Molybdenum(II) chloride
Encyclopedia
Molybdenum dichloride describes chemical compound
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.
, rutile
, and cadmium iodide
motifs. 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.
One form of MoCl2 has the formula Mo6Cl12. This species is polymeric consisting of cubic Mo6Cl84+ clusters interconnected by chloride ligand
s that bridge from one cluster to cluster. This material converts readily to salts of the dianion [Mo6Cl14]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 a "magic" electron count of 24e, four being provided by each Mo2+.
with molybdenum
metal:
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[Mo6Cl14]. The terminal chloride ligands, labeled "ausser" are readily exchanged:2[Mo6Cl14] + 6 HI → (H3O)2[Mo6Cl8I6] + 6 HCl
Under more forceful conditions, all 14 ligands can be exchanged, to giving salts of [Mo6Br14]2- and [Mo6I14]2-.
Sulfido and selenido derivatives are also well studied. [Re6Se8Cl6]4- has the same number of valence electrons as does [Mo6Cl12]2-.
The Mo-S clusters Mo6S8L6, analogues of the "Chevrel phases", have been prepared by the reaction of sulfide
sources with Mo6Cl12 in the presence of donor ligands L.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
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.
Structure
At first glance, a species with the formula MoCl2 might be expected to adopt a close-packed structure, e.g. the cadmium chlorideCadmium chloride
Cadmium chloride is a white crystalline compound of cadmium and chlorine, with the formula CdCl2. It is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. Although it is considered to be ionic, it has considerable covalent character to its bonding...
, rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
, and cadmium iodide
Cadmium iodide
Cadmium iodide, CdI2, is a chemical compound of cadmium and iodine. It is notable for its crystal structure, which is typical for compounds of the form MX2 with strong polarization effects.-Uses:...
motifs. Molybdenum(II), which is a rather large ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
, 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.
One form of MoCl2 has the formula Mo6Cl12. This species is polymeric consisting of cubic Mo6Cl84+ clusters interconnected by chloride ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s that bridge from one cluster to cluster. This material converts readily to salts of the dianion [Mo6Cl14]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 a "magic" electron count of 24e, four being provided by each Mo2+.
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Ball-and-stick model In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them... of part of a layer in the crystal structure of Mo6Cl12 |
Thermal ellipsoid Thermal ellipsoids, more formally termed atomic displacement parameters, are ellipsoids used in crystallography to indicate the magnitudes and directions of the thermal vibration of atoms in crystal structures... model of the [Mo6Cl8]4+ cluster |
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Synthesis and reactions
Mo6Cl12 is prepared by the reaction of molybdenum(V) chlorideMolybdenum(V) chloride
Molybdenum chloride is the inorganic compound with the formula [MoCl5]2. This dark volatile solid is an important starting reagent in the preparation of molybdenum compounds. In the solid state molybdenum pentachloride exists as a dimer with the formula Mo2Cl10, with a structure similar to that...
with molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
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[Mo6Cl14]. The terminal chloride ligands, labeled "ausser" are readily exchanged:2[Mo6Cl14] + 6 HI → (H3O)2[Mo6Cl8I6] + 6 HCl
Under more forceful conditions, all 14 ligands can be exchanged, to giving salts of [Mo6Br14]2- and [Mo6I14]2-.
Related clusters
A variety of clusters are structurally related to [Mo6Cl12]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 [Ta6Cl18]4-.Sulfido and selenido derivatives are also well studied. [Re6Se8Cl6]4- has the same number of valence electrons as does [Mo6Cl12]2-.
The Mo-S clusters Mo6S8L6, analogues of the "Chevrel phases", have been prepared by the reaction of sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
sources with Mo6Cl12 in the presence of donor ligands L.