14.2 Building Blocks Identified from Gas Phase
245
Through the point of view of material science, researchers in Khanna group [64]
proposed cluster complexes and assemblies on a basis of the phosphorus-like superatoms. For example, the cluster As
3–
7 was used as a stable building block and linked
together with multiple lithium, potassium, rubidium or caesium atoms, in which they
demonstrated the assemblies of a new class of semiconductor cluster materials for
potential electronics [64]. Further, interesting cluster assemblies were postulated with
a focus on superatom units of both Al 13 and K 3 O [29]. Among various (Al 13 K 3 O) n
superatom compounds that they studied, (Al 13 K 3 O) 3 has its first two ionization potentials lower than any other atom in the periodic table and was described as an ultraalkali motif (3.17 eV for K 3 O). Calculation results on assembly structures of three
typical species, (Al 13 K 3 O) 4,5,6 .
14.3 Nanoclusters Synthesized via Wet Chemistry
Metal nanoclusters (NCs) consisting of a metallic core and protection ligands have
attracted extensive research interest indicating potential use in various fields [57–
60]. The reported Au/Ag nanoclusters with precise formulas are mostly protected
by thiolate ligands, such as Au 102 [52], Au 92 [61], Au 60 [62], Au 55 [63], Au 52
[64], Au 44 [65], Au 40 [64], Au 38 [66], Au 37 [67], Au 36 [68, 69], Au 30 [69, 70],
Au 28 [71–73], Au 25 [74–76], Au 24 [77–79], Au 23 [80], Au 22 [81], Au 21 [82], Au 20
[83, 84], Au 18 [85], and Au 13 [86, 87]; also Ag 14 (SR) 12 [88], Ag 16 (SR) 14 [89],
Ag 20 /Ag 21 ((Se/S) 2 R) 12 [90, 91], Ag 25 (SR) 18 [92], Ag 29 (S 2 R) 12 [93], Ag 32 (SR) 24
[89], Ag 33 [94], Ag 34 [95], Ag 38 (SR) 26 [96], Ag 44 (SR) 30 [97, 98], Ag 48 (SR) 42 [99],
Ag 50 (SR) 30 [100], Ag 63 (SR) 36 [96], Ag 67 (SR) 32 [101], etc. Besides, a few silylated
chalcogenide sources [102], and electron-deficient alkynyl ligands were also applicable to successful synthesis procedures, such as Ag 19 (C ≡ CR) 14 [103], Ag 25 (C
≡ CR) 20 [103], Ag 74 (C ≡ CPh) 44 [104]. On the other hand, water-soluble ligands
such as 4-mercaptobenzoic acid (MBA), mercaptosuccinic acid (MSA), dimercaptosuccinic acid (DMSA), glutathione (GSH), and D-penicillamine (DPA) have also
been utilized to synthesize water-soluble silver nanoclusters. Utilizing these interesting ligands, various monolayer protected water-soluble silver clusters have been
synthesized, such as Ag 5,6 (DDT) 4,2 [105], Ag 7 (DMSA) 4 [106], Ag 7,8 (MSA) 7,8,12
[107], Ag 9 (MSA) 7 [108], Ag 9 (SG) 6 [109], Ag 11 (SG) 7 [110], [Ag 12 (HSMA) 6 Na 6 ]
2+
[111], Ag 14 (SG) 11,12 [112, 113], Ag 15 (SG) 11 [114], Ag 16 (SG) 9 [109], Ag 20 (DPA) 18
[115], Ag 31 (SG) 19 [114], Ag 32 (SG) 19 [116], Ag 44 (SR) 30 [117], Ag 75 (SG) 40 [118],
etc. There are similar systems leading to the isolation and determination of several
gold NCs, such as Au 10 (SG) 10 , Au 15 (SG) 13 , Au 18 (SG) 14 , Au 22 (SG) 16 , Au 22 (SG) 17 ,
Au 25 (SG) 18 , Au 29 (SG) 20 , Au 33 (SG) 22 , and Au 39 (SG) 24 , etc., mainly synthesized in
Tsukuda group [119]. The assembly of these coordination clusters could exhibit
unique characteristics, e.g., high stability, low cytotoxicity, and decent fluorescence
in the solid state and in solution, giving rise to promising application as a fluorescent probe in vivo and in vitro [120]. An example shown in Fig. 14.3 illustrates the
superatomic Ag 14 NCs stabilized by face-capping ligands [57].
245
Through the point of view of material science, researchers in Khanna group [64]
proposed cluster complexes and assemblies on a basis of the phosphorus-like superatoms. For example, the cluster As
3–
7 was used as a stable building block and linked
together with multiple lithium, potassium, rubidium or caesium atoms, in which they
demonstrated the assemblies of a new class of semiconductor cluster materials for
potential electronics [64]. Further, interesting cluster assemblies were postulated with
a focus on superatom units of both Al 13 and K 3 O [29]. Among various (Al 13 K 3 O) n
superatom compounds that they studied, (Al 13 K 3 O) 3 has its first two ionization potentials lower than any other atom in the periodic table and was described as an ultraalkali motif (3.17 eV for K 3 O). Calculation results on assembly structures of three
typical species, (Al 13 K 3 O) 4,5,6 .
14.3 Nanoclusters Synthesized via Wet Chemistry
Metal nanoclusters (NCs) consisting of a metallic core and protection ligands have
attracted extensive research interest indicating potential use in various fields [57–
60]. The reported Au/Ag nanoclusters with precise formulas are mostly protected
by thiolate ligands, such as Au 102 [52], Au 92 [61], Au 60 [62], Au 55 [63], Au 52
[64], Au 44 [65], Au 40 [64], Au 38 [66], Au 37 [67], Au 36 [68, 69], Au 30 [69, 70],
Au 28 [71–73], Au 25 [74–76], Au 24 [77–79], Au 23 [80], Au 22 [81], Au 21 [82], Au 20
[83, 84], Au 18 [85], and Au 13 [86, 87]; also Ag 14 (SR) 12 [88], Ag 16 (SR) 14 [89],
Ag 20 /Ag 21 ((Se/S) 2 R) 12 [90, 91], Ag 25 (SR) 18 [92], Ag 29 (S 2 R) 12 [93], Ag 32 (SR) 24
[89], Ag 33 [94], Ag 34 [95], Ag 38 (SR) 26 [96], Ag 44 (SR) 30 [97, 98], Ag 48 (SR) 42 [99],
Ag 50 (SR) 30 [100], Ag 63 (SR) 36 [96], Ag 67 (SR) 32 [101], etc. Besides, a few silylated
chalcogenide sources [102], and electron-deficient alkynyl ligands were also applicable to successful synthesis procedures, such as Ag 19 (C ≡ CR) 14 [103], Ag 25 (C
≡ CR) 20 [103], Ag 74 (C ≡ CPh) 44 [104]. On the other hand, water-soluble ligands
such as 4-mercaptobenzoic acid (MBA), mercaptosuccinic acid (MSA), dimercaptosuccinic acid (DMSA), glutathione (GSH), and D-penicillamine (DPA) have also
been utilized to synthesize water-soluble silver nanoclusters. Utilizing these interesting ligands, various monolayer protected water-soluble silver clusters have been
synthesized, such as Ag 5,6 (DDT) 4,2 [105], Ag 7 (DMSA) 4 [106], Ag 7,8 (MSA) 7,8,12
[107], Ag 9 (MSA) 7 [108], Ag 9 (SG) 6 [109], Ag 11 (SG) 7 [110], [Ag 12 (HSMA) 6 Na 6 ]
2+
[111], Ag 14 (SG) 11,12 [112, 113], Ag 15 (SG) 11 [114], Ag 16 (SG) 9 [109], Ag 20 (DPA) 18
[115], Ag 31 (SG) 19 [114], Ag 32 (SG) 19 [116], Ag 44 (SR) 30 [117], Ag 75 (SG) 40 [118],
etc. There are similar systems leading to the isolation and determination of several
gold NCs, such as Au 10 (SG) 10 , Au 15 (SG) 13 , Au 18 (SG) 14 , Au 22 (SG) 16 , Au 22 (SG) 17 ,
Au 25 (SG) 18 , Au 29 (SG) 20 , Au 33 (SG) 22 , and Au 39 (SG) 24 , etc., mainly synthesized in
Tsukuda group [119]. The assembly of these coordination clusters could exhibit
unique characteristics, e.g., high stability, low cytotoxicity, and decent fluorescence
in the solid state and in solution, giving rise to promising application as a fluorescent probe in vivo and in vitro [120]. An example shown in Fig. 14.3 illustrates the
superatomic Ag 14 NCs stabilized by face-capping ligands [57].