Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712-1224, United States.
Department of Chemistry, Zhejiang University , Hangzhou 310027, China.
J Am Chem Soc. 2016 Apr 6;138(13):4573-9. doi: 10.1021/jacs.6b00564. Epub 2016 Mar 23.
An inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bis(3,4-diethyl-5-carboxy-1H-pyrrol-2yl)pyridine (compound 1), is able to distinguish between different zinc(II) cation sources, namely Zn(acac)2 and Zn(OAc)2, respectively. This differentiation is manifest both in terms of the observed fluorescent behavior in mixed organic media and the reaction chemistry. Treatment of 1 with Zn(acac)2 gives rise to a cage dimer, cage-1, wherein two molecules of compound 1 act as double bridging units to connect two individual cage subunits. As inferred from X-ray crystallographic studies, this cage system consists of discrete zinc dimers with hydroxide bridges that, with the assistance of bound DMF solvent molecules, serve to fix the geometry and orientation of the pyridine dipyrrolate building blocks. When a different zinc source, Zn(OAc)2, is used to carry out an ostensibly similar complexation reaction with compound 1, an acetate-bridged 1D abacus-like cage polymer is obtained as inferred from X-ray diffraction analysis. This extended solid state structure, cage-2, contains individual zinc dimer cage submits and appears stabilized by solvent molecules (DMF) and the counteranion (acetate). Rod-like assemblies are also observed by DLS and SEM. This construct, in contrast to cage-1, proved fluorescent in mixed organic media. The structure of the ligand itself (i.e., in the absence of Zn(II)) was confirmed by X-ray crystallographic analysis and was found to assemble into a supramolecular polymer. Conversion to a dimer form was seen upon the addition of TBAOAc. On the basis of the metric parameters, the structures seen in the solid state are stabilized via hydrogen bonding interactions involving solvent molecules.
一种固有非线性的吡啶二吡咯配体，即 2,6-双（3,4-二乙基-5-羧基-1H-吡咯-2 基）吡啶（化合物 1），能够分别区分不同的锌（II）阳离子源，即 Zn(acac)2 和 Zn(OAc)2。这种区分在混合有机介质中观察到的荧光行为和反应化学中都表现出来。用 Zn(acac)2 处理 1 生成笼状二聚体 cage-1，其中两个化合物 1 分子作为双桥接单元将两个独立的笼状亚基连接起来。从 X 射线晶体学研究推断，该笼状系统由离散的锌二聚体组成，其中含有氢氧化物桥，在结合的 DMF 溶剂分子的协助下，固定吡啶二吡咯构建块的几何形状和取向。当使用不同的锌源 Zn(OAc)2 与化合物 1 进行看似类似的配位反应时，从 X 射线衍射分析推断得到了一个醋酸盐桥接的 1D 算盘状笼聚合物。这种扩展的固态结构 cage-2 包含单独的锌二聚体笼状亚基，并且似乎通过溶剂分子（DMF）和抗衡阴离子（醋酸盐）稳定。通过 DLS 和 SEM 也观察到棒状组装体。与 cage-1 不同，这种构建体在混合有机介质中表现出荧光。配体本身的结构（即没有 Zn(II)）通过 X 射线晶体学分析得到证实，并被发现组装成超分子聚合物。在加入 TBAOAc 时观察到转化为二聚体形式。根据度量参数，在固态中看到的结构通过涉及溶剂分子的氢键相互作用稳定。
