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首页> 外文期刊>Chemistry: A European journal >Stepwise Coordination of Pt~(II)-180° and Pd~(II)-90° Metal Fragments to the Purine Nucleobase 9-Methylhypoxanthine Affords a Closed Octadecanuclear Pt6Pd12 Cluster
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Stepwise Coordination of Pt~(II)-180° and Pd~(II)-90° Metal Fragments to the Purine Nucleobase 9-Methylhypoxanthine Affords a Closed Octadecanuclear Pt6Pd12 Cluster

机译：Pt〜（II）-180°和Pd〜（II）-90°金属片段与嘌呤核碱基9-甲基次黄嘌呤的逐步配位导致封闭的八聚核Pt6Pd12簇

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Nucleobases represent ideal building blocks for supramolecular constructs with metal ions in that they provide several potential donor sites of different donor strengths and different directionalities of the coordinative bonds, depending on the respective combinations. On top of that, secondary interactions resulting from hydrogen bonding and/or p-p stacking, are possible.~([1]) N9-blocked purines, for example, provide three endocyclic N atoms (N1, N3, N7) for metal binding, spanning angles of about 90°, 120°, and 150° between the various N atoms (Scheme 1). There are additional possibilities for metal coordination and/or hydrogen bond formation involving the exocyclic X-6 and Y-2 sites, or even metal binding to C-8.~([2]) We have recently utilized a combination of the monofunctional metal fragment (NH_3)_3Pt~(II) and the cis-bifunctional [Pd~(II)(en)]) (en=ethylenediamine) to prepare an open triangular vase with 9-methylhypoxanthine (9-MeHxH), which acts as a host for tetrahedral oxo anions.~([3]) Unlike typical "spontaneous" self-assembly processes containing a single ligand and a single metal species,~([4]) the synthesis of this mixed-metal complex required a stepwise synthesis strategy, in which the substitutionally inert building block [Pt(NH_3)_3(9-MeHxH-N7)]~(2+) was prepared first, and subsequently treated with [Pd~(II)(en)]) to connect N1 and N3 sites of the purine nucleobase in a cyclic fashion. Using the same approach, we have now mixed 9-MeHxH with trans- [Pt(NH_3)_2(H_2O)_2]~(2+) to give trans-[Pt(NH_3)_2(9-MeHxH-N7)_2]~(2+) (1) initially, which was then treated with [Pd~(II)(en)] at a pH of about four in water. The isolated compound proved to be an octadecanuclear Pt_6Pd_(12) species, {trans- (NH_3)_2Pt(N7-9-MeHx-N1,N3)_2[Pd(en)]_2}_6(ClO_4)_(24)·63H_2O (2), having the appearance of a truncated tetrahedron with its twelve corners built by the Pd ions, and with an inscribed regular octahedron of Pt ions. Thus, four Pd_3(9-MeHx) vases, forming the capped corners of an original tetrahedron, are cross-linked by six trans-(NH_3)_2Pt~(II) units, which represent the sides of the original tetrahedron (Scheme 2).
机译：核糖核酸代表了具有金属离子的超分子构建体的理想构建基块，因为它们提供了多个潜在的供体位点，这些位点具有不同的供体强度和不同的配位键方向，具体取决于各自的组合。最重要的是，由氢键和/或pp堆​​积引起的二次相互作用是可能的。〜（[1]）N9封闭的嘌呤，例如为金属结合提供了三个内环N原子（N1，N3，N7）， N个原子之间的跨度约为90°，120°和150°（方案1）。金属的配位和/或氢键的形成还可能涉及环外的X-6和Y-2位，甚至金属与C-8结合。〜[[2]）我们最近利用了单官能金属的组合片段（NH_3）_3Pt〜（II）和顺式双功能[Pd〜（II）（en）]）（en =乙二胺）制备带有9-甲基次黄嘌呤（9-MeHxH）的开口三角形花瓶， 〜（[3]）与包含单个配体和单个金属物种的典型“自发”自组装过程不同，〜（[4]）这种混合金属配合物的合成需要逐步合成策略，其中首先制备了取代惰性的结构单元[Pt（NH_3）_3（9-MeHxH-N7）]〜（2+），然后用[Pd〜（II）（en）]）处理以连接N1和嘌呤核碱基的N3位点呈环状。使用相同的方法，我们现在将9-MeHxH与反式[Pt（NH_3）_2（H_2O）_2]〜（2+）混合，得到反式[Pt（NH_3）_2（9-MeHxH-N7）_2]最初是〜（2+）（1），然后在水中将其用[Pd〜（II）（en）]在大约4的pH中处理。分离出的化合物被证明是八核Pt_6Pd_（12）物种，{反式（（NH_3）_2Pt（N7-9-MeHx-N1，N3）_2 [Pd（en）] _ 2} _6（ClO_4）_（24）· 63H_2O（2）的外观为截短的四面体，其十二个角由Pd离子构成，并带有内切的Pt离子正八面体。因此，形成原始四面体顶角的四个Pd_3（9-MeHx）花瓶通过代表原始四面体侧面的六个反式（NH_3）_2Pt〜（II）单元交联（方案2） 。

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