DO THE LANTHANIDES FORM INNER SPHERE COMPLEXES WITH CLO4- IONS IN COMPETITION WITH H2O MOLECULES

As part of a research program concerning the structural aspects of the interaction between lanthanide ions and perchlorate anions the compound [Eu(OH)(H2O)3ClO4]ClO4 was crystallized and has been studied by X-ray diffraction and luminescence spectroscopy. The unit cell (monoclinic, space group: P2(1/c) (no. 14), a = 1071.9(3), b = 943.5(3), c = 962.3(3) pm, beta = 103.58(2)-degrees, Z = 4, R = 0.023, R(w) = 0.022) contains four Eu3+ in eightfold oxygen coordination. Four O2- from inner-sphere perchlorate anions and four O2- from three water molecules and one hydroxide anion form a distorted bicapped trigonal prism \dBAR(Eu-O) = 242 pm for C.N. 8\. Another oxygen ligand from the outer-sphere perchlorate anion at a considerably larger distance (d = 327 pm) would complete the coordination polyhedron to a tricapped trigonal prism of oxygen atoms around Eu3+. The crystal structure may be described as being built up from cationic layers of the composition infinity (2)[Eu(ClO4)(OH)(H2O)3]+ parallel (100) between which outer-sphere perchlorate anions complete for charge neutrality and through hydrogen bonding. Broadening of the lines observed in luminescence spectrum indicate the polymeric nature of the compound.