Solution-Phase Structures of Gallium-Containing Pyrogallol[4]arene Scaffolds
Solution-Phase Structures of Gallium-Containing Pyrogallol[4]arene Scaffolds
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DOI：
10.1002/anie.201200209
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Atwood, Jerry L.
中科院分区：
文献类型：
--
作者：
Kumari, Harshita;Kline, Steven R.;Atwood, Jerry L.
金属缝结构的合成一直是超分子化学家关注的热点。了解这种金属接缝系统的性质可能会导致实际应用，如生物探针，[1]电子纳米器件，[2]或发光超顺磁性混合物。[3]金属缝合的连苯三酚[4]芳烃有机纳米胶囊（MONC）的研究可以追溯到2005年，当时形成了铜缝合的C-丙-3-羟连苯三酚[4]芳烃六聚体。[4]在该组装中，六个连苯三酚[4]芳烃部分去质子化，得到具有八个三角形[（O-Cu-O）3单元]和十八个正方形面的小菱形立方八面体。后来，锌缝C-丙基邻苯三酚[4]芳烃（PgC 3 Zn，其中3是烷基链长）二聚纳米胶囊的合成。[5]镓是特别感兴趣的MONC，由于其半导体性质和组装成有趣的架构的能力。例如，镓笼，[6]镓纳米颗粒，[7]单壁氮化镓纳米管，[8]和GaP纳米线，纳米电缆和纳米带[9]已经报道。在邻苯三酚[4]芳烃骨架中，含镓支架在几个方面是独特的，例如结构的多样性，金属与邻苯三酚[4]芳烃的比例和金属氧化态。与其他观察到的二聚体和六聚体焦性没食子酸[4]芳烃纳米帽（其是球形的）不同，镓接缝的C-丁基焦性没食子酸[4]芳烃（PgC 4Ga）六聚体具有扭曲的“橄榄球”形状。[10]与典型的球形六聚体中的24个铜原子相比，只有12个镓原子，沿着4个水分子，接合这个六聚体组装体。这些镓缝纳米胶囊是特别令人感兴趣的，因为Ga 3+离子占据在相对平面上的Ga 3-（μ3-O）3（O）6单元，仅缝合六聚体框架的六个PgC 4部分中的四个。[10]水分子缝其余两个PgC 4部分，提供第一个部分氢键金属缝合六聚体。门控水性通道可用于将离子运输到胶囊内部。[11]镓继续表现出独特的行为时，混合金属六聚体的合成。[11a]在预先形成的镓六聚体中添加第二种金属，导致结构从扭曲的橄榄球转变为球体（图1）。随后，发现了镓-锌、镓-铜、镓-镍和镓-钴组合的六聚体球。[11a]然而，使用单晶XRD很难区分金属原子，因为所涉及的金属的电子密度相似。因此，进行电感耦合等离子体（ICP）分析以确认第二金属的存在并获得骨架中金属离子的近似比率。[11 a]鉴于镓基纳米胶囊有趣的固态性质，我们已经用小角中子散射（SANS）研究了它们在溶液中的几何尺寸和形状。我们还进行了固态胶囊的即时伽马激活分析（PGAA），以支持早期的ICP结果。据我们所知，PgC 4Ga混合金属六聚体的唯一其他溶液相研究是比较PgC 4GaZn六聚体与PgC 4Ga六聚体的1HNMR研究（CD 3CN）。[12]从这些研究中获得的一个明确结论是溶剂仅在锌存在下包封。为了获得更具体的结构细节，我们对PgC 4Ga和PgC 4GaZn纳米组装体进行了SANS测量，1-D NMR和2-D HMQC以及扩散有序NMR光谱。
The synthesis of metal-seamed architectures continues to attract wide attention among supramolecular chemists. Understanding the properties of such metal-seamed systems could lead to practical applications such as biological probes,[1] electronic nanodevices,[2] or luminescent superparamagnetic hybrids.[3] Investigation of metal-seamed pyrogallol [4] arene organic nanocapsules (MONCs) dates back to 2005 with the formation of copper-seamed C-propan-3-olpyrogallol [4] arene hexamers.[4] In this assembly, six pyrogallol [4] arenes are partially deprotonated to yield a small rhombicuboctahedron with eight triangular [of (O-Cu-O) 3 units] and eighteen square faces. Later, zinc-seamed C-propylpyrogallol [4] arene (PgC3Zn, where 3 is the alkyl chain length) dimeric nanocapsule was synthesized.[5] Gallium is of particular interest with respect to MONCs, owing to its semiconducting properties and its ability to assemble into interesting architectures. For example, gallium cages,[6] gallium nanoparticles,[7] single-wall gallium nitride nanotubes,[8] and GaP nanowires, nanocables and nanobelts [9] have been reported. Amongst the pyrogallol [4] arene frameworks, gallium-containing scaffolds are unique in several aspects, such as the diversity of architectures, the metal to pyrogallol [4] arene ratio and the metal oxidation state. Unlike the other observed dimeric and hexameric pyrogallol [4] arene nanocapsules, which are spherical, the galliumseamed C-butylpyrogallol [4] arene (PgC4Ga) hexamers have a distorted “rugby-ball” shape.[10] Compared to 24 copper atoms in a typical spherical hexamer, only 12 gallium atoms, along with four water molecules, seam this hexameric assembly. These gallium-seamed nanocapsules are particularly interesting owing to the Ga3+ ions occupying Ga3-(μ3-O) 3 (O) 6 units on opposite planes seaming only four of the six PgC4 moieties of the hexameric framework.[10] Water molecules seam the remaining two PgC4 moieties, providing the first partially hydrogen-bonded metal-seamed hexamer. The gated aqueous channels can be utilized for ion transportation to the interior of the capsules.[11] Gallium continued to show distinctive behavior when mixed-metal hexamers were synthesized.[11a] Addition of a second metal to a pre-formed gallium hexamer caused a transition in structure from the distorted rugby ball to a sphere (Figure1). Subsequently, hexameric spheres of gallium–zinc, gallium–copper, gallium–nickel, and gallium–cobalt combinations were found.[11a] It was, however, difficult to distinguish between the metal atoms using single-crystal XRD because of the similar electronic densities of the metals involved. Hence, inductively coupled plasma (ICP) analyses were conducted to confirm the presence of the second metal and to obtain an approximate ratio of the metal ions in the framework.[11a]Given the interesting solid-state properties of the galliumbased nanocapsules, we have investigated their geometric dimensions and shapes in solution with small-angle neutron scattering (SANS). We have also performed prompt gamma activation analysis (PGAA) of the solid-state capsules to support the earlier ICP results. To our knowledge, the only other solution-phase study of PgC4Ga mixed-metal hexamers is a 1HNMR study (CD3CN) comparing the PgC4GaZn hexamer to the PgC4Ga hexamer.[12] The one definitive conclusion obtained from these studies was that solvent is encapsulated only in the presence of zinc. To obtain more specific structural details, we performed SANS measurements, 1-D NMR and 2-D HMQC and diffusion-ordered NMR spectroscopy for the PgC4Ga and PgC4GaZn nanoassemblies …