A comparison of analogous 4f-and 5f-element compounds:: syntheses and crystal structures of triphenylphosphine oxide complexes of lanthanide(III) and uranium(III) triflates and iodides [MX2(OPPh3)4][X] (X=OTf and M = Ce or U; X = I and M = Nd, Ce, La, U)

The X-ray crystal structures of the title complexes show that the differences between the U-O and Ln-O distances reflect the variation in the ionic radii of the trivalent uranium and lanthanide ions while the U-I bond lengths are smaller than those predicted from a purely ionic bonding model. The results indicate that the uranium ion interacts more strongly than the lanthanide ions with the softer iodide ligand, and that the counterions would have a major influence on the differentiation of trivalent 4f and 5f ions. (C) 2003 Elsevier Ltd. All rights reserved.