Everything about Molybdenum Ii Chloride totally explained
Molybdenum dichloride describes
chemical compounds with the empirical formula MoCl
2. 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. In general, compounds composed only of an element and chloride are considered valuable.
Structure
At first glance, a species with the formula MoCl
2 might be expected to adopt a close-packed structure, for example the
cadmium chloride,
rutile, and
cadmium iodide motifs. Molybdenum(II), which is a rather large
ion, prefers to form compounds with metal-metal bonds, for example
metal clusters. In fact all "lower halides" (for example where halide/M ratio is <4) in the "early transition metal series (Ti, V, Cr, Mn triads).
One form of MoCl
2 has the formula Mo
6Cl
12. This species is polymeric consisting of cubic Mo
6Cl
84+ clusters interconnected by chloride
ligands that bridge from one cluster to cluster. This material converts readily to salts of the dianion [Mo
6Cl
14]
2-. In this anion, each Mo bears one terminal chloride but is otherwise part of an Mo
6 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 Mo
2+.
Synthesis and reactions
Mo
6Cl
12 is prepared by the reaction of
molybdenum(V) chloride with
molybdenum metal:
» 12 MoCl
5 + 18 Mo → 5 Mo
6Cl
12
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, Mo
6Cl
12 undergoes many reactions with retention of the Mo
6]
12+ core. Heating in concentrated HCl gives (H
3O)
2[Mo
6Cl
14]. The terminl chloride ligands, labeled "ausser" are readily exchanged:
» (H
3O)
2[Mo
6Cl
14] + 6
HI → (H
3O)
2[Mo
6Cl
8I
6] + 6 HCl
Under more forcing conditions, all 14 halides can be exchanged to give salts of [Mo
6Br
14]
2- and [Mo
6I
14]
2-.
Related clusters
A variety of clusters are structurally related to [Mo
6Cl
12]
2-. The tungsten analogue is known. Ta and Nb form related clusters where halides are bridge edges of the Ta
6 octahedron vs faces. The resulting formula is [Ta
6Cl
18]
4-.
Sulfido and selenido derivatives are also well studied. [Re
6Se
8Cl
6]
4- has the same number of valence electrons as does [Mo
6Cl
12]
2-.
The Mo-S clusters Mo
6S
8L
6, analogues of the "Chevrel phases", have been prepared by the reaction of
sulfide sources with Mo
6Cl
12 in the presence of donor ligands L.
Further Information
Get more info on 'Molybdenum Ii Chloride'.
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