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In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. "C60" and "C-60" redirect here For other uses see C60 (disambiguation. In chemistry a borane is a chemical compound of Boron and Hydrogen. Transition metals and main group elements form especially robust clusters. [1].

The phrase cluster was coined by F.A. Cotton in the early 1960s as compounds containing metal–metal bonds. Frank Albert Cotton ( April 9 1930 – February 20 2007) was the W 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].

The main cluster types are naked clusters without stabilizing ligands or those with ligands. In Chemistry, a ligand is either an Atom, Ion, or Molecule (see also Functional group) that bonds to a central metal generally Typical ligands that stabilize clusters include carbon monoxide, halides, isocyanides, alkenes, and hydrides. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic 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 An isocyanide (also called an isonitrile) is an Organic compound with the Functional group R-N≡C In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon Hydride is the name given to the negative Ion of Hydrogen, H−

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Applications of clusters in catalysis

Synthetic metal carbonyl cluster compounds have been evaluated as catalysts for a wide range of industrial reactions, especially related to carbon monoxide utilization,[3] but no industrial applications exist. The clusters Ru3(CO)12 and Ir4(CO)12 catalyse the Water gas shift reaction, also catalyzed by iron oxide, and Rh6(CO)16 catalyzes the conversion of carbon monoxide into hydrocarbons, reminiscent of the Fischer-Tropsch process, although again iron-oxide based heterogeneous catalysts are used industrially. The water gas shift reaction (WGS is a Chemical reaction in which Carbon monoxide reacts with Water to form Carbon dioxide and Hydrogen The Fischer-Tropsch process (or Fischer-Tropsch Synthesis is a catalyzed chemical reaction in which synthesis gas ( Syngas) a mixture of Carbon monoxide

Although discrete clusters have no well-defined role in industrial catalysis, they are widespread in Nature. Most prevalent are the iron-sulfur proteins, which are involved with electron-transfer but also catalyse certain transformations. Iron-sulfur proteins are Proteins characterized by the presence of iron-sulfur clusters containing Sulfide -linked di- tri- and tetrairon centers in variable Nitrogen is reduced to ammonia at an Fe-Mo-S cluster at the heart of the enzyme nitrogenase. Nitrogenase ( is the Enzyme used by some organisms to fix atmospheric Nitrogen gas (N2 CO is oxidized to CO2 by the Fe-Ni-S cluster carbon monoxide dehydrogenase. Hydrogenases rely on Fe2 and NiFe clusters. A hydrogenase is an Enzyme that catalyses the reversible oxidation of molecular Hydrogen (H2 [4]

Electronic structure

Metal cluster are prominently found with refractory metals. Refractory metals are a class of Metals that are extraordinarily resistant to Heat and Wear. In general metal centers with large d-orbitals form stable clusters because of favorable overlap of valence orbitals. In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other Thus, metals with a low oxidation state for the later metals and mid-oxidation states for the early metals tend to form stable clusters. In Chemistry, the oxidation state is an indicator of the degree of Oxidation of an Atom in a Chemical compound. Polynuclear metal carbonyls are generally found in late transition metals with low formal oxidation states. Metal carbonyls are Coordination 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 In Chemistry, the oxidation state is an indicator of the degree of Oxidation of an Atom in a Chemical compound.

The polyhedral skeletal electron pair theory or Wade's electron counting rules predict trends in the stability and structures of many metal clusters. In Chemistry the polyhedral skeletal electron pair theory provides Electron counting rules used to predict the structure of electron deficient clusters.

History and classification

The development of cluster chemistry occurred contemporaneously along several independent lines, which are roughly classified in the following sections. The first synthetic metal cluster was probably calomel, which was known in India already in the 12th century. Mercury(I chloride is the Chemical compound with the formula Hg2Cl2 India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country The existence of a mercury to mercury bond in this compound was established in beginning of the 20th century. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum

Transition metal carbonyl clusters

The development of metal carbonyl compounds such as Ni(CO)4 and Fe(CO)5 led quickly to the isolation of Fe2(CO)9 and Fe3(CO)12. Diiron nonacarbonyl (referred to as diiron enneacarbonyl in the older literature is the Chemical compound with the formula Fe2(CO9 Triiron dodecarbonyl is the Chemical compound with the formula Fe3(CO12 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. Dimanganese decacarbonyl is the Chemical compound with the formula Mn2(CO10 In the 1970's, Paolo Chini demonstrated that very large clusters could be prepared from the platinum metals, one example being [Rh13(CO)24H3]2-.

Transition metal halide clusters

Linus Pauling showed that "MoCl2" consisted of Mo6 octahedra. Linus Carl Pauling (February 28 1901 – August 19 1994 was an American Scientist, Peace activist, Author and educator. Molybdenum dichloride describes Chemical compounds with the empirical formula MoCl2 F. Albert Cotton established that "ReCl3" in fact features subunits of the cluster Re3Cl9, which could be converted to a host of adducts without breaking the Re-Re bonds. Frank Albert Cotton ( April 9 1930 – February 20 2007) was the W Because this compound is diamagnetic and not paramagnetic the rhenium bonds are double bonds and not single bonds. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Rhenium (ˈriːniəm is a Chemical element with the symbol Re and Atomic number 75 In the solid state further bridging occurs between neighbours and when this compound is dissolved in hydrochloric acid a Re3Cl123- complex forms. Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water 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. Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Molybdenum dichloride describes Chemical compounds with the empirical formula MoCl2 Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo Octahedral clusters are inorganic or organometallic cluster compounds composed of six metals in an octahedral array A related group of clusters with the general formula MxMo6X8 such as PbMo6S8 form a Chevrel phase, which exhibit superconductivity at low temperatures. Superconductivity is a phenomenon occurring in certain Materials generally at very low Temperatures characterized by exactly zero electrical resistance The eclipsed structure of potassium octachlorodirhenate(III), K2Re2Cl8 was explained by invoking Quadruple bonding. A quadruple bond is a type of Chemical bond between two Atoms involving 8 Electrons This bond is an extension of the more familiar types Double bonds This discovery led to a broad range of derivatives including di-tungsten tetra(hpp), the currect (2007) record holder low ionization energy. Di-tungsten tetra(hpp or W2(hpp4 is a di- Tungsten paddlewheel compound with four hpp or hexahydropyrimidopyrimidine The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron

Boron hydrides

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. Alfred Stock ( July 16 1876 – August 12 1946) was a German inorganic chemist. Clusters of boron are boranes such as pentaborane and decaborane. In chemistry a borane is a chemical compound of Boron and Hydrogen. Pentaborane, also called pentaboron nonahydride, stable pentaborane, or pentaborane(9 (to distinguish it from B5H11 is a Decaborane, also called decaborane(14, is the Borane with formula B 10 H 14 Composite clusters containing CH and BH vertices are carboranes. A carborane is a cluster composed of Boron and Carbon atoms Like many of the related Boranes, these clusters are Polyhedra and are similarly

Fe-S clusters in biology

In the 1970s, ferredoxin was demonstrated to contain Fe4S4 clusters and later nitrogenase was shown to contain a distinctive MoFe7S9 active site. Ferredoxins (from Latin ferrum: Iron + Redox, often abbreviated "fd" are Iron-sulfur proteins that mediate Electron Nitrogenase ( is the Enzyme used by some organisms to fix atmospheric Nitrogen gas (N2 [5] With the development of bioinorganic chemistry, a variety of synthetic analogues of these clusters have been described. Bioinorganic chemistry is a specialized field that spans the Chemistry of Metal -containing Molecules within biological systems

Zintl clusters

Zintl compounds feature naked anionic clusters that are generated by reduction of metalloids with a alkali metals, often as a solution in anhydrous ammonia. In Chemistry a Zintl phase is the product of a reaction between group 1 ( alkali metals) or group 2 ( alkaline earths) and Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Examples of Zintl anions are [Bi3]3-, [Sn9]4-, [Pb7]4-, and [Sb7]3-. Although these species are called "naked clusters," they are usually strongly associated with alkali metal cations. Some examples have been isolated using cryptate complexes of the alkali metal cation, e. Cryptands are a family of synthetic bi- and polycyclic multidentate Ligands for a variety of cations g. , Pb102- anion, which features a capped square antiprismatic shape. 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 [6]. According to Wade's rules (2n+2) the number of cluster electrons is 22 and therefore a closo cluster. 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 compound is prepared from oxidation of K4Pb9 [7] by Au+ in PPh3AuCl (by reaction of tetrachloroauric acid and triphenylphosphine) in ethylene diamine with 2.2.2-crypt. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Chloroauric acid is a Inorganic compound with the formula HAuCl4 Triphenylphosphine (in Europe triphenylphosphane is a common Organophosphorus compound with the formula P(C6H53 - often abbreviated to Ethylenediamine (abbreviated as en when a Ligand) is the Organic compound with the formula C2H4(NH22 Cryptands are a family of synthetic bi- and polycyclic multidentate Ligands for a variety of cations This type of cluster was already known as is the endohedral Ni@Pb102- (the cage contains one nickel atom). Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 The icosahedral tin cluster Sn122- or stannaspherene anion is another closed shell structure observed (but not isolated) with photoelectron spectroscopy [8] [9]. In Geometry, an icosahedron ( Greek: eikosaedron, from eikosi twenty + hedron seat /ˌaɪ Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 In the context of Atomic orbitals, an open shell is a Valence shell which is not completely filled with Electrons or that has not given all of its valence Photoemission Spectroscopy (PES, also known as photoelectron spectroscopy, refers to energy measurement of electrons emitted from solids gases or liquids by the Photoelectric 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 ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal "C60" and "C-60" redirect here For other uses see C60 (disambiguation.

Gas-phase clusters and fullerenes

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. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles 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. Photoemission Spectroscopy (PES, also known as photoelectron spectroscopy, refers to energy measurement of electrons emitted from solids gases or liquids by the Photoelectric Their properties (Reactivity, Ionization potential, HOMO-LUMO-gap) often show a pronounced size dependence. The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron HOMO and LUMO are Acronyms for highest occupied Molecular orbital and lowest unoccupied Molecular orbital, respectively HOMO and LUMO are Acronyms for highest occupied Molecular orbital and lowest unoccupied Molecular orbital, respectively Examples of such clusters are certain aluminium clusters as superatoms and certain gold clusters. Superatoms are clusters of Atoms that 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 Certain metal clusters are considered to exhibit metal aromaticity. In metal aromaticity the concept of Aromaticity found in many Hydrocarbons is extended to Metals. In some cases, the results of laser ablation experiments are translated to isolated compounds, and the premier cases are the Clusters of carbon called the fullerenes, notably clusters with the formula C60, C70, and C84. "C60" and "C-60" redirect here For other uses see C60 (disambiguation. The fullerene sphere can be filled with small molecules in Endohedral fullerenes.

Extended metal atom chains

Extended metal atom chain complexes (EMAC) are a novel topic in academic research. They are comprised of linear chains of metal atoms stabilized with ligands. In Chemistry, a ligand is either an Atom, Ion, or Molecule (see also Functional group) that bonds to a central metal generally EMACS are known based on nickel (with 9 atoms), chromium and cobalt (7 atoms) and ruthenium (5 atoms). Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. In theory it should be possible to obtain infinite one-dimensional molecules and research is oriented towards this goal. In one study [10] an EMAC was obtained that consisted of 9 chromium atoms in a linear array with 4 ligands (based on an oligo pyridine) wrapped around it. An oligonucleotide (or oligo) is a short segment of RNA or DNA, typically with twenty or fewer bases. Pyridine is a Chemical compound with the formula C5[[Hydrogen H5]] N. In it the chromium chain contains 4 quadruple bonds. A quadruple bond is a type of Chemical bond between two Atoms involving 8 Electrons This bond is an extension of the more familiar types Double bonds

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+Sn122- by laser evaporation from solid tin containing 15% potassium and isolated by mass spectrometer before analysis
  9. ^ Sn122-: Stannaspherene Li-Feng Cui, Xin Huang, Lei-Ming Wang, Dmitry Yu. Angewandte Chemie is a weekly Peer-reviewed Chemistry journal that covers all disciplines of chemistry Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles 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. The Journal of the American Chemical Society (usually abbreviated as J A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
  10. ^ Four quadruple metal–metal bonds lined up: linear nonachromium(II) metal string complexes Rayyat H. Ismayilov, Wen-Zhen Wang, Rui-Ren Wang, Chen-Yu Yeh, Gene-Hsiang Lee and Shie-Ming Peng Chem. Commun., 2007, 1121 - 1123, doi:10.1039/b614597c

External links

See also

Chemical Communications, known as ChemComm, is a peer-reviewed Scientific journal. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. In physics the term clusters denotes small multiatom particles In Chemistry a water cluster is a discrete Hydrogen bonded assembly or cluster of Molecules of water.
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