The crystal chemistry of uranium carboxylates

Abstract

The fieldof uranium carboxylates has been studied for several decades and an important library of coordination complexes and network solids is now well defined. It mainly concerns the reactivity of hexavalent uranium (uranyl) with the different types of carboxylic acids containing monodentate or polydentate functions, aliphatic or aromatic carbon backbone, or hetero-systems offering other functionalities (N-donor, S-donor, phosphonates…). A rich variety of molecular complexes or extended multi-dimensional networks (1D, 2D, 3D) has been identified and depends mainly on the equatorial connectivity of the uranyl cation (UO₂²⁺) in different coordination numbers (tetragonal, pentagonal or hexagonal bipyramid). The yl oxo groups remain relatively inert to condensation process (except rare case of cation-cation interaction). For lower oxidation state of uranium (+3, + 4, + 5), the knowledge is at the infancy stage since very few contributions are available in literature. Nevertherless, recent contributions have shown the possibilities of the reactivity of tetravalent uranium in relatively stable architectures, either at the molecular level, with high nuclearities (up to U₃₈), or engaged in three-dimensional frameworks. The scope of this review is a comprehensive presentation of the crystal structures resulting from the different types of complexation of uranium with carboxylic acid molecules (excepting oxalate ligand) and their classification as a function of the nuclearity of identified buiding units.