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:

Structure

The compound is isomorphous with K₂PtCl₆, i.e., their connectivities and structures are the same. The 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 ⁴⁻, ⁴⁻, and ²⁻ anions.

Although Mg₂FeH₆ is not soluble in ordinary solvents, related derivatives are. For example, the related salt Mg₄Br₄₄FeH₆ is soluble as are related alkoxides. Measurements on such compounds suggest that the hydride ligand exerts a weaker crystal field than cyanide.