCO)3]Br (2) (dppe = 1,2-bis(diphenylphosphino)ethane), have been synthesized by substitution between [Mo3S4(dppe)3Br3]Br and potassium thiocyanate or sodium cyanate, respectively, in boiling acetonitrile. The compounds were characterized by IR-spectroscopy, elemental analysis, electrospray mass-spectrometry, and single-crystal X-ray diffraction analysis. Both compounds crystallize as toluene solvates (1·3C6H5CH3 and 2·2.5C6H5CH3) in space group with similar unit cell dimensions and adopt very similar molecular geometries. Both structures consist of discrete cluster cations [Mo3S4(dppe)3X3]+, NCS− or Br− anions, and solvate toluene molecules.

Non‐isothermal Crystallization Kinetics of Biobased Poly(ethylene 2,5‐furandicarboxylate) Synthesized via the Direct Esterification Process

Poly(ethylene 2,5‐furandicarboxylate) (PEF) is an emergent biobased polyester whose chemical structure is analogous to poly(ethylene terephthalate). Pilot‐scale PEF is synthesized through the direct esterification process from 2,5‐furandicarboxylic acid and bio‐ethylene glycol. Wide‐angle X‐ray diffraction (WAXD) measurements reveal similar crystallinities and unit cell structures for melt‐crystallized and glass‐crystallized samples. The non‐isothermal crystallization of PEF sample is investigated by means of DSC experiments both from the glass and the melt. The temperature dependence of the effective activation energy of the growth rate is obtained from these data, and the results show that the glass and early stage of the melt crystallization share common dynamics. Hoffman–Lauritzen parameters and the temperature at maximum crystallization rate are evaluated. It is found that the melt‐crystallization kinetics undergo a transition from regime I to II; however, the crystal growth rate from the melt shows an atypical depression at T < 171 °C compared with the predicted Hoffman–Lauritzen theory. image

Chirality control of the Quadruple helixes of the metal strings

Novel chiral pentadentate ligands with naphthyridine and camphorsulfonyl groups have been designed and used to control the chirality of quadruple helixes of metal strings directly:Δ-Ni5((-)camnpda)4 (1) and Λ-Ni5((+)camnpda)4 (2). Compound 1 is a Δ form metal string complex with H2(-)camnpda and 2 is Λ form one with H2(+)camnpda. By X-ray single-crystal diffraction, The structures of the compound 1 and 2 are both 2,2-trans form in the same monoclinic space group C2 and have the similar unit cell. Further, it demonstrates that two metal strings are chiral isomers each other by CD spectra. In theoretical computation, the local minimum (Λ-Ni5((+)camnpda)4 with the Δ form) becomes energetically unfavourable by about 100 kcal/mol due to the strong steric repulsion introduced by the camphor groups. Finally, the racemic crystal is obtained with a 1:1 mixture of compounds 1 and 2 in triclinic space group P-1. Both the external dinickel distance in 1 and 2, about 2.280 Å, and the SQUID experiment reveal mixed valence [Ni2]3+ characters and the magnetic behaviors are anti-ferromagnetic (J = -55.0 cm-1 for 1 and -63.3 cm-1 for 2). In the electrochemistry, the three reversible oxidation waves in 1 and 2 are -0.13, 0.20 and 0.97 V.