Molecular Assemblies of a Series of Mixed Tetravalent Uranium and Trivalent Lanthanide Complexes Associated with the Dipicolinate Ligand, in Aqueous Medium

Abstract

The investigations of the chemical system involving tetravalent uranium associated with trivalent lanthanides (La, Ce, Nd, Sm–Er, Lu) and dipicolinic acid (H2dpa) led to the identification of six distinct types of heterometallic coordination complexes (I–VI). These compounds, obtained at room temperature from aqueous solution, have been characterized by single-crystal X-ray diffraction. They consist of tris-chelated dipicolinate uranium subunits {U(dpa)3} interacting with poly oxo/aquo or mixed polyoxo/aquo chelated dipicolinate lanthanide subunits (LnO1–3(H2O)5–8 or Ln(dpa)O0–3(H2O)4–6) in different arrangements. Complex I (La, Ce) exhibits the assembly of molecular dinuclear [ULn] and [ULnU] trinuclear units, with a linkage between U and Ln via bidentate carboxylate groups of the dipicolinate molecules. The same carboxylate bridging connection mode creates a linear chainlike coordination polymer in complex II (La, Ce), with a strict alternating U–Ln sequence. Complex III (Ce, Nd) contains an octanuclear...