Potassium nonahydridorhenate

Potassium nonahydridorhenate(VII) is an inorganic compound having the formula K₂[ReH₉]. This colourless salt is soluble in water but only poorly soluble in most alcohols. This salt contains the nonahydridorhenate(VII) anion, [ReH₉]²⁻, which is a rare example of a coordination complex bearing only hydride ligands.

Potassium nonahydridorhenate

Names
Other names Potassium nonahydridorhenate(VII) Potassium nonahydrorhenate(VII)
Identifiers
CAS Number	25396-46-7^N
3D model (JSmol)	Interactive image
InChI InChI=1S/2K.Re.9H/q2*+1;-2;;;;;;;;; Key: VDZMOWIIXPKPTA-UHFFFAOYSA-N
SMILES [K+].[K+].[ReH9-2]
Properties
Chemical formula	K2[ReH9]
Molar mass	273.473 g/mol
Appearance	white solid
Solubility in water	soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is ^YN ?) Infobox references

History

The study of rhenium hydrides can be traced to the 1950s and included reports of the "rhenide" anion, supposedly Re⁻. These reports led to a series of investigations by A. P. Ginsberg and coworkers on the products from the reduction of perrhenate.^[1]

The rhenide anion, Re⁻, was based on the product of the reduction of perrhenate salts, such as the reduction of potassium perrhenate (KReO₄) by potassium metal.^[2] "Potassium rhenide" was shown to exist as a tetrahydrated complex, with the postulated chemical formula KRe·4H₂O (potassium rhenide tetrahydrate).^[3] This compound exhibits strongly reducing properties, and slowly yields hydrogen gas when dissolved in water. The lithium and thallous salts were also reported. Later research, however, indicates that the "rhenide" ion is actually a hydridorhenate complex. "Potassium rhenide" was shown to be in fact the potassium nonahydridorhenate(VII), K₂[ReH₉], containing the nonahydridorhenate(VII) anion, [ReH₉]²⁻, in which the oxidation state of rhenium is actually +7.^[4][5] Other methods of reduction of perrhenate salts yield compounds containing other hydrido- complexes, including ReH₃(OH)₃(H₂O)⁻.^[6]

Structure, synthesis, and properties

 

Structure of the [ReH₉]²⁻ anion, a tricapped trigonal prism.

[ReH₉]²⁻ is an unusual example of a nonacoordinated complex, its high coordination number being attributed to the small size of the hydride ligand and the high positive charge on the Re(VII) central atom. Its structure consists of a tricapped trigonal prism,^[7][8] as determined by neutron crystallography.^[9][10] The diamagnetic sodium salt, like the analogous technetium compound, is prepared by treating an ethanol solution of sodium perrhenate, NaReO₄, with sodium metal.^[11] Via cation exchange, it can be converted to the corresponding tetraethylammonium salt, ([(CH₃CH₂)₄N]⁺)₂[ReH₉]²⁻ (tetraethylammonium nonahydridorhenate(VII)).

Isostructural with [TcH₉]²⁻ (nonahydridotechnetate(VII)), [ReH₉]²⁻ consists of a trigonal prism with Re atom in the center and six hydrogen atoms at the corners. Three more hydrogen ligands define a triangle lying parallel to the base and crossing the prism in its center (see figure). Although those hydride ligands are not equivalent, their electronic structure is almost the same. The coordination number of 9 in this complex is the highest known for any rhenium complex.

Recent DFT calculations on [ReH₉]²⁻ indicate that this dianion adopts the D_3h⇌C_4v⇌D_3h pathway in gas phase and solution, such interconversion originally proposed by Muetterties^[12] featuring a capped square antiprism structure as transition state has very low energy barrier. In K₂[ReH₉] solid, intramolecular motions of [ReH₉]²⁻ include (1) circle-dance mechanism (resembling Matisse's painting Dance (II)) and (2) three-arm turnstile rotation.^[13]

References

1. A. P. Ginsberg; J. M. Miller; J. R. Cavanaugh & B. P. Dailey (1960). "Evidence for the Existence of a Potassium Rhenium Hydride and its Bearing on the Nature of the (−1)-Oxidation State of Rhenium". Nature. 185 (4712): 528–9. Bibcode:1960Natur.185..528G. doi:10.1038/185528a0. S2CID 4166868.
2. Cobble, J. W. (June 1957). "On the Structure of the Rhenide Ion". The Journal of Physical Chemistry. 61 (6): 727–729. doi:10.1021/j150552a005.
3. Bravo, J. B.; Griswold, E.; Kleinberg, J. (January 1954). (PDF). The Journal of Physical Chemistry. 58 (1): 18–21. doi:10.1021/j150511a004. hdl:1808/26443. Archived from the original (PDF) on March 4, 2016.
4. Floss, J. G.; Grosse, A. V. (1960). "Alkali and alkaline earth rhenohydrides". Journal of Inorganic and Nuclear Chemistry. 16 (1–2): 36–43. doi:10.1016/0022-1902(60)80083-8.
5. Kenneth Malcolm Mackay; Rosemary Ann Mackay; W. Henderson (2002). Rosemary Ann Mackay (ed.). Introduction to modern inorganic chemistry (6th ed.). CRC Press. pp. 368–369. ISBN 0-7487-6420-8.
6. Green, M. L. H.; Jones, D. J. (1965). Emeleus, H.J.; Sharpe, A.G. (eds.). Advances in inorganic chemistry and radiochemistry. Academic Press. pp. 169–172. ISBN 0-12-023607-9.
7. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
8. Housecroft, C.E. and Sharpe A.G. "Inorganic Chemistry" (2nd edn, Pearson 2005. ISBN 0130-39913-2), p.254
9. Abrahams, S. C.; Ginsberg, A. P.; Knox, K. (1964). "Transition Metal-Hydrogen Compounds. II. The Crystal and Molecular Structure of Potassium Rhenium Hydride, K₂ReH₉". Inorg. Chem. 3 (4): 558–567. doi:10.1021/ic50014a026.
10. Bronger, W.; à Brassard, L.; Müller, P.; Lebech, B.; Schultz, Th. (1999). "K₂ReH₉, eine Neubestimmung der Struktur". Z. Anorg. Allg. Chem. 625 (7): 1143–1146. doi:10.1002/(SICI)1521-3749(199907)625:7<1143::AID-ZAAC1143>3.0.CO;2-V.^{[dead link]}
11. A. P. Ginsberg; C. R. Sprinkle (1972). Nonahydridorhenate Salts. Inorganic Syntheses. Vol. 13. pp. 219–225. doi:10.1002/9780470132449.ch45. ISBN 978-0-470-13244-9.
12. Guggenberger, L. J.; Muetterties, E. L. (1976). "Reaction path analysis. 2. The nine-atom family". J. Am. Chem. Soc. 98 (23): 7221–7225. doi:10.1021/ja00439a019.
13. Tao, Y.; Wang, X.; Zou, W.; Luo, G.; Kraka, E. (2022). "Unusual Intramolecular Motion of ReH₉^2– in K₂ReH₉ Crystal: Circle Dance and Three-Arm Turnstile Mechanisms Revealed by Computational Studies". Inorg. Chem. 61 (2): 1041–1050. doi:10.1021/acs.inorgchem.1c03118. PMID 34965110. S2CID 245567595.

 

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