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:

Magnesium iron hexahydride

Names
Other names dimagnesium iron hexahydride
Identifiers
CAS Number	89959-23-9 Y
3D model (JSmol)	Interactive image
InChI InChI=1S/Fe.2Mg.6H/q3*+2;6*-1 Key: VJOPJGZJJZUMMB-UHFFFAOYSA-N
SMILES [Mg+2].[Mg+2].[FeH6-4]
Properties
Chemical formula	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

2 Mg + Fe + 3 H₂ → Mg₂FeH₆

Structure

Interaction between one (of four) MgBr(thf)₂⁺ centers and FeH₆^4-.

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.

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.