Potassium octachlorodimolybdate explained

Potassium octachlorodimolybdate (systematically named potassium bis(tetrachloromolybdate)(Mo–Mo)(4−)) 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:^{[1] [2]}

The reaction of the acetate with HCl was first described as providing trimolybdenum compounds,^[3] but subsequent crystallographic analysis confirmed that the salt contains the anion, with D_4h 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 Mo–Mo distance is 214 pm.^[4]

Notes and References

1. Book: A. B. . Brignole . F. A. . Cotton . F. A. Cotton . Z. . Dori . Inorganic Syntheses . Rhenium and Molybdenum Compounds Containing Quadruple Bonds . . 1972 . 13 . 81–89 . 10.1002/9780470132449.ch15 . 978-0-470-13244-9.
2. Book: Girolami. G. S.. Rauchfuss. T. B.. Angelici. R. J.. Synthesis and Technique in Inorganic Chemistry. University Science Books. Mill Valley, CA. 1999 . 978-0-935702-48-4.
3. G. B.. Allison. I. R. . Anderson. J. C. . Sheldon . The Preparation of Halogenotrimolybdate(II) Compounds . Aust. J. Chem. . 1967 . 20 . 869–876 . 10.1071/CH9670869 . 5.
4. Jurij V.. Brencic . F. Albert. Cotton . F. Albert Cotton . Octachlorodimolybdate(II) Ion. Species with a Quadruple Metal–Metal Bond . . 1969 . 8 . 7–10 . 10.1021/ic50071a002.