Uranyl Ion Complexes with trans-3-(3-Pyridyl)acrylic Acid Including a Uranyl-Copper(II) Heterometallic Framework.

As a heterofunctional pro-ligand with both hard and soft coordination sites, trans-3-(3-pyridyl)acrylic acid (LH) is of potential interest for the design of heterometallic complexes of f- and d-block cations, as previously shown in the case of lanthanides. The reaction of LH with uranyl nitrate in water/acetonitrile at 180 °C yields the complex [(UO₂)₃(L)(HL)(O)(OH)₃] ·2.5H₂O ·CH₃CN ( 2), which is different from the previously reported complex [UO₂(L)(OH)] ( 1). Complex 2 crystallizes as a ribbon-like 1D coordination polymer with a skeleton bridged by oxido and hydroxido ligands, in which the uranyl cation is bound to the bridging bidentate carboxylato groups, and the pyridyl groups (one of them protonated) are directed sideways. In the presence of copper nitrate, the reaction affords the heterometallic complex [(UO₂)₂Cu(L)₃(O)(H₂O)](NO₃) ( 3), in which the harder uranium atom is bound to two μ₃-oxido anions and to chelating and bridging carboxylato groups to generate a tetranuclear secondary building unit, whereas the softer copper cations are bound to three pyridyl groups and only one carboxylato donor. The copper atoms are further involved in cation-cation interactions with uranyl oxido groups, and the Cu-O(oxido) bond lengths of 2.162(13) and 2.248(16) Å are among the shortest measured to date. 3 crystallizes as a 3D assembly, which displays narrow channels, and it illustrates the ability of copper cations, in combination with a ditopic ligand, to assemble discrete uranyl-containing units into a framework structure. The emission spectra of complexes 1 and 2 in the solid state display the usual vibronic progression of the uranyl ion in the range 450-650 nm, and the width of the bands indicates that they may be the superposition of slightly different series, due to the inequivalent uranyl centres in the lattices. [ABSTRACT FROM AUTHOR]