Cu12 and Cd16 coordination cages and their Cu3 and Cd3 subcomponents, and the role of inter-ligand π-stacking in stabilising cage complexes
Cu12 and Cd16 coordination cages and their Cu3 and Cd3 subcomponents, and the role of inter-ligand π-stacking in stabilising cage complexes
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DOI：
10.1039/c3dt50161b
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发表时间：
2013-01-01
影响因子：
4
通讯作者：
Ward, Michael D.
中科院分区：
文献类型：
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作者：
Stephenson, Andrew;Sykes, Daniel;Ward, Michael D.
桥联配体L-1,4 Nap含有两个由萘-1，4-二基间隔基隔开的吡唑基-吡啶螯合单元，已被用于多面体配位笼的自组装。最大的这种笼是[Cd-16（L-14 Nap）（24）]（BF 4）（32），其具有四帽截短四面体Cd-16核，其中桥连配体跨越每个边缘。该络合物在稀溶液中无限期稳定，这使得它与先前报道的同构笼[Cd-16（L-1, 4Ph）（24）]（BF 4）（32）（基于1，4-苯基桥）完全不同，后者在结晶时形成，但在溶液中缓慢重排为较小的笼。与苯基被萘基取代相关的配体片段之间的额外配体间π-堆叠允许络合物在溶液中稳定，提供了配体间π-堆叠在这些笼的组装中的重要性的决定性证据。用Cu（II）代替Cd（II），形成较小的笼[Cu-12（L-14 Nap）（15）]（ClO 4）（24），其含有三螯合（六配位）和二螯合（四配位，或五配位，如果存在额外的单齿配位体）Cu（II）离子的混合物;两种结构之间的差异部分源于两种金属离子的不同立体电子偏好。尽管有这种差异，Cd-16和Cu-12笼都含有{M-3（L-14 Nap）（3）}（6+）三角螺旋单元作为形成多面体三角面的子组分。通过使用1：1个配体：这些化合物的合成实例中的金属比可以被分离和表征;三核环状螺旋酸酯[Cd-3（L-14 Nap）（3）（BF 4）（4）（EtOAc）（2）]（BF 4）（2）和[Cu-3（L-14 Nap）（3）（BF 4）（MeCN）（2）]（BF 4）（5）的结构也已经被确定。
The bridging ligand L-14Nap, which contains two chelating pyrazolyl-pyridine units separated by a naphthalene-1,4-diyl spacer, has been used in self-assembly of polyhedral coordination cages. The largest such cage is [Cd-16(L-14Nap)(24)](BF4)(32) which has a tetra-capped truncated tetrahedral Cd-16 core with a bridging ligand spanning every edge. The complex is indefinitely stable in dilute solution, which makes it quite different from the previously-reported isostructural cage [Cd-16(L-14Ph)(24)](BF4)(32) (based on a 1,4-phenyl bridge) that forms on crystallisation but slowly rearranges to smaller cages in solution. The additional inter-ligand pi-stacking between ligand fragments associated with replacement of a phenyl group by a naphthyl group allows the complex to be stable in solution, providing conclusive proof of the importance of inter-ligand pi-stacking in the assembly of these cages. With Cu(II) in place of Cd(II) a smaller cage [Cu-12(L-14Nap)(15)](ClO4)(24) was formed which contains a mixture of tris-chelated (six-coordinate) and bis-chelated (four-coordinate, or five-coordinate if an additional monodentate ligand is present) Cu(II) ions; the difference between the two structures arises in part from the different stereoelectronic preferences of the two metal ions. Despite this difference both the Cd-16 and Cu-12 cages contain {M-3(L-14Nap)(3)}(6+) triangular helical units as subcomponents which form the triangular faces of the polyhedra. By using a 1 : 1 ligand : metal ratio in the synthesis examples of these can be isolated and characterised; the structures of the trinuclear cyclic helicates [Cd-3(L-14Nap)(3)(BF4)(4)(EtOAc)(2)](BF4)(2) and [Cu-3(L-14Nap)(3)(BF4)(MeCN)(2)](BF4)(5) have also been determined.