Tetrahedral and Cuboidal Clusters in Complexes of Uranyl and Alkali or Alkaline-Earth Metal Ions with rac- and (1R,2R)-trans-1,2-Cyclohexanedicarboxylate

Pierre Thuéry (1) , Jack Harrowfield (2)

1 LCMCE - Laboratoire de Chimie Moléculaire et de Catalyse pour l'Energie (ex LCCEF)
2 ISIS - Institut de Science et d'ingénierie supramoléculaires

Uranyl nitrate was treated with racemic or enantiopure (1R,2R) forms of trans-1,2-cyclohexanedicarboxylic acid (H2chdc and R-H2chdc, respectively) in the presence of additional cations, mostly alkali or alkaline-earth metal cations, under solvo-hydrothermal conditions to generate a series of one homo-and seven heterometallic complexes which all contain the pseudotetrahedral [(UO2)4((R-)chdc)6] 4– cluster previously found in sodium(I)-, silver(I)-and lead(II)-containing derivatives. These clusters are for the first time obtained as isolated species in [NH4]4[(UO2)4(chdc)6] (1), in which the ammonium cations are held by hydrogen bonds close to the faces of the tetrahedron. In both compounds [(UO2)4K4(R-chdc)6(H2O)6] (2) and [(UO2)4Ba2(R-chdc)6(H2O)8] (8), the uranyl tetrahedra are assembled into three-dimensional frameworks by bridging potassium(I) or barium(II) cations, these being bound to carboxylate groups from different clusters. A closer association of uranyl tetrahedra and countercations is found with alkali metal ions of larger ionic radius, leading to the formation of heterometallic cuboidal clusters. The three rubidium(I)-containing compounds [H2NMe2][(UO2)4Rb3(R-chdc)6(H2O)1.75] (3), [(UO2)4Rb4(R-chdc)6(NMP)0.5(H2O)3.75]0.5NMP0.25H2O (4), and [(UO2)4Rb4(R-chdc)6(H2O)1.5]0.5H2O (5) form a regular progression, the incomplete heptanuclear cuboids found in 3 being linked by additional external Rb I cations in 4, and complete octanuclear clusters being present in 5. The clusters closer to the ideal cubic symmetry are found in the cesium(I)-containing compounds [(UO2)4Cs4(chdc)6(H2O)3]H2O (6) and [(UO2)4Cs4(R-chdc)6(H2O)4]3H2O (7). In contrast to 1, which has fourfold roto-inversion symmetry, 6 is a mixture of homochiral clusters with threefold rotation symmetry, thus showing countercation dependence of the isomeric form in the racemic species. In compounds 3–6, multiple bonding of the alkali metal ions to the uranyl oxo groups located inside the cage probably contribute to the cluster stability.

Domaines: Matériaux

Pierre Thuéry, Jack Harrowfield. Tetrahedral and Cuboidal Clusters in Complexes of Uranyl and Alkali or Alkaline-Earth Metal Ions with rac- and (1R,2R)-trans-1,2-Cyclohexanedicarboxylate. Crystal Growth & Design, 2017, 17, pp.2881-2892. ⟨10.1021/acs.cgd.7b00448⟩. ⟨cea-01510312⟩