Prism Clusters Research Articles

Formation of a Metallomacrocycle Possessing Nitrogen Donors Assembled in the Cavity and Unique Water Clusters.

2,2'-Bipyridyl (bpy) is widely used as a chelating unit for metal complexation but is not usually considered as a hydrogen-bonding unit. This is because the metal-free bpy units are usually in a transoid conformation, and the two nitrogen lone pairs are pointed to the opposite sides. We now report a metallomacrocycle whose three metal-free bpy units are in a cisoid conformation and are fixed in the cavity. The complexation of nickel(II) only at the salen units of the triangular bpytrisalen ligand produced this rigid and planar macrocycle. Its cavity is surrounded by hydrogen-bond acceptors (N of bpy and O of salen), and it was found that unique pentagonal prism clusters of water molecules templated by the cavity were formed in the crystal. This study has not only increased the variation of the synthetic methodologies of multinuclear complexes but has also provided the structural platform on which multiple bpy units exert hydrogen-bonding functions.

A medium-range structure motif linking amorphous and crystalline states.

Amorphous materials have no long-range order, but there are ordered structures at short range (2-5 Å), medium range (5-20 Å) and even longer length scales1-5. While regular6,7 and semiregular polyhedra8-10 are often found as short-range ordering in amorphous materials, the nature of medium-range order has remained elusive11-14. Consequently, it is difficult to determine whether there exists any structural link at medium range or longer length scales between the amorphous material and its crystalline counterparts. Moreover, an amorphous material often crystallizes into a phase of different composition15, with very different underlying structural building blocks, further compounding the issue. Here, we capture an intermediate crystalline cubic phase in a Pd-Ni-P amorphous alloy and reveal the structure of the medium-range order, a six-membered tricapped trigonal prism cluster (6M-TTP) with a length scale of 12.5 Å. We find that the 6M-TTP can pack periodically to several tens of nanometres to form the cube phase. Our experimental observations provide evidence of a structural link between the amorphous and crystalline phases in a Pd-Ni-P alloy at the medium-range length scale and suggest that it is the connectivity of the 6M-TTP clusters that distinguishes the crystalline and amorphous phases. These findings will shed light on the structure of amorphous materials at extended length scales beyond that of short-range order.

Solvothermal synthesis and structural characterization of three polyoxotitanium-organic acid clusters.

Three new titanium oxo-clusters Ti4O2(OiPr)10(OOCPhMe)2 (I), Ti6O4(OEt)8(OOCPhMe)8 (II) and Ti6O6(OEt)6(OOCCHPh2)6 (III) were obtained by easy one-step solvothermal reactions of titanium(iv) isopropoxide, alcohols and carboxylic acids. The three compounds were characterized by single-crystal and powder X-ray diffraction, TGA/DSC, optical and electron microscopy, and FTIR and NMR spectroscopy. X-ray powder diffraction and spectroscopy confirmed the purity of the compounds. Structural analysis indicates that in all compounds the titanium(iv) ions are six-coordinated (distorted octahedra). (I) is a tetranuclear complex containing a Ti4(μ4-O)(μ2-O) core, which is linked by two (μ2-OOCPhMe), four (μ2-OiPr) and six OiPr ligands. (II) and (III) are hexanuclear complexes with different cores, respectively Ti6(μ3-O)2(μ2-O)2 and Ti6(μ3-O)6. The coordination sphere of the Ti atoms is filled by eight (μ2-OOCPhMe), two (μ2-OEt) and six OEt in (II) and six (μ2-OOCHPh2) and six OEt in (III). Different steric hindrance of substituents attached to the carboxyl group or different concentrations lead to three main different cluster geometries with two ligands. The tetranuclear and the hexanuclear clusters were obtained with the OOCPhMe ligand, while the hexagonal prism cluster was obtained with the OOCCHPh2 ligand. Hirshfeld surface calculations indicated that the packing is driven by C–O⋯H–C weak hydrogen bonds. The clusters can be used as molecular models of organic molecules bonded to titania surface, used in organic photovoltaic (dye sensitized solar cells) or other optoelectronic applications.

Hexagonal cluster Mn-MOF nanoflowers with super-hydrophilic properties for efficient and continuous solar-driven clean water production

Superhydrophilic, robust, hexagonal prism cluster Mn-MOF nanoflowers with superior solar thermal conversion performance are grown on surface of soft copper mesh as a conformal and uniform coating for a stable, portable and efficient solar evaporator.

Tooth Morphology and Enamel Microstructure of the Lesser Bamboo Rat (Cannomys badius)

The lesser bamboo rat is a fossorial rodent monotypic within the genus Cannomys, family Spalacidae. The present study revealed the first detailed information on its dental morphology, particularly the enamel microstructure, as examined by stereoscopic dissection and scanning electron microscopy. The lesser bamboo rat possesses proodont incisors covered with orange-pigmented enamel on the smooth front surface. The molars are mesodont-lophodont. The first upper molars are characterized by a tetralophodont (four lophs) pattern with four roots, whereas the first lower ones are pentalophodont and have three roots. Concerning the enamel microstructure, the incisors are comprised of a relatively thick Portio externa of radial enamel and prismless enamel (PLEX), and the Portio interna, formed by uniserial Hunter-Schreger Bands. Molar enamel microstructure shows a primitive (P)-type schmelzmuster with an occasional appearance of either irregular prism clusters or PLEX. The teeth and enamel of the lesser bamboo rat are somewhat different from those of other spalacid relatives. Although retaining a primitive state, they show some structural adaptations to feeding and tooth-digging lifestyles.

Investigation of PdCuSi metallic glass film for hysteresis-free and fast response capacitive MEMS hydrogen sensors

In this study, we investigated PdCuSi metallic glass (MG) as a sensing material for capacitive MEMS hydrogen sensors. We first confirmed by film analysis that the fabricated PdCuSi film was MG and that it had a trigonal prism cluster. The measured pressure-composition-temperature curve of PdCuSi MG exhibited no hysteresis during hydrogen absorption and desorption. The response time was found to become faster by two orders of magnitudes compared with that of Pd polycrystal. These properties were attributed to the trigonal prism clusters. Strain was evaluated in the low hydrogen concentration regime of 0.05 vol% to 4.0 vol%, and the strain of PdCuSi MG was found to follow Sieverts' law well, indicating that hydrogen is present in the MG in a diffuse state. The hydrogen-concentration dependence of a capacitive MEMS hydrogen sensor was measured and hysteresis-free characteristics were obtained, implying advantages in hydrogen leak detection applications.

Infrared detection of (H2O)20 isomers of exceptional stability: a drop-like and a face-sharing pentagonal prism cluster.

Water clusters with internally solvated water molecules are widespread models that mimic the local environment of the condensed phase. The appearance of stable (H2O)n cluster isomers having a fully coordinated interior molecule has been theoretically predicted to occur around the n = 20 size range. However, our current knowledge about the size regime in which those structures become energetically more stable has remained hypothetical from simulations in lieu of the absence of precisely size-resolved experimental measurements. Here we report size and isomer selective infrared (IR) spectra of (H2O)20 clusters tagged with a sodium atom by employing IR excitation modulated photoionization spectroscopy. The observed absorption patterns in the OH stretching region are consistent with the theoretically predicted spectra of two structurally distinct isomers of exceptional stability: a drop-like cluster with a fully coordinated (interior) water molecule and an edge-sharing pentagonal prism cluster in which all atoms are on the surface. The drop-like structure is the first experimentally detected water cluster exhibiting the local connectivity found in liquid water.

Remelting treatment and heredity phenomenon in the formation of Fe78Si9B13 amorphous alloy

The microstructures of Fe78Si9B13 ingots including the primary master alloy (PMA) and secondary melted alloy (SMA), as well as the precipitates in the annealed amorphous ribbons spun from PMA and SMA ingots have been investigated. The presented data show that SMA ingot performances a better glass forming ability (GFA) than PMA ingot, indicating that remelting treatment can improve the GFA of Fe78Si9B13 alloy. The metastable Fe23B6 phase forms in SMA ribbons after annealing at 600°C and 700°C. The lattice parameter a0 of α-Fe in the annealed SMA ribbons is higher than that in the annealed PMA ribbons, similar to the higher a0 of α-Fe in SMA ingot than that in PMA ingot. The variation of lattice parameter a0 of α-Fe in the present ingots and annealed ribbons shows a heredity phenomenon, which is closely associated with the Fe23B6 structural units (distorted tri-capped trigonal prism clusters) in the melts.

The sphericity of the diverse 10-vertex polyhedra found in bare post-transition metal clusters: germanium clusters with interstitial magnesium atoms as model systems

The diverse polyhedra found experimentally in bare 10-vertex centered post-transition element clusters characterized structurally by X-ray crystallography include the D 4d bicapped square antiprism Zn@In 10 8− in the intermetallic K8In10Zn as well as the centered lead clusters M@Pb10 2− in [K(2,2,2-crypt)]2[M@Pb10] (M = Ni, Pd, Pt), the C3v tetracapped trigonal prism M@In 10 10− in the intermetallic K10In10M (M = Ni, Pd, Pt), the D 5d pentagonal antiprism Pd@Bi10 4+ in Bi14PdBr16, and the D 5h pentagonal prism in the trianions M@Ge 10 3− (M = Fe, Co). The structures of the 10-vertex germanium clusters containing an interstitial magnesium atom (atomic radius 1.30 A), namely Mg@Ge 10 (z = +2, 0, −2, −4), have been optimized as models to analyze the frontier molecular orbitals of the four experimentally known 10-vertex polyhedra noted above. In this connection, the molecular orbital patterns of the most spherical D 4d bicapped square antiprism cluster Mg@Ge10 as well as that of an approximately spherical C 3v cluster Mg@Ge 10 2+ derived from the tetracapped trigonal prism exhibit the spherical harmonic ordering of the jellium model. In this ordering scheme, the 20-orbital {1s, 1p, 1d, 2s, 1f, 2p} shell is filled before any of the 1g molecular orbitals. However, the molecular orbital patterns of the oblate D 5d pentagonal antiprism cluster Mg@Ge 10 4− and the D 5h pentagonal prism cluster Mg@Ge10 no longer exhibit the spherical harmonic ordering of the jellium model. In these clusters, the polar 1f(z 3) orbital is raised to antibonding levels and the pair of hexagonal prism g molecular orbitals become bonding orbitals. The sphericities of the four distinct 10-vertex polyhedra found experimentally in centered bare 10-vertex post-transition metal clusters have been evaluated by comparing the relative energies of the cluster bonding molecular orbitals in model Mg@Ge 10 (z = −4 to +2) species with the spherical harmonic ordering predicted by the jellium model. Using this as a criterion, the D 4d bicapped square antiprismatic and C 3v tetracapped trigonal prismatic structures can be regarded as essentially spherical. However, the molecular orbital patterns of the oblate D 5d pentagonal antiprismatic and D 5h pentagonal prismatic clusters deviate significantly from spherical harmonic ordering.

Magnesium Imide: Synthesis and Structure Determination of an Unconventional Alkaline Earth Imide from Decomposition of Magnesium Amide

Magnesium imide (MgNH) was produced by monitoring the decomposition process of magnesium amide with in situ neutron diffraction. Significant changes in the structure of magnesium amide are detected during heat treatment and eventually result in the formation of crystalline MgNH. A model for the crystal structure of magnesium imide (MgNH) is presented for the first time. Remarkably, magnesium imide offers unique structural features similar to the cyclosilicate class and can be described as a porous solid formed by a sequence of linked chains of face sharing Mg(6)N(6) hexagonal prism clusters.

Composition Control of Pd-Cu-Si Metallic Glassy Alloys for Thin Film Hydrogen Sensor

Pd-Cu-Si metallic glassy alloys were investigated as materials for a hydrogen sensor. We prepared thin films of Pd-Cu-Si metallic glassy alloys with varying compositions by RF magnetron sputtering method. And effects of their composition on thermal properties (T g : glass transition temperature, T x : crystallization temperature) and H 2 response were examined. The H 2 response was examined by measuring changes of electric resistance of the thin films exposed in N 2 and H 2 . Thermal stability depending on thermal properties and large response to hydrogen are key requirements of the hydrogen sensor. T g and T x and H 2 response were significantly affected by Si content. T g and T x became higher and H 2 response decreased when Si content was increased. As for metals, Pd and Cu, T g increased and H 2 response decreased with decreasing Pd/Cu atomic ratio among the samples having almost the same Si contents. These results can be explained by a trigonal prism cluster that is reported as a structural unit of Pd-based amorphous alloy. We discussed the effects of a trigonal prism cluster on thermal properties and H 2 response, as well as the effects of Si content and Cu content on constructing trigonal prism clusters.

A theoretical study of water equilibria: The cluster distribution versus temperature and pressure for (H2O)n, n=1–60, and ice

The size distribution of water clusters at equilibrium is studied using quantum-chemical calculations in combination with statistical thermodynamics. The necessary energetic data is obtained by quantum-chemical B3LYP computations and through extrapolations from the B3LYP results for the larger clusters. Clusters with up to 60 molecules are included in the equilibrium computations. Populations of different cluster sizes are calculated using both an ideal gas model with noninteracting clusters and a model where a correction for the interaction energy is included analogous to the van der Waals law. In standard vapor the majority of the water molecules are monomers. For the ideal gas model at 1 atm large clusters [56-mer (0-120 K) and 28-mer (100-260 K)] dominate at low temperatures and separate to smaller clusters [21-22-mer (170-280 K) and 4-6-mer (270-320 K) and to monomers (300-350 K)] when the temperature is increased. At lower pressure the transition from clusters to monomers lies at lower temperatures and fewer cluster sizes are formed. The computed size distribution exhibits enhanced peaks for the clusters consisting of 21 and 28 water molecules; these sizes are for protonated water clusters often referred to as magic numbers. If cluster-cluster interactions are included in the model the transition from clusters to monomers is sharper (i.e., occurs over a smaller temperature interval) than when the ideal-gas model is used. Clusters with 20-22 molecules dominate in the liquid region. When a large icelike cluster is included it will dominate for temperatures up to 325 K for the noninteracting clusters model. Thermodynamic properties (C(p), DeltaH) were calculated with in general good agreement with experimental values for the solid and gas phase. A formula for the number of H-bond topologies in a given cluster structure is derived. For the 20-mer it is shown that the number of topologies contributes to making the population of dodecahedron-shaped cluster larger than that of a lower-energy fused prism cluster at high temperatures.

Hydrothermal syntheses and structures of three novel coordination polymers assembled from 1,2,3-triazolate ligands

Three new coordination polymers with 1,2,3-triazolate ligands, [Cd3(ta)3Cl3]n (1), {[Cd3(ta)6]·6H2O}n (2) and [Cu6(ta)3I3]n (3) (Hta = 1,2,3-triazole), have been hydrothermally synthesized and structurally characterized. In complex 1, the Cd2+ and Cl− ions form a 3D [(Cd3Cl3)3+]n inorganic framework with (82.12)(4.8.10) topology while the Cd2+ ions and ta− ligands give a {[Cd3(ta)3]3+}n double helical chain. The two moieties are fused with each other by sharing “hinge” Cd2+ ions leading to a 3D organic–inorganic hybrid structure. The 3D porous metal–organic framework of complex 2 shows the topology of the diamond net with the Cd-centered CdCd4 tetrahedron units as the connecting nodes. The desolvated structure of 2 has 48% solvent accessible space of the total volume. Complex 3 is an undulating 1D organic–inorganic hybrid complex consisting of interesting discrete five-capped [Cu6I5]− triangular prism clusters and arched metallacycle [Cu6(ta)6I]+ moieties.

Effect of Sawtooth Shape on Switching Process of Write Head

The static states and reversal processes of write head are studied and compared by two micromagnetic models with sawtooth edges or smooth edges, respectively. In the calculation of magnetostatic interaction with smooth edges, the analytical expression of demagnetization matrix for right-angle triangular prism clusters at hypotenuse has been found. The static domain structures in the main pole tip of both models have a slight difference and differ a little more with higher exchange constant. The switching processes in the two models also have similar behavior, except when the down-track film thickness is less than the pole tip width. Both the exchange field and film thickness affect the ultimate magnetization perpendicular to media and the speed of reversal.

関連結晶相の局所構造解析を利用したＺｒ‐Ｎｉ‐Ａｌバルクアモルファス相の安定性の解明

Stability of the Zr-Ni-Al bulk metallic glass (BMG) was investigated by making full use of its relevant crystals. The local atomic arrangements (characteristic atomic clusters) commonly existing in the BMG and its relevant crystals were identified by the experimentally determined radial distribution functions. We found that the local atomic arrangements of the BMG were characterized by the prism clusters with a transition element, Zr or Ni, in their center and the Kasper polyhedrons about an Al atom. Internal energy of these clusters was investigated by combinational use of the DVXα cluster calculation and the high-resolution photoemission spectroscopy. The prism clusters about the transition metal elements were confirmed to possess a low internal energy. We propose, as a consequence of present analyses, that the Zr-Ni-Al BMG is stabilized by the low internal-energy of the clusters and the large entropy caused by the freedom in the bond-direction between the clusters.

Free-Energy Analysis of the Zr–Ni–Al Bulk Metallic Glass from the Local Atomic Arrangements of the Relevant Crystals

Free-energy of Zr–Ni–Al bulk metallic glass (BMG) was estimated by making full use of coordination clusters in the relevant crystals. The clusters in the BMG were determined by using the BMG’s experimentally determined radial distribution functions. and the electronic structure of the identified clusters was calculated by the DVXα cluster calculation. The local atomic arrangements in the Zr–Ni–Al BMG are found to be characterized by the prism clusters with Zr or Ni atom in their center and the Kasper polyhedrons about Al atoms. It was conclude, as a consequence of the present analysis, that the Zr–Ni–Al BMG are stabilized by the low internal-energy of the constituent local atomic clusters assisted by the large entropy caused by the freedom in the bond-direction between the prism clusters and the Kasper polyhedrons.

Structure and photoluminescence property of two-dimensional coordination polymer complexes involving CuI6X6(X = Cl, Br, I) hexagon prism cluster supported by a tripodal tripyridine ligand with 1,3,5-triethylbenzene spacer

Treatment of cuprous halide (Cu(I)X, X = Cl, Br, and I) and a tripodal tripyridine ligand (L) consisting of a 1,3,5-triethylbenzene spacer gave a unique two-dimensional (2D) polymer sheet structure involving a rare Cu(I)(6)X(6) hexagon prism cluster unit, which exhibits intense fluorescence around 448-476 nm.

Three-Dimensional Structure Analyses of Cu Species Dispersed on TiO2(110) Surfaces Studied by Polarization-Dependent Total-Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS)

Three-dimensional analysis of structures for dispersed Cu species on a TiO2(110) surface has been performed by a polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) technique. The dispersed Cu species were prepared by a chemical reaction between Cu(DPM)2 and a TiO2(110) surface and reduced with H2. The Cu(DPM)2 dissociatively adsorbed on the 2-fold site of bridging oxygen atoms of the TiO2(110) surface to form a Cu(DPM)(O-)2 species. Subsequent reduction of the Cu species with H2 at 363 K produced Cu3 trimers that were bound to the bridging oxygen atoms with the trimer plane inclined at about 30° from the TiO2(110) normal. There were direct Cu−O bonds at the Cu3 trimer/TiO2(110) interface in addition to Cu−Cu bonds. Further reduction at 473 K produced three-dimensional prismatic small Cu6 clusters by vertical growth in the [110] direction of the Cu fcc lattice. Orientations of the Cu3 triangle and Cu6 prism clusters may be regulated by the interaction between t...

Electron diffraction structure analysis for amorphous materials

Amorphous structures of liquid-quenched Fe90Zr7B3 and ion-bombarded SiC were studied using modern electron diffraction structure analysis techniques. From a reverse Monte-Carlo (RMC) structural simulation on the experimental atomic pair distribution function (PDF) of amorphous Fe90Zr7B3, “nano-scale phase separation” was found to occur in this structure with spatial distributions of body-centered cubic-like, icosahedral and trigonal prism clusters. In amorphous SiC, the network includes not only heteronuclear (Si–C) bonds but also homonuclear (Si–Si and C–C) bonds. The ratio of homonuclear to heteronuclear bonds changes due to structural relaxation.

Synthesis, Crystal Structures and Magnetism of a Series of Heptanuclear Rare‐Earth‐Centered Trigonal Prism Clusters

AbstractA series of heptanuclear rare‐earth‐centered trigonal prism clusters [LnCu6(μ‐OH)3(HL)2(L)4]·(ClO4)2·25H2O (Ln = La−Ho and Y; H2L = iminodiacetic acid) was synthesized and their crystal structures were determined by X‐ray diffraction. The rare‐earth center and the copper ions are bridged by three μ3‐OH and six μ2‐O moieties from the carboxyl groups of six different ligands. The rare earth ion is nine‐coordinate and the coordination polyhedron is an unusual, highly symmetrical tricapped trigonal prism (C3h). The cluster has an interesting, highly symmetrical eclipsed structure (C3h) which utilizes the central rare earth cation as a template. The temperature‐dependence of the magnetic susceptibility of the cluster series was investigated and was found to vary with the central rare‐earth ions. The magnitude of the antiferromagnetic interaction constants J between Cu2+ ions in [LaCu6] and [YCu6] were compared and estimated to be −24 cm−1 and −7 cm−1, respectively, indicating a significant effect of the central diamagnetic ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)