Potassium octacyanomolybdate(IV)

Potassium octacyanomolybdate(IV)
Names
	IUPAC name Potassium octacyanidomolybdate(IV)
	Other names Potassium octacyanomolybdate(IV)
Identifiers
CAS Number	anhydrous: 17456-18-7; dihydrate: 17457-89-5;
3D model (JSmol)	anhydrous: Interactive image; dihydrate: Interactive image;
PubChem CID	dihydrate: 71308809;
	InChI dihydrate: InChI=1S/8CN.4K.Mo.H2O/c81-2;;;;;;/h;;;;;;;;;;;;;1H2/q8-1;4*+1;+4; Key: JJVZTQPHXSHIOV-UHFFFAOYSA-N;
	SMILES anhydrous: [K+].[K+].[K+].[K+].N#C[Mo-4](C#N)(C#N)(C#N)(C#N)(C#N)(C#N)C#N; dihydrate: O.O.[K+].[K+].[K+].[K+].N#C[Mo-4](C#N)(C#N)(C#N)(C#N)(C#N)(C#N)C#N;
Properties
Chemical formula	K4[Mo(CN)8]
Molar mass	460,47 g/mol (anhydrous) ; 496.5 g/mol (dihydrate)
Appearance	yellow powder
Melting point	>300 °C
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H315, H319, H335
Precautionary statements	P261, P305+P351+P338
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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. The salt is often prepared as its dihydrate K₄[Mo(CN)₈]^.(H₂O)₂.

Preparation

The dihydrate K₄[Mo(CN)₈] · 2 H₂O can be prepared by the reduction of molybdate (MoO₄^2-) with potassium borohydride (KBH₄) in a solution with potassium cyanide and acetic acid.^[1]^[2] Yields of 70% are typical and the method is suited for scale-up.

4 MoO₄^2- + 32 CN⁻ + BH₄⁻ + 25 H⁺ → 4 [Mo(CN)₈]^4- + 13 H₂O + H₃BO₃

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 + 8 KCN → K₄[Mo(CN)₈] + 4 KCl + 2 Et₂O

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.
^ ^a ^b Bonadio, Federica; Larionova, Joulia; Gross, Mathias; Biner, Margret; Stoeckli-Evans, Helen; Decurtins, Silvio; Pilkington, Melanie (2004). "Cyanide Compounds". Inorganic Syntheses. Vol. 34. p. 156. doi:10.1002/0471653683.ch4. ISBN 978-0-471-64750-8.
^ 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=Mo^IV, W^IV) from Superacids", Angew. Chem. Int. Ed., 2020 volume 59, pp. 10519-10522.doi:10.1002/anie.202002366

[1] 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.

[IS-2] Bonadio, Federica; Larionova, Joulia; Gross, Mathias; Biner, Margret; Stoeckli-Evans, Helen; Decurtins, Silvio; Pilkington, Melanie (2004). "Cyanide Compounds". Inorganic Syntheses. Vol. 34. p. 156. doi:10.1002/0471653683.ch4. ISBN 978-0-471-64750-8.

[3] 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

[4] M. Sellin, V. Marvaud, M. Malischewski, "Isolation and Structural Characterization of Eightfold Protonated Octacyanometalates [M(CNH)₈]⁴⁺ (M=Mo^IV, W^IV) from Superacids", Angew. Chem. Int. Ed., 2020 volume 59, pp. 10519-10522.doi:10.1002/anie.202002366

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