Crystal structure of Na2Mg2NiH6 revisited.

The crystal structure of Na(2)Mg(2)NiH(6) as published by Kadir and Noreus (Inorg. Chem. 2007, 46, 2220-2223) is revised. While the reported space group symmetry and cell parameters are correct, the Mg and hydride positions need to be interchanged. Consequently, the tetrahedral [NiH(4)](4-) complexes are stabilized by both Na(+) and Mg(2+) ions and not by Na(+) ions only, as was stated by the authors. The metal-hydrogen bond distances of the revised structure model differ by up to 0.6 A from those reported and are more in line with those usually observed in these sorts of hydrides. An overview of the known cation configurations around solid-state [NiH(4)](4-) complexes is given.