Controlling magnetism of Au₁₃₃(TBBT)₅₂ nanoclusters at single electron level and implication for nonmetal to metal transition

Abstract

The transition from the discrete, excitonic state to the continuous, metallic state in thiolate-protected gold nanoclusters is of fundamental interest and has attracted significant efforts in recent research. Compared with optical and electronic transition behavior, the transition in magnetism from the atomic gold paramagnetism (Au 6s 1 ) to the band behavior is less studied. In this work, the magnetic properties of 1.7 nm [Au 133 (TBBT) 52 ] 0 nanoclusters (where TBBT ¼ 4-tert-butylbenzenethiolate) with 81 nominal "valence electrons" are investigated by electron paramagnetic resonance (EPR) spectroscopy.Quantitative EPR analysis shows that each cluster possesses one unpaired electron (spin), indicating that the electrons fill into discrete orbitals instead of a continuous band, for that one electron in the band would give a much smaller magnetic moment. Therefore, [Au 133 (TBBT) 52 ] 0 possesses a nonmetallic electronic structure. Furthermore, we demonstrate that the unpaired spin can be removed by oxidizing [Au 133 (TBBT) 52 ] 0 to [Au 133 (TBBT) 52 ] + and the nanocluster transforms from paramagnetism to diamagnetism accordingly. The UV-vis absorption spectra remain the same in the process of singleelectron loss or addition. Nuclear magnetic resonance (NMR) is applied to probe the charge and magnetic states of Au 133 (TBBT) 52 , and the chemical shifts of 52 surface TBBT ligands are found to be affected by the spin in the gold core. The NMR spectrum of Au 133 (TBBT) 52 shows a 13-fold splitting with 4-fold degeneracy of 52 TBBT ligands, which are correlated to the quasi-D 2 symmetry of the ligand shell. Overall, this work provides important insights into the electronic structure of Au 133 (TBBT) 52 by combining EPR, optical and NMR studies, which will pave the way for further understanding of the transition behavior in metal nanoclusters. rather than the desired sole change of charge state as in Au 25 (SR) 18 À . 46-48 Scheme 1 Comparison between the X-ray structures of (A) Au 25 (-SC 2 H 4 Ph) 18 and (B) Au 133 (TBBT) 52 (TBBT ¼ S-Ph-p-t Bu). Redrawn from ref. 65 and 67.This journal is

Spin‐Polarized Photoluminescence in Au25(SC8H9)18 Monolayer‐Protected Clusters

“…[ 1–4 ] Structurally well‐defined monolayer‐protected clusters (MPCs) have emerged in recent decades as a multifaceted class of photonic materials that exhibit tunable spin‐sensitivity and magnetism. [ 5–10 ] Oxidation‐state‐dependent conversion between paramagnetic and diamagnetic character was demonstrated for the Au 25 (SC 8 H 9 ) 18 and Au 102 (pMBA) 44 where pMBA stands for para‐mercaptobenzoic acid, clusters. [ 5,6 ] In addition, low‐temperature magnetism in Au 102 (pMBA) 44 clusters, resulting from d‐band vacancies, was recently reported.…”

Multiple Ways Realizing Charge‐State Transform in AuCu Bimetallic Nanoclusters with Atomic Precision

“…[ 7,8,28 ] More recently, Jin and co‐workers found that the larger gold clusters [Au 133 (TBBT) 52 ] 0 (TBBT = 4‐tert‐butylbenzenethiolate) can be oxidized to [Au 133 (TBBT) 52 ] + using H 2 O 2 . [ 36 ]…”

Ligand Effects on Intramolecular Configuration, Intermolecular Packing, and Optical Properties of Metal Nanoclusters

“…Specifically, the intramolecular control of nanoclusters touches upon the manipulation of their metal-ligand compositions and bonding environment at the single molecular level, while the intermolecular control of nanoclusters refers to the manipulation over their aggregating patterns among several cluster molecules in amorphous or crystallographic forms [ 30 ]. Several control methods, including (i) intracluster approaches (e.g., ligand exchange [ 31 , 32 , 33 , 34 ], heteroatom alloying [ 35 , 36 , 37 , 38 , 39 ], and molecular charge regulation [ 40 , 41 , 42 ]) and (ii) intercluster approaches (e.g., cluster-based metal-organic framework [ 43 , 44 , 45 , 46 ], aggregation-induced emission [ 47 , 48 , 49 ], and intercluster metallophilic reaction [ 50 , 51 ]), have been exploited to control clusters or their assemblies and to dictate their properties. Of note, the intracluster and intercluster controls are not a binary separation, but an interrelated and inseparable whole to regulate the nanocluster system simultaneously.…”