Université de Rennes 1, Institut des Sciences Chimiques de Rennes, UMR CNRS 6226, 263 avenue du Général Leclerc, CS 74205, 35042 Rennes Cedex, France.
J Am Chem Soc. 2012 Sep 26;134(38):16017-32. doi: 10.1021/ja307349d. Epub 2012 Sep 18.
Metal ion migration in a bis-strapped porphyrin ligand with overhanging carboxylate groups has been investigated in solution. Two types of homobimetallic complexes are generated with Pb(II) and Bi(III) cations, which stand on both sides of the macrocycle: (i) a dissymmetric complex with one cation bound to the porphyrin N core and the other cation hung over the N core through bonding with a carboxylate of a strap; (ii) a C(2)-symmetric complex with both cations coordinated to the N core and to the carboxylate groups of the straps. Variable-temperature NMR studies and 2D rotational Overhauser effect spectroscopy NMR experiments have shown that in the former dissymmetric complexes, the two cations undergo a coupled intramolecular migration resulting in exchange of their coordination modes. Such complexes constitute active states of Newton's cradle-like devices (NCDs), with the ion migration rate depending on the lability of the metal-ligand interactions [Pb(II) faster than Bi(III) NCDs]. On the other hand, the C(2)-symmetric complexes constitute either an inactive state [with Pb(II)] or a resting state [with Bi(III)] of an NCD, since they correspond respectively to a precursor or an intermediate in the motion of the cations. The NCDs are under both allosteric and acid-base control: (i) with Pb(II), the addition of an allosteric effector such as an acetate anion to the medium allows the conversion of the symmetric form to the dissymmetric one, thus triggering the Newton's cradle-like motion of the cations; (ii) with Bi(III), a lifted state was converted to a resting one by the addition of protons and then restored by the addition of a base. As an extension to nondegenerate systems, a heterobimetallic Bi(III)-Pb(II) complex was selectively obtained, and it constitutes a frozen lifted state of a dissymmetric NCD. All of these homo- and hetero-NCDs could be successively formed by selective metal ion exchange. These unique findings open the way to novel tristable devices.
在具有悬垂羧酸盐基团的双带卟啉配体中，研究了金属离子在溶液中的迁移。用 Pb(II) 和 Bi(III) 阳离子生成了两种同型双金属配合物，它们位于大环的两侧：(i) 一种不对称配合物，一个阳离子与卟啉 N 核结合，另一个阳离子通过与带的羧酸盐键合悬挂在 N 核上方；(ii) 一种 C(2)对称配合物，两个阳离子均与 N 核和带的羧酸盐基团配位。变温 NMR 研究和 2D 旋转 OVERHAUSER 效应光谱 NMR 实验表明，在前一种不对称配合物中，两个阳离子经历了耦合的分子内迁移，导致它们的配位模式发生交换。这种配合物构成了牛顿摆式装置 (NCD) 的活性状态，离子迁移率取决于金属-配体相互作用的稳定性[Pb(II)比 Bi(III) NCD 更快]。另一方面，C(2)对称配合物构成了 NCD 的非活性状态[用 Pb(II)]或休息状态[用 Bi(III)]，因为它们分别对应于阳离子运动的前体或中间体。NCD 受到变构和酸碱控制：(i) 用 Pb(II)，向介质中添加变构效应物如醋酸盐阴离子，允许将对称形式转化为不对称形式，从而触发阳离子的牛顿摆式运动；(ii) 用 Bi(III)，通过添加质子将 lifted 状态转化为休息状态，然后通过添加碱将其恢复。作为非简并系统的扩展，选择性地获得了异双金属 Bi(III)-Pb(II)配合物，它构成了不对称 NCD 的冻结 lifted 状态。所有这些同型和异型 NCD 都可以通过选择性的金属离子交换来连续形成。这些独特的发现为新型三稳态器件开辟了道路。
