Gold Quantum Boxes: On the Periodicities and the Quantum Confinement in the Au₂₈, Au₃₆, Au₄₄, and Au₅₂ Magic Series

Abstract

Revealing the size-dependent periodicities (including formula, growth pattern, and property evolution) is an important task in metal nanocluster research. However, investigation on this major issue has been complicated, as the size change is often accompanied by a structural change. Herein, with the successful determination of the Au44(TBBT)28 structure, where TBBT = 4-tert-butylbenzenethiolate, the missing size in the family of Au28(TBBT)20, Au36(TBBT)24, and Au52(TBBT)32 nanoclusters is filled, and a neat "magic series" with a unified formula of Au8n+4(TBBT)4n+8 (n = 3-6) is identified. Such a periodicity in magic numbers is a reflection of the uniform anisotropic growth patterns in this magic series, and the n value is correlated with the number of (001) layers in the face-centered cubic lattice. The size-dependent quantum confinement nature of this magic series is further understood by empirical scaling law, classical "particle in a box" model, and the density functional theory calculations.

Bonding properties of FCC-like Au44(SR)28 clusters from X-ray absorption spectroscopy

“…After reacting at 60 ℃for 24 hours, Au 44 (SR) 28 NCs were produced in high field. 8 All the syntheses The data measured from Au foil can then be used to determine the amplitude reduction factor (S 0 2 = 0.9) as shown in the EXAFS equation, where N is the coordination number, σ 2 is the Debye-Waller factor, ߣ(k) is the photoelectron mean-free path and R is the scattering distance. Scattering amplitude functions (f(k)) and phase-shift functions (ߣ(k)) in the EXAFS equation can be used to simulate specific scattering route by theoretical calculations.…”

“…8 Three scattering shells were found, To verify the reliability of the assignment of these three shells, a three shell Au L 3 -edge EXAFS (Au-S, Au-Au 1 , Au-Au 2 ) fit was performed for Au 44 (SR) 28 at LT since the total structure was also previously obtained at LT. 8 Figure 4a) …”

“…size-controlled synthesis of these Au clusters allows for a variety of size-specific studies [5][6][7][8][9][10][11][12][13][14][15] such as the bonding and electronic properties 3,[16][17][18][19][20] . Recent studies on the thiolate stabilized Au clusters indicated their varied core structures such as the icosahedral Au core 7,12,21 the face-centered-cubic (FCC)-like Au core [8][9][10][11] and others 6,14 .…”

“…Recent studies on the thiolate stabilized Au clusters indicated their varied core structures such as the icosahedral Au core 7,12,21 the face-centered-cubic (FCC)-like Au core [8][9][10][11] and others 6,14 . Among these clusters, FCC-like Au clusters attract significant amount of interest because these ultrasmall particles exhibit unexpected core structure of FCC geometry, similar to that of bulk gold.…”

“…16,17,[22][23][24] The reported Au 44 (SR) 28 is one of the thiolate protected Au clusters with a FCC-like core structure in the FCC-like series including the well-studied Au 28 (SR) 20 and Au 36 (SR) 24 . 8,10,11 In the research of Au clusters, XAS has been found useful to probe the bonding properties of these Au clusters. 3 For instance, the unique structural and electronic properties were found in Au 28 (SR) 20 and Au 36 (SR) 24 clusters by comparing with icosahedral Au clusters, where the small tetrahedral Au 4 units within the gold cores play a very important role in controlling their bonding and electronic properties.…”