Potassium octacyanomolybdate(IV) is the inorganic salt with the formula K4[Mo(CN)8].

A yellow light-sensitive solid, it is the potassium salt of the cyanometalate with the coordination number eight.

The complex anion consists of a Mo(IV) center bound to eight cyanide ligands resulting in an overall charge of −4, which is balanced with four potassium cations.

[3] This synthesis is convenient for lower batch sizes than the earlier method but the MoCl4(Et2O)2 is typically less available than the molybdate.

The cyanide ligands in [Mo(CN)8]4- remain basic.