Structural characterization of NaMgH2F and NaMgH3

The direct reaction of hydrogen on a mixture of Na + Mg or NaF + Mg allowed for synthesis of NaMgH3 and NaMgH2F, respectively. Both phases were indexe d with an orthorhombic unit cell with dimensions a = 546.34, b = 770.30, c = 541.08 pm for NaMgH3 and a = 547.59, b = 769.68, c = 540.31 pm for NaMgH2 F. The crystal structures were refined by X-ray Rietveld refinement. They d erive from the perovskite structure type by a Pmm --> Pnma distortion. In t he hydridofluoride, H- and F- anions are equally distributed in the two ani onic sites in a disordered way. (C) 2000 Elsevier Science Ltd. All rights r eserved.