Magnesium iron hexahydride

Magnesium iron hexahydride is an inorganic compound with the formula Mg2FeH6. It is a green diamagnetic solid that is stable in dry air. The material is prepared by heating a mixture of powdered magnesium and iron under high pressures of hydrogen:[1]

2 Mg + Fe + 3 H2 → Mg2FeH6
Magnesium iron hexahydride
Names
Other names
dimagnesium iron hexahydride
Identifiers
Properties
FeH6Mg2
Molar mass 110.503 g·mol−1
Appearance green solid
Density 2.74 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Structure
Interaction between one (of four) MgBr(thf)2+ centers and FeH64-.

The compound is isomorphous with K2PtCl6, i.e., their connectivities and structures are the same. The [FeH6]4− centre adopts octahedral molecular geometry with Fe-H distances of 1.56 Å. The Mg2+ centres are bound to the faces of the octahedron, with Mg-H distances of 2.38 Å. Several related compounds are known including salts of [RuH6]4−, [OsH6]4−, and [PtH6]2− anions.[2]

Soluble derivatives

Although Mg2FeH6 is not soluble in ordinary solvents, related derivatives are. For example, the related salt Mg4Br4(THF)4FeH6 is soluble as are related alkoxides. Measurements on such compounds suggest that the hydride ligand exerts a weaker crystal field than cyanide.[3]

References
  1. J. J. Didisheim, P. Zolliker, K. Yvon, P. Fischer, J. Schefer, M. Gubelmann, A. F. Williams "Dimagnesium iron(II) hydride, Mg2FeH6, containing octahedral FeH64− anions" Inorganic Chemistry 1984, vol. 23, pp 1953–1957. doi:10.1021/ic00181a032.
  2. Robert Bau, Mary H. Drabnis "Structures of transition metal hydrides determined by neutron diffraction" Inorganica Chimica Acta 1997, vol. 259, 27ff.doi:10.1016/S0020-1693(97)89125-6
  3. R.B. King "Structure and bonding in homoleptic transition metal hydride anions" Coordination Chemistry Reviews, 2000, vol. 200–202, p. 813–829. doi:10.1016/S0010-8545(00)00263-0
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