Tetrahedral Holes Research Articles

Hexamine Role on Pseudocapacitive Behaviour of Cobalt Oxide (Co₃O₄) Nanopowders.

Influence of hexamine surfactant concentration on crystallite size, structure, morphology, vibrational and optical properties of cobalt oxide nanopowders were explored. The cobalt oxide nanopowders were synthesized by employing a simple chemical reduction method using cobalt (II) nitrate hexahydrate (Co(NO3)2 ·6H2O) as precursor and sodium borohydride (NaBH4) as reducing agent along with hexamine as surfactant. XRD studies revealed the formation of face-centered cubic (Fd3m) crystalline structure of Co3O4 with an average crystallite size of 8-18 nm. The observed prominent characteristic Raman active modes of A1g, Eg, and F2g revealed the formation of Co3O4 nanopowders. The optical properties of Co3O4 nanopowders are examined by photoluminescence spectra. The obtained IR results confirmed the formation of Co3O4 nanopowders. The band observed 569 cm-1 is the characteristic of the Co3+ ions in the octahedral hole vibration and the 665 cm-1 band is attributable to the Co2+ ions in the tetrahedral hole vibration in the cubic lattice. The estimated specific capacitance of the obtained Co3O4 nanopowders was 291 F/g at 10 mV/s which could be a potential candidate for pseudo capacitive nature of the active materials.

Radius Ratio Rule Rescue

Making optimal pedagogical and predictive use of the radius ratio rule to distinguish between solid state structures that feature tetrahedral, octahedral and cubic holes requires several updated insights. A comparative analysis of the Born–Landé equation for lattice energy is developed to show that the rock salt structure is a suitable choice for radius ratios between 0.326 and 1.00. The lower bound is the ratio at which the energy of the rock salt structure matches that of the zinc blende structure, all other things being equal. The upper bound extends all the way to unity because the relative energy of the rock salt and CsCl structures are within 1% of each other for radius ratios above 0.717, which is the ratio at which the energy of the rock salt structure matches that of the CsCl structure. Geometric analysis of 154 1:1 ionic compounds that can potentially adopt the zinc blende, rock salt, or CsCl structure demonstrates that while existing ionic radii can be used for predictions with substantial success, a more applicable set of predictive ionic radii based on cubic lattice parameters can be deduced.

Ammonothermal Synthesis and Characterization of Cs2[Zn(NH2)4

Cs2[Zn(NH2)4] was synthesized under ammonothermal conditions (sc‐NH3, 523 K, 155 MPa) from CsNH2 and Zn. Growth of cm‐sized crystals succeeded upon application of a temperature gradient. The crystal structure is based on the motif of a hexagonal closed packing of [Zn(NH2)4]2– ions with occurrence of no significant hydrogen bridges according to distances and vibrational spectroscopy. Cs+ ions are located within octahedral and tetrahedral holes of the packing.

An insight in the structural, morphological, electrical and optical properties of spray pyrolysed Co3O4 thin films

The spray pyrolysis deposition of stable and single phase cobalt oxide (Co3O4) thin films at three different deposition temperatures viz. 350 °C, 420 °C and 470 °C was undertaken in the present work. It was found that substrate temperature played a pivotal role in obtaining pure thin layers. X-ray diffraction analysis confirmed the cubic spinel type structure (a = 8.094 Å) of polycrystalline Co3O4 with predominant orientation along (311) plane. The average crystallite size was found to be around 49 nm. Fourier transform IR spectra revealed the presence of an OB3 vibration at 540 cm−1 and an ABO3 vibration at 640 cm−1 where, B denotes Co3+ ions in an octahedral hole and A denotes Co2+ ions in a tetrahedral hole. The Raman spectra recorded in the wave number range 200–800 cm−1 indicated five Raman peaks and the strong characteristic peak at 694 cm−1 was assigned to the A1g mode which corresponds to Co–O breathing vibration of Co2+ ions in tetrahedral coordination. Surface analysis was carried out with the aid of SEM and AFM. The formation of Co3O4 was confirmed by analyzing the binding energies and intensities of Co 3s, Co 2p and O 1s obtained from XPS. Temperature dependent resistivity was realized from the two probe electrical measurements validating the semiconducting behaviour of the prepared films. Co3O4 films had low transmittance values in the order of 23%–43% in the UV–Vis-NIR region. Estimation through Tauc plots revealed direct optical band gap energies around 2–2.24 eV due to charge transfer transition between p states of O2− and t2 states of Co2+. Related optical parameters like extinction coefficient (k) and refractive index (μ) were calculated using Swanepoel method.

Effect of Sol-Gel Ageing Time on Three Dimensionally Ordered Macroporous Structure of 80SiO2-15CaO-5P2O5 Bioactive Glasses

Three dimensionally ordered macroporous bioactive glasses (3DOM-BGs), namely 80SiO 2 -15CaO-5P 2 O 5 , were synthesized by sol-gel method. PMMA colloidal crystals and non-ionic block copolymers P123 were used as cotemplates. The amorphous 3DOM-BGs had skeletal walls enclosing macropores. Such structure resulted from octahedral and tetrahedral holes of the face-centered cubic ( fcc ) closest packed PMMA templates and windows interconnecting through macropores network. The thicknesses of the walls were around 50 nm – 80 nm and the windows were 90 nm – 110 nm in diameter. These wall thickness is increased by with an increase in ageing time up to 24 h and then gradually reduced with further increase in aging time. Vibration bands of Si–O–Si and P–O were evident in infrared spectra which are in agreement with EDS spectra indicating Si, P and Ca compositions. After in vitro bioactivity testing by soaking 3DOM-BGs in simulated body fluid at 37 °C, the crystallization of amorphous calcium phosphate layers compatible to the bone component of hydroxyl carbonate apatite were rapidly formed within 3 h. These results indicated that these 3DOM-BGs resembled ideal bone implant materials. DOI: http://dx.doi.org/10.5755/j01.ms.20.1.4755

Studying Crystal Structures through the Use of Solid-State Model Kits

A solid-state crystal structure laboratory exercise for undergraduates in either a general chemistry course or a more advanced inorganic chemistry course is described. Students explore the lattice arrangement of atoms in unit cells by building models supplied by the Institute for Chemical Education. Emphasis is placed on building three-dimensional visual models of various crystal systems to display close packing of atoms, to identify tetrahedral and octahedral holes, to reveal number of atoms per unit cell, and to highlight ion coordination numbers and size differences. The relationship between solid-state bonding and a material’s physical properties is emphasized for elemental carbon.

結晶構造学習のための携帯用体験型教材の試作と実践

A portable training kit for constructing crystal structures by students themselves was prepared as an experimental educational tool for learning in and outside of class. The training kit mainly consisted of a round-hole-punched mesh aluminum plate and glass bolls (15 mm dia.) for closest packing structures. Plastic balls with different diameter (3 mm and 6 mm dia.) were added in the training kit for placing in the tetrahedral and octahedral holes, respectively. From comparing with the questionnaires for the student evaluation of the lectures with and without using the training kit, it was inferred that the training kit would be effective for the improvement of a positive attitude toward the lecture and of understanding of crystal structures for the students.

Characterization of hydrogen-induced structural changes in Zr-based bulk metallic glasses using positron annihilation spectroscopy

Abstract

WHn under pressure

An initial observation of the formation of WH under pressure from W gaskets surrounding hydrogen in diamond anvil cells led to a theoretical study of tungsten hydride phases. At P = 1 atm no stoichiometry is found to be stable with respect to separation into the elements, but as the pressure is raised WHn (n = 1–6, 8) stoichiometries are metastable or stable. WH and WH4 are calculated to be stable at P > 15 GPa, WH2 becomes stable at P > 100 GPa and WH6 at P > 150 GPa. In agreement with experiment, the structure computed for WH is anti-NiAs. WH2 shares with WH a hexagonal arrangement of tungsten atoms, with hydrogen atoms occupying octahedral and tetrahedral holes. For WH4 the W atoms are in a distorted fcc arrangement. As the number of hydrogens rises, the coordination of W by H increases correspondingly, leading to a twelve-coordinated W in WH6. In WH8 H2 units also develop. All of the hydrides considered should be metallic at high pressure, though the Fermi levels of WH4 and WH6 lie in a deep pseudogap. Prodded by these theoretical studies, experiments were then undertaken to seek phases other than WH, exploring a variety of experimental conditions that would favor further reaction. Though a better preparation and characterization of WH resulted, no higher hydrides have as yet been found.

Synthesis of NaA zeolite using PTMAOH(phenyltrimethylammoniumhydroxide): hydrothermal and microwave heating methods and comparison of their XRD patterns

Ion exchanging is one of the characteristics of the zeolites. Zeolites have octahedral and tetrahedral holes to trap ions and molecules. They also can exchange many ions in solution because of the size of the attendant ions. As a matter of fact, the property of the ion-exchanged zeolites depends on the ligands involved in the ion exchanging solutions. Ion exchanged zeolites are used as catalyst for studying the anodic oxidation of methanol in an acidic medium to investigate their suitability for use in direct methanol fuel cells (DMFCs). Some of the zeolites that have exchanged ions are shown to have redox and catalytic properties [1-3]. As an example A. Itadani et al., have reported the preparation of copper ion exchanged ZSM-5 for calorimetric study of N2 adsorption on Cu-ZSM-5 zeolite [4]. In another study, A. Ribera et al. have reported the characterization of redox properties and application of Fe-ZSM-5 catalysts [5]. In this research we prepared silicate solutions by dissolving silica in sodium hydroxide. Aluminosilicate solutions with different Al/Si ratios were prepared by mixing appropriate quantities of sodium silicate solutions with freshly prepared sodium aluminate solutions and the NaA zeolites were made by hydrothermal method. Then, their XRD patterns and IR spectra were also considered. Obviously, those zeolites which have Al-OH and Si-OH groups can lose their protons in basic solutions. In this way zeolites can adsorb many ions with positive charge. We investigated ion exchange property of Fe3+, Cu2+, Ni2+ and Hg2+ in systems with pH equals to 2, 4, 6 and 8. We found that the aluminosilicate with Si/Al = 1, has greatest exchange capacity for all of the ions studied in this work.

Structural ordering of casein micelles on silicon nitride micro-sieves during filtration

The paper reports on the structure and formation of casein micelle deposits on silicon nitride micro-sieves during the frontal filtration. The most frequent radius of the fractionated casein micelles we use is R=60 nm as detected by static light scattering (SLS) and atomic force microscopy (AFM). We estimate the size and size distribution of the casein micelles which pass through the micro-sieve during the filtration process. A sharpening of the size distribution at the beginning of the filtration process (t=40s) is followed by a broadening and a shift of the most frequent radii towards smaller sizes at later times (t=840 s). The size distribution of the micelles deposited on the micro-sieve during filtration is bimodal and consists of the largest and smallest micelles. At larger filtration times, we observe a shift of both deposited size classes towards smaller sizes. The atomic force micrographs of the reference sample reveal a tendency of the casein micelles to order in a hexagonal lattice when deposited on the micro-sieves by solution casting. The deposition of two size classes can be explained by a formation of a mixed hexagonal lattice with large micelles building up the basis lattice and smaller sizes filling octahedral and tetrahedral holes of the lattice. The accompanied compression with increasing thickness of the casein layer could result from preferential deposition of smaller sizes in the course of the filtration.

NMR evidence of strongly correlated superconductivity in LiFeAs: Tuning toward a spin-density-wave ordering

In this Rapid Communication, we reported the results of NMR study on LiFeAs single crystals. We find a strong evidence of the low-temperature spin fluctuations; by changing sample preparation conditions, the system can be tuned toward a spin-density-wave (SDW) quantum-critical point. The detection of an interstitial Li(2) ion, possibly locating in the tetrahedral hole, suggests that the off-stoichiometry and/or lattice defect can probably account for the absence of the SDW ordering in LiFeAs. These facts show that LiFeAs is a strongly correlated system and the superconductivity is likely originated from the SDW fluctuations.

ChemInform Abstract: Hydrogen-Stabilized Mg2RhH1.1 with Filled Ti2Ni-Type Structure.

Mg2RhH1.1 is the first example for a hydrogen stabilized binary metal compound with filled Ti2Ni-type structure. Its composition was refined from X-ray and neutron powder diffraction data on the deuteride and found to be Mg2RhD1.1. The deuterium atoms in the structure occupy octahedral holes formed by Mg atoms and tetrahedral holes formed by Mg and/or Rh atoms. Retrieval of hydrogen by desorption destabilizes the structure and leads to a hitherto unknown binary metal compound of composition Mg2Rh which crystallizes with the Ti2Pd-type structure, a branch of the MoSi2-type structure.

ChemInform Abstract: Strontium Dimagnesium Iron Octahydride, SrMg2FeH8, Containing Octahedral (FeH6)4- Complex Anions.

Abstract SrMg2FeH8 and its deuteride were synthesized by reacting alkaline earth alloy powders of nominal composition SrMg2.2 with iron powder at 490–510 °C and 130–140 bar hydrogen (deuterium) pressure, and characterized by X-ray and neutron powder diffraction. The compounds crystallize with a new trigonal structure type, space group P3m1, and lattice parameters a = 4.5174(2) A and c = 6.5807(4) A (hydride), a = 4.5072(2) A and c = 6.5663(4) A (deuteride). The structure contains two types of deuterium atoms, one surrounding iron in an octahedral configuration with bond distances [ Fe-D1 ] = 1.578(4) A , and the other situated in a tetrahedral hole formed by one magnesium and three strontium atoms with bond distances [ Mg-D2 ] = 1.919(7) A , [ Sr-D2 ] = 2.662(1) A . The limiting ionic formula SrD2 - Mg22+[FeD6]4- suggests that the transition metal complex conforms to the 18-electron rule.

ChemInform Abstract: Synthesis and Structure of the Zintl Compounds Na2BaTt4 (Tt: Si, Ge).

Abstract The isotypic title compounds ate obtained from reactions of stoichiometric mixtures of the elements in welded Ta containers at 700–800 °C. The structure of Na 2 BaSi 4 was determined by single-crystal X-ray diffraction (orthorhombic, Ima2 (No. 46), Z = 8, a = 9.524, b = 17.980(3), c = 8.570(3) A). The compound crystallizes in a novel structure type with Na + and Ba 2+ cations and two crystallographically-independent isolated Si 4 4− anions. The anions are nearly regular tetrahedra with bond distances of 2.385(3) to 2.448(4) A and bond angles between 59.2 and 61.7°. The overall structure may be described as a distorted face-centered-cubic array of Si 4 4− anions in which Na + and Ba 2+ atoms occupy all tetrahedral and octahedral holes in an ordered way. The result is closely related to the topology of f.c.c. Li 3 Bi type but with ordering of the two cations. Magnetic measurements showed that Na 2 BaSi 4 is diamagnetic, and its family can be formulated in terms of oxidation states as Zintl phases (Na + ) 2 Ba 2+ (Tt 4 4− ).

Lithium Argyrodites with Phosphorus and Arsenic: Order and Disorder of Lithium Atoms, Crystal Chemistry, and Phase Transitions

Crystal chemical data of high- (HT) and low-temperature (LT) modifications of lithium argyrodites with the compositions Li(7)PCh(6) (Ch=S, Se), Li(6)PCh(5)X (X=Cl, Br, I), Li(6)AsS(5)Br, and Li(6)AsCh(5)I (Ch=S, Se) based on single-crystal, powder X-ray (113 K<T<503 K) and neutron measurements (5 K<T<293 K) are presented. In the HT modifications, the Li atoms are strongly disordered over a fraction of the available tetrahedral holes, whereas in the LT modifications they occupy ordered crystallographic positions with a pronounced site preference that is analysed on a crystal chemical basis. The Ch/X partial structures remain nearly unchanged upon the reversible phase transitions. Crystal chemical and crystallographic relations between HT and LT modifications based on the Frank-Kasper model of tetrahedral close packing are discussed. X-ray single-crystal data for HT-Li(6)PS(5)I show the electron density of the disordered Li to be smeared out over an extended region preferably inside face-sharing double tetrahedra. A series of temperature-dependent powder neutron data for Li(6)PS(5)I gives clear evidence for an HT/LT phase transition at approximately 175 K with an ordering of the Li atoms in different polyhedra with coordination numbers between three and four.

Synthesis, crystal and electronic structures of the new quaternary phases A5Cd2Sb5F (A = Sr, Ba, Eu), and Ba5Cd2Sb5Ox (0.5&lt;x&lt;0.7)

A new family of quaternary fluoro-antimonides A(5)Cd(2)Sb(5)F (A = Sr, Ba, Eu) and oxyantimonides Ba(5)Cd(2)Sb(5)O(x) (0.5<x<0.7) have been synthesized and structurally characterized. The title compounds are isotypic, and crystallize with a novel structure type in the orthorhombic space group Cmcm (Z = 4, Pearson symbol oC52). The crystal structures feature one-dimensional double-strands of corner-shared CdSb(4) tetrahedra, [Cd(2)Sb(5)](9-). The arrangement of the chains is such that two of the unshared Sb vertices are close together to form a Sb-Sb bond, effectively making pentagonal quasi-channels. One of the five A(2+) cations reside inside the tubes with the remaining four surrounding them. The electron balance is provided by O(2-) or F(-) anions, which fill suitable tetrahedral holes, left between the outer A(2+) cations. The chemical bonding in the new family has been investigated using TB-LMTO-ASA band structure calculations, which suggest that the presence of the electron acceptor, oxygen or fluorine, is essential for optimization of the bonding interactions.

Synthesis, crystal structure, and properties of the rhombohedral modification of the thiospinel CuZr 1.86(1)S 4

The rhombohedral modification of the thiospinel, CuZr 1.86(1)S 4, has been synthesized by the reaction of the constituent elements in an alkali metal halide flux and structurally characterized by single crystal X-ray diffraction techniques. The title compound crystallizes in the rhombohedral space group D 3 d 5 ‐ R 3 ¯ m (#166, a=7.3552(2) Å, c=35.832(2) Å, V=1678.76(13) Å 3, Z=12, and R/ wR=0.0239/0.0624). The structure is composed of close packed S layers, with a stacking order of ⋯ABCBCABABCACAB⋯·along the c axis. The Zr and Cu atoms occupy the octahedral and tetrahedral holes between S layers, respectively. Three different kinds of S-M-S layers exist in the structure: layer I has fully occupied Zr and Cu sites, layer II has fully occupied Zr sites but no Cu, and layer III has partially occupied Zr and fully occupied Cu sites. Transport and optical properties indicate that the title compound is a small band gap (1.26 eV) n-type semiconductor.

Template Trapping and Crystal Structure of the Magic Number (H2O)21 Cluster in the Tetrahedral Hole of a Nanoscale Global Ion Packed in a Face-Centered Cubic Pattern

A nanoscale global ionic cluster [Co(H(2)O)(6) [symbol: see text] Co(8)L(12)](6+) packed in a face-centered cubic pattern was constructed as a "host", in which a magic number (H(2)O)(21) cluster was captured and stabilized in the tetrahedral hole as a "guest".

RbGa3S5 und CsGa3S5 – Zwei neue Strukturtypen

RbGa3S5 and CsGa3S5 – Two New Structure TypesThe title compounds RbGa3S5 and CsGa3S5 were synthesized by a solid state reaction starting from GaS, S and MN3 (M = Rb, Cs) as alkaline metal source. They crystallize in the space group P21/c with comparable lattice parameters but with completely different structures (RbGa3S5: a = 7,1530(6), b = 12,715(1), c = 10,1282(9) Å, β = 102,43(1)°, Z = 4; CsGa3S5: a = 10,6717(8), b = 12,763(1), c = 6,9265(6) Å, β = 91,168(9)°, Z = 4). In RbGa3S5 Rb together with S shows the topology of a hexagonal close packing in which Ga occupies 3/12 of the tetrahedral holes. The GaS4 tetrahedra are connected by common corners and edges forming a 3D‐network. The structure of CsGa3S5 is characterized by corrugated layers of edge‐ and corner‐sharing GaS4‐tetrahedra. Both compounds represent so far unknown structure types and thus two further structural alternatives for compounds with the composition MM3′Ch5.