Potassium octachlorodimolybdate

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Potassium octachlorodimolybdate(4−)

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Appearance	red crystals
Density	2.54 g/cm3

Potassium octachlorodimolybdate (systematically named potassium bis(tetrachloromolybdate)(Mo–Mo)(4−)) is an inorganic compound with the chemical formula Template:Chem2. 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 octachlorodimolybdate(II) anion, Template:Chem2, which features a quadruple Mo–Mo bond

The compound is prepared in two steps from molybdenum hexacarbonyl:

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The reaction of the acetate with HCl was first described as providing trimolybdenum compounds, but subsequent crystallographic analysis confirmed that the salt contains the Template:Chem2 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|Template:Chem2]] ligands by a single bond. Each Template:Chem2 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.