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 cyanideligands resulting in an overall charge of −4, which is balanced with four potassium cations. The salt is often prepared as its dihydrate K4[Mo(CN)8].(H2O)2.
An alternative route starts from MoCl4(Et2O)2 avoiding the need for reductants. The yield of this route is typically around 70%.[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.
MoCl4(Et2O)2 + 8KCN → K4[Mo(CN)8] + 4KCl + 2Et2O
Reactions
Octacyanomolybdate(IV) can be oxidized to the paramagnetic octacyanomolybdate(V).
The cyanide ligands in [Mo(CN)8]4- remain basic. Strong acids lead to the hydrogen isocyanide complex [Mo(CNH)8]4+, in common with many cyanometalate complexes.[4] These ligands can be substituted by others, for example H2O. The cyanide ligands also bind to other metals, leading to cages.[2]
References
^Leipoldt, J. G.; Bok, L. D. C.; Cilliers, P. J. (1974). "The Preparation of Potassium Octacyanomolybdate(IV) Dihydrate". Zeitschrift für anorganische und allgemeine Chemie. 409 (3): 343–344. doi:10.1002/zaac.19744090310.
^G. Handzlik, M. Magott, B. Sielucka, D. Pinkowicz, "Alternative Synthetic Route to Potassium Octacyanidoniobate(IV) and its Molybdenum Congener", Eur. J. Inorg. Chem., 2016, pp. 4872-77.doi:10.1002/ejic.201600669
^M. Sellin, V. Marvaud, M. Malischewski, "Isolation and Structural Characterization of Eightfold Protonated Octacyanometalates [M(CNH)8]4+ (M=MoIV, WIV) from Superacids", Angew. Chem. Int. Ed., 2020 volume 59, pp. 10519-10522.doi:10.1002/anie.202002366
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