Vertex-Shared Linear Superatomic Molecules: Stepping Stones to Novel Materials Composed of Noble Metal Clusters

Abstract

Extremely small metal clusters composed of noble metal atoms (M) have orbitals similar to those of atoms and therefore can be thought of as artificial atoms or superatoms. If these superatoms can be assembled into molecular analogs, it might be possible to create materials with new characteristics and properties that are different from those of existing substances. Therefore, the concept of superatomic molecules has attracted significant attention. The present review focuses on vertex-shared linear M_12n+1 superatomic molecules formed via the sharing of a single metal atom between M₁₃ superatoms having icosahedral cores and summarizes the knowledge obtained to date in this regard. This summary discusses the most suitable ligand combinations for the synthesis of M_12n+1 superatomic molecules along with the valence electron numbers, stability, optical absorption characteristics, and luminescence properties of the M_12n+1 superatomic molecules fabricated to date. This information is expected to assist in the production of many M_12n+1 superatomic molecules with novel structures and physicochemical properties in the future.

Keywords: connections; geometrical structures; ligand-protected metal clusters; superatomic molecules.

Figure 1

Diagram showing the formation of a superatomic molecule and the associated orbitals. ^[3b]

Figure 2

a–c) Diagrams of vertex‐sharing (a), edge‐sharing (b), and face‐sharing (c) superatomic molecules.

Figure 3

a) The anatomy of an M₂₅ superatomic molecule comprising an M₂₅ core and three types of ligands. b) The five different metal sites in an M₂₅ core. c) Characteristic geometrical parameters of an M₂₅ superatomic molecule. In these figures, carbon and hydrogen atoms in the phosphine ligands are omitted for clarity.

Figure 4

Classification of ligands used for the formation of superatomic molecules based on a Venn diagram. L₁, L₂, and L₃ represent characteristic ligand sites (see also Figure 3). a) Ethanethiolate, b) 2‐phenylethanethiolate, c) benzenethiolate, d) benzeneselenolate, e) triphenylphosphine, f) tri(p‐tolyl)phosphine, g) methyldiphenylphosphine, h) bis(diphenylphosphino)methane, i) 1,1′‐bis(diphenylphosphino)ferrocene, j) 1,3‐di‐i‐propylbenzimidazol‐2‐ylidene, k) 1,3‐di(2,4,6‐trimethylbenzyl)benzimidazol‐2‐ylidene, l) bromide, m) chloride, n) 1‐adamantanethiolate, o) O,O‐dipropyldithiophosphate, p) 4‐tert‐buthylbenzenethiolate, and q) dipyridylaminide ligands.

Figure 5

Framework structures of bimetallic M₂₅ superatomic molecules protected by PR₃ and X ligands. a) [Ag₁₂Au₁₃(P(p‐tol)₃)₁₀Cl₇]⁺ (entry 1), ^[10a] b) [Ag₁₂Au₁₃(PPh₃)₁₀Br₈]⁺ (entry 2), ^[10b] c) [Ag₁₂Au₁₃(PPh₃)₁₀Br₈]⁺ (entry 3), ^[10c] d) [Ag₁₂Au₁₃(P(p‐tol)₃)₁₀Br₈]⁺ (entry 4), ^[10d] e) [Ag₁₂Au₁₃(PPh₃)₁₀Cl₈]⁺ (entry 5), ^[10e,f] f) [Ag₁₂Au₁₃(PPh₃)₁₀Cl₈]⁺ (entry 6), ^[10f] g) [Ag₁₂Au₁₃(P(p‐tol)₃)₁₀Cl₈]⁺ (entry 7), ^[10g] h) [Ag_12+x Au_13−x (PPh₃)₁₀Cl₈]²⁺ (entry 8), ^[10h] i) [Ag₁₃Au₁₂(PPh₂Me)₁₀Br₉]⁰ (entry 9), ^[10i] and j) [Ag₁₇Au₈(PPh₃)₁₀Cl₁₀]⁰ (entry 10). ^[10j] In each structure, the left and right images indicate a side and top view, respectively. In the top views, only the M_C1 and M_L1 site metal atoms and L₁ atoms are shown for the clarity. These structures are classified by the number of halogen ligands and bonding motifs.

Figure 6

Framework structures of Ag₂₃M₂ cores protected by PPh₃ and X ligands. a) [Ag₂₃Pd₂(PPh₃)₁₀Br₇]⁰ (entry 11), ^[10k] b) [Ag₂₃Pd₂(PPh₃)₁₀Cl₇]⁰ (entry 12), ^[10l] c) [Ag₂₃Pt₂(PPh₃)₁₀Br₇]⁰ (entry 13), ^[10k] and d) [Ag₂₃Pt₂(PPh₃)₁₀Cl₇]⁰ (entry 14). ^[10m] In each structure, the left and right figures indicate the side and top view, respectively.

Figure 7

a) The geometrical structure of [Au₂₃Pd₂(PPh₃)₁₀Br₇]⁰ (entry 15). ^[10n] b) Electrospray ionization‐mass spectra of [Au₂₃Pt₂(PPh₃)₁₀Br₇]⁰ and [Au₂₃Pd₂(PPh₃)₁₀Cl₇]⁰. b) Reproduced with permission. ^[10n] Copyright 2017, American Chemical Society.

Figure 8

Framework structures of trimetallic M₂₅ superatomic molecules. a) [Ag₁₂Au₁₂Ni(PPh₃)₁₀Cl₇]⁺ (entry 16), ^[10o] b) [Ag₁₂Au₁₂Pt(PPh₃)₁₀Cl₇]⁺ (entry 17), ^[10p] c) [Ag₁₂Au₁₁Pt₂(PPh₃)₁₀Cl₇]⁰ (entry 18), ^[10q] and d) [Ag₁₃Au₁₀Pt₂(PPh₃)₁₀Cl₇]⁰ (entry 20). ^[10r]

Figure 9

a) Framework structure of [Au₂₅(PPh₃)₁₀(SR)₅Cl₂]²⁺ (SR = SEt (entry 20), ^[10s] PET (entry 21), ^[10t] or SPh (entry 22) ^[10u] ). b) UV–visible absorption/PL spectra of [Au₂₅(PPh₃)₁₀(PET)₅Cl²]²⁺. b) Reproduced with permission.^{[ 23 ]} Copyright 2021, Wiley‐VCH. c) Excited state deactivation pathway of [Au₂₅(PPh₃)₁₀(SR)₅Cl₂]²⁺. Reproduced with permission.^{[ 24 ]} Copyright 2022, Royal Society of Chemistry.

Figure 10

a) Framework structure of [Au₂₄(PPh₃)₁₀(PET)₅X₂]⁺ (X = Br or Cl)^{[ 26 ]} and b) UV–vis absorption/PL spectra of [Au₂₄(PPh₃)₁₀(PET)₅Cl₂]⁺. b) Reproduced with permission.^{[ 23 ]} Copyright 2021, Wiley‐VCH. c) The effect of a central Au atom on the excitation relaxation rate.^{[ 23 ]}

Figure 11

A) Framework structures of: a) [Au₂₅(PPh₃)₁₀(PET)₅Cl₂]²⁺ (entry 21), ^[10t] b), [Ag _x Au_25−x (PPh₃)₁₀(PET)₅X₂]²⁺ (x ≤ 12), c) [Ag _x Au_25−x (PPh₃)₁₀(PET)₅X₂]²⁺ (x ≤ 13; entry 23), ^[10v] and d) [Au_25−x Cu _x (PPh₃)₁₀(PET)₅Cl₂]²⁺ (entry 24). ^[10w] B) UV–vis absorption and C) PL spectra of [Ag _x Au_25−x (PPh₃)₁₀(SR)₅X₂]²⁺. Data in (B,C) are replotted from ref. [10v].

Figure 12

Framework structures of monometal doped [Au₂₄M(PPh₃)₁₀(PET)₅Cl₂] ^z . a) [AgAu₂₄(PPh₃)₁₀(PET)₅Cl₂]²⁺ (entry 25), ^[10x] b) [Au₂₄Cu(PPh₃)₁₀(PET)₅Cl₂]²⁺ (entry 26), ^[10x] and c) [Au₂₄Pd(PPh₃)₁₀(PET)₅Cl₂]⁺ (entry 27). ^[10y] d) Comparison of UV–vis absorption spectra of [Au₂₄M(PPh₃)₁₀(PET)₅Cl₂] ^z incorporating various metals. Data in (d) are replotted from refs. [10x] (yellow, gray, and brown lines) and ref. [10y] (blue line).

Figure 13

a) Geometrical structures, b) EPR spectra at 5 K, and c) magnetic susceptibilities versus temperature plots for [Au₂₅(PPh₃)₁₀(SePh)₅Cl₂]^2+/+ (entries 28 and 29). ^[10z] b,c) Reproduced with permission. ^[10z] Copyright 2016, American Chemical Society. d) Excited state relaxation dynamics for these same molecules. Reproduced with permission.^{[ 30 ]} Copyright 2021, The Royal Society of Chemistry.

Figure 14

a) The electrospray ionization mass spectrum of [Au₂₅(PPh₃)₁₀(PA)₅X₂]²⁺ and b) the UV–vis absorption spectra of [Au₂₅(PPh₃)₁₀(PET)₅X₂]²⁺ and [Au₂₅(PPh₃)₁₀(PA)₅X₂]²⁺. a,b) Reproduced with permission. ^[14r] Copyright 2014, American Chemical Society.

Figure 15

Framework structures of NHC‐protected Au₂₅ superatomic molecules. a) [Au₂₅( ⁱ Pr₂‐bimy)₁₀Br₇]²⁺ (entry 30), ^[10aa] b) [Au₂₅(^MesCH2bimy)₁₀Br₇]²⁺ (entry 31), and c) [Au₂₅(^MesCH2bimy)₁₀Br₈]⁺ (entry 32). ^[10ab] Side views of the main structures and top views around the M_C1, M_L1, and L₁ atoms are depicted in the upper and lower part of each figure, respectively.

Figure 16

Geometrical structures and the anatomies of: a) [Ag_31−x Au _x (dppm)₆(S‐Adm)₆Cl₇]²⁺ (entry 33), ^[10h] b) [Au₂₉Cd₂(dppf)₂(TBBT)₁₇]⁰ (entry 34), ^[10ac] and c) [Ag₃₃Pt₂(dpt)₁₇]⁰ (entry 35). ^[10ad]

Figure 17

A) Framework structures of: a) the [Au₁₃(dppe)₅Cl₂]³⁺ superatom, ^[5a] b) the [Au₂₅(PPh₃)₁₀(PET)₅Cl₂]²⁺ superatomic molecule (entry 21), ^[10t] and c) the [Au₃₇(PPh₃)₁₀(PET)₁₀X₂]⁺ superatomic molecule (entry 37). ^[10t] B) UV–vis–NIR absorption and C) PL spectra of these compounds. Note that each PL spectra was recorded on a different spectrometer and so these spectra cannot be directly compared. Data in (B) and (C) are replotted from refs. [10ae] (red lines), [23] (green lines), and [27] (blue lines).

Figure 18

A) The geometrical structures of: a) [Ag₂₀Pt(dpt)₁₂]⁰, b) [Ag₃₃Pt₂(dpt)₁₇]⁰ (entry 35), and c) [Ag₄₄Pt₃(dpt)₂₂] (entry 36). ^[10ad] B) The UV–vis–NIR absorption spectra of [Ag₂₀Pt(dpt)₁₂]⁰, [Ag₃₃Pt₂(dpt)₁₇]⁰ (entry 35), and [Ag₄₄Pt₃(dpt)₂₂] (entry 36). B) Data in (B) are replotted from ref. [10af].

Figure 19

A) Geometrical structures of: a) the [Ag₂₁(dpa)₁₂]⁺ superatom^{[ 36 ]} and b) the [Ag₆₁(dpa)₂₇]⁴⁺ superatomic molecule (entry 38). ^[10af] B) The binding motifs of the dpa ligands. Reproduced with permission. ^[10af] Copyright 2021, American Chemical Society. C) The UV–vis–NIR absorption spectra of [Ag₂₁(dpa)₁₂]⁺ and [Ag₆₁(dpa)₂₇]⁴⁺. Data in (C) are replotted from ref. [10af].