Molybdenum dichloride describes

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, molybdenum(II) chloride forms a structure based on clusters. Molybdenum(II), which is a rather large ion, prefers to form compounds with metal-metal bonds, i.e. metal clusters. 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 with a 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 el ...

s that

bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...

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⁺. ]

Synthesis and reactions

Mo₆Cl₁₂ is prepared by the reaction of molybdenum(V) chloride with

molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...

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−. :.

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 of

sulfide Sulfide (also sulphide in British English) 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 large families o ...

sources with Mo₆Cl₁₂ in the presence of donor ligands L.

References

{{Chlorides Chlorides Molybdenum halides Molybdenum(II) compounds