Potassium octachlorodimolybdate (systematically named potassium bis(tetrachloromolybdate)(MoâÂÂMo)(4âÂÂ)) is an inorganic compound with the chemical formula . 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.
The compound is prepared in two steps from molybdenum hexacarbonyl:
The reaction of the acetate with HCl was first described as providing trimolybdenum compounds, but subsequent crystallographic analysis confirmed that the salt contains the anion, with D<sub>4h</sub> symmetry, in which the two Mo atoms are linked by a quadruple bond. Each Mo atom is bounded with four ligands by a single bond. Each 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 MoâÂÂMo distance is 214 pm.