Template:Isocyanidecomplexes

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Isocyanidecomplexes
Names
IUPAC name
Potassium tetracyanidoborate
Other names
Potassium octacyanoborate
Identifiers
3D model (JSmol)
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Properties
K[B(CN)4]
Molar mass 153.98 g/mol
Appearance white-yellow powder to crystal
Melting point 413 °C[1]
Hazards
GHS pictograms GHS07: Harmful
GHS Signal word Warning [→Category:GHS errors]
H302, H315, H319, H335
Template:P-phrases
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 solid, it is the potassium salt of the homoleptic cyanometalate with the coordination number eight. The complex anion consists of a molybdenum cation in the oxidation state IV and eight anionic cyanide ligands resulting in an overall charge of -4, which is compensated with four potassium cations. K4[Mo(CN)8] is often found as a dihdydrate.

Synthesis

A facile one-pot-synthesis for K4[Mo(CN)8] · 2 H2O is the reduction of molybdate (MoO42-) with potassium borohydride (KBH4 in a solution with potassium cyanide and acetic acid. [2] This synthesis was one of the first syntheses, where the molybdate is reduced in the same synthetic step, where the cyanometalate is formed. The yield is typically about 70%. This synthetic route is useful for big batches, because the work-up is more efficent with more substance and of the inexpensive starting materials compared to the second method.

4 MoO42- + 32 CN- + BH4- + 31 H+ → 4 [Mo(CN)8]4- + 16 H2O + H3BO3

Molybdenum has a high affinity towards oxygen. To avoid the energy consuming molybdenum-oxygen-bond cleavage, an alternative route to the potassium octacyanotungstate(IV) dihydrate starts from MoCl4(Et2O)2 directly from the oxidation state IV, so no reduction is needed in the first step. Also with this route the yield is typically around 70%. [3] This synthesis is simpler than the first one and can be made in lower batch sizes than the first synthesis. But the MoCl4(Et2O)2 is typically less available than the Molybdate (MoO42-).

MoCl4(Et2O)2 + 8 KCN → K4[Mo(CN)8] + 4 KCl + 2 Et2O

Redox Chemistry

One electron oxidation of the octacyanomolybadate(IV) leads to the paramagnetic octacyanomolybdate(V), which is a 17 electron complex and often used in magnetochemistry.

Protonation

Like many cyanometalate complexes, octacyanomolybdate(IV) is sensitive towards strong acids.[4] In strong acids the cyanide ligands are getting protonated, leading to the corresponding hydrogen isocyanide ligands. These ligands can be substituted by other ligands e. g., H2O. Potonation of [Mo(CN)8]4- leads to the homoleptic hydrogen isocyanide complex [Mo(CNH)8]4+.[5]

References

  1. Template:TCIchemicals.
  2. J. G. Leipoldt, L. D. C. Bok,P. J. Cilliers, "The preparation of Potassium OctacyanomolybdateIV) Dihydrate", Z. anorg. allg. Chem., 1974, volume 409, pp. 343-44.doi:10.1002/zaac.19744090310Template:Only in print
  3. G. Handzlik, M. Magott, B. Sielucka, D. Pinkowicz, "Alternative Synthetic Route to Potassium Octacyanidoniobate(IV ) and I ts Molybdenum Congener", Eur. J. Inorg. Chem., 2016, pp. 4872-77.doi:10.1002/ejic.201600669Template:Only in print
  4. Cite error: Invalid <ref> tag; no text was provided for refs named Sigma-Aldrich
  5. 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.202002366Template:Only in print