Assembling Au4 Tetrahedra to 2D and 3D Superatomic Crystals Based on Superatomic-Network Model.

Thiolate-protected gold nanoclusters (denoted as Au m (SR) n or Au n L m ) have received extensive attention both experimentally and theoretically. Understanding the growth mode of the Au4 unit in Au m (SR) n is of great significance for experimental synthesis and the search for new gold clusters. In this work, we first build six clusters of Au7(AuCl2)3, Au12(AuCl2)4, Au16(AuCl2)6, Au22(AuCl2)6, and Au30(AuCl2)6 with the Au4 unit as the basic building blocks. Density functional theory (DFT) calculations show that these newly designed clusters have high structural and electronic stabilities. Based on chemical bonding analysis, the electronic structures of these clusters follow the superatom network (SAN) model. Inspired by the cluster structures, we further predicted an Au4 two-dimensional (2D) monolayer and a three-dimensional (3D) crystal using graphene and diamond as templates, respectively. The computational results demonstrate that the two structures have high dynamic, thermal, and mechanical stabilities, and both structures exhibit metallic properties according to the band structures calculated at the HSE06 level. The chemical bonding analysis by the solid-state natural density partitioning (SSAdNDP) method indicates that they are superatomic crystals assembled by two electron Au4 - superatoms. With this construction strategy, the new bonding pattern and properties of Au n L m are studied and the structure types of gold are enriched.

Introduction

Thiolate-protected gold nanoclusters (donated as Au(SR) or AuL) have become a research hotspot in the field of nanoscience owing to their unique physicochemical properties.[1−7] Since the structure determination of Au102(SR)44[8] and Au25(SR)18–,[9,10] a large amount of Au(SR) has been successfully characterized.[11−17] Particularly, due to the relatively outstanding chemical stability of Au(SR), enormous efforts have been devoted to the study of Au(SR) both experimentally and theoretically.[18−21] On this basis, the structure evolution behaviors of Au(SR) were further explored.[22,23] According to X-ray single-crystal diffraction analyses of Au(SR), some gold atoms were arranged in an ordered Au core. The rest of the gold atoms were combined with the ligands to form a series of gold–thiolate protecting units (e.g., −RS–Au–SR– and −RS–Au–SR–Au–SR–, also called staple motifs) capping the Au core. As more Au(SR) structures were acquired, it was found that these clusters possessed diverse configurations of core structures. In addition, the types and the numbers of staple motifs were extremely sensitive to the number of gold atoms and thiolate ligands.

The structure determination of thiolate-protected gold nanoclusters provides an effective theoretical model for understanding the relationship between their structures and properties. The “divide and protect” model was first proposed by Häkkinen et al..[24] In this model, Au(SR) can be viewed as an Au core protected by different staple motifs.[25−30] Pei et al. developed a structural partition formula for Au(SR) (presented as Au[Au(SR)2][Au2(SR)3][Au3(SR)4]..., where a, a′, b, c, d, ... were integers[31]), which was first applied to the experimentally synthesized Au38(SR)24.[32] Following the proposed structural partition formula, a low-energy isomer of Au38(SR)24 was acquired and written as [Au]5+18[Au(SR)2]3[Au2(SR)3]6, which was in good agreement with later experimental reports.[33] Some Au(SR) clusters with magic numbers were well explained by the superatom complex (SAC) concept based on the jellium model,[34] such as Au15(SR)13,[35] Au25(SR)18–,[9] and Au44(SR)26,[36] having 2, 8, and 18 free valence electrons, respectively.

However, not all of the gold nanoclusters satisfy the framework of the SAC model. Cheng et al. developed the super valance bond (SVB) model[37−39] to explain the electronic stability of nonspherical shells of Au38(SR)24 metal clusters.[40] Nonetheless, the high stability of some low-symmetry ligand-protected gold nanoclusters also cannot be clearly explained. Subsequently, the superatom network (SAN) model[41] was proposed by Cheng et al., combined with the adaptive natural density partitioning (AdNDP) method, to explain the electronic stability. The Au core of these gold clusters can be viewed as networks of nonconjugated 4-center-2-electron (4c-2e) tetrahedral Au4 superatoms.[42] The experimentally synthesized Au18(SR)14,[43] Au20(SR)16,[44] Au22(SR)18,[45] and Au24(SR)20[46] are compounds with four valance electrons, following the SAN model. Au18(SR)14 is composed of an Au9 core and five staple motifs. According to the SAN model, the Au9 core can be regarded as a unique combination of two fused superatom octahedral Au6 units. The structure of Au20(SR)16 features a vertex-sharing bi-tetrahedral Au7 kernel and a “ring” motif Au8(SR)8. The structure of Au22(SR)18 also has an Au7 kernel, which is surrounded by one Au6(SR)6 and three Au3(SR)4 motifs. This Au7 kernel is formed by two Au4 units sharing vertices. The structure of Au24(SR)20 has a bi-tetrahedral Au8 kernel protected by two pairs of tetrameric staples. According to the SAN model, the Au kernels of these three clusters can all be seen as networks of two Au4 superatoms. In addition, Pei et al. reported many Au(SR) clusters with face-centered-cubic (fcc) type of Au4 kernel.[47,48] These clusters have a unique growth pattern and grow into a double-helix structure through the Au4 unit sharing the vertex, such as Au36(SR)24,[49] Au44(SR)28,[17] Au52(SR)32,[50] Au60(SR)36,[51] and Au76(SR)44[52] clusters. The thiolate-protected gold nanowire (RS-AuNW) can be obtained by infinite growth according to its growth mode. Moreover, the Au44(SR)28 cluster was confirmed by Jin et al.[53] Therefore, the developed theoretical models not only logicalize the existing structures but also facilitate the design of new structures.

Because the synthesis and characterization of thiolate-protected gold nanoclusters remain challenging, density functional theory (DFT) calculations play a prominent part in structural prediction.[54,55] The tetrahedral Au4 unit is a basic block in thiolate-protected gold nanoclusters and is often used to predict new Au(SR) clusters and crystal materials.[56−59] In this work, we predicted five Au(SR) clusters based on the SAN model, using the tetrahedral Au4 unit as basic building blocks, including Au10(SR)6, Au16(SR)8, Au28(SR)12, Au36(SR)12, and Au22(SR)12. DFT calculations show that these clusters have high electronic and structural stabilities. Based on the growth patterns of these clusters, a graphene-like two-dimensional (2D) Au4 monolayer and a diamond-like three-dimensional (3D) Au4 solid were predicted to be stable. Both the 2D-Au4 monolayer and 3D Au4 solid have strong light absorption ability. This cluster assembly material based on cluster superatoms can be regarded as an extension of the SAN complexes.

Computational Method and Details

Geometry optimizations, frequency analyses, and electronic properties calculations of all cluster structures were carried out at the PBE[60] level of theory with the def2tzvp basis set[61] as implemented in the Gaussian 09 package.[62] Considering the computational cost, we used halogen (Cl) instead of thiolate (SR) to complete the calculation because Cl and SR are isolobal ligands.[63] All clusters were verified by frequency check to be true local minimum on the potential energy surface. DFT calculations of the Au4 monolayer and the Au4 bulk structure were performed in the Vienna ab initio simulation page (VASP) code.[64] The ion–electron interaction was described by the projector-augmented plane-wave (PAW) method.[65] Generalized gradient approximation (GGA)[60] was used for treating the exchange-correlation functional within the Perdew–Burke–Ernzerhof (PBE)[66] functional form. During the geometry optimizations, the energy cutoff of the plane wave was set to 450 eV. The Brillouin zone was represented by 5 × 5 × 1 and 6 × 6 × 6 Monkhorst–Pack k-point mesh for the Au4 monolayer and Au4 solid, respectively. The Hellmann–Feynman force convergence criterion was less than 0.01 eV Å–1 and the self-consistent field procedures were performed with an energy of 10–6 eV for the total energy. To eliminate the effect between adjacent Au4 layers, a vacuum distance of ∼15 Å was used. For multilayers, the intralayer van der Waals interactions were corrected by the DFT-D3 approach in Grimme’s scheme.[67]

To research the dynamic stability of the materials, we utilized the PHONOPY code[68] to calculate the phonon dispersion spectra. To assess the thermal stability of the periodical structure, ab initio molecular dynamic (AIMD) was carried out by the Nosé–Hoover method.[69] The AIMD simulation in an NVT canonical ensemble (constant number, volume, and temperature) with a time step of 1.0 fs lasts for 5 ps at 300 K. In addition, the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional[70] was used to reach more accurate electronic band structures. The chemical bonding analyses were calculated by adopting the (solid state) adaptive natural density partitioning ((SS)AdNDP) method,[71−74] which can demonstrate the chemical bonding pattern of delocalized bonds.[75,76] We chose the def2tzvp basis set for the plane-wave projection of the electron density matrix in the solid-state natural density partitioning SSAdNDP calculation.

Results and Discussion

Geometric and Electronic Characters of Au7(AuCl2)3, Au12(AuCl2)4, Au22(AuCl2)6, and Au30(AuCl2)6 Clusters

It is well known that a series of Au(SR) clusters have been successfully synthesized and designed with the bi-tetrahedral Au7 unit as a building block, such as Au20(SR)16,[77] Au22(SR)18,[47] and Au24(SR)20.[78] Here, according to the SAN model, we build an Au7(AuCl2)3 cluster, which features a vertex-sharing bi-tetrahedral Au7 core protected by three [Cl–Au–Cl] ligands. The optimized Au7(AuCl2)3 cluster with a fairly large highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap (EHL) of 2.47 eV is shown in Figure a, indicating high electronic stability. The average Au–Au bond length within the Au4 tetrahedrons is 2.70–2.77 Å. The bond lengths of Au–Cl are 2.39 Å. Au (5d106s1) has one free valence electron, and each Au atom of the three Au atoms in the Au4 unit transfers 0.5 valence electrons to the surrounding Cl atoms to satisfy the 8 electron rule. The remaining centered Au atom contributes 0.5 valence electrons to each Au4 unit. Thus, the whole Au4 unit has two valence electrons in total, donated as the Au4 (2e) superatom. To clearly understand the bonding mode of the monomer, chemical bonding analyses were carried out by the AdNDP method. The results show that Au7(AuCl2) has two 4c-2e Au4 σ bonds with the occupancy numbers (ON) = 1.90 |e| and twelve 2c-2e Au–Cl σ bonds with ON = 1.97 |e|.

Figure 1

Optimized geometric structure and AdNDP localized natural bonding orbitals of (a) Au7(AuCl2)3, (b) Au12(AuCl2)4, (c) Au22(AuCl2)6, and (d) Au30(AuCl2)6 clusters. Au, yellow and Cl, green.

Next, we adopt Au7(AuCl2) as a monomer to design a dimer. The dimer is composed of four [Cl–Au–Cl] ligands and an Au12 core, which is formed by two bi-tetrahedral Au7 units via sharing two Au atoms. Figure b shows that the optimized dimer Au12(AuCl2)4 has an EHL of 1.86 eV, and the dimer contains four 4c-2e Au4 σ bonds with ON = 1.90 |e|. The bond lengths of Au–Cl are 2.39 Å, and the Au–Au bond lengths within the Au4 tetrahedra are in the range of 2.70–2.80 Å. Following a similar construction method, tetramer Au22(AuCl2)6 and hexamer Au30(AuCl2)6 are designed and shown in Figure c,d, respectively. Their Au–Au bond lengths within the Au4 tetrahedra are in the range of 2.70–2.83 Å, and the Au–Cl bond lengths are 2.41 Å. The AdNDP results indicate that Au22(AuCl2)6 and Au30(AuCl2)6 clusters have eight 4c-2e σ bonds with ON = 1.82 |e| and twelve 4c-2e σ bonds with ON = 1.81 |e|, respectively.

The nucleus-independent chemical shift (NICS) method[79] is widely used to measure the aromaticity of delocalized bonds. It has been successfully used to confirm many Au4 superatomic systems.[41,42] Here, we perform a NICS method to further prove the existence of Au4 superatoms. We take the Au7(AuCl2)3 cluster as a test. The NICS scan points are located at the geometric center of Au4 units, and the corresponding NICS values are both −26.8 ppm, which is much more negative than that of benzene (−9.7 ppm).[80] This strong aromaticity indicates electron delocalization with shell closure in the Au4 core, which confirms the presence of Au4 superatoms.

Geometric Structure, Stability, and Electronic Character of the Au4 Monolayer

The cyclic hexamer Au30(AuCl2)6 has a similar structure to benzene and can be extended to a graphene-like Au4 monolayer. As shown in Figure a, the space group of the monolayer is P6/mmm (number 191, a = b = 5.45 Å, and c = 15 Å), where one unit cell is composed of eight Au atoms. Similar to the clusters, adjacent Au4 units are connected by a shared Au atom. The structure of the Au4 monolayer is a three-layered sandwich structure, similar to the recently discovered AlB6 monolayer with high stability, unique motif, and superconductivity.[81] The average length of the Au–Au bond in this monolayer is 2.77 Å. For the Au4 monolayer, we use the SSAdNDP method to analyze its bond patterns. According to the results, there are five d-type localized lone pairs (LPs) on each Au atom with ON = 1.91–2.00 |e| as shown in Figure S1. Therefore, it is implied that they are not involved in the bonding process. Figure b shows the 4c-2e Au4 σ bonds (ON = 1.82 |e|) in each Au4 unit. Similar to the previously predicted Cu2Si and Cu2Ge monolayers, their special 4c-2e bonds lead to strong connections between atoms, thereby enhancing the stability of the structure.[82,83]

Figure 2

(a) Top and side views of the Au4 monolayer. The primitive cell is outlined by red lines in this work. (b) Schematic of the SSAdNDP chemical bonding pattern of the Au4 monolayer. (c) Phonon spectrum of the Au4 monolayer along the high-symmetry points in the Brillouin zone.

Although the Au4 monolayer has rather intriguing structural properties, the stability of the structure is still unknown. To assess the relative stability of this material, we first calculate the cohesive energy Ecoh,Au4-monolayer = (mEAu-atom – EAu4-monolayer)/m, where m, EAu-atom, and EAu4-monolayer are the atom number, the total energies of a single Au atom, and one unit cell of the Au4 monolayer, respectively. The cohesive energy of the Au4 monolayer is 2.63 eV per atom, indicating that the Au4 monolayer has a strongly bonded network. To verify the kinetic stability of the Au4 monolayer, we perform phonon dispersion calculations for its geometric configuration (Figure c). All positive frequencies in the first Brillouin zone indicate kinetic stability. Moreover, we perform AIMD simulations with a supercell (containing 4 × 4 × 1 primitive cell involving 144 Au atoms) to examine its thermal stability, where the time step and time duration are 1.0 fs and 5 ps, respectively. As shown in Figure a, the Au4 monolayer can maintain its structural integrity at 300 K in AIMD simulations, indicating its thermal stability. Moreover, it can be seen from Figure S2 that the structure of the Au4 monolayer can maintain its integrity, whereas the structure breaks at 1000 K. Therefore, the melting point of the Au4 monolayer is between 700 and 1000 K. We also study the mechanical properties of the Au4 monolayer by calculating the elastic constants, Young’s modulus (E), and Poisson’s ratio (ν), and the results are listed in Table . For this monolayer, the elastic constants satisfy C11C22 – C122 > 0 and C66 > 0, suggesting its mechanical stability.[84]

Figure 3

(a) Energy fluctuation depending on the simulated time at 300 K and the snapshot of the Au4 monolayer after a 5 ps AIMD simulation. (b) Schematic of the cleavage process of the Au4 monolayer.

Table 1

Calculated Elastic Constants (C, in N m–1), Young’s Modulus (E, in N m–1), and Poisson’s Ratio (ν) for the Au4 Monolayer

structure	C11	C12	C66	E	ν
2D-Au4	71.06	29.34	20.86	58.95	0.41

Generally speaking, mechanical and liquid striping techniques are widely used to prepare most 2D materials.[85,86] Here, the process of mechanical striping is studied theoretically. The cleavage energy (Ecl) is the minimum energy required during the exfoliation process. We first constructed a five-layer slab, four layers of which were fixed with the monolayer being removable. As shown in the schematic of Figure b, d is the separation distance between the exfoliated top layer and the remanent four layers, and d0 (2.70 Å) is the original interlayer distance of bulk. The cleavage energy is defined as Ecl = Ed – EAu4-monolayer, where Ed and EAu4-monolayer are the separation distance d and no separation energy between the exfoliated top layer and the remanent four layers, respectively.[87,88] It can be seen that as the separation distance increases, the cleavage energy gradually increases, and finally converges to a constant value of 0.91 J m–2, which has the same order of magnitude as the experimentally measured value of graphene (0.37 J m–2).[89] Therefore, the results indicate that it is possible to exfoliate Au4 monolayer by the mechanical method from its bulk structure experimentally.

We further investigated the electronic properties of the Au4 monolayer by calculating the band structures and projected density of states (PDOS) at the HSE06 level. As shown in Figure a, there is a valence band (VB) passing through the Fermi level, and the monolayer exhibits metallic properties. It is also worth noting that the valence band maximum (VBM) is slightly separated from the conduction band minimum (CBM), so there is a tendency to open the band gap. The projected density of states (PDOS) show that the valence band (VB) energy states are mainly contributed by the d orbitals of Au atoms.

Figure 4

(a) Electronic band structure and projected density of states (PDOS) of the Au4 monolayer at the HSE06 level. Fermi levels are set to zero and marked with pink dashed lines. (b) Optical absorption coefficient along the x- and z-directions of the Au4 monolayer.

The unique optical properties of gold nanomaterials make it of great application value in surface plasmon optics, information storage, surface-enhanced Raman scattering (SERS), and sensing devices. We further calculated the optical absorption spectrum of the Au4 monolayer by the HSE06 method as shown in Figure b. The area within the dotted line is in the visible-light range. The Au4 monolayer has no anisotropy in x- and y-directions, so we analyze the optical properties in the x- and z-directions. The Au4 monolayer has very obvious light absorption in the infrared, visible, and ultraviolet regions in the z-direction, while it only has strong absorption in the visible and ultraviolet regions in the x-direction. The intensity of light absorption in the visible region is particularly important because visible light contains almost half the energy of sunlight. In the visible-light region, the absorption coefficients in both the x- and z-directions reach 105 cm–1, indicating a high absorption efficiency of solar energy. Moreover, it can be seen that the Au4 monolayer has a stronger light absorption ability in the ultraviolet region. Therefore, the Au4 monolayer has a large absorption coefficient in the visible and ultraviolet regions and may be a very promising optoelectronic material in the future.

Geometric and Electronic Characters of the Au16(AuCl2)6 Cluster

In a similar approach, we build an Au16(AuCl2)6 cluster, which is composed of six [Cl–Au–Cl] ligands and an Au16 core. To highlight the Au core, we used a different color (blue) for the ligand Au atoms to distinguish them. The core of the Au16(AuCl2)6 cluster contains five vertex-sharing Au4 units, which are protected by six [Cl–Au–Cl] stable motifs. The optimized geometric configuration of Au16(AuCl2)6 with a large EHL of 2.47 eV is shown in Figure . The average Au–Au bond length is 2.72–2.75 Å. There are two types of Au–Cl bonds with bond lengths of 2.39 Å (connected with the Au4 unit) and 2.32 Å (connected with the ligand Au atom). The chemical bonding pattern of Au16(AuCl2)6 clusters is studied by the AdNDP method. As shown in Figure , there are five 4c-2e Au4 σ bonds with ON = 1.86 |e|. In addition, two different Au–Cl σ bonds with ON = 1.97 |e| are also shown.

Figure 5

Optimized geometric structure and AdNDP localized natural bonding orbitals of the Au16(AuCl2)6 cluster. Au, yellow and Cl, green.

Geometric Structure, Stability, and Electronic Character of the Au4 Crystal

The Au16 core of the Au16(AuCl2)6 cluster is similar to an sp3 hybrid C atom. Motivated by sp3 hybrid C atoms in diamond, a super-tetrahedral structure can be designed by replacing C atoms with regular tetrahedral units, and some previous theoretical works have proved this.[90−92] Therefore, we use the diamond lattice as a template where all carbon atoms are substituted by Au4 units, then connected all of the Au4 units by sharing vertices to design a diamond-like Au4 crystal. The fully optimized structure of the designed Au4 crystal is shown in Figure a. One unit cell of the Au4 crystal contains 16 Au atoms, the space group is Fd3̅m (number 227) and the lattice constants are a = b = c = 7.76 Å. All of the Au–Au bond lengths are 2.74 Å, slightly shorter than the average Au–Au bond length (2.77 Å) in the Au4 monolayer. To gain insight into the chemical bonds in the Au4 crystal, the SSAdNDP method was used. The SSAdNDP results indicate that there are five lone pairs of electrons on each Au atom (Figure S3), and another valence electron forms 4c-2e σ bonds in the Au4 unit (Figure b). Thus, the Au4 crystal can be viewed as a superatomic crystal stacked by Au4 (2e) superatoms.

Figure 6

(a) Unit cell structure of the Au4 crystal. (b) Bond and occupation number of Au4 unit cell obtained from SSAdNDP analyses. (c) Phonon spectrum for the Au4 crystal.

As shown in Table , compared with the gold in the classic fcc phase, the density of the Au4 crystal is much smaller due to its larger pore size. The cohesive energy is calculated by Ecoh = (mEAu-atom – EAu-bulk)/m, where m, EAu-atom, and EAu-bulk are the atom number, the total energies of a single Au atom, and one unit cell in the Au4 crystal, respectively. The cohesive energy of the Au4 crystal is 2.75 eV atom–1, which is slightly smaller than that of the fcc-phase Au of 3.11 eV atom–1. The Au4 crystal has a higher strain strength and lower plasticity compared with the fcc-phase Au from the results of Young’s modulus and Poisson’s ratio value. Moreover, the Vickers hardness calculated with the same empirical formula[93] also illustrates this point. The computed phonon spectra of the Au4 crystal exhibit all positive phonon frequencies (Figure c), confirming its dynamic stability. To test the thermal stability of the Au4 crystal, we carry out AIMD simulations under an NVT ensemble with the temperature controlled at 300, 700, and 1000 K. Here, a supercell containing a 4 × 2 primitive cell (involving 128 Au atoms) was adopted as the initial configuration. The AIMD simulations lasted for 5 ps with a time step of 1 fs. As shown in Figure S4, after 5 ps simulations at 1000 K, the structure is still intact and the total energy remains almost unchanged, which suggests its high thermal stability. The Au4 crystal can be used at extremely high temperatures.

Table 2

Density (ρ, g cm–3), Cohesive Energy (Ecoh, eV), Young’s Modulus (E, GPa), Poisson’s Ratio (ν), and Vickers Hardness (H, GPa) for the Au4 Crystala

structure	ρ	Ecoh	E	ν	H
Au4 bulk	11.18	2.75	173.00	0.20	13.65
fcc-Au	18.03	3.11	81.30	0.45	1.81

For comparison, the experimental values of the fcc-Au structure are also given.

In comparison with the fcc-phase Au, the Au4 crystal presents different structural properties and bonding patterns that may lead to unexpected physical properties. We calculated the band structure of the fcc-phase Au and the Au4 crystal at the HSE06 level. As shown in Figure , both structures are metallic. The VB and conduction band (CB) of the fcc-phase Au are slightly overlapped, while the VB and CB of the Au4 crystal phase are clearly separated, and there is a tendency to form a semiconductor. This may be due to the partial electronic localization in the Au4 unit resulting from the special geometric structure of the Au4 crystal. Similarly, we calculated the light absorption coefficients of the Au4 crystal and fcc-phase Au by the HSE06 method, as shown in Figure S5. The area within the dotted line is in the visible-light range. We can clearly see that the Au4 crystal and the fcc-phase Au have great light absorption in the visible and ultraviolet regions, and even their absorption coefficients in the ultraviolet region reach 106 cm–1. The large absorption coefficient of the Au4 crystal makes it a potential material for photovoltaic solar cells and optoelectronic devices.

Figure 7

Electronic band structure of (a) fcc-phase Au and (b) Au4 crystal at the HSE06 level. The Fermi level is set at zero and marked with pink dashed lines.

Conclusions

To summarize, we first adopt the Au4 unit and [Cl–Au–Cl] as basic building blocks to construct Au7(AuCl2)3, Au12(AuCl2)4, Au22(AuCl2)6, Au30(AuCl2)6, and Au16(AuCl2)6 clusters. DFT calculations show that each cluster is a real local minimum on the potential energy surface and has a large HOMO–LUMO energy gap. In particular, the HOMO–LUMO energy gap of the Au7(AuCl2)3 cluster is 2.47 eV. AdNDP and NICS analyses reveal that all of the structures follow the SAN model. Based on Au30(AuCl2)6 and Au16(AuCl2)6 clusters, we use the graphene and diamond as templates to design a graphene-like Au4 monolayer and a diamond-like Au4 crystal. The computational results demonstrate that both Au4 monolayer and Au4 crystal have a high dynamic, thermal, and mechanical stability. The Au4 crystal can remain stable even at 1000 K. The cleavage energy of the Au4 monolayer is similar to that of graphene, indicating that the exfoliation of its bulk form to achieve freestanding monolayers is very feasible. The calculated band structures of both the Au4 monolayer and the Au4 crystal at the HSE06 level show metallicity. The optical properties show that the Au4 monolayer has a large light absorption coefficient. The SSAdNDP analyses indicate that these two structures are composed of Au4 (2e) units, thus they can be viewed as superatomic crystals. All these findings provide new insights for the study of thiolate-protected gold nanoclusters. In addition, we predicted two new types of superatom crystal gold, enriching the structure types of gold.