Crystalline Motifs Research Articles

Nanoparticle-directed bimodal crystallization of the quasi-1D van der Waals phase, Bi4I4.

Anisotropy often yields unexpected structures and properties in the solid state. In van der Waals (vdW) solids comprised of 1D or quasi-1D (q-1D) building blocks, anisotropy in both intra- and inter-chain directions results in an abundance of crystalline packing motifs and drastically altered physical states. Among these, structurally and chemically complex 1D/q-1D vdW solids that display topologically protected states, unique optical properties, and enhanced electrical transport properties in 1D are sought after owing to their potential as building blocks for next-generation quantum devices that approach the sub-nanometer regime. Yet, the access to such facet- and edge-specific physical states is still limited by the stochastic nature of micromechanical exfoliation. Here, we demonstrate that the representative Bi4I4 phase, an established pnictohalide q-1D vdW topological insulator in the bulk, can be crystallized from the vapor phase either into well-defined nanowires or quasi-2D nanosheets. We find that gold nanoparticles (Au NPs) on the growth substrate, in conjunction with the highly anisotropic structure of Bi4I4 common to many q-1D vdW crystals, direct the dimensionality of high-purity Bi4I4 nanostructures. Systematic variation of Au NP diameters, Bi : I precursor ratios, and growth-deposition temperatures reveal that Au NPs generally act as nucleation sites for vapor-solid (VS) growth of Bi4I4 nanowires. Strikingly, post-synthesis analyses of the elemental composition of 20 nm Au NPs on the substrate surface show an equisotichiometric 1 : 1 ratio of Bi to I within the Au NP that triggers the vapor-liquid-solid (VLS) growth of [001]-oriented quasi-2D nanosheets comprised of laterally-ordered [Bi4I4]n chains along the perpendicular [100] direction. We rationalize the observed bimodal growth pathways and the morphologically distinct nanostructures based on crystallization habits and orientations of the nanostructures, Bi : I ratios in the resulting Au NPs post-synthesis, and the orientation of stereochemically active Bi lone pairs between adjacent chains. We anticipate that these growth pathways are adaptable to the synthesis of emergent halide- and chalcogen-based 1D vdW nanocrystals with diverse physical and quantum properties.

Pt-induced atomic-level tailoring towards paracrystalline high-entropy alloy

Paracrystalline state achieved in the diamond system guides a direction to explore the missing link between amorphous and crystalline states. However, such a state is still challenging to reach in alloy systems in a controlled manner. Here, based on the vast composition space and the complex atomic interactions in the high-entropy alloys (HEAs), we present an “atomic-level tailoring” strategy to create the paracrystalline HEA. The addition of atomic-level Pt with the large and negative mixing enthalpy induces the local atomic reshuffling around Pt atoms for the well-targeted local amorphization, which separates severe-distorted crystalline Zr-Nb-Hf-Ta-Mo HEA into the high-density crystalline MRO motifs on atomic-level. The paracrystalline HEA exhibits high hardness (16.6 GPa) and high yield strength (8.37 GPa) and deforms by nanoscale shear-banding and nanocrystallization modes. Such an enthalpy-guided strategy in HEAs can provide the atomic-level tailoring ability to purposefully regulate structural characteristics and desirable properties.

The Crystalline Behavior and Device Function of Nonfullerene Acceptors in Organic Solar Cells

AbstractThe current research investigates the structure features and intermolecular interactions of nonfullerene acceptors (NFAs) in single crystal and thin films, as well as their solar cell applications. Guiding parameters and key intermolecular forces that lead to 2D brickwork or 3D web packing are identified. The atomic modification is shown as the key to induce hydrogen bonding or π–π stacking column, which results in different crystalline packing. The molecular assembly in thin film is initiated by hydrogen bonding, and completed by π–π stacking reorganization. The packing energy is seen as a guiding parameter that dictates the NFA crystalline morphology in blended thin films. The crystalline packing motif is not directly related with device efficiency. However, the crystalline morphology is the key parameter to influence exciton/carrier dynamics and device performance. A broader picture on the scaling behavior of organic semiconductor crystals ranging from oligoacenes to NFAs is established.

Understanding first-order Raman spectra of boron carbides across the homogeneity range

Boron carbide, a lightweight, high temperature material, has various applications as a structural material and as a neutron absorber. The large solubility range of carbon in boron, between $\ensuremath{\approx}9%$ and 20%, has been theoretically explained by some of us by the thermodynamical stability of three icosahedral phases at low temperature, with respective carbon atomic concentrations: 8.7% (${\mathrm{B}}_{10.5}\mathrm{C}$, named ${\mathrm{OPO}}_{1}$), 13.0% (${\mathrm{B}}_{6.7}\mathrm{C}$, named ${\mathrm{OPO}}_{2}$), whose theoretical Raman spectra are still unknown, and 20% (${\mathrm{B}}_{4}\mathrm{C}$), from which the nature of some of the Raman peaks are still debated. We report theoretical and experimental results of the first-order, nonresonant, Raman spectrum of boron carbide. Density functional perturbation theory enables us to obtain the Raman spectra of the ${\mathrm{OPO}}_{1}$ and ${\mathrm{OPO}}_{2}$ phases, which are perfectly ordered structures with however a complex crystalline motif of 414 atoms, due to charge compensation effects. Moreover, for the carbon-rich ${\mathrm{B}}_{4}\mathrm{C}$, with a simpler 15-atom unit cell, we study the influence of the low energy point defects and of their concentrations on the Raman spectrum, in connection with experiments, thus providing insights into the sensitivity of experimental spectra to sample preparation, experimental conditions, and setup. In particular, this enables us to propose a new structure at 19.2% atomic carbon concentration, ${\mathrm{B}}_{4.2}\mathrm{C}$, that, within the local density approximation of density functional theory (DFT-LDA), lies very close to the convex hull of boron carbide, on the carbon-rich side. This new phase, derived from what we name the ``3+1'' defect complex, helps in reconciling the experimentally observed Raman spectrum with the theory around 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$. Finally, we predict the intensity variations induced by the experimental geometry and quantitatively assess the localization of bulk and defect vibrational modes and their character, with an analysis of ``chain'' and ``icosahedral'' modes.

Ring structure of selected two-dimensional procrystalline lattices.

Recent work has introduced the term "procrystalline" to define systems which lack translational symmetry but have an underlying high-symmetry lattice. The properties of five such two-dimensional (2D) lattices are considered in terms of the topologies of rings which may be formed from three-coordinate sites only. Parent lattices with full coordination numbers of four, five, and six are considered, with configurations generated using a Monte Carlo algorithm. The different lattices are shown to generate configurations with varied ring distributions. The different constraints imposed by the underlying lattices are discussed. Ring size distributions are obtained analytically for two of the simpler lattices considered (the square and trihexagonal nets). In all cases, the ring size distributions are compared to those obtained via a maximum entropy method. The configurations are analyzed with respect to the near-universal Lemaître curve (which connects the fraction of six-membered rings with the width of the ring size distribution) and three lattices are highlighted as rare examples of systems which generate configurations which do not map onto this curve. The assortativities are considered, which contain information on the degree of ordering of different sized rings within a given distribution. All of the systems studied show systematically greater assortativities when compared to those generated using a standard bond-switching method. Comparison is also made to two series of crystalline motifs which shown distinctive behavior in terms of both the ring size distributions and the assortativities. Procrystalline lattices are therefore shown to have fundamentally different behavior to traditional disordered and crystalline systems, indicative of the partial ordering of the underlying lattices.

Composition and in silico structural analysis of fibroin from liquid silk of non-mulberry silkworm Antheraea assamensis

Silk is spun from the liquid precursor known as liquid silk secreted from the posterior part and stored in the silk gland lumen with occurrence of many momentary events. The liquid silk in the silk gland is transformed to the spun silk fibre. In this study the elucidation of the protein components of liquid silk from the posterior part of the silk gland (PSG) of saturniid silkworm Antheraea assamensis along with its structural characterization has been reported. The 3D model of the N-terminal amorphous portion with some repeat crystalline motifs (19–255) of core protein fibroin has also been constructed. 1D and 2D electrophoresis revealed the homo-dimeric structure of the silk protein. Secondary structure analysis by Circular dichroism, FTIR spectroscopy showed α helical structural component as predominant conformation in the liquid silk. The crystalline structure investigated through X ray diffraction (XRD) analysis also revealed the presence of less ordered amorphous α helical conformation in the liquid silk. The 3D structural model proposed of the residues from 19 to 255 has revealed structural stability throughout the molecular dynamics simulation process. This study will provide the detailed structural information and in silico analysis of the core protein present in the liquid silk of PSG.

Let the light be a guide: Chromophore communication in metal-organic frameworks

The photonic characteristics of chromophore-containing metal-organic frameworks (MOFs) have led to extensive photophysical studies in an effort to capitalize on the potency of precisely controlled chromophore ensembles. Several examples have laid the foundation that demonstrates how photophysical properties of chromophores can be manipulated by tuning their communications (interactions) through integration within a MOF matrix. The main focus of this review is on harnessing the versatile MOF platform to accentuate the photophysical properties of integrated chromophores. In particular, this review will highlight chromophore dynamics that enhance, alter, or tune the photoluminescence response of single- and multi-chromophore-containing scaffolds, as well as alignment-guided anisotropic fluorescence. Building upon this groundwork, utilization of a hybrid crystalline motif can induce preferential orientation of chromophores resulting in enhanced communication and tailored behavior compared to randomly oriented emissive molecules. Moreover, frameworks that produce upconverted emission via sensitized triplet-triplet annihilation (sTTA), excited-state absorption (ESA), energy transfer upconversion (ETU), multi-photon absorption (MPA), or second-harmonic generation (SHG) can invoke dynamic control of material properties using photochromic linkers and will be discussed herein with a focus on the effects of chromophore alignment. Integration within a framework is a vehicle to fuse chromophores into solid-state platforms, opening an avenue for chromophore utilization in applications such as portable electronics that require solids or thin films. For those reasons, the design of chromophore-containing MOFs with desirable properties that rely on the alignment and communication of hundreds of chromophores within a single platform is a pressing demand for the development of futuristic technologies.

"Dumb" pH-Independent and Biocompatible Hydrogels Formed by Copolymers of Long-Chain Alkyl Glycidyl Ethers and Ethylene Oxide.

The formation and rheological properties of hydrogels based on amphiphilic ABA triblock polyether copolymers are described, relying solely on the hydrophobic interaction of long-chain alkyl glycidyl ether (AlkGE)- based A-blocks that are combined with a hydrophilic poly(ethylene glycol) (PEG) midblock. Via anionic ring-opening copolymerization (AROP), ethylene oxide (EO) and long-chain alkyl glycidyl ethers (AlkGEs) were copolymerized, using deprotonated poly(ethylene glycol) (PEG) macroinitiators (Mn of 10, 20 kg mol-1). The polymerization afforded amphiphilic ABA triblock copolymers with molar masses in the range of 21-32 kg mol-1 and dispersities (Đ) of Đ = 1.07-1.17. Kinetic studies revealed random copolymerization of EO and AlkGE, indicating random spacing of the hydrophobic AlkGE units by polar EO units. Following this approach, the hydrophobicity of the apolar blocks of amphiphilic ABA triblock polyethers can be tailored. Detailed rheological measurements confirmed the successful formation of hydrogels at different pH values as a consequence of nonpolar interactions and alkyl chain crystallization. Hydrogel formation was also observed at different ionic strengths (i.e., varied salt concentration), based on the hydrophobic aggregates. This behavior is in contrast to other often-used supramolecular cross-linking strategies, such as Coulomb interactions, complexation, or hydrogen bonding. Micro-differential scanning calorimetry (μ-DSC) measurements of the hydrogels revealed crystalline hydrophobic domains with melting temperatures in the physiological temperature range. In 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide (MTT) assays, diblock copolymers possessing structural analogy to the triblock copolymers were studied to assess the general cytotoxicity of amphiphilic polyethers bearing long alkyl chains at the polyether backbone, using splenic immune cells. At intermediate polymer concentrations, no cytotoxic effects were observed. This indicates that long-chain alkyl glycidyl ethers are promising for the introduction of highly hydrophobic as well as crystalline motifs at the polyether backbone in hydrogels for biomedical purposes.

Amorphous nickel-cobalt bimetal-organic framework nanosheets with crystalline motifs enable efficient oxygen evolution reaction: Ligands hybridization engineering

The proposed “ligands hybridization” strategy and the application of novel MOF-based catalysts in OER were introduced. The OER mechanism highlights the importance of Ni doping effect. Development of high-efficiency and low-cost electrocatalyst for oxygen evolution reaction (OER) is very important for use at alkaline water electrolysis. Metal-organic frameworks (MOF) provide a rich platform for designing multi-functional materials due to their controllable composition and ultra-high surface area. Herein, we report our findings in the development of amorphous nickel–cobalt bimetal-organic framework nanosheets with crystalline motifs via a simple “ligands hybridization engineering” strategy. These complexes’ ligands contain inorganic ligands (H 2 O and NO 3 − ) and organic ones, hexamethylenetetramine (HMT). Further, we investigated a series of mixed-metal with multi-ligands materials as OER catalysts to explore their possible advantages and features. It is found that the Ni doping is an effective approach for optimizing the electronic configuration, changing lattice ordering degree, and thus enhancing activities of HMT-based electrocatalysts. Also, the crystalline-amorphous boundaries of various HMT-based electrocatalyst can be easily controlled by simply changing amounts of Ni-precursor added. As a result, the optimized ultrathin (Co, 0.3Ni)-HMT nanosheets can reach a current density of 10 mA cm −2 at low overpotential of 330 mV with a small Tafel slope of 66 mV dec −1 . Our findings show that the electronic structure changes induced by Ni doping, 2D nanosheet structure, and MOF frameworks with multi-ligands compositions play critical roles in the enhancement of the kinetically sluggish electrocatalytic OER. The present study emphasizes the importance of ligands and active metals via hybridization for exploring novel efficient electrocatalysts.

Structural Ordering in Liquid Gallium under Extreme Conditions.

The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high pressure (p) and high temperature (T) up to 26GPa and 900K by insitu synchrotron x-ray diffraction. Abinitio molecular dynamics simulations up to 33.4GPa and 1000K are in excellent agreement with the experimental measurements, providing detailed insight at the level of pair distribution functions. Theresults reveal an absence of dimeric bonding in the liquid state and a continuous increase in average coordination number n[over ¯]_{Ga}^{Ga} from 10.4(2) at 0.1GPa approaching ∼12 by 25GPa. Topological cluster analysis of the simulation trajectories finds increasing fractions of fivefold symmetric and crystalline motifs at high p-T. Although the liquid progressively resembles a hard-sphere structure towards the melting curve, the deviation from this simple description remains large (≥40%) across all p-T space, with specific motifs of different geometries strongly correlating with low local two-body excess entropy at high p-T.

Towards a morphology of cobalt nanoparticles: size and strain effects

Cobalt nanoparticles with diameters of 8 nm have recently shown promising performance for biomedical applications. However, it is still unclear how the shape of cobalt clusters changes with size when reaching the nanoparticle range. In the present work, density functional theory calculations have been employed to compare the stabilities of two non-crystalline (icosahedron and decahedron) shapes, and three crystalline motifs (hcp, fcc, and bcc) for magic numbered cobalt clusters with up to 1500 atoms, based on the changes in the cohesive energies, coordination numbers, and nearest-neighbour distances arising from varying geometries. Obtained trends were extrapolated to a 104 size range, and an icosahedral shape was predicted for clusters up to 5500 atoms. Larger sized clusters adopt hcp stacking, in correspondence with the bulk phase. To explain the crystalline/non-crystalline crossovers, the contributions of the elastic strain density and twin boundary from the specimen surfaces to the cohesive energy of different motifs were evaluated. These results are expected to aid the design and synthesis of cobalt nanoparticles for applications ranging from catalysis to biomedical treatments.

Thermo-optically responsive phase change materials for passive temperature regulation

Many phase change materials (PCMs) experience a change in transparency when undergoing a phase transition. These thermo-optically responsive materials can be used to generate passive temperature control systems for building enclosures. The integration of optical and thermal switches into smart temperature-controlling elements requires rationally designed PCMs featuring tunable optical and thermal properties. Two polymers, poly (Octadecyl methacrylate) (PSMA) and poly(2-(2-(octadecyloxy) ethoxy) ethyl methacrylate) (PE2SMA) were synthesized and evaluated for their potential use in passive thermal energy storage systems. UV–Visible Spectroscopy, Near Infra-Red Spectroscopy, and Differential Scanning Calorimetry were used to evaluate the effect that changes in the polymer chemical structure had on the optical and thermal properties of the resulting materials. Insertion of a 6-atom flexible spacer (diethylene glycol) between the pendant crystalline motif and the polymer backbone of PSMA resulted in increases of latent heat storage capacity from 62 J/g to 94 J/g and thermal conductivity from 0.218 W/mK to 0.318 W/mK. Notably, insertion of a flexible spacer also resulted in a melting transition temperature increase from 37.7 °C for PSMA to 48 °C for PE2SMA. The visible transmittance of the polymers increased from 0% to 90% upon transition from crystalline to amorphous state. This study presents a synthetic strategy to control thermal and optical properties of polymeric PCMs materials. The material properties and structure-property relationships derived from this study will enable the refinement of the models used to predict the performance of passive temperature-regulating systems. More accurate models will guide the development of the thermo-responsive polymeric materials required for better perfoming temperature-regulating building enclosures.

Theoretical phase diagram of boron carbide from ambient to high pressure and temperature

The phase diagram of boron carbide is calculated within the density functional theory as a function of temperature and pressure up to 80 GPa, accounting for icosahedral, graphitelike, and diamondlike atomic structures. Only some icosahedral phases turn out to be thermodynamically stable with atomic carbon concentrations (c) of 8.7% (B10.5C), 13.0% (B6.7C), 20% (B4C), and 28.6% (B2.5C), respectively. Their respective ranges of stability under pressure and temperature are calculated, and the theoretical T-P-c phase diagram boundaries are discussed. At ambient conditions, the introduction in the phase diagram of the new phase B10.5C with an ordered crystalline motif of 414 atoms is shown to bring the theoretical solubility range of carbon in boron close to the experimental one. The link with the experimental phase diagram consisting of one single phase having the R3¯m space group is discussed, and the concept of partial occupation of Wyckoff’s site is introduced. At high pressure, the phase diagram is defined by a new carbon-rich phase B2.5C, which is stabilized by both pressure and temperature in our calculations. All of the other diamond and graphite phases reported previously turn out to be thermodynamically unstable in our calculations, although some of them are observed in high pressure experiments.

Imaging Unstained Synthetic Polymer Crystals and Defects on Atomic Length Scales Using Cryogenic Electron Microscopy

Properties of soft crystalline materials such as synthetic polymers are governed by locations of constituent atoms. Determining atomic-scale structures in these materials is difficult because they degrade rapidly when studied by electron microscopy, and techniques such as X-ray scattering average over volumes much larger than coherent blocks of the unit cells. We obtained cryo-electron microscopy images of self-assembled nanosheets of a peptoid polymer, made by solid-phase synthesis, in which we see a variety of crystalline motifs. A combination of crystallographic and single-particle methods, developed for cryo-electron microscopy of biological macromolecules, was used to obtain high-resolution images of the crystals. Individual crystals contain grains that are mirror images of each other with concomitant grain boundaries. We have used molecular dynamic simulations to build an atomic model of the crystal structure to facilitate the interpretation of electron micrographs. Direct visualization of crystalli...

Inside PEF: Chain Conformation and Dynamics in Crystalline and Amorphous Domains

A thorough vibrational spectroscopy and molecular modeling study on poly(ethylene 2,5-furandicarboxylate) (PEF) explores its conformational preferences, in the amorphous and crystalline regions, while clarifying structure–property correlations. Despite the increasing relevance of PEF as a sustainable polymer, some of its unique characteristics are not yet fully understood and benefit from a deeper comprehension of its microstructure and intermolecular bonding. Results show that in the amorphous domains, where intermolecular interactions are weak, PEF chains favor a helical conformation. Prior to crystallization, polymeric chains undergo internal rotations extending their shape in a zigzag pattern—an energetically unfavorable geometry which is stabilized by C–H···O bonds among adjacent chain segments. The zigzag conformation is the crystalline motif present in the α and β PEF polymorphs. The energy difference among the amorphous and crystalline chains of PEF is higher than in PET poly(ethylene terephthalat...

Amorphous Cobalt Phyllosilicate with Layered Crystalline Motifs As Water Oxidation Catalyst

The development of a high-performance oxygen evolution reaction (OER) catalyst is pivotal for the practical realization of a water-splitting system. Although an extensive search for OER catalysts has been performed in the past decades, cost-effective catalysts remain elusive. Herein, an amorphous cobalt phyllosilicate (ACP) with layered crystalline motif prepared by a roomtemperature precipitation is introduced as a new OER catalyst; this material exhibits a remarkably low overpotential (η ≈ 367 mV for a current density of 10 mA cm−2). A structural investigation using X-ray absorption spectroscopy reveals that the amorphous structure contains layered motifs similar to the structure of CoOOH, which is demonstrated to be responsible for the OER catalysis based on density functional theory calculations. However, the calculations also reveal that the local environment of the active site in the layeredcrystalline motif in the ACP is significantly modulated by the silicate, leading to a substantial reduction of η of the OER compared with that of CoOOH. This work proposes amorphous phyllosilicates as a new group of efficient OER catalysts and suggests that tuning of the catalytic activity by introducing redox-inert groups may be a new unexplored avenue for the design of novel high-performance catalysts.

Crystalline packing in pentacene-like organic semiconductors

Combining Hirshfeld surface analysis with single molecule electrostatic property calculations allows rationalizing crystalline packing motifs of organic semiconductors.

Amorphous Cobalt Phyllosilicate with Layered Crystalline Motifs as Water Oxidation Catalyst.

The development of a high-performance oxygen evolution reaction (OER) catalyst is pivotal for the practical realization of a water-splitting system. Although an extensive search for OER catalysts has been performed in the past decades, cost-effective catalysts remain elusive. Herein, an amorphous cobalt phyllosilicate (ACP) with layered crystalline motif prepared by a room-temperature precipitation is introduced as a new OER catalyst; this material exhibits a remarkably low overpotential (η ≈ 367 mV for a current density of 10 mA cm-2 ). A structural investigation using X-ray absorption spectroscopy reveals that the amorphous structure contains layered motifs similar to the structure of CoOOH, which is demonstrated to be responsible for the OER catalysis based on density functional theory calculations. However, the calculations also reveal that the local environment of the active site in the layered crystalline motif in the ACP is significantly modulated by the silicate, leading to a substantial reduction of η of the OER compared with that of CoOOH. This work proposes amorphous phyllosilicates as a new group of efficient OER catalysts and suggests that tuning of the catalytic activity by introducing redox-inert groups may be a new unexplored avenue for the design of novel high-performance catalysts.

Theoretical insight into the interaction between SnX2 (X = H, F, Cl, Br, I) and benzene.

For a series of five model complexes composed of a singlet SnX2 molecule (X = H, F, Cl, Br, I) and a benzene molecule, the first-principles calculations of their energetics and the analysis of their electron density topology have been performed. The CCSD(T)/CBS interaction energy between SnX2 and C6H6 fall into the range between −10.0 and −11.2 kcal/mol, which indicates that the complexes are rather weakly bound. The relevant role of electrostatic and dispersion contributions to the interaction energy between SnX2 and C6H6 is highlighted in the results obtained from the symmetry-adapted perturbation theory (SAPT). The electron density topological analysis has been carried out using the quantum theory of atoms in molecules (QTAIM) and the noncovalent interactions (NCI) visualization index. Both QTAIM and NCI prove the closed-shell, noncovalent and attractive character of the interaction. A very small charge transfer from C6H6 to SnX2 has been detected. The formation of the five complexes is accompanied by the electron density deformations that are spatially restricted mostly to the region around the Sn atom and its adjacent C atom. The results presented in this work shed some light on the nature of the interactions associated with crystalline structural motifs involving low-valent tin complexed with neutral aryl rings.Electronic supplementary materialThe online version of this article (doi:10.1007/s00894-016-3053-6) contains supplementary material, which is available to authorized users.

Hydrothermal synthesis of W–Ta–O complex metal oxides by assembling MO6 (M = W or Ta) octahedra and creation of solid acid

Layered-type tungsten and tantalum oxides (W–Ta–O) were synthesized by the hydrothermal method. The synthesized W–Ta–O showed characteristic peaks at 2θ=22.7° and 46.2° in an X-ray diffraction pattern (Cu Kα), indicating linear corner sharing of MO6 (M=W, Ta) octahedra in the c-direction. The same layered-type materials were obtained with a wide range of W and Ta composition ratios using soluble Lindqvist-type tantalum polyoxometalate (Na8(Ta6O19)·24.5H2O). Na+ cations of as-synthesized W–Ta–O were replaced with NH4+ and then calcined at 500°C to form Brønsted acid sites. The catalytic activity of W–Ta–O increased with increasing W ratio, suggesting that strong acid sites were generated. From Raman and adsorption measurements of W–Ta–O with various crystalline structures, it was revealed that the crystalline motif of W–Ta–O in the a–b plane was an interconnection of MO6 (M=W, Ta) octahedra and {M6O21} pentagonal units and micropore channels, but without long-range order.