Atom-by-Atom Evolution of the Same Ligand-Protected Au21, Au22, Au22Cd1, and Au24 Nanocluster Series

Atom-by-atom manipulation on metal nanoclusters (NCs) has long been desired, as the resulting series of NCs can provide insightful understanding of how a single atom affects the structure and properties as well as the evolution with size. Here, we report crystallizations of Au22(SAdm)16 and Au22Cd1(SAdm)16 (SAdm = adamantanethiolate) which link up with Au21(SAdm)15 and Au24(SAdm)16 NCs and form an atom-by-atom evolving series protected by the same ligand. Structurally, Au22(SAdm)16 has an Au3(SAdm)4 surface motif which is longer than the Au2(SAdm)3 on Au21(SAdm)15, whereas Au22Cd1(SAdm)16 lacks one staple Au atom compared to Au24(SAdm)16 and thus the surface structure is reconstructed. A single Cd atom triggers the structural transition from Au22 with a 10-atom bioctahedral kernel to Au22Cd1 with a 13-atom cuboctahedral kernel, and correspondingly, the optical properties are dramatically changed. The photoexcited carrier lifetime demonstrates that the optical properties and excited state relaxation are highly sensitive at the single atom level. By contrast, little change in both ionization potential and electron affinity is found in this series of NCs by theoretical calculations, indicating the electronic properties are independent of adding a single atom in this series. The work provides a paradigm that the NCs with continuous metal atom numbers are accessible and crystallizable when meticulously designed, and the optical properties are more affected at the single atom level than the electronic properties.长期以来，科研人员一直期望实现金属纳米团簇（NCs）的原子级精准操控，因为由此得到的系列团簇可深入阐释单个原子如何影响团簇的结构与性能，以及团簇随尺寸演变的内在规律。本文报道了Au22(SAdm)16与Au22Cd1(SAdm)16的合成与结晶，其中SAdm为金刚烷硫醇盐（adamantanethiolate）；这两种团簇分别与Au21(SAdm)15、Au24(SAdm)16纳米团簇相连，形成了由同一配体保护的原子级演化系列。结构分析表明，Au22(SAdm)16具有Au3(SAdm)4表面基元，其长度长于Au21(SAdm)15表面的Au2(SAdm)3基元；而相较于Au24(SAdm)16，Au22Cd1(SAdm)16缺少一个订书针状金原子，因此其表面结构发生重构。单个镉原子触发了结构转变：从具有10原子双八面体核的Au22团簇，转变为具有13原子立方八面体核的Au22Cd1团簇，相应地其光学性能也发生了显著改变。光激发载流子寿命测试结果显示，光学性能与激发态弛豫过程在原子级尺度下具有极高的敏感性。与之相对，通过理论计算发现，该系列团簇的电离势与电子亲和势几乎无变化，表明此系列团簇的电子性能不受单个原子添加的影响。本研究提供了一个研究范式：通过精心设计，可获得具有连续金属原子数的纳米团簇并实现其结晶；且相较于电子性能，光学性能在原子级尺度下受单个原子变化的影响更为显著。