Perrhenate anion encapsulation in a uranyl ion–zwitterionic dicarboxylate coordination polymer

The zwitterionic dicarboxylate 1,1′-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-4-carboxylate) (L) has been reacted with uranyl nitrate under solvo-hydrothermal conditions and in the presence of KReO₄ to give the complex [UO₂(L)(OH)(H₂O)](ReO₄) (1). This compound crystallizes as a cationic, monoperiodic coordination polymer with ReO₄^– as a simple counterion. The daisy-chain polymer is based on dinuclear rings built by the convergent zwitterionic ligands, these rings being linked to one another by double hydroxide bridges. In addition to a Coulombic interaction with a pyridinium ring, ReO₄^– is involved in one OH(water)⋅⋅⋅O and four CH⋅⋅⋅O interactions, and it is thus nestled in a cavity formed by three chains, seemingly with some selectivity over nitrate and chloride anions also present in the reaction mixture. This result illustrates the interest of zwitterionic dicarboxylates in building cationic assemblies able to trap ReO₄^–, a surrogate for the radioactive TcO₄^–, an anion of environmental relevance.

A zwitterionic dicarboxylate ligand was reacted with the uranyl ion to generate a cationic, daisychain coordination polymer including perrhenate as counterion. Examination of the Hirshfeld surface of the anion allows for an analysis of the weak interactions involved.