In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group elements form especially robust clusters.^[1]. This article or section includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ... In science, a molecule is a group of atoms in a definite arrangement held together by chemical bonds. ... For other uses, see Solid (disambiguation). ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Atomic mass 10. ... The fullerenes, discovered in 1985 by researchers at Rice University, are a family of carbon allotropes named after Richard Buckminster Fuller and are sometimes called buckyballs. ... A borane is an inorganic chemical compound of boron and hydrogen. ...

The phrase cluster was coined by F.A. Cotton in the early 1960's as compounds containing metal-metal bonds. In another definition a cluster compound contains a group of two or more metal atoms where direct and substantial metal metal bonding is present ^[2]. Frank Albert Cotton (April 9, 1930 – February 20, 2007) was the W.T. Doherty-Welch Foundation Chair and Distinguished Professor of Chemistry at Texas A&M University. ...

The main cluster types are naked clusters without stabilizing ligands or those with ligands. Typical ligands that stabilize clusters include as carbon monoxide, halides, isocyanides, alkenes, and hydrides. In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a... Carbon monoxide, with the chemical formula CO, is a colourless, odourless, and tasteless gas. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ... An isocyanide (erroneously called isonitrile) is a functional group in organic synthesis containing carbon and nitrogen. ... The chemical structure of ethylene, the simplest alkene. ... A hydride is a compound of hydrogen with more electropositive elements. ...

Applications of clusters in catalysis

Synthetic cluster compounds were once proposed to be useful as catalysts for a wide range of industrial reactions, especially related to carbon monoxide utilization^[3], but few industrial exist. The clusters Ru₃(CO)₁₂ and Ir₄(CO)₁₂ are catalysts for the Water gas shift reaction, also catalyzed by iron oxide, and Rh₆(CO)₁₆ catalyzes the Fischer-Tropsch process, although again iron-based heterogeneous catalysts are used industrially. The water gas shift reaction is an organic reaction in which water and carbon monoxide react to form carbon dioxide and hydrogen (water splitting) CO + H2O → CO2 + H2 The water gas shift reaction is part of steam reforming of hydrocarbons and is involved in the chemistry of catalytic converters While... // The Fischer-Tropsch process is a catalyzed chemical reaction in which carbon monoxide and hydrogen are converted into liquid hydrocarbons of various forms. ...

The major role of clusters in catalysis are found in Nature. Nitrogen is converted to ammonia via the Fe-Mo-S cluster at the heart of the nitrogenase. CO is oxidized to CO₂ by carbon monoxide dehydrogenase. Hydrogenases rely on Fe₂ and NiFe clusters.^[4] Nitrogenase (EC 1. ... A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2). ...

Electronic structure

Metal cluster are prominently found with refractory metals. In general metal centers with large d-orbitals form stable clusters because of favorable overlap of valence orbitals. Thus, metals with a low oxidation state and therefore small effective charges tend to form stable clusters. Polynuclear metal carbonyls are generally found in late transition metals with low formal oxidation states. Polynuclear halides and oxides are found with early transition metals. Refractory metals are a class of metals extraordinarily resistant to heat, wear and corrosion. ... The d-block of the periodic table of elements consists of those periodic table groups that contain elements in which, in the atomic ground state, the highest-energy electron is in a d-orbital. ... In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. ... Metal carbonyls are organometallic complexes of transition metals with carbon monoxide. ... In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. ... The oxidation state or oxidation number is defined as the sum of negative and positive charges in an atom, which indirectly indicates the number of electrons it has accepted or donated. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ... An oxide is a chemical compound containing an oxygen atom and other elements. ...

The polyhedral skeletal electron pair theory or Wade's electron counting rules predict trends in the stability and structures of clusters. The polyhedral skeletal electron pair theory or Wades rules in chemistry are electron counting rules that apply to electron-poor cages such as boron hydrides which consist of many boron atoms linked together. ...

History

The oldest identified metal cluster was probably calomel which was known in India already in the 12th century. The existence of a mercury to mercury bond in this compound was established in beginning of the 20th century. Calomel (chemical formula Hg2Cl2) is a mild chloride of mercury, a heavy, white or yellowish white substance, insoluble and tasteless, much used in medicine as a mercurial and purgative; mercurous chloride. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Atomic mass 200. ...

The development of metal carbonyl compounds led quickly to the isolation of Fe₂(CO)₉ and Fe₃(CO)₁₂. Linus Pauling characterized MoCl₂ to contain Mo₆ octahedra. Rundle and Dahl discovered that Mn₂(CO)₁₀ featured an “unsupported” Mn-Mn bond, thereby verifying the ability of metals to bond to one another in molecules. F. Albert Cotton established that ReCl₃ was in fact the cluster Re₃Cl₉, which could be converted to a host of adducts without breaking the Re-Re bonds. Contemporaneously with the development of metal cluster compounds, numerous boron hydrides were discovered by Alfred Stock and his successors who popularized the use of vacuum-lines for the manipulation of these often volatile, air-sensitive materials. In the 1970's, ferredoxin was demonstrated to contain Fe₄S₄ clusters and later nitrogenase was shown to contain a distinctive MoFe₇S₉ active site.^[5] Diiron nonacarbonyl is the chemical compound Fe2(CO)9. ... Linus Carl Pauling (February 28, 1901 – August 19, 1994) was an American quantum chemist and biochemist. ... Molybdenum dichloride describes chemical compounds with the empirical formula MoCl2. ... Dimanganese decacarbonyl is the chemical compound Mn2(CO)10. ... Alfred Stock (1876-August 1946) was a German inorganic chemist. ... Ferredoxin is an electron receptor used in both Cyclic and Non cyclic photophosphorylation. ... Nitrogenase (EC 1. ...

The development of metal carbonyl compounds led quickly to the isolation of Fe₂(CO)₉ and Fe₃(CO)₁₂. Rundle and Dahl discovered that Mn₂(CO)₁₀ featured an “unsupported” Mn-Mn bond, thereby verifying the ability of metals to bond to one another in molecules. Metal carbonyls are organometallic complexes of transition metals with carbon monoxide. ...

The CO ligand can add to the polynuclear complex in three different ways:

• two-center or terminal carbonyl (μ₁ CO) in which the CO molecule is bonded to one vertex only. The M-CO bond can be linear or bent.
• three-center or edge-bridging carbonyl (μ₂ CO) in which CO bonds to two metal centers.
• four-center or triangular face-bridging (μ₃ CO) in which CO bonds to three metal centers sharing a face.

An often studied metal cluster compounds is dinuclear potassium octachlorodirhenate(III) or K₂Re₂Cl₈ whose peculiar molecular structure is explained by Quadruple bonding. Another dinuclear compound is di-tungsten tetra(hpp), the currect record holder low ionization energy. Covalently bonded hydrogen and carbon in a molecule of methane. ... the hpp ligand anion Di-tungsten tetra(hpp) or W2(hpp)4 is a di-tungsten paddlewheel compound with four hpp or hexahydropyrimidopyrimidine ligands. ... The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ...

In trinuclear rhenium(III) chloride or (ReCl₃)₃ the metal centers bond directly and through chlorine bridges. Albert Cotton established that ReCl₃ was in fact the cluster Re₃Cl₉, which could be converted to a host of adducts without breaking the Re-Re bonds.

Because this compound is diamagnetic and not paramagnetic the rhenium bonds are double bonds and not single bonds. In the solid state further bridging occurs between neighbours and when this compound is dissolved in hydrochloric acid a Re₃Cl₁₂^3- complex forms. An example of a tetranuclear complex is hexadecamethoxytetratungsten W₄(OCH₃)₁₂ with tungsten single bonds and molybdenum chloride (Mo₆Cl₈)Cl₄ is a hexanuclear molybdenum compound and an example of an octahedral cluster. A special group of clusters with the general structure M_xMo₆X₈ such as PbMo₆S₈ form a Chevrel phase which exhibit superconductivity at low temperatures. Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ... Paramagnetism is the tendency of the atomic magnetic dipoles, due to quantum-mechanical spin, in a material that is otherwise non-magnetic to align with an external magnetic field. ... General Name, Symbol, Number rhenium, Re, 75 Chemical series transition metals Group, Period, Block 7, 6, d Appearance grayish white Atomic mass 186. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... The chemical compound hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride gas (HCl). ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ... Molybdenum dichloride describes chemical compounds with the empirical formula MoCl2. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ... Octahedral clusters are inorganic or organometallic hexameric cluster compounds based on an octahedral geometry. ... A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. ...

Zintl clusters

Zintl compounds represent a separate class of metal clusters. Historically, they were generated by reduction of metalloids with a solution of sodium in liquid ammonia. Examples of Zintl anions are [[Bi₃]]^3-, [[Sn₉]]^4-, [Pb₇]^4- and [Sb₇]^3-. These anions do not require ligands and are called naked clusters but are unstable and their isolation requires the use of cryptate complexes of the alkali metal cation. In chemistry a Zintl phase is the product of a reaction between group 1 (alkali metals) or group 2 (alkaline earths) and post transition metals or metalloids from group 13, 14, 15 or 16. ... Ammonia is a compound with the formula NH3. ... Cryptands (trade name Kryptofix) are a group of chemicals that are used in the synthesis of other molecules. ...

The structure of the Pb₁₀^2- anion is that of a capped square antiprism ^[6]. According to Wade's rules (2n+2) the number of cluster electrons is 22 and therefore a closo cluster. The compound is prepared from oxidation of K₄Pb₉ ^[7] by Au⁺ in PPh₃AuCl (by reaction of Hydrogen tetrachloroaurate and triphenylphosphine) in ethylene diamine with 2.2.2-crypt. This type of cluster was already known as is the endohedral Ni@Pb₁₀^2- (the cage contains one nickel atom). In geometry, the Square antiprism is the second in an infinite set of antiprisms formed by an even-numbered sequence of triangle sides closed by two polygon caps. ... In chemistry the polyhedral skeletal electron pair theory provides electron counting rules used to predict the structure of electron deficient clusters. ... In chemistry the polyhedral skeletal electron pair theory provides electron counting rules used to predict the structure of electron deficient clusters. ... The most fundamental reactions in chemistry are the redox processes. ... Triphenylphosphine (in Europe: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. ... Ethylene diamine (EDA or en), or 1,2-diaminoethane, is an organic compound from the amines group. ... Crystal structure of a potassium ion bound within a cryptand[2. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic and silvery with a gold tinge Atomic mass 58. ...

The icosahedral tin cluster Sn₁₂^2- or stannaspherene anion is another closed shell structure observed (but not isolated) with photoelectron spectroscopy ^{[8] [9]}. With an internal diameter of 6.1 Angstrom it is of comparable size to fullerene and should be capable of containing small atoms as in endohedral fullerenes. An icosahedron [ˌaıkəsəhiːdrən] noun (plural: -drons, -dra [-drə]) is a polyhedron having 20 faces. ... General Name, Symbol, Number tin, Sn, 50 Chemical series poor metals Group, Period, Block 14, 5, p Appearance silvery lustrous gray Standard atomic weight 118. ... Photoemission Spectroscopy refers to two separate techniques/ X-Ray Photoemission Spectroscopy (XPS, formerly known as ESCA - Electron Spectroscopy for Chemical Analysis) was developed at Uppsala University, Sweden in the 1960s by a group headed by Kai Siegbahn, who in 1981 won the Nobel Prize for Physics for his work in... An angstrom, angström, or Ã¥ngström (symbol Ã…) is a unit of length. ... The fullerenes, discovered in 1985 by researchers at Rice University, are a family of carbon allotropes named after Richard Buckminster Fuller and are sometimes called buckyballs. ... Endohedral fullerenes are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. ...

Bioinorganic clusters

In bioinorganic chemistry in the 1970's, ferredoxin was demonstrated to contain Fe₄S₄ clusters and later nitrogenase was shown to contain a strikingly distinctive MoFe₇S₉ active site. Bioinorganic Chemistry is a specialized field that spans the chemistry of metal-containing molecules. ... Ferredoxin is an electron receptor used in both Cyclic and Non cyclic photophosphorylation. ... Nitrogenase (EC 1. ...

Gas-phase clusters

Unstable clusters can also be observed in the gas-phase by means of mass spectroscopy even though they may be thermodynamically unstable and aggregate easily upon condensation. Such naked clusters, i.e. those that are not stabilized by ligands, are often produced by laser induced evaporation - or ablation - of a bulk metal or metal-containing compound. Typically, this approach produces a broad distribution of size distributions. Their electronic structures can be interrogated by techniques such as photoelectron spectroscopy. Their properties (Reactivity, Ionization potential, HOMO-LUMO-gap) often show a pronounced size dependence. Examples of such clusters are certain aluminium clusters as superatoms and certain gold clusters. Certain metal clusters are considered to exhibit metal aromaticity. Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ... Photoemission Spectroscopy refers to two separate techniques/ X-Ray Photoemission Spectroscopy (XPS, formerly known as ESCA - Electron Spectroscopy for Chemical Analysis) was developed at Uppsala University, Sweden in the 1960s by a group headed by Kai Siegbahn, who in 1981 won the Nobel Prize for Physics for his work in... Reactivity refers to the rate at which a chemical substance tends to undergo a chemical reaction in time. ... The ionization potential, or ionization energy, of an atom or molecule is the energy required to strip it of an electron. ... Look up homo in Wiktionary, the free dictionary. ... HOMO and LUMO are acronyms for Highest Occupied Molecular Orbitals and Lowest Unoccupied Molecular Orbitals respectively. ... Superatoms are clusters of atoms which seem to exhibit some of the properties of elemental atoms. ... Gold clusters in cluster chemistry are gold-derived materials that can either be discrete molecules or larger colloidal particles. ... In Metal aromaticity the concept of aromaticity found in many hydrocarbons is extended to metals. ...

Carbon and Boron clusters

Contemporaneously with the development of metal cluster compounds, numerous boron hydrides were discovered by Alfred Stock and his successors who popularized the use of vacuum-lines for the manipulation of volatile, air-sensitive materials. Clusters of boron are boranes such as pentaborane and decaborane. Alfred Stock (1876-August 1946) was a German inorganic chemist. ... A borane is an inorganic chemical compound of boron and hydrogen. ... Pentaborane is a chemical compound considered in the 1950s as a good prospect for a rocket or jet fuel by the U.S. armed services, a so-called exotic fuel. Its chemical structure is that of five atoms of boron compounded with nine atoms of hydrogen (B5H9). ... Decaborane (B10H14) is a stable, crystalline borane. ...

Clusters of carbon are fullerenes and nanotubes. The fullerene sphere can be filled with small molecules in Endohedral fullerenes. The fullerenes, discovered in 1985 by researchers at Rice University, are a family of carbon allotropes named after Richard Buckminster Fuller and are sometimes called buckyballs. ... An electronic device known as a diode can be formed by joining two nanoscale carbon tubes with different electronic properties. ... Endohedral Fullerenes are fullerenes that have incorporated in their inner sphere atoms, ions or clusters. ...

Composite clusters of carbon and boron are carboranes. 3D model of carborane acid, colors: Hydrogen - white, Chlorine - yellow, Boron - green, Carbon - black A carborane is a cluster composed of boron and carbon atoms. ...

References

1. ^ Inorganic Chemistry Huyee, JE , 3rd ed. Harper and Row, New York
2. ^ Introduction to cluster chemistry by D. M. P. Mingos, David J Wales 1990 ISBN 0-13-479049-9
3. ^ Cluster Chemistry: Introduction to the Chemistry of Transition Metal and Main Group Element Molecular Clusters Guillermo Gonzalez-Moraga 1993 ISBN 0-387-56470-5
4. ^ Bioorganometallics: Biomolecules, Labeling, Medicine; Jaouen, G., Ed. Wiley-VCH: Weinheim, 2006.3-527-30990-X.
5. ^ "Metal Clusters in Chemistry" P. Braunstein, L. A. Oro, P. R. Raithby, eds Wiley-VCH, Weinheim, 1999. ISBN 3-527-29549-6.
6. ^ The Zintl Ion [Pb₁₀]^2-: A Rare Example of a Homoatomic closo Cluster A. Spiekermann, S. D. Hoffmann, T. F. Fässler Angewandte Chemie International Edition Volume 45, Issue 21 , Pages 3459 - 3462 2006 Abstract
7. ^ itself made by heating elemental potassium and lead at 350°C
8. ^ Tin particles are generated as K⁺Sn₁₂^2- by laser evaporation from solid tin containing 15% potassium and isolated by mass spectrometer before analysis
9. ^ Sn₁₂^2-: Stannaspherene Li-Feng Cui, Xin Huang, Lei-Ming Wang, Dmitry Yu. Zubarev, Alexander I. Boldyrev, Jun Li, and Lai-Sheng Wang J. Am. Chem. Soc.; 2006; 128(26) pp 8390 - 8391; (Communication) DOI:10.1021/ja062052f 10.1021/ja062052f.

Angewandte Chemie or Angewandte Chemie International Edition is the chemistry journal of the Gesellschaft Deutscher Chemiker (Society of German Chemists). ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... For PB or pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series poor metals Group, Period, Block 14, 6, p Appearance bluish gray Atomic mass 207. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ... The Journal of the American Chemical Society (usually abbreviated as , or JACS), is a peer-reviewed scientific journal, published since 1879 by the American Chemical Society. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

http://cluster-science.net - scientific community portal for clusters, fullerenes, nanotubes, nanostructures, and similar small systems

See also

• Cluster (physics)