Octahedral cluster

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Octahedral clusters are inorganic or organometallic cluster compounds composed of six metals in an octahedral array. [1] Many types of compounds are known, but all are synthetic.

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Octahedral chalcogenide and halide clusters

These compounds are bound together by metal-metal bonding as well as two kinds of ligands. Ligands that span the faces or edges of the M6 core are labeled Li, for inner (innen in the original German description), and those ligands attached only to one metal are labeled outer, or La for ausser. [2] Typically, the outer ligands can be exchanged whereas the bridging ligands are more inert toward substitution.

Face-capped halide clusters

The premier example is of the class is Mo6Cl142−. This dianion is available as a variety of salts by treating the polymer molybdenum(II) chloride with sources of chloride, even hydrochloric acid. A related example is W6Cl142− anion, which is obtained by extraction of tungsten(II) chloride.

Structure of [M6Cl14] (M = Mo or W). Mo6Cl14-anion-from-xtal-2008-CM-3D-ellipsoids.png
Structure of [M6Cl14] (M = Mo or W).

Chalcohalide clusters

A related class of octahedral clusters are of the type M6X8L6 where M is a metal usually of group 6 or group 7, X is a ligand and more specifically an inner ligand of the chalcohalide group such as chloride or sulfide and L is an "outer ligand." The metal atoms define the vertices of an octahedron. The overall point group symmetry is Oh. Each face of the octahedron is capped with a chalcohalide and eight such atoms are at the corners of a cube. For this reason this geometry is called a face capped octahedral cluster. Examples of this type of clusters are the Re6S8Cl64− anion.

Chevrel clusters

A well-studied class of solid-state compounds related to the chalcohalides are molybdenum clusters of the type AxMo6X8 with X sulfur or selenium and Ax an interstitial atom such as Pb. These materials, called Chevrel phases or Chevrel clusters, have been actively studied because they are type II superconductors with relatively high critical fields. [3] Such materials are prepared by high temperature (1100 °C) reactions of the chalcogen and Mo metal. Structurally related, soluble analogues have been prepared, e.g., Mo6S8(PEt3)6. [4]

Edge-Capped Halide Clusters

With metals in group 4 or 5 a so-called edge-capped octahedral clusters are more common. Twelve halides are located along the edge of the octahedron and six are terminal. Examples of this structure type are tungsten(III) chloride, Ta6Cl14(H2O)4, [5] [6] Nb6F15, and Nb6F182−. [1]

Structure of edge-capped octahedral clusters such as Ta6Cl18 . EntryWithCollCode26094.png
Structure of edge-capped octahedral clusters such as Ta6Cl18 .

Many of the early metal clusters can only be prepared when they incorporate interstitial atoms. One example is Zr6CCl12. [2]

Tin(II) clusters

Octahedral clusters of tin(II) have been observed in several solid state compounds. The reaction of tin(II) salts with an aqueous base leads to the formation of tin(II) oxyhydroxide (Sn6O4(OH)4), the structure of which comprises discrete Sn6O4(OH)4 clusters. In Sn6O4(OH)4 clusters, the six tin atoms form an octahedral array with alternate faces of the octahedron occupied by an oxide or hydroxide moiety, each bonded in a µ3-binding mode to three tin atoms. [8] Crystal structures have been reported for compounds with the formula Sn6O4(OR)4, where R is an alkoxide such as a methyl or ethyl group. [9] [10]

Recently, it was demonstrated that anionic tin(II) clusters [Sn6O8]4- may form the close packed arrays as in the case of α-Sn6SiO8, which adopts the zinc blende structure, comprising a face-centred-cubic array of [Sn6O8]4- clusters with Si4+ occupying half of the tetrahedral holes. [11] A polymorph, β-Sn6SiO8, has been identified as a product of pewter corrosion in aqueous conditions, and is a structural analogue of wurtzite. [12]

Electron counting in octahedral halide and chalcogenide clusters

The species Mo6Cl142− feature Mo(II) (d4) centers. Six Mo(II) centers gives rise to a total of 24 valence electrons, or 2e/Mo-Mo vector. More electron-deficient derivatives such as Ta6Cl184− have fewer d-electrons. For example, the naked cluster Ta614+, the core of Ta6Cl184− would have 5(6) - 14 = 16 valence electrons. Fewer d-electrons result in weakened M-M bonding and the extended Ta---Ta distances accommodate doubly bridging halides.

Other classes of octahedral clusters

In the area of metal carbonyl clusters, a prototypical octahedral cluster is [Fe6C(CO)16]2−, which is obtained by heating iron pentacarbonyl with sodium. Some of the CO ligands are bridging and many are terminal. A carbide ligand resides at the center of the cluster. A variety of analogous compounds have been reported where some or all of the Fe centres are replaced by Ru, Mn and other metals.

Outside of carbonyl clusters, gold forms octahedral clusters.

The complex [Au6C(PPh3)6] , containing a carbon-gold core. Au6C(PPh3)6.png
The complex [Au6C(PPh3)6] , containing a carbon-gold core.

Related Research Articles

<span class="mw-page-title-main">Coordination complex</span> Molecule or ion containing ligands datively bonded to a central metallic atom

A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the coordination centre, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds, especially those that include transition metals, are coordination complexes.

<span class="mw-page-title-main">Inorganic chemistry</span> Field of chemistry

Inorganic chemistry deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disciplines is far from absolute, as there is much overlap in the subdiscipline of organometallic chemistry. It has applications in every aspect of the chemical industry, including catalysis, materials science, pigments, surfactants, coatings, medications, fuels, and agriculture.

<span class="mw-page-title-main">Octahedral molecular geometry</span> Molecular geometry

In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The octahedron has eight faces, hence the prefix octa. The octahedron is one of the Platonic solids, although octahedral molecules typically have an atom in their centre and no bonds between the ligand atoms. A perfect octahedron belongs to the point group Oh. Examples of octahedral compounds are sulfur hexafluoride SF6 and molybdenum hexacarbonyl Mo(CO)6. The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves. For example, [Co(NH3)6]3+, which is not octahedral in the mathematical sense due to the orientation of the N−H bonds, is referred to as octahedral.

The coordination geometry of an atom is the geometrical pattern defined by the atoms around the central atom. The term is commonly applied in the field of inorganic chemistry, where diverse structures are observed. The coodination geometry depends on the number, not the type, of ligands bonded to the metal centre as well as their locations. The number of atoms bonded is the coordination number. The geometrical pattern can be described as a polyhedron where the vertices of the polyhedron are the centres of the coordinating atoms in the ligands.

<span class="mw-page-title-main">Chalcogenide</span>

A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant.

<span class="mw-page-title-main">Molybdenum(V) chloride</span> Chemical compound

Molybdenum(V) chloride is the inorganic compound with the empirical formula MoCl5. This dark volatile solid is used in research to prepare other molybdenum compounds. It is moisture-sensitive and soluble in chlorinated solvents.

Technetium compounds are chemical compounds containing the chemical element technetium. Technetium can form multiple oxidation states, but often forms in the +4 and +7 oxidation states. Because technetium is radioactive, technetium compounds are extremely rare on Earth.

<span class="mw-page-title-main">Tungsten hexacarbonyl</span> Chemical compound

Tungsten hexacarbonyl (also called tungsten carbonyl) is an organometallic compound with the formula W(CO)6. This complex gave rise to the first example of a dihydrogen complex.

<span class="mw-page-title-main">Molybdenum(II) chloride</span> Chemical compound

Molybdenum dichloride describes chemical compounds with the empirical formula MoCl2. At least two forms are known, and both have attracted much attention from academic researchers because of the unexpected structures seen for these compounds and the fact that they give rise to hundreds of derivatives. The form discussed here is Mo6Cl12. The other molybdenum(II) chloride is potassium octachlorodimolybdate.

In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central ion/molecule/atom is called a ligand. This number is determined somewhat differently for molecules than for crystals.

<span class="mw-page-title-main">Molybdenum tetrachloride</span> Chemical compound

Molybdenum tetrachloride is the inorganic compound with the empirical formula MoCl4. The material exists as two polymorphs, both being dark-colored paramagnetic solids. These compounds are mainly of interest as precursors to other molybdenum complexes.

<span class="mw-page-title-main">Organomolybdenum chemistry</span> Chemistry of compounds with Mo-C bonds

Organomolybdenum chemistry is the chemistry of chemical compounds with Mo-C bonds. The heavier group 6 elements molybdenum and tungsten form organometallic compounds similar to those in organochromium chemistry but higher oxidation states tend to be more common.

<span class="mw-page-title-main">Molybdenum(III) chloride</span> Chemical compound

Molybdenum(III) chloride is the inorganic compound with the formula MoCl3. It forms purple crystals.

<span class="mw-page-title-main">Transition-metal allyl complex</span>

Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2−, which is usually described as two equivalent resonance structures.

Tungsten(IV) chloride is an inorganic compound with the formula WCl4. It is a diamagnetic black solid. The compound is of interest in research as one of a handful of binary tungsten chlorides.

<span class="mw-page-title-main">Tungsten(II) chloride</span> Chemical compound

Tungsten(II) chloride is the inorganic compound with the formula W6Cl12. It is a polymeric cluster compound. The material dissolves in concentrated hydrochloric acid, forming (H3O)2[W6Cl14](H2O)x. Heating this salt gives yellow-brown W6Cl12. The structural chemistry resembles that observed for molybdenum(II) chloride.

<span class="mw-page-title-main">Tantalum(III) chloride</span> Chemical compound

Tantalum(III) chloride or tantalum trichloride is non-stoichiometric chemical compound with a range of composition from TaCl2.9 to TaCl3.1 Anionic and neutral clusters containing Ta(III) chloride include [Ta6Cl18]4− and [Ta6Cl14](H2O)4.

<span class="mw-page-title-main">Metal cluster compound</span> Cluster of three or more metals

Metal cluster compounds are a molecular ion or neutral compound composed of three or more metals and featuring significant metal-metal interactions.

<span class="mw-page-title-main">Transition metal chloride complex</span> Coordination complex

In chemistry, a transition metal chloride complex is a coordination complex that consists of a transition metal coordinated to one or more chloride ligand. The class of complexes is extensive.

<span class="mw-page-title-main">Transition metal ether complex</span>

In chemistry, a transition metal ether complex is a coordination complex consisting of a transition metal bonded to one or more ether ligand. The inventory of complexes is extensive. Common ether ligands are diethyl ether and tetrahydrofuran. Common chelating ether ligands include the glymes, dimethoxyethane (dme) and diglyme, and the crown ethers. Being lipophilic, metal-ether complexes often exhibit solubility in organic solvents, a property of interest in synthetic chemistry. In contrast, the di-ether 1,4-dioxane is generally a bridging ligand.

References

  1. 1 2 Eric J. Welch and Jeffrey R. Long Atomlike Building Units of Adjustable Character: Solid-State and Solution Routes to Manipulating Hexanuclear Transition Metal Chalcohalide Clusters in Progress in Inorganic Chemistry, Volume 54 Kenneth D. Karlin ISBN   0-471-72348-7 2005 Link
  2. 1 2 Arndt Simon "Metal clusters inside out" Phil. Trans. R. Soc. A 2010 vol. 368, 1285-1299. doi : 10.1098/rsta.2009.0271
  3. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  4. ↑ Saito, T. and Imoto, H., "Chalcogenide Cluster Complexes of Chromium, Molybdenum, Tungsten, and Rhenium", Bulletin Chemical Society of Japan, 1996, volume 69, pp. 2403-2417. doi : 10.1246/bcsj.69.2403
  5. ↑ Duraisamy, Thirumalai; Hay, Daniel N. T.; Messerle, Louis (2014). "Octahedral Hexatantalum Halide Clusters". Inorganic Syntheses: Volume 36. Vol. 36. pp. 1–8. doi:10.1002/9781118744994.ch1. ISBN   9781118744994.
  6. ↑ Koknat, F. W.; Marko, D. J. "Tetradecachlorohexatantalum Octahydrate, Ta6Cl14.8H2O" Inorganic Syntheses, 2004, volume 34, pp. 187-191. ISBN   0-471-64750-0. (describes Na4Ta6Cl18)
  7. ↑ Thaxton, C. B.; Jacobson, R. A. (1971). "The Crystal Structure of H2(Ta6Cl18)(H2O)6". Inorganic Chemistry. 10: 1460–1463. doi:10.1021/ic50101a029.
  8. ↑ Abrahams, I.; Grimes, S. M.; Johnston, S. R.; Knowles, J. C. (1996-02-15). "Tin(II) Oxyhydroxide by X-ray Powder Diffraction". Acta Crystallographica Section C Crystal Structure Communications. 52 (2): 286–288. doi: 10.1107/S0108270195012625 .
  9. ↑ Harrison, Philip G.; Haylett, Bernard J.; King, Trevor J. (1978). "X-Ray crystal structure of Sn6O4(OMe)4: an intermediate in the hydrolysis of tin(II) dimethoxide". Journal of the Chemical Society, Chemical Communications (3): 112–113. doi:10.1039/c39780000112. ISSN   0022-4936.
  10. ↑ Suslova, E. V.; Turova, N. Ya.; Kessler, V. G.; Belokon’, A. I. (November 2007). "Electrosynthesis of tin(II) alkoxides". Russian Journal of Inorganic Chemistry. 52 (11): 1682–1686. doi:10.1134/S0036023607110083. ISSN   0036-0236. S2CID   93819431.
  11. ↑ Parsons, Daniel S.; Savva, Savvaki N.; Tang, Wai Chi; Ingram, Andrew; Hriljac, Joseph A. (2019-12-16). "Sn 6 SiO 8 , a Tin(II) Silicate with a Zinc Blende Related Structure and High Thermal Stability". Inorganic Chemistry. 58 (24): 16313–16316. doi: 10.1021/acs.inorgchem.9b02615 . ISSN   0020-1669. PMID   31804067.
  12. ↑ Locock, A. J.; Ramik, R. A.; Back, M. E. (2006-12-01). "THE STRUCTURES OF TWO NOVEL Sn2+ OXYSALTS FOUND WITH ROMARCHITE AND HYDROROMARCHITE AS CORROSION PRODUCTS OF PEWTER ARTIFACTS". The Canadian Mineralogist. 44 (6): 1457–1467. Bibcode:2006CaMin..44.1457L. doi:10.2113/gscanmin.44.6.1457. ISSN   0008-4476.
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