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).

本研究以商业可得的起始原料，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Salophen（uranyl 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。从所获得的19种固态络合结构（其中6种对应R1、13种对应R2）中，可归纳出三类典型的相互作用模式I至III。相互作用模式I呈现分离型离子对结构：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为聚合型结构：铀酰配位的阴离子与相邻受体冠醚中配位的阳离子形成接触型离子对。相互作用模式III则为更普适的受体堆积组装结构，可伴随或不伴随离子对的存在。从所获固态结构中，络合物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铀酰（O=U=O）单元形成近乎线性的一维链状结构。本研究同时首次获得了铀酰Salophen乙酸根络合物的固态结构（R2·KAcO）。