The Eu (l)-Cl (1) and Eu (l)-CI (2) bond distances are shorter than the sum of the appropriate ionic radii (0.85 A for Eu (IV)*, I0 and 1.81 for CI-8), indicating a strong covalent interaction. To date, only relatively weak covalent interactions have been reported for the lanthanides, in a few organolanthanide complexes" for example. Some features of this structure encourage particularly covalent Eu-CI interactions. First, the zeolite framework itself highly favors the ...