Abstract:

Metal nanoclusters are rising stars in material science, and one advantage is their atomically precise tunability. It is well known that metal doping can efficiently modify the properties of metal nanoclusters. In particular, without altering the parent nanocluster framework, doping a single heterometal atom can tailor the properties of metal nanoclusters and aid investigations of the structure–property relationship of metal nanoclusters. To our knowledge, the simultaneous synthesis of a single heterometal-doped nanocluster and its parent nanocluster is challenging and has not been previously reported; however, this is highly desirable because it can prevent the influence of trace impurities and allow comparison between doped and undoped nanoclusters. The single Cd-doped gold nanocluster Au₂₂Cd₁(S-Adm)₁₆ (S-Adm = 1-adamantanethiolate) has been previously synthesized and structurally elucidated. However, the structure of the parent nanocluster, Au₂₃(S-Adm)₁₆, remains unknown, inspiring this investigation. In this study, we synthesized Au₂₃(S-Adm)₁₆ and its single-doped Au₂₂Cd₁(S-Adm)₁₆ nanocluster in one pot for the first time, and we resolved their structures using single-crystal X-ray crystallography. The structure of Au₂₂Cd₁(S-Adm)₁₆ is similar to that of Au₂₃(S-Adm)₁₆ except that a kernel Au atom in Au₂₃(S-Adm)₁₆ is replaced with a Cd atom. This Cd replacement causes the kernel Au―Au bond length to increase owing to the loosening of the original closely packed structure. In contrast to prior reports, Au₂₃(S-Adm)₁₆ is surprisingly more stable than Au₂₂Cd₁(S-Adm)₁₆, as determined via ultraviolet visible-near infrared (UV-Vis-NIR) spectroscopy at 80 ℃. This stability was attributed to the decrease in the kernel Au―Au bond length. Although the maximum absorption of Au₂₂Cd₁(S-Adm)₁₆ slightly red-shifted from 605 to 608 nm after Cd doping, the molar extinction coefficient of Au₂₃(S-Adm)₁₆ at 605 nm was approximately twice that of Au₂₂Cd₁(S-Adm)₁₆ at 608 nm. Thus, the increase in kernel Au―Au bond length may decrease the photoexcitation electron transfer efficiency owing to lengthening of the photoexcitation electron transfer pathway. As further support for this opinion, although the two nanoclusters showed similar emission profiles and maxima (750 nm for Au₂₃(S-Adm)₁₆ and 760 nm for Au₂₂Cd₁(S-Adm)₁₆), they exhibited obvious emission intensity differences. Specifically, the quantum yield of Au₂₃(S-Adm)₁₆ (approximately 3.160 × 10⁻⁵) was found to be 1.13 times that of Au₂₂Cd₁(S-Adm)₁₆ (approximately 2.793 × 10⁻⁵). Thus, the stability and absorption and emission intensities correlate with the kernel Au―Au bond length.This study shows that two metal nanoclusters with slight structural differences can exhibit different properties in terms of optical and thermal stability, providing a good reference for studying their structure–property relationships.

Key words: Metal nanoclusters, Synthesis, Au―Au bond length, Property, Property–structure correlation