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).

以市售起始底物为原料，成功合成了两款分别带有苯并-15-冠-5（benzo-15-crown-5）与苯并-18-冠-6（benzo-18-crown-6）单元的双位点铀酰水杨醛缩邻苯二胺（salophen）受体，分别记为R1与R2。针对该类受体与各类碱金属卤化物、卤化铵的固态离子对络合行为，本研究开展了系统性研究。在所获得的19种固态晶体结构（其中R1相关结构6种、R2相关结构13种）中，共观察到三类典型的相互作用模式I至III：相互作用模式I为分离型离子对，阳离子与冠醚单元配位，阴离子或含氧溶剂分子则与铀酰中心配位；相互作用模式II呈现聚合结构，铀酰配位的阴离子与相邻受体冠醚配位的阳离子形成接触型离子对；相互作用模式III为更通用的受体堆叠堆积结构，可存在或不存在离子对。在所获固态结构中，配合物R2·NaI展现出一种有趣的无限配位聚合结构：冠醚配位的钠离子与相邻受体的O=U=O（铀酰）单元形成近似线性的一维链状结构。此外，本研究还首次获得了铀酰salophen乙酸根配合物的固态晶体结构（R2·KAcO）。