Structural Consequences of 1,4-Cyclohexanedicarboxylate $Cis/trans$ Isomerism in Uranyl Ion Complexes: From Molecular Species to 2D and 3D Entangled Nets

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

$trans$-1,4-Cyclohexanedicarboxylic acid ($t$-1,4-chdcH$_2$) or the commercially available mixture of the $cis$ and $trans$ isomers ($c,t$-1,4-chdcH$_2$) have been used in the synthesis of a series of 14 uranyl ion complexes, all obtained under solvo-hydrothermal conditions, and some of them in the presence of additional metal cations and/or 2,2'-bipyridine (bipy). With its two isomeric forms having very different shapes and its great sensitivity to the experimental conditions, 1,4-chdc$^2$– appears to be suitable for the synthesis of uranyl ion complexes displaying a wide range of architectures. Under the conditions used, the pure $trans$ isomer gives only the complexes [UO$_2$($t$-1,4-chdc)(H$_2$O)$_2$] (1) and [UO$_2$($t$-1,4-chdc)] (2), which crystallize as one-and two-dimensional (1D and 2D) species, respectively. Complexes containing either the $cis$ isomer alone, or mixtures of the two isomers in varying proportion, were obtained from the isomer mixture. The neutral complexes [UO$_2$($c$-1,4-chdc)(DMF)] (3) and [UO$_2$($c$-1,4-chdc)(bipy)] (4) are 2D and 1D assemblies, respectively, while all the other complexes are anionic and include various counterions. [C(NH$_2$)$_3$]$_3$[H$_2$NMe$_2$][(UO$_2$)$_4$($c$-1,4-chdc)$_6$]⋅H$_2$O (5) crystallizes as a three-dimensional (3D) framework with {10$^3$ } topology. While [H$_2$NMe$_2$]$_2$[(UO$_2$)$_2$($c$-1,4-chdc)$_2$($t$-1,4-chdc)]⋅DMF⋅2H$_2$O (6) is a 1D ladder-like polymer, [H$_2$NMe$_2$]$_2$[(UO$_2$)$_2$($c$-1,4-chdc)($t$-1,4-chdc)$_2$]⋅2H$_2$O (7), which differs in the $cis/trans$ ratio, is a threefold 2D interpenetrated network with {6$^3$ } honeycomb topology. The related [H$_2$NMe$_2$]$_2$[(UO$_2$)$_2$($c,t$-1,4-chdc)$_3$]⋅2.5H$_2$O (8), with one disordered ligand of uncertain geometry, is a threefold 3D interpenetrated system. The two isomorphous complexes [Co(bipy)$_3$][(UO$_2$)2($c$-1,4-chdc)3]⋅1.5H$_2$O (9) and [Cd(bipy)$_3$][(UO$_2$)$_2$($c$-1,4-chdc)$_3$]⋅1.5H$_2$O (10) form 3D frameworks with the {10$^3$ } srs topological type. In contrast, [Ni(bipy)$_3$]$_2$[(UO$_2$)$_4$($c$-1,4-chdc)$_2$($t$-1,4-chdc)(NO$_3$)$_6$]⋅2H$_2$O (11) is a molecular, tetranuclear complex due to the presence of terminal nitrate ligands. Twofold 3D interpenetration of frameworks with {10$^3$ } ths topology is observed in [Cu(bipy)$_2$]$_2$[(UO$_2$)$_2$($c$-1,4-chdc)$_2$($t$-1,4-chdc)]⋅2H$_2$O (12), while [Zn(bipy)$_3$][(UO$_2$)$_2$($c$-1,4-chdc)$_3$]⋅4H$_2$O (13) crystallizes as a 2D net with the common {4.8$^2$ } fes topological type. The additional Pb$^{II}$ cation is an essential part of the 3D framework formed in [UO$_2$Pb$_2$($c$-1,4-chdc)($t$-1,4-chdc)$_2$(bipy)$_2$ (14), in which uranyl and its ligands alone form 1D subunits. Together with previous results, the solid state uranyl emission properties of seven of the present complexes evidence a general trend, with the maxima for the complexes with O$_6$ equatorial environments being blue-shifted with respect to those for O$_5$ environments.

Domains: Material chemistry

Pierre Thuéry, Jack Harrowfield. Structural Consequences of 1,4-Cyclohexanedicarboxylate $Cis/trans$ Isomerism in Uranyl Ion Complexes: From Molecular Species to 2D and 3D Entangled Nets. Inorganic Chemistry, 2017, 56, pp.13464-13481. ⟨10.1021/acs.inorgchem.7b02176⟩. ⟨cea-01618737⟩