Ion Pair Binding in the Solid-State with Ditopic Crown Ether Uranyl Salophen Receptors

Two
ditopic uranyl salophen receptors with benzo-15-crown-5 and benzo-18-crown-6
units (R1 and R2, respectively) have been synthesized from commercially
available starting materials. Comprehensive studies on the solid-state
ion pair complexation with various alkali and ammonium halides have
been conducted. From the 19 obtained solid-state structures (6 structures
with R1, 13 structures with R2), three general interaction motifs I–III have been observed. Interaction
motif I has a separated ion pair with the cation coordinated
to the crown ether unit, and the anion or oxygen containing solvent
molecule coordinated to the uranyl center. The interaction motif II manifests a polymeric structure with a contact ion pair
between the uranyl-coordinated anion and cation coordinated in the
crown ether in the adjacent receptor. Interaction motif III consists of a more general stacked packing structure of the receptors
with or without ion pairs. From the obtained solid-state structures,
the complex R2·NaI shows an interesting formation of infinite coordination polymeric
structure where the crown ether complexed sodium cations and the OUO
units of the adjacent receptors form a nearly linear 1-D chains. In
the course of this work also the first solid-state structure of uranyl
salophen acetate complex was obtained (R2·KAcO).