THE EFFECTS OF CHOICE OF ANION (X=CL-, SCN-, NO3-) AND POLYETHYLENE-GLYCOL (PEG) CHAIN-LENGTH ON THE LOCAL AND SUPRAMOLECULAR STRUCTURES OFLNX(3) PEG COMPLEXES/

We have structurally characterized many LnCl(3), Ln(SCN)(3) and Ln(NO3 )(3) complexes of triethylene through heptaethylene glycols. The chain length typically controls the primary coordination sphere and the num ber of additional inner-sphere ligands (anions, water or solvent molec ules) present. Of the three anions studied, the nitrate anion, with it s preference for bidentate coordination and its hard oxygen donors, ha s the greatest effect on the PEG conformations. A third aspect of thes e complexes which has typically been overlooked is the nature of the s upramolecular structures generated by hydrogen bonding of the PEG alco holic termini and water molecules. In this presentation we review the several different structural series and discuss subtle trends that are apparent from small differences in the observed inner and outer-spher e coordination as a function of anion type, PEG chain length, and meta l ionic radius.