Department of Chemistry, Nanoscience Center, University of Jyväskylä , FI-40014 Jyväskylä, Finland.
Department of Physics, Nanoscience Center, University of Jyväskylä , FI-40014 Jyväskylä, Finland.
ACS Nano. 2017 Dec 26;11(12):11872-11879. doi: 10.1021/acsnano.7b07787. Epub 2017 Nov 21.
Ligand-stabilized, atomically precise gold nanoclusters with a metal core of a uniform size of just 1-3 nm constitute an interesting class of nanomaterials with versatile possibilities for applications due to their size-dependent properties and modifiable ligand layers. The key to extending the usability of the clusters in applications is to understand the chemical bonding in the ligand layer as a function of cluster size and ligand structure. Previously, it has been shown that monodispersed gold nanoclusters, stabilized by meta-mercaptobenzoic acid (m-MBA or 3-MBA) ligands and with sizes of 68-144 gold atoms, show ambient stability. Here we show that a combination of nuclear magnetic resonance spectroscopy, UV-vis absorption, infrared spectroscopy, molecular dynamics simulations, and density functional theory calculations reveals a distinct chemistry in the ligand layer, absent in other known thiol-stabilized gold nanoclusters. Our results imply a low-symmetry C ligand layer of 3-MBA around the gold core of Au and Au and suggest that 3-MBA protects the metal core not only by the covalent S-Au bond formation but also via weak π-Au and O═C-OH···Au interactions. The π-Au and -OH···Au interactions have a strength of the order of a hydrogen bond and thus are dynamic in water at ambient temperature. The -OH···Au interaction was identified by a distinct carbonyl stretch frequency that is distinct for 3-MBA-protected gold clusters, but is missing in the previously studied Au(p-MBA) cluster. These thiol-gold interactions can be used to explain a remarkably low ligand density on the surface of the metal core of these clusters. Our results lay a foundation to understand functionalization of atomically precise ligand-stabilized gold nanoclusters via a route where weak ligand-metal interfacial interactions are sacrificed for covalent bonding.
配体稳定的、原子精度的金纳米簇具有均一的金属核尺寸，仅为 1-3nm，由于其尺寸依赖性的性质和可修饰的配体层，构成了一类具有广泛应用前景的有趣纳米材料。扩展纳米簇在应用中的可用性的关键是了解配体层中的化学结合作为纳米簇尺寸和配体结构的函数。以前已经表明，由间巯基苯甲酸（m-MBA 或 3-MBA）配体稳定且尺寸为 68-144 个金原子的单分散金纳米簇在环境中具有稳定性。在这里，我们展示了核磁共振波谱、紫外可见吸收、红外光谱、分子动力学模拟和密度泛函理论计算的结合，揭示了配体层中的一种独特化学，这在其他已知的硫醇稳定的金纳米簇中是不存在的。我们的结果表明，在 Au 和 Au 的金核周围，3-MBA 的配体层具有低对称 C 结构，并表明 3-MBA 不仅通过共价 S-Au 键形成，而且还通过弱π-Au 和 O═C-OH···Au 相互作用来保护金属核。π-Au 和 -OH···Au 相互作用的强度与氢键相当，因此在环境温度下在水中是动态的。-OH···Au 相互作用通过独特的羰基伸缩频率来识别，这种频率对于 3-MBA 保护的金簇是独特的，但在之前研究的 Au(p-MBA) 簇中则不存在。这些硫醇-金相互作用可以用来解释这些纳米簇金属核表面的配体密度非常低的原因。我们的研究结果为通过牺牲弱配体-金属界面相互作用来实现原子精度的配体稳定的金纳米簇的功能化提供了基础。
