title: Magnesium iron hexahydride
text: # Magnesium iron hexahydride
  
  Magnesium iron hexahydride is an inorganic compound with the formula $Mg_2FeH_6.$ 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:
  
      2 Mg + Fe + 3 $H_2$ → $Mg_2FeH_6$
  
  ## Structure
  
  The compound is isomorphous with $K_2PtCl_6,$ i.e., their connectivities and structures are the same. The $[FeH_6]^{4−}$ centre adopts octahedral molecular geometry with Fe-H distances of 1.56 Å. The $Mg^{2+}$ 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 $[RuH_6]^{4−},$ $[OsH_6]^{4−},$ and $[PtH_6]^{2−}$ anions.
  
  ## Soluble derivatives
  
  Although $Mg_2FeH_6$ is not soluble in ordinary solvents, related derivatives are. For example, the related salt $Mg_4Br_4(THF)_4FeH_6$ is soluble as are related alkoxides. Measurements on such compounds suggest that the hydride ligand exerts a weaker crystal field than cyanide.
  
  