View source for Chemistry:Potassium octachlorodimolybdate

{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 434381923
| Name = Potassium octachlorodimolybdate(4−)
| ImageFile = K4Mo2Cl8.jpg
|ImageFile2 = Potassium octachlorodimolybdate.svg
| ImageFile1 = 
| 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/cm<sup>3</sup>
| Solubility = soluble
| MeltingPt = 
| BoilingPt = 
  }}
|Section3 = {{Chembox Hazards
  }}
}}

'''Potassium octachlorodimolybdate''' (systematically named '''potassium bis(tetrachloromolybdate)(''Mo''–''Mo'')(4−)''') is an [[Chemistry:Inorganic compound|inorganic compound]] with the [[Chemistry:Chemical formula|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 [[Chemistry:Quadruple bond|quadruple bond]]ing. The salt is usually obtained as the pink-coloured dihydrate.

[[File:Octachlorodirhenate(III)-3D-balls.png|thumb|left|150px|The octachlorodimolybdate(II) anion, {{chem2|[Mo2Cl8](4−)}}, which features a quadruple Mo–Mo bond]]
The compound is prepared in two steps from [[Chemistry:Molybdenum hexacarbonyl|molybdenum hexacarbonyl]]:<ref>{{cite book | first1 = A. B. | last1 = Brignole | first2 = F. A. | last2 = 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}}</ref><ref>{{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}}</ref>

:{{chem2|2 [[Chemistry:Molybdenum hexacarbonyl|Mo(CO)6]] + 4 [[Chemistry:Acetic acid|CH3CO2H]] → [[Chemistry:Molybdenum(II) acetate|(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,<ref>{{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}}</ref> but subsequent crystallographic analysis confirmed that the salt contains the {{chem2|[Cl4Mo\qMoCl4](4–)}} anion, with D<sub>4h</sub> symmetry, in which the two [[Chemistry:Molybdenum|Mo]] atoms are linked by a quadruple bond. Each Mo atom is bounded with four [[Chemistry:Chloride|{{chem2|Cl−}}]] ligands by a [[Chemistry:Single bond|single bond]]. Each {{chem2|MoCl4}} group is an [[Physics:Square pyramidal molecular geometry|regular square pyramid]], with an Mo atom at the [[Pyramid (geometry)|apex]], and four [[Chemistry:Chlorine|Cl]] atoms at the vertices of the [[Square|square]] base of the [[Pyramid (geometry)|pyramid]]. The Mo–Mo distance is 214 pm.<ref>{{cite journal | first1= Jurij V.|last1= Brencic |first2=F. Albert|last2=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}}</ref>

==References==
{{reflist}}

{{Potassium compounds}}

[[Category:Molybdates]]
[[Category:Chloro complexes]]
[[Category:Potassium compounds]]
[[Category:Chlorometallates]]

{{Sourceattribution|Potassium octachlorodimolybdate}}