Comments on “Experimental Multivalent Ionic Radii”

Abstract

CHUA¹ has listed the ionic radii for a number of divalent lanthanide species, La⁺², Ce⁺², Nd⁺², Sm⁺², Eu⁺², Yb⁺², some of which are probably incorrect. For convenience the radii given by Chua are listed in Table 1. Inspection of these values shows immediately that the value for Eu⁺² is anomalously high compared with those lanthanides with lower atomic numbers, La⁺² to Sm⁺². At first one might be inclined to believe the value for Eu⁺² is incorrect. But further examination reveals that these radii were calculated from the lattice parameters reported for the respective RO(NaCl-type) compounds listed by me² (Chua's reference 14). Of these six RO compounds the only definitely known cation valence state is that of Eu which has been shown by magnetic measurements to be divalent³. Very little is known about the other HO compounds, and their existence has been seriously questioned⁴. If they should exist there is no reason why La, Ce and Nd would be expected to be divalent in these compounds (Sm and Yb, however, could be divalent). Indeed, if one examines the corresponding RSe, RS and RTe, one finds that La, Ce and Nd in these NaCl-type compounds are trivalent. Because the valence state of these five lanthanide ions in the RO compounds has not been established, the divalent radii given for La⁺², Ce⁺², Nd⁺², Sm⁺² and Yb⁺² are open to question.