Sibert John W, Forshee Philip B, Lynch Vincent
Department of Chemistry, The University of Texas at Dallas, Richardson, Texas 75083, USA.
Inorg Chem. 2005 Nov 14;44(23):8602-9. doi: 10.1021/ic051125d.
Two isomeric redox-responsive azathiacrown ethers, based on p-phenylenediamine, have been synthesized in traditional crown (L1) and crownophane (L2) architectures. Each of these "Wurster's crowns" was designed to target the encapsulation of transition or heavy metal ions. The solid-state structures of these ligands show binding cavities defined by three exocyclic sulfur atoms and either a N donor atom (L1) or the electron-rich pi face of the phenylenediamine subunit (L2). The ability of these ligands to form complexes with platinum(II) was investigated by various techniques including 1H NMR spectroscopy, electrospray mass spectrometry, cyclic voltammetry, and single-crystal X-ray analysis. The traditional crown geometry proved to be better at forming stable endocyclic complexes with Pt(II) than the crownophane geometry. The square-planar Pt(II) crown complex includes direct bonding to the redox center (Pt1-N1 = 2.125 angstroms and Pt1-S(av) = 2.278 angstroms) with concomitant polarization of the phenylenediamine moiety. This results in the crown complex oxidizing 916 mV more anodically than the free ligand. In contrast, modest shifts in the oxidation potential of the crownophane isomer indicate poor interaction between the redox center and complexed Pt(II) ion.
基于对苯二胺的两种同分异构的氧化还原响应型氮杂冠醚已通过传统冠醚（L1）和冠醚环番（L2）结构合成。这些“沃斯特冠醚”中的每一种都旨在用于包封过渡金属离子或重金属离子。这些配体的固态结构显示出由三个环外硫原子以及一个氮供体原子（L1）或对苯二胺亚基的富电子π面（L2）所定义的结合腔。通过包括1H NMR光谱、电喷雾质谱、循环伏安法和单晶X射线分析在内的各种技术研究了这些配体与铂（II）形成配合物的能力。事实证明，传统冠醚结构在与Pt（II）形成稳定的内环配合物方面比冠醚环番结构表现更好。平面正方形的Pt（II）冠醚配合物包括与氧化还原中心的直接键合（Pt1-N1 = 2.125埃，Pt1-S（平均） = 2.278埃），同时对苯二胺部分发生极化。这导致冠醚配合物的氧化电位比游离配体的氧化电位正移916 mV。相比之下，冠醚环番异构体氧化电位的适度变化表明氧化还原中心与配位的Pt（II）离子之间的相互作用较弱。
