Hydrides versus fluorides: Structural comparisons

The closeness of the ionic radii of the hydride and fluoride ions results in close structural analogies between the corresponding binary and ternary compounds of the highly electronegative elements. The analogies are closest for the alkalis, the alkaline earths, and aluminum. For the binary lanthanide and actinide compounds, the structures are related, but modified for the hydrides by the nonstoichiometry. The relative difficulty so far encountered in attempts to prepare ternary hydrides involving these elements is probably also due to nonstoichiometry. For the transition metals, the hydride and fluoride structural patterns differ considerably, the metallic nature of the hydrides here being involved as well. On the basis of these analogies, the known structures of corresponding hydrides and fluorides are correlated and the possible new ternary hydride compounds may be predicted.