Molybdenum(II) Chloride on:
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Molybdenum dichloride describes
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chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
s 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
Potassium octachlorodimolybdate (systematically named potassium bis(tetrachloromolybdate)(''Mo''–''Mo'')(4−)) is an inorganic compound with the chemical formula . It is known as a red-coloured, microcrystalline solid. The anion is of historic ...
.
Structure
Rather than adopting a close-packed structure typical of metal dihalides, e.g.,cadmium chloride
Cadmium chloride is a white crystalline compound of cadmium and chloride, with the formula CdCl2. This salt is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. The crystal structure of cadmium chloride (describe ...
, molybdenum(II) chloride forms a structure based on clusters. Molybdenum(II), which is a rather large ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
, prefers to form compounds with metal-metal bonds, i.e. metal cluster
In chemistry, an atom cluster (or simply cluster) is an ensemble of bound atoms or molecules that is intermediate in size between a simple molecule and a nanoparticle; that is, up to a few nanometers (nm) in diameter. The term ''microcluster ...
s. In fact all "lower halides" (i.e. where halide/M ratio is <4) in the "early transition metal series (Ti, V, Cr, Mn triads) do. The species Mo6Cl12 is polymeric, consisting of cubic Mo6Cl84+ clusters interconnected by chloride ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s that bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
from cluster to cluster. This material converts readily to salts of the dianion o6Cl14sup>2−. In this anion, each Mo bears one terminal chloride but is otherwise part of an Mo6 octahedron embedded inside a cube defined by eight chloride centers. Thus, the coordination environment of each Mo is four triply bridging chloride ligands, four Mo neighbors, and one terminal Cl. The cluster has 24e−, four being provided by each Mo2+.
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Synthesis and reactions
Mo6Cl12 is prepared by the reaction ofmolybdenum(V) chloride
Molybdenum(V) chloride is the inorganic compound with the empirical formula . This dark volatile solid is used in research to prepare other molybdenum compounds. It is moisture-sensitive and soluble in chlorinated solvents.
Structure
Usually cal ...
with molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
metal:
:12 MoCl5 + 18 Mo → 5 Mo6Cl12
This reaction proceeds via the intermediacy of MoCl3 and MoCl4, which also are reduced by the presence of excess Mo metal. The reaction is conducted in a tube furnace at 600–650 °C.
Once isolated, Mo6Cl12 undergoes many reactions with retention of the Mo612+ core. Heating in concentrated HCl gives (H3O)2 o6Cl14 The terminal chloride ligands, labeled "ausser" are readily exchanged:
:(H3O)2 o6Cl14 + 6 HI → (H3O)2 o6Cl8I6 + 6 HCl
Under more forcing conditions, all 14 ligands can be exchanged, to giving salts of o6Br14sup>2− and o6I14sup>2−.
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Related clusters
A variety of clusters are structurally related to o6Cl14sup>2−. The tungsten analogue is known. Ta and Nb form related clusters where halides are bridge edges of the Ta6 octahedron vs faces. The resulting formula is a6Cl18sup>4−. Sulfido and selenido derivatives are also well studied. e6Se8Cl6sup>4− has the same number of valence electrons as does o6Cl14sup>2−. The Mo-S clusters Mo6S8L6, analogues of the "Chevrel phases", have been prepared by the reaction ofsulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
sources with Mo6Cl12 in the presence of donor ligands L.
References