The Supramolecular Isomerism Based on Argentophilic Interactions: The Construction of Helical Chains with Defined Right-Handed and Left-Handed Helicity

The reactions of racemic and enantiopure macrocyclic compounds [Ni(α-rac-L)](ClO4)2 (containing equal amounts of SS and RR enantiomers), [Ni(α-SS-L)](ClO4)2, and [Ni(α-RR-L)](ClO4)2 with K[Ag(CN)2] in acetonitrile/water afford three 1D helical chains of {[Ni(f-rac-L)][Ag(CN)2]2}n (1), {[Ni(f-SS-L)]2[Ag(CN)2]4}n (Δ-2), and {[Ni(f-RR-L)]2[Ag(CN)2]4}n (Λ-2); one dimer of [Ni(f-rac-L)][Ag(CN)2]2 (3); and one trimer of [Ni(f-rac-L)Ag(CN)2]3·(ClO4)3 (4) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Compounds 1, Δ-2, Λ-2, and 3, which are supramolecular isomers, are constructed via argentophilic interactions. In 1, [Ni(f-RR-L)][Ag(CN)2]2 enantiomers alternately connect with [Ni(f-SS-L)][Ag(CN)2]2 enantiomers through intermolecular argentophilic interactions to form a 1D meso-helical chain, and the 1D chains are further connected through the interchain hydrogen bonds to generate a 2D network. When chiral [Ni(α-SS-L)](ClO4)2 and [Ni(α-RR-L)](ClO4)2 were used as building blocks, two supramolecular stereoisomers of Δ-2 and Λ-2 were obtained, which show the motif of homochiral right-handed and left-handed helical chains, respectively, and the 1D homochiral helical chains are linked by the interchain hydrogen bonds to form a 3D structure. In 3, a pair of enantiomers of [Ni(f-RR-L)][Ag(CN)2]2 and [Ni(f-SS-L)][Ag(CN)2]2 connect with each other through intermolecular argentophilic interactions to form a dimer. The reaction of [Ni(α-rac-L)](ClO4)2 with K[Ag(CN)2] in acetonitrile gives a trimer of 4; each trimer is chiral with unsymmetrical RR, RR, and SS, or RR, SS, and SS configurations. The homochiral nature of Δ-2 and Λ-2 was confirmed by the results of solid circular dichroism spectra measurements. The solid samples of 1−4 show strong fluorescent emissions at room temperature.

外消旋及对映纯大环化合物[Ni(α-rac-L)](ClO₄)₂（含等量SS与RR对映体）、[Ni(α-SS-L)](ClO₄)₂及[Ni(α-RR-L)](ClO₄)₂，与氰合银(I)酸钾K[Ag(CN)₂]在乙腈/水混合溶剂中发生反应，得到三种一维螺旋链化合物{[Ni(f-rac-L)][Ag(CN)₂]₂}ₙ（1）、{[Ni(f-SS-L)]₂[Ag(CN)₂]₄}ₙ（Δ-2）与{[Ni(f-RR-L)]₂[Ag(CN)₂]₄}ₙ（Λ-2）；一种二聚体化合物[Ni(f-rac-L)][Ag(CN)₂]₂（3）；以及一种三聚体化合物[Ni(f-rac-L)Ag(CN)₂]₃·(ClO₄)₃（4）（其中L=5,5,7,12,12,14-六甲基-1,4,8,11-四氮杂环十四烷）。化合物1、Δ-2、Λ-2与3均为超分子异构体(supramolecular isomers)，通过亲银相互作用(argentophilic interactions)构建而成。在化合物1中，[Ni(f-RR-L)][Ag(CN)₂]₂与[Ni(f-SS-L)][Ag(CN)₂]₂对映体通过分子间亲银相互作用交替连接，形成一维内消旋螺旋链；该一维链进一步通过链间氢键相互连接，构筑得到二维网络结构。当以手性的[Ni(α-SS-L)](ClO₄)₂与[Ni(α-RR-L)](ClO₄)₂作为构筑单元时，分别得到Δ-2与Λ-2这两种超分子立体异构体，它们分别呈现同手性右手螺旋链与同手性左手螺旋链的结构基元；一维同手性螺旋链通过链间氢键相互连接，最终形成三维结构。在化合物3中，一对[Ni(f-RR-L)][Ag(CN)₂]₂与[Ni(f-SS-L)][Ag(CN)₂]₂对映体通过分子间亲银相互作用彼此结合，形成二聚体。当[Ni(α-rac-L)](ClO₄)₂与K[Ag(CN)₂]在乙腈中反应时，得到三聚体4；每个三聚体均具有手性，其构型为不对称的RR、RR、SS或RR、SS、SS。Δ-2与Λ-2的同手性属性通过固体圆二色谱(solid circular dichroism spectra)测试结果得到了证实。化合物1~4的固体样品在室温下均表现出强烈的荧光发射。