Complexation of Uranyl and Rare-Earth Ions by a Fluorinated Tetracarboxylate. Formation of a Layered Assembly and Three-Dimensional Frameworks

The reaction of uranyl and rare-earth
nitrates with 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)­diphthalic
acid (H4L) under hydro-/solvo-thermal conditions (2:1 water/acetonitrile
at 180 °C) gives a series of complexes, most of which have been
crystallographically characterized. In the lattice of the uranyl complex
[(UO2)2­(L)­(H2O)2]·2H2O (1), the metal atoms are chelated
by two adjacent carboxylate groups, each of the latter being bridging
bidentate, and the resulting coordination polymer is two-dimensional.
The ∼14 Å thick layers comprise two uranyl-covered faces
linked to one another by L4– pillars, a claylike
architecture likely due to the hydrophobic interactions between the
organic ligands. The complexes [Ce­(HL)­(H2O)]·1.5H2O (2) and [Nd­(HL)­(H2O)]·2.5H2O (3) are isomorphous and they display a high
degree of connectivity, with the metal atoms in ten- or eleven-coordinate
environments being bound to five or six HL3– ligands.
The three-dimensional (3D) framework formed contains one-dimensional
subunits of adjacent metal ions with each coordination polyhedron
sharing two triangular faces with its neighbors. The hydrophobic CF3 groups are oriented divergently from the exterior of wide
channels (∼22 × 8 Å), which are occupied by the solvent
water molecules. The complexes with rare-earth ions of smaller ionic
radii, [M4(L)3(H2O)9]·7H2O with M = Er (4), Yb (5), and Y
(6), are isomorphous to the previously reported terbium­(III)
complex, and they crystallize as 3D frameworks containing di- and
tetra-nuclear subunits. In the visible region, only the uranyl and
europium (and terbium) complexes display significant solid-state luminescence.