Interstitial Metal Research Articles

Vibrations of the Interstitial Atoms in Transition Metal Clusters

Abstract The interstitial metal clusters form a fascinating class of complexes of the transition metals, where a non-metallic atom X is uniquely bonded to the metal atoms of the core. From the structural point of view, two subclasses might be distinguished, the properly called “interstitial” clusters, where the heteroatom is completely surrounded by the metal atoms of the cage in which it is inserted, and the “semi-interstitial” or “exposed” clusters, where the heteroatom is placed on, or nearby, a face or an edge of a metal polihedron. Moreover, even if the carbon atom remains the first reported and the most commonly encountered heteroatom, one example at least has appeared with hydrogen1, nitrogen,2 boron,3 phosphorous,4 sulphur,5 silicium,6 arsenic7 and antimony8 interstitial atoms. Together with these more common systems, there is an increasing number of policarbido and polihydrido complexes, containing several interstitial heteroatoms9; recently, an example of a cluster with carbon and hydrogen together was reported.10 Furthermore, some dicarbido clusters have a C2 unit, with the two carbon atoms bonded to each other, in both interstitial11 and exposed12 configurations. Some selected examples of the core structures of interstitial (Fig. l),exposed (Fig. 2) and polihetero- atom (Fig. 3) metal clusters are illustrated.

Electronic defect structure in TiO and MnO

The electronic structure, charge distribution, magnetic moment, and binding energies are studied in transition-metal monoxides using the discrete variational method in the embedded scheme within the local density formalism. Defect structures such as 1:0, 2:1, 4:1, and 7:2 (vacancy:interstitial ratio) were evaluated with respect to the ideal structure. Ti loses its moment in the 4:1 structure as the 3d electrons are depopulated in the process of redistribution. Mn shows the highest magnetic moment as in the atomic case but varies over a range of 2.23–4.96 μB depending upon the defect structure. Our calculations predict greater stability for the 2:1 defect structure in TiO and MnO. The interstitial metal ion tends to be in a trivalent state in accord with experiments.

Defect structure in transition-metal monoxides.

The electronic structure and stabilization energy of metal vacancy and vacancy-interstitial clusters are studied in transition-metal monoxides using the first-principles local-density theory. The discrete-variational method in the embedded-cluster scheme is used to obtain both the one-electron properties and cohesive energies. Our calculations predict greater stability for 2:1 (vacancy:interstitial) defect structure over simple vacancies. This is in agreement with experiments for MnO and the heavier 3d compounds, but for TiO and VO lattice vacancies at the metallic or oxygen sites are experimentally predominant. The energy for the single metal vacancy is calculated to be close to the 2:1 defect energy, and so cluster-size effects and computational limitations need to be considered further. For FeO and CoO, however, the 4:1 interstitial complex is found to be more stable than other simple defects, in accord with experiment. The probability of formation of 4:1 clusters and their aggregates in TiO and MnO is explored; the interstitial metal ion tends to be in a trivalent state as previously determined for FeO and CoO.

Preparation and structure of [(C6H5)4P]3[NbTe10].cntdot.DMF: a soluble tellurium cluster containing an interstitial transition metal atom

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation and structure of [(C6H5)4P]3[NbTe10].cntdot.DMF: a soluble tellurium cluster containing an interstitial transition metal atomWalter A. Flomer and Joseph W. KolisCite this: J. Am. Chem. Soc. 1988, 110, 11, 3682–3683Publication Date (Print):May 1, 1988Publication History Published online1 May 2002Published inissue 1 May 1988https://doi.org/10.1021/ja00219a066RIGHTS & PERMISSIONSArticle Views110Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Titanium in large silicon clusters

The application of molecular ab initio methods to investigate the electronic structure of localized impurities in semiconductors requires the study of the convergence of the results with increasing cluster size. Here we compare results for interstitial Ti in silicon, obtained with clusters of increasing size: TiSi10H16, TiSi30H40, and TiSi66H64. These clusters contain one, two, or three shells of silicon atoms, respectively, centered around Ti at a Td interstitial site. The hydrogen atoms serve as saturators of the dangling bonds. The Si core electrons are replaced by an effective potential. The calculations are based on open shell RHF theory and limited CI extensions. The charge distribution in the central part of the three clusters is very similar. In the clusters the partially occupied orbitals are much more delocalized than the 3d orbitals in the free ions. The total impurity-induced electronic charge, however, is quite localized, due to the compensating response of the Si closed shell density. Ionization of the impurity also causes a compensating response of the Si closed shells: only about 10% of the density difference is in the impurity region and the major part is behind the outermost shell of Si atoms. Transition metal associated (3d-like) excitation energies are not very dependent on the cluster size, and the relative ordering of the lowest lying states remains unchanged. Impurity associated ionization energies decrease considerably due to the extra relaxation offered by the additional shells of Si atoms. Our results indicate that a reliable description of interstitial transition metals in silicon can be provided by calculations on reasonably small clusters: Si30H40 is sufficiently large.

Electronic structure and properties of NiSi2 and CoSi2 in the fluorite and adamantane structures.

An electronic-band-structure study of ${\mathrm{NiSi}}_{2}$ and ${\mathrm{CoSi}}_{2}$ is performed by means of the linear-muffin-tin-orbital method for both the fluorite and the hypothetical adamantane structures, i.e., silicon with tetrahedral interstitial metal atoms. Energy bands along symmetry lines, densities of states, charge densities, and total energies are presented. In addition, the equilibrium lattice constant, bulk modulus, and cohesive energies are obtained from total-energy and pressure calculations as a function of volume. Special attention is given to the relative stability of both structures. The experimentally observed fluorite structure is found to be lower in energy by more than 1 eV in both cases. The total-energy difference is analyzed and discussed in terms of the electronic structure. The electrostatic energy due to the charge transfer is found to play a significant role, as well as the tendency to form Ni\char22{}Si covalent bonds in the fluorite case.

Trends in hydrogen heats of solution and vacancy trapping energies in transition metals

Heats of solution and impurity-induced lattice relaxations are calculated for hydrogen in all the transition metals. The hydrogen-metal interaction is described using the effective-medium theory and the metal-lattice relaxations are included in a harmonic-continuum model. The authors find that the trends in the heats of solution can be related to the magnitude of the electron density of the interstitial metal. The trends in the hydrogen trapping energies for vacancies are estimated from the difference between the calculated heats of solution and chemisorption energies. A very simple conceptual picture of the hydrogen-metal interaction results, which can easily be extended to treat for instance hydrogen in metal alloys.

Interstitial Transition Metal Impurities as a Possible Cause of Enhanced Reactivities

AbstractTrivalent ions of Fe, Cr and Mo are easily incorporated into CsCl‐type lattices. Evidently their geometries partly derive from those for divalent ions by exchange of a neutral molecule by hydroxyl or halide. In the ammonium halides hydrogen bonding manifests itself in predominance of low site symmetries and dynamic effects. Evidence for interstitial incorporation of di‐ and trivalent ions in quartz and isomorphous ABO4 compounds is also presented. EPR data for Fe3+ indicate simultaneous incorporation of O2− or OH− in the c‐axis channels. A kinetic reason for preferred interstitial incorporation is proposed. Enhanced mobilities of these as well as certain main constituents may also enhance the reactivities.

Hartree‐Fock cluster study of interstitial transition metals in silicon

AbstractResults are presented of a Hartree‐Fock cluster study of interstitial Ti, V, Cr, and Mn impurities in silicon. A Si10 cluster models the nearest Si atoms around a tetrahedral interstitial site in crystalline Si. The dangling bonds of the Si atoms are saturated by hydrogens. The effect of the Si core electrons is represented by an effective potential. Characteristic for the electronic structure of the low‐lying states of the neutral, singly positive, and doubly positive ions in silicon is the presence of fairly delocalized but still predominantly transition‐metal (3d)‐like orbitals of t2 and e symmetry. For all ions the energy of the weighted average of the terms belonging to a configuration is lowest for the configuration with maximum occupation of the t2 orbitals. Ground states with maximum spin multiplicity are found for all ions, except Ti0.

A model calculation of transition metal impurities in silicon

A model calculation of interstitial transition metal impurities in Si is performed along the lines of the theory of Haldane and Anderson. The electronic states of silicon are described by a simple tight binding Hamiltonian while the transition metal impurity is modeled by taking into account the intra atomic coulombic interactions between the d electrons. Results obtained for neutral Co and Mn are found to be in good qualitative agreement with previous calculations.

Metal Oxide Chemistry in Solution: The Early Transition Metal Polyoxoanions

Many of the early transition elements form large polynuclear metal-oxygen anions containing up to 200 atoms or more. Although these polyoxoanions have been investigated for more than a century, detailed studies of structure and reactivity were not possible until the development of modern x-ray crystallographic and nuclear magnetic resonance spectroscopic techniques. Systematic studies of small polyoxoanions in inert, aprotic solvents have clarified many of the principles governing their structure and reactivity, and also have made possible the preparation of entirely new types of covalent derivatives such as CH(2)Mo(4)O(15)H(3-), C(5)H(5)TiMo(5)O(18)(3-), and (OC)(3)Mn(Nb(2)W(4)O(19))(3-). Since most early transition metal polyoxoanions have structures based on close-packed oxygen arrays containing interstitial metal centers, their chemistry offers a rare opportunity to study chemical transformations in detail on well-defined metal oxide surfaces.

Conditions for dislocation loop punching by helium bubbles

Under continuous helium but insufficient vacancy supply, bubbles in metals grow by pressure-driven athermal processes such as metal interstitial emission and dislocaton loop punching. To discuss the energetic conditions for these processes, the formation and interaction energies of bubbles and interstitial type metal defects are analyzed. The only condition which has been considered to date is that the decrease in the free energy of a bubble associated with the emission of an interstitial type metal defect must be equal to or larger than the formation free energy of the latter defect. Consideration of the elastic interaction energies result in additional conditions controlling loop punching for bubbles with radii larger than about 10 Burgers vectors. Possible modes for the loop punching process are discussed.

Oxidation of two-phase Co-54.86 wt.% Cu alloy at 700?1000�C

The oxidation in 1 atm of pure oxygen of a binary two-phase Co-Cu alloy has been studied as a simple example of the oxidation behavior of a multiphase alloy. The two-phase alloy oxidizes according to a parabolic rate law to a good approximation throughout the entire exposure period over the temperature range 700–1000°C with an oxidation rate constant greater than that for pure cobalt in the whole temperature range, and greater than that for pure copper at 900–1000°C, but lower below 900°C. The scale presents essentially the same type of layered structure at all the temperatures investigated, with an outer region composed of copper oxides, while cobalt is preferentially accumulated in the inner region of the scale, mainly in the form of CoO. A subscale formed by internal oxidation of the particles of the Co-rich phase is also present. The observed increase of the oxidation rate of the alloy in comparison with pure cobalt is attributed mainly to the presence of a high concentration of copper dissolved in CoO in the form of monovalent ions, which produces a significant modification of the concentration of defects of cobalt oxide with a consequent increase of the oxidation rate constant of the alloy if a suitable model for the defect structure of pure CoO is considered, which takes into account also the presence of a small concentration of interstitial metal ions.

New preparation method for doped polycrystalline titanium(IV) oxide and niobium(V) oxide and their photoelectrochemical properties

Doped polycrystalline TiO/sub 2/ and Nb/sub 2/O/sub 5/ have been prepared by a new method and examined as photoanodes. Polycrystalline oxide films on metal substrates which are thick and porous are prepared by anodic oxidation accompanied by sparking in various electrolytes. It was found that cations in the electrolyte are doped into the oxide films during anodic oxidation, which has been proved by ion microprob analysis and mass spectroscopy. Therefore, this is a new easy method of preparing doped polycrystalline TiO/sub 2/ and Nb/sub 2/O/sub 5/. The TiO/sub 2/ film prepared in Na/sub 2/SO/sub 4/ solution at 100 V is a good photoanode, showing a relatively high photocurrent under visible-light illumination. The doping is carried out by addition of the doping ions in saturated Na/sub 2/SO/sub 4/ solution. The Cr-, Ir- and Rh-doped TiO/sub 2/ films exhibit a high visible photocurrent but a low UV photocurrent. The Cr-doped Nb/sub 2/O/sub 5/ films also exhibit similar spectral responses. An increase in the UV photoresponse and a decrease in the visible photoresponse by reduction are observed. The relationship in which the band-gap photocurrents decrease with increasing visible photocurrents is obtained for the doped oxide films. This suggests, with the reduction effects, thatmore » the impurity and the interstitial metal d bands or states bringing about the visible response also act as recombination centers. 6 figures, 2 tables.« less

High nuclearity carbonyl clusters of rhodium. Part 3. Crystal and molecular structure of hexadeca-µ-carbonyl-enneacarbonyl-polyhedro-tetradecarhodate(4–) in its tetraethylammonium salt

The title compound, [NEt4]4[Rh14(CO)25], crystallises in the tetragonal space group P4/ncc, with unit-cell dimensions a= l7.060(3), c= 27.220(6)A, and Z= 4. The structure has been solved by Patterson and Fourier methods from X-ray single-crystal counter data and refined by least-squares methods to R= 0.046 for 1 224 significant reflections. The [Rh14(CO)25]4– anion contains a metal-atom cluster which can be described as a distorted fragment of a body-centred cubic lattice, of C4v idealized symmetry, with one interstitial metal atom which exhibits eight short metal–metal bonds (mean 2.638 A), four longer contacts (3.076 A), and one very long interaction [3.372(4)A] with the capping atom on the four-fold axis. The Rh–Rh surface interactions are very scattered, ranging from 2.724(2) to 3.325(2)A. There are nine terminally bound carbonyls (mean Rh–C and C–O, 1.80 and 1.17 A respectively) and 16 edge-bridging groups. Of these, 12 are symmetric (mean Rh–C and C–O, 1.99 and 1.19 A) and four, on the Rh(3)–Rh(5) edges, are markedly asymmetric [Rh(3)–C(6) 1.91(2) and Rh(5)–C(6) 2.33(2)A].

On the catalytic growth of synthetic diamonds

Synthetic diamond crystals crystallized in the presence of cobalt and nickel were studied by X-ray diffraction methods. Inclusions of metastable cobalt or nickel carbides are the most common imperfections in these crystals. Because of the presence of the forbidden 200 and 600 reflections, it is supposed that interstitial metal atoms are located in octahedral holes of the diamond structure. This observation suggests an active role played by the metal atoms in the nucleation and crystallization processes, so the metal acts simultaneously as a solvent and as a catalyst.

Hyperfine fields in iron-metalloid ferromagnetic metals

A new coordination parameter Z eff is defined at each inequivalent iron site in the interstitial iron-metalloid ferromagnetic metals which uniquely determines the hyperfine field at that site with considerable accuracy. The dependence of Z eff upon bonding lenghts is defined and can be directly used to generate hyperfine field distributions for amorphous aggregates. It thereby promises to provide a fairly quantitative bridge between computer models and hyperfine field probes in iron metglasses.

Chemical vapor deposition and solar thermal energy conversion

Chemical vapor deposition (CVD) is a useful technique for applying a variety of coatings to a wide range of substrate materials. Some interstitial transition metal compounds already applied commercially by CVD show a degree of spectral selectivity of interest for apllication as solar absorbers; these materials also display the refractory and oxidation-resistant properties required for solar applications.

Localized Orbital Approach to Electronic Structure of Covalent Semiconductors. II. The Impurity States in Silicon

The impurity states in Si are investigated theoretically on the basis of a previously proposed formalism, which emphasizes the local environment around the impurity center. The impurity potential is made self-consistent in a finite region surrounding the impurity atom. The difference of substitutional Ga (shallow) and Zn (deep) impurities is discussed from a chemical viewpoint based on atomic properties. The electronic structures of interstitial 3d transition metal impurities Cr, Mn and Fe are calculated for the first time. The obtained result can be interpreted in terms of the difference in chemical bonding between the substitutional and interstitial cases.

Synthesis and X-ray crystal structure of the novel high nuclearity rhodium-cluster dianion [Rh14(µ-CO)15(CO)11]2–

An X-ray crystallographic study has shown that the novel dianion [Rh14(CO)26]2–, which has been isolated from the products obtained in the pyrolysis of Na2[Rh13H3(CO)24] or of mixtures of Rh4(CO)12 and NaOH in propan-2-ol at reflux, contains a metal atom cluster, with one interstitial metal atom, which can be described as intermediate between a compact close-packed and a body-centred cubic array.