Magnesium iron hexahydride is an inorganic compound with the formula Mg₂FeH₆. It is a green

diamagnetic Diamagnetism is the property of materials that are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagn ...

solid that is stable in dry air. The material is prepared by heating a mixture of powdered

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

and

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

under high pressures of

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

: :2 Mg + Fe + 3 H₂ → Mg₂FeH₆

Structure

The compound is isomorphous with K₂PtCl₆, i.e., their connectivities and structures are the same. The eH₆sup>4− centre adopts

octahedral molecular geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The o ...

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 uH₆sup>4−, sH₆sup>4−, and tH₆sup>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

alkoxide In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organyl substituent. Alkoxides are strong bases and, whe ...

s. Measurements on such compounds suggest that the

hydride In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and has been more frequently in the past) applied to all che ...

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

exerts a weaker crystal field than

cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

.R.B. King "Structure and bonding in homoleptic transition metal hydride anions" Coordination Chemistry Reviews, 2000, vol. 200–202, p. 813–829.

References

{{Iron compounds Metal hydrides Magnesium compounds Iron(II) compounds Iron complexes