- Octahedral cluster
Octahedral clusters are inorganic or organometallic cluster compounds composed of six metals in an octahedral array. One important class of octahedral clusters are chalcohalide clusters 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 chlorine or sulfur 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 and the W6I142- anion, the last one by reaction of tungsten hexacarbonyl with iodine at elevated temperatures. Molybdenum(II) chloride is an example of a polymeric octahedral cluster; it reacts with chloride sources to afford Mo6Cl142-.
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, commonly called Chevrel phase, have been actively studied because they are type II superconductors with relatively high critical fields. Such materials are prepared by high temperature reactions of the chalcogen and Mo metal. Related, soluble analogues have been prepared, e.g. Mo6S8(PEt3)6.
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. Example of this type of species are the anion Ta6Cl184-., Nb6F15 or the Nb6F182- anion.
Electron counting in octahedral 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 Ta6+14, 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.
- ^ a b 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
- ^ 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.
- ^ 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)
Wikimedia Foundation. 2010.
Look at other dictionaries:
Cluster chemistry — 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,… … Wikipedia
Borane — In chemistry, a borane is a chemical compound of boron and hydrogen. The boranes comprise a large group of compounds with the generic formulae of BxHy. These compounds do not occur in nature. Many of the boranes readily oxidise on contact with… … Wikipedia
Suboxide — Suboxides are a class of oxides wherein the electropositive element is in excess relative to the “normal” oxides.Simon, A. ”Group 1 and 2 Suboxides and Subnitrides Metals with Atomic Size Holes and Tunnels” Coordination Chemistry Reviews 1997,… … Wikipedia
Palladium(II) chloride — Identifiers CAS number 7647 10 1 … Wikipedia
Polyhedral skeletal electron pair theory — In chemistry the polyhedral skeletal electron pair theory provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth… … Wikipedia
chemical bonding — ▪ chemistry Introduction any of the interactions that account for the association of atoms into molecules, ions, crystals, and other stable species that make up the familiar substances of the everyday world. When atoms approach one another … Universalium
Coordination complex — Cisplatin, PtCl2(NH3)2 A platinum atom with four ligands In chemistry, a coordination complex or metal complex, is an atom or ion (usually metallic), bonded to a surrounding array of molecules or anions, that are in turn known as ligands or… … Wikipedia
Keggin structure — is the best known structural form for heteropoly acids. It is the structural form of α–Keggin anions, which have a general formula of [XM12O40] n , where X is the heteroatom (most commonly are P5+, Si4+, or B3+), M is the addenda atom (most… … Wikipedia
Crystal structure of boron-rich metal borides — Two single crystals of YB66 (1 cm diameter) grown by floating zone technique using (100) oriented seeds. In the top crystal, the seed (left from the black line) has same diameter as the crystal. In the bottom crystal (sliced), the seed is much… … Wikipedia
Complex (chemistry) — The term complex in chemistry is usually used to describe molecules or ensembles formed by the combination of ligands and metal ions. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds … Wikipedia