:Potassium octachlorodimolybdate

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| Verifiedfields = changed

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| verifiedrevid = 434381923

| Name = Potassium octachlorodimolybdate(4−)

| ImageFile = K4Mo2Cl8.jpg

|ImageFile2 = Potassium octachlorodimolybdate.svg

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| IUPACName =

| OtherNames =

|Section1 = {{Chembox Identifiers

| CASNo_Ref = {{cascite|correct|CAS}}

| CASNo = 25448-39-9

| SMILES=[K+].[K+].[K+].[K+].Cl[Mo-2](Cl)(Cl)(Cl)$[Mo-2](Cl)(Cl)(Cl)Cl

| StdInChI=1S/8ClH.4K.2Mo/h8*1H;;;;;;/q;;;;;;;;4*+1;2*+2/p-8

| StdInChIKey=IPKVUDXOBCRDJX-UHFFFAOYSA-F

}}

|Section2 = {{Chembox Properties

| Formula = {{chem2|K4[Mo2Cl8]}}

| K=4|Mo=2|Cl=8

| Appearance = red crystals

| Density = 2.54 g/cm³

| Solubility = soluble

| MeltingPt =

| BoilingPt =

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|Section3 = {{Chembox Hazards

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Potassium octachlorodimolybdate (systematically named potassium bis(tetrachloromolybdate)(Mo–Mo)(4−)) is an inorganic compound with the chemical formula {{chem2|K4[Mo2Cl8]}}. It is known as a red-coloured, microcrystalline solid. The anion is of historic interest as one of the earliest illustrations of a quadruple bonding. The salt is usually obtained as the pink-coloured dihydrate.

File:Octachlorodirhenate(III)-3D-balls.png

The compound is prepared in two steps from molybdenum hexacarbonyl:{{cite book | first1 = A. B. | last1 = Brignole | first2 = F. A. | last2 = Cotton | author2-link = F. A. Cotton | first3 = Z. | last3 = Dori | title = Inorganic Syntheses | chapter = Rhenium and Molybdenum Compounds Containing Quadruple Bonds | journal = Inorg. Synth. | year = 1972 | volume = 13 | pages = 81–89 | doi = 10.1002/9780470132449.ch15 | isbn = 978-0-470-13244-9}}{{cite book|last1= Girolami|first1= G. S.|last2= Rauchfuss|first2= T. B.|last3= Angelici|first3= R. J.| title=Synthesis and Technique in Inorganic Chemistry| publisher=University Science Books| location= Mill Valley, CA| year= 1999 | isbn=978-0-935702-48-4}}

:{{chem2|2 Mo(CO)6 + 4 CH3CO2H → (CH3CO2)4Mo2 + 2 H2 + 12 CO}}

:{{chem2|(CH3CO2)4Mo2 + 4 HCl + 4 KCl → K4[Mo2Cl8] + 4 CH3CO2H}}

The reaction of the acetate with HCl was first described as providing trimolybdenum compounds,{{cite journal | first1= G. B.|last1= Allison|first2= I. R. |last2=Anderson|first3= J. C. |last3=Sheldon | title = The Preparation of Halogenotrimolybdate(II) Compounds | journal = Aust. J. Chem. | year = 1967 | volume = 20 | pages = 869–876 | doi = 10.1071/CH9670869 | issue = 5}} but subsequent crystallographic analysis confirmed that the salt contains the {{chem2|[Cl4Mo\qMoCl4](4–)}} anion, with D_4h symmetry, in which the two Mo atoms are linked by a quadruple bond. Each Mo atom is bounded with four Chloride ligands by a single bond. Each {{chem2|MoCl4}} group is a regular square pyramid, with an Mo atom at the apex, and four Cl atoms at the vertices of the square base of the pyramid. The Mo–Mo distance is 214 pm.{{cite journal | first1= Jurij V.|last1= Brencic |first2=F. Albert|last2=Cotton |author2-link=F. Albert Cotton | title = Octachlorodimolybdate(II) Ion. Species with a Quadruple Metal–Metal Bond | journal = Inorg. Chem. | year = 1969 | volume = 8 | pages = 7–10 | doi = 10.1021/ic50071a002}}