Cage Atoms Research Articles

Theoretical study of N20, C20, and B20 clusters “squeezed” inside icosahedral C80 and He80 cages

The equilibrium geometries and spectroscopic and energetic characteristics of model endohedral M20@C 80 n− clusters, in which the guest clusters M20 = N20, C20, and B20 are squeezed inside the fullerene C 80 n− cages (n = 0, 2, 4, and 6), have been calculated at the density functional theory B3LYP/6-31G and B3LYP/6-31G* levels. Analogous calculations with partial geometry optimization have been performed for their congeners M20@He 80 n− with a fixed icosahedral helium cage He80. According to the calculations, all the structures of the N20@C80, C20@C80, and B20@C80 series correspond to local minima of the potential energy surface (all vibrational frequencies are real). In the first cluster, the N20 guest has a structure of a dodecahedron with a diameter of ∼4.0 A. The alternative 10N2@C80 structure containing ten separated endohedral N2 molecules is considerably less favorable and transforms without a barrier to the dodecahedral N20@C80 isomer upon geometry optimization. It has been suggested that, under extreme supercompresison conditions, molecular nitrogen can be associated without barriers into highly endothermal chemically bound clusters of the N20 type. In the helium analogues, the relative position of the N20@He80 and 10N20@He80 structures on the energy scale is determined by the degree of compression and can change its sign with a change in the diameter of the external cage D(He80). The mechanism of gradual assembly of the N20 dodecahedron from the 10N2 set has been traced with a decrease in the diameter D(He80) in the range 7.5–8.6 A. In the C20@C80 cluster, the C20 guest has a structure of a distorted dodecahedron bound to the C80 cage through four “inner” (endohedral) bonds. In the B20@C80 cluster, the B20 guest is severely squeezed along the C5 axis. Its equatorial atoms form ten endohedral B-C bonds to C80 cage atoms. In similar systems, the division of the endoclusters into the internal guest and external cage becomes uncertain. Calculations predict that the isolated “salt” molecules of the L n C20 and L n B20 type in which the C20 and B20 clusters function as anions surrounded by the L atoms of alkali metals (n = 1–6) should be stable to stepwise dissociation accompanied by elimination of separate L atoms and L2 molecules.

Synthesis, Structure, and Transport Properties of Type-I Derived Clathrate Ge46–xPxSe8–y (x = 15.4(1); y = 0–2.65) with Diverse Host–Guest Bonding

A first clathrate compound with selenium guest atoms, [Ge(46-x)P(x)]Se(8-y)□(y) (x = 15.4(1); y = 0-2.65; □ denotes a vacancy), was synthesized as a single-phase and structurally characterized. It crystallizes in the space group Fm3 with the unit cell parameter a varying from 20.310(2) to 20.406(2) Å and corresponding to a 2 × 2 × 2 supercell of a usual clathrate-I structure. The superstructure is formed due to the symmetrical arrangement of the three-bonded framework atoms appearing as a result of the framework transformation of the parent clathrate-I structure. Selenium guest atoms occupy two types of polyhedral cages inside the positively charged framework; all selenium atoms in the larger cages form a single covalent bond with the framework atoms, relating the title compounds to a scanty family of semiclathrates. According to the measurements of electrical resistivity and Seebeck coefficient, [Ge(46-x)P(x)]Se(8-y)□(y) is an n-type semiconductor with E(g) = 0.41 eV for x = 15.4(1) and y = 0; it demonstrates the maximal thermoelectric power factor of 2.3 × 10(-5) W K(-2) m(-1) at 660 K.

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi6−x

One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present a combined neutron scattering and theoretical investigation of the lattice dynamics in the type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe a strong hybridization between phonons of the Ba guest atoms and acoustic phonons of the Ge-Ni host structure over a wide region of the Brillouin zone which is in contrast with the frequently adopted picture of isolated Ba atoms in Ge-Ni host cages. It occurs without a strong decrease of the acoustic phonon lifetime which contradicts the usual assumption of strong anharmonic phonon--phonon scattering processes. Within the framework of ab-intio density functional theory calculations we interpret these hybridizations as a series of an ti-crossings which act as a low pass filter, preventing the propagation of acoustic phonons. To highlight the effect of such a phononic low pass filter on the thermal transport, we compute the contribution of acoustic phonons to the thermal conductivity of Ba$_8$Ge$_{40}$Ni$_{6}$ and compare it to those of pure Ge and a Ge$_{46}$ empty-cage model system.

The Cage Compound Ce2Pt9Al16: A Low-Temperature Magnetic Field Study

We present results of physical properties studies of the new cerium compound Ce2Pt9Al16. The crystal structure may be described in terms of cerium-filled atomic cages. Magnetic susceptibility indicates that the magnetism in this compound originates from a stable local moment in trivalent cerium. Incoherent Kondo scattering is evident in the electrical resistivity close to room temperature. The combined results of susceptibility, resistivity and heat capacity show that 4f-spins in Ce2Pt9Al16 produce three successive magnetic phase transitions at low temperatures. Using applied magnetic fields we demonstrate how details of the ground state can be manipulated.

Complex changes in the framework of endohedrally Na-doped type II Si clathrates with respect to Na content

Crystal structures of endohedrally Na-doped type II silicon clathrates with variable Na content were refined by Rietveld analysis. Type II Si clathrates have two types of cages: small and large. The large cages were preferentially occupied by Na atoms. Upon occupation by Na in the large cages, the lattice constant of the clathrates decreased slightly. The attractive interaction of the Na atoms in the large cages with a framework that caused displacement of the Na atoms from the center might influence lattice shrinkage. Moreover, in the region where almost large cages contained Na atoms and the small cages were partially occupied by Na, the lattice constant increased with the Na content; however, the relationship between these features was complex. The lattice constant demonstrated a linear relationship with the size of the small cages; however, the enlargement of the small cages was not linear with respect to its Na occupancy, resulting in complex changes in the lattice constant with respect to the Na content. It was inferred that enlargement of the small cages by Na insertion may be dependent on the Na occupancy of neighboring small cages.

Structures, electronic properties, and nonlinear optical properties of Ce/Dy-encapsulated C20-glycine: a density-functional theory investigation

Structures, electronic properties, and nonlinear optical (NLO) properties of Ce/Dy-encapsulated C20-glycine have been systematically studied using density-functional theory method. The results show that the encapsulated Ce/Dy atom increases the volume of C20 cage, by ~31.4 and 18.3 %, respectively. Besides the C20-glycine, the Ce@C20-glycine displays the thermodynamic stability, while the Dy@C20-glycine has high-kinetic stability and low chemical reactivity. The density of states (DOS) was beneficially used to analyze the main features of bonding interactions, and the OPDOS indicate that the orbitals at −18.4 eV exhibit strong antibonding character between Ce atom and C20 cage. In addition, the study also proposes that the structural modification by Ce/Dy atom weakens the NLO properties. Expectantly, this study could provide some theoretical insights into the potential applications in pharmacology, such as antitumor activity.

Photoionization of atoms encapsulated by cages using the power-exponential potential

The systems of confined atoms in cages have received considerable attention for decades due to interesting phenomena arising from the effect of cage environment on the atom. For early theoretical work based on empirical model potentials, the Dirac δ-potential, i.e. the so-called bubble potential, and the attractive short-range spherical shell potential are conventionally used for the description of interaction between the valence electron of confined atom and the cage. In this work, the power-exponential potential with a flexible confining shape is proposed to model the cages. The methods of complex scaling in the finite-element discrete variable representation are implemented to investigate the hydrogen, hydrogen-like ions and alkali metals encapsulated by the cages. The energy spectrum varying with the confining well depth exhibits avoided crossings. The influence of cage on atomic photoionization leading to the oscillation behaviour or the so-called confinement resonances in cross sections is demonstrated in a variety of confined atomic systems. In comparisons with existing predictions using the Dirac δ-potential and the attractive short-range spherical shell potentials, our results show the significant influence of cage thickness and smooth shell boundary on the photoionization. The drastic changes of cross sections due to the character of cage are presented and discussed for the encaged lithium and sodium atoms. The present model is useful for clarifying the boundary effect of confining shell on the endohedral atoms.

TDDFT studies on the structures and ECD spectra of chiral bisarylimidos bearing different lengths of o-alkoxy chain-substituted polyoxomolybdates

The chiroptical properties of bisarylimidos bearing o-alkoxy chain-substituted polyoxomolybdates [Mo6O17(2,2′-NC6H4OCnH2nOC6H4N)]2− [n=4(2), 6(3±), 8(4)] were investigated using the time-dependent density functional method. The results showed that the studied chiral polyoxometalates (POMs) manifested similar absorption sites but displayed different shapes and magnitudes in their electronic circular dichroism (ECD) spectra. The ECD spectra of the studied chiral POMs originated from charge-transfer (CT) transitions from arylimido fragments to the POM cages and from oxygen atoms to the molybdenum atoms in the POM cages. The o-alkoxy chain served as a scaffold for generating chirality rather than contributing to the ECD spectrum of the studied POMs. The induced chiralities of the POM cages were defined by the CT transitions, which were completely localized on the POM cages. Furthermore, the long-range corrected CAM-B3LYP hybrid functional and a basis set that is larger than Lanl2DZ should be used for ECD calculations of chiral POMs. Our work establishes the use of computational studies to investigate the chiroptical properties of chiral POMs and provides theoretical interpretations.

Quantum oscillations of nitrogen atoms in uranium nitride

The vibrational excitations of crystalline solids corresponding to acoustic or optic one-phonon modes appear as sharp features in measurements such as neutron spectroscopy. In contrast, many-phonon excitations generally produce a complicated, weak and featureless response. Here we present time-of-flight neutron scattering measurements for the binary solid uranium nitride, showing well-defined, equally spaced, high-energy vibrational modes in addition to the usual phonons. The spectrum is that of a single atom, isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms, each found in an octahedral cage of heavy uranium atoms. This is an unexpected and beautiful experimental realization of one of the fundamental, exactly solvable problems in quantum mechanics. There are also practical implications, as the oscillator modes must be accounted for in the design of generation IV nuclear reactors that plan to use uranium nitride as a fuel.

A Computational Study of Sprays Produced by Rotary Cage Atomizers

This article describes a computational study of poly-dispersed droplet spray plumes produced by Micronair AU4000 and AU6539 rotary cage atomizers that are commonly used in agriculture and forestry management. It combines experimental measurements of the droplet size spectrum and computational fluid dynamics (CFD) methods to develop a comprehensive understanding of droplet dispersion and spatial segregation in the near wake of the atomizer. The results will assist the development of improved measurement methodologies of pesticide droplet spectra. A parametric study of the Micronair AU4000 atomizer examines the effects of air speed, atomizer speed, liquid flow rate, and power source on spatial segregation of the plume. The RANS model uses a combined Lagrangian (droplet phase) and Eulerian (gas phase) procedure and includes the sprayer with blades and a large portion of the wind tunnel geometry. The computational results are compared to full-scale experimental measurements of pressure, gas phase velocity, turbulence intensity, and droplet size spectra measured using phase Doppler interferometry (PDI).

Cesium and strontium incorporation into zeolite-type phases during homogeneous nucleation from caustic solutions

Formation of faujasite- and sodalite/cancrinite-type phases associated with caustic waste reactions in the environment may structurally incorporate contaminant species such as radioactive Sr2+ and Cs+, and thus provide a mechanism of attenuation. To investigate mineral evolution and structural incorporation of cations in simplified experiments, aluminosilicate solids were precipitated homogeneously at room temperature from batch solutions containing a 1:1 molal ratio of Si to Al and 10-3 molal Sr and/or Cs, and aged for 30 or 548 days. Syntheses were done with solutions in equilibrium with atmospheric CO2 and with gas-purged solutions. Experimental products were characterized by bulk chemical analyses, chemical extractions, XRD, SEM/TEM, TGA, solid-state 27Al NMR, and Sr EXAFS. Chemical analysis showed that solids had a 1:1 Al:Si molar ratio, and that Sr was sequestered at higher amounts than Cs. After 30 days of aging in purged solutions, XRD showed that zeolite X (faujasite-type) was the only crystalline product. After aging 30 and 548 days in solutions equilibrated with atmospheric CO2, a mixture of sodalite, cancrinite, and minor zeolite X were produced. Surface areas of solids at 30 days were much lower than published values for zeolite phases synthesized at high temperature, although particle aging produced more crystalline and less aggregated phases with higher bulk surface areas. Characterization of products by 27Al NMR indicated only tetrahedrally coordinated Al. Measured isotropic shifts of primary resonances did not change substantially with precipitate aging although the primary mineral phase changed from zeolite X to sodalite/cancrinite, indicating local ordering of Al-Si tetrahedra. Analysis of reaction products by Sr EXAFS suggested Sr bonding in hexagonal prisms and six-membered rings of the supercages of zeolite X that may be more site specific than those of monovalent cations. For samples aged for 548 days, interatomic distances from Sr-EXAFS are consistent with partial Sr dehydration and bonding to framework oxygen atoms in sodalite cages or in large channels in cancrinite. Incorporation of Sr into both faujasite and sodalite/cancrinite phases is favored over Cs during room-temperature synthesis, possibly because of increased cation site competition between Cs+ and Na+. Results of this study help to constrain cation incorporation into sodalite/cancrinite mineral assemblages that form at caustic waste-impacted field sites and may aid in the predictive modeling of contaminant release.

Pd3Sn8Bi6]4–: A 14-Vertex Sn/Bi Cluster Embedding a Pd3 Triangle

The endohedral cluster anion [Pd(3)Sn(8)Bi(6)](4-) crystallizes as its K([2.2.2]crypt)(+) salt 1 upon reaction of [K([2.2.2]crypt)](2)[Sn(2)Bi(2)]·en and Pd(dppe)(2) in 1,2-diaminoethane (en)/toluene and incorporates a complete Pd(3) triangular cluster within a medium-size 14-vertex cage of Sn and Bi atoms. 1 was characterized by a combination of single crystal diffraction, ESI mass spectrometry, elemental analysis, and magnetic measurements. According to quantum chemical investigations, the Pd(3) triangle interacts only weakly with the Sn/Bi cluster shell despite the relatively small cavity inside the cage.

H 2 O in a Desert of Carbon Atoms

A chemical process has been developed to trap a single water molecule within a cage of carbon atoms.

Computational synthesis of C60 cyano- and azopolyderivatives

The cyanation of C(60) to C(60)(CN)(18) and the aziridination of C(60) to C(60)(NH)(9) were studied by an unrestricted broken spin symmetry Hartree-Fock approach implemented in semiempirical codes based on the AM1 technique. The calculations focused on the successive addition of CN and NH moieties to the fullerene cage following the identification of the target cage atoms as those with the highest atomic chemical susceptibilities calculated at each step. The results obtained were analyzed from the viewpoint of the parallelism between these derivatives as well as C(60) fluorides and hydrides. The difference between the first-stage C(60) chlorination and other sterically free processes is discussed.

탄소 나노 튜브 구조의 특성에 대한 교환과 상관 효과: DFT 연구

전자구조의 계산에서 교환과 상관 효과에 대한 기술을 개선하기 위해서는 교환-상관범함수에 대한 개념을 명확히 하는 것이 바람직하다. 이 목적을 성취하기 위해서는 많은 그룹의 물질에 대하여 다른 이론 방법을 적용할 필요가 있다. 본 연구에서는 탄소나노튜브의 고리와 바구니 내원자들의 밀도전하를 연구하기 위하여 혼성 밀도함수 이론(DFT) 계산을 수행하였다. 핵-핵 에너지, 전자-핵 에너지와 운동에너지에 대한 교환 및 상호작용을 관찰하였으며, B3P86, B3PW91, B1B96, BLYP와 B3LYP 수준에서 계산하였다. As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is desirable to have a clear picture of concepts of exchange-correlation functionals in computational calculations. For achieving this aim, it is necessary to perform different theoretical methods for many groups of materials. We have performed hybrid density functional theory (DFT) methods to investigate the density charges of atoms in rings and cages of carbon nanotube. DFT methods are engaged and compared their results. We have also been inclined to see the impression of exchange and correlation on nuclearnuclear energy and electron-nuclear energy and kinetic energy. With due attention to existence methods, B3P86, B3PW91, B1B96, BLYP and B3LYP have used in this work.

Simple and Onion-Type Fullerenes Shells as Resonators and Amplifiers

We discuss the influence of a single or double fullerenes shell upon photoionization and vacancy decay of an atom, stuffed inside the fullerenes construction. The main manifestations of this influence are additional structures in the photoionization cross-section and variation of the vacancy decay probability. The main mechanisms, with which fullerenes shells affect the processes in caged atoms is the scattering of the outgoing electrons by the fullerenes shell and modification of the photon beam due to fullerenes shell polarization. General consideration will be illustrated by numeric calculations where C60 and C240 will be chosen as fullerenes and Ar and Xe as caged atoms.

M-Al-Mgroups trapped in cages ofAl13M4(M=Co, Fe, Ni, Ru)complex intermetallic phases as seen via NMR

The crystallographic structures of decagonal quasicrystals and their periodic approximants are traditionally described as a periodic stacking of atomic planes. By performing a $^{27}\text{A}\text{l}$ NMR spectroscopic study of the ${\text{Al}}_{13}{M}_{4}$ ($M=\text{transition}$ metal) family of four-layer decagonal approximants, including the orthorhombic ${\text{o-Al}}_{13}{\text{Co}}_{4}$, the monoclinic ${\text{Al}}_{13}{\text{Fe}}_{4}$, its ternary derivative ${\text{Al}}_{13}{(\text{Fe},\text{Ni})}_{4}$, and the monoclinic ${\text{Al}}_{13}{\text{Ru}}_{4}$, we show that all these phases contain structural detail of a nearly linear $M\text{-Al-}M$ atomic group trapped inside an elongated cage, resembling the three-dimensional (3D) ``cage-compound'' structure of the intermetallic clathrates. We determined the electric-field-gradient- (EFG) and the magnetic-shielding tensors at the Al site of the $M\text{-Al-}M$ groups. The asymmetry parameter of the EFG tensor was estimated theoretically by a point-charge model, taking into account the charges of both the $M\text{-Al-}M$ atoms and the surrounding cage atoms. The calculations support ionic bonding of the $M\text{-Al-}M$ group to the cage atoms and the existence of a 3D chemical bonding network in the ${\text{Al}}_{13}{M}_{4}$ phases. The above results show that the traditional description of the ${\text{Al}}_{13}{M}_{4}$ decagonal approximant phases in terms of two-dimensional (2D) atomic layers stacked along the pseudotenfold crystallographic direction is a convenient geometrical approach to describe their complex structures but is not appropriate for the description of their physical properties, which should be analyzed by taking into account the full 3D nature of the chemical bonding framework. This favors the 3D cage-compound structural description of the ${\text{Al}}_{13}{M}_{4}$ phases over the pseudo-2D stacked-layer description.

Stepwise computational synthesis of fullerene C60 derivatives. Fluorinated fullerenes C60F2k

The reactions of fullerene C60 with atomic fluorine have been studied by unrestricted broken spin-symmetry Hartree-Fock (UBS HF) approach implemented in semiempirical codes based on AM1 technique. The calculations were focused on a sequential addition of fluorine atom to the fullerene cage following indication of the cage atom highest chemical susceptibility that is calculated at each step. The effectively-non-paired-electron concept of the fullerene atoms chemical susceptibility lays the foundation of the suggested computational synthesis. The obtained results are analyzed from energetic, symmetry, and the composition abundance viewpoints. A good fitting of the data to experimental findings proves a creative role of the suggested synthesis methodology.

ChemInform Abstract: Effects of Morphology and Electronic Structure on the Catalysis of Zeolite Encaged Palladium Particles

Abstract After calcination of ion exchanged Pd/Nay at 500°C, the Pd 2+ ions have lost their ligands and are located in sodalite cages, but after calcination at 250° Pd(NHY 3 ) 2+2 ions are present in supercages. Reduction leads to Pd atoms in sodalite cages or to Pd particles in supercages. An important difference between these cases is due to the co-product of hydrogen reduction: NH 4 + ions or protons. Probing these catalysts with the conversion of neopentane shows that Pd particle morphology has only a minor influence on the rate of conversion, but the presence of protons has a marked effect, increasing the activity per site by two orders of magnitude. This result is tentatively ascribed to electron deficient [Pd n -H x ] x+ clusters as superactive sites.

SPRAY SPECTRA, DEPOSITION AND SEDIMENTATION CHARACTERISTICS FOR LOW PRESSURE LIQUID ATOMIZERS

The focus of this investigation was on assessing the feasibility of the evaluation new developing nozzles that will target and spray the biological pest control materials and herbicides. As well as comparing the spray characteristics for external mixing twin fluid nozzles with the low liquid atomizers motorized Backpack mistblower and ProptecTM rotary atomizer. The Stihl SR 340 Powerful knapsack Mist-blower 2.6 kW, rotary atomizer, Ledebuhr Industries, Inc. 11429 Upton Road Bath, Michigan-48808) and five developed an external mixing twin fluid (EMTF) nozzles were tested under laboratory condition to measure the spray droplet spectra, the spray deposition and sedimentation. Droplet size spectra produced by three atomizers, mistblower, rotary cage and EMTF nozzles were measured using the Malvern laser (particle size analyzer). The three atomizers were tested at flow-rate 0.5 l min -1and 1 l min -1. As well as, the motorized Backpack Mistblower and ProptecTM rotary cage atomizer were tested under four levels for rotational speed. The rotational speeds for ProptecTM Rotary cage atomizer were 3000 r.p.m, 3500 r.p.m 4600r.p.m and 5000 r.p.m; and its were 3000 r.p.m, 4000 r.p.m, 5000 r.p.m and 6000 r.p.m for Backpack Mistblower. On the other hand, the five EMTF nozzles were tested at 150 kPa air pressure. The three atomizers was operated at low various pressures, five external twin-fluid nozzles at 30 kPa , mistblower at 28 kPa and rotary atomizer at 90 kPa liquid pressures. The different atomizers were compared by using the spray spectra, spray deposition and spray sedimentation parameters. The result indicated that, the rotary cage atomizer generally gave droplet spectra with lower Dvo.1 , D vo.5 and Dvo.9 values than the Backpack motorized Mistblower and the five EMTF air-shear nozzles. The ProptecTM rotary cage atomizes gave very fine droplets spectra with higher deposition than the Backpack mistblower and the five EMTF air-shear nozzles. The spray spectra D0.1, Dv0.5 and D0.9 for EMTF nozzles at 0.5 l min -1 flow rate were 42.7 µm, 100.9 µm and 195.4 µm; and 46.7 µm, 107.0 µm and 206.1 µm for both N3 and N5 respectively. The deposition percentage for N3 (Lechler FT 5 – 608 + Lechler LU 120-015 POM) and N5 (Lechler FT 5 - 608 + Tee Jet XR8004 VK) were 57.7 % and 58.8 % at flow-rate 1.0 l min-1. The sediment percentage for N3 (Lechler FT 5 – 608 + Lechler LU 120-015 POM) and N5 (Lechler FT 5 - 608 + Tee Jet XR8004 VK) were 16.3 % and 14.6 % at flow-rate 0.5 l min-1.