Superatomic Au25(SC2H5)18 Nanocluster under Pressure

Abstract

The past decade has witnessed significant advances in the synthesis and structure determination of atomically precise metal nanoclusters. However, little is known about the condensed matter properties of these nanosized metal nanoclusters packed in a crystal lattice under high pressure. Here using density functional theory calculations, we simulate the crystal of a representative superatomic gold cluster, Au₂₅(SR)₁₈ ⁰ (R = C₂H₅), under various pressures. At ambient conditions, Au₂₅(SC₂H₅)₁₈ ⁰ clusters are packed in a crystal via dispersion interactions; being a 7e superatom, each cluster carries a magnetic moment of 1 μ_B or one unpaired electron. Upon increasing compression (from 10 to 110 GPa), we observe the formation of intercluster Au-Au, Au-S, and S-S covalent bonds between staple motifs, thereby linking the clusters into a network. The pressure-induced structural change is accompanied by the vanishment of the magnetic moment and the semiconductor-to-metal transition. Our work shows that subjecting crystals of atomically precise metal nanoclusters to high pressures could lead to new crystalline states and physical properties.

Figure 1

Ambient pressure structure of the crystal phase of Au₂₅(SC₂H₅)₁₈⁰ cluster (a,c) and the corresponding Au–S framework omitting the ethyl (C₂H₅) groups (b,d), viewed along two different directions: (a,b) are projected along the c-axis; (c,d) are projected along the b-axis. Color code: Au, orange; S, green; C, gray; H, blue (lines with some highlighted balls). Same color code is used subsequently.

Figure 2

Au₂₅(SC₂H₅)₁₈ crystal at 10 GPa (C₂H₅ omitted for clarity): (a) viewed along the c-axis; (b) viewed along the b-axis; (c) perspective view of four 1D nanowires along the b-axis; (d,e) two different side views of the Au₂₅(SC₂H₅)₁₈ nanowire and the intercluster Au–Au linkages.

Figure 3

Au₂₅(SC₂H₅)₁₈ crystal at 25 GPa (C₂H₅ omitted for clarity): (a) viewed along the c-axis; (b) zoom-in on the Au–Au bond formed along the diagonal or a + b + c direction; (c) viewed along the b-axis; (d) zoom-in on the interstaple Au–S bonds and rectangle along the c-axis.

Figure 4

Au₂₅(SC₂H₅)₁₈ crystal at 50 GPa (C₂H₅ omitted for clarity): (a) viewed along the c-axis; (b) zoom-in view of the intercluster Au–Au bond formed along the a-axis; (c) zoom-in view of the intercluster Au–Au and S–S bonds along the diagonal (a + b + c); (d) viewed along the b-axis; (e) zoom-in view of the deformation of the intercluster −Au–S–Au–S– ring along the c-axis.

Figure 5

Au₂₅(SC₂H₅)₁₈ crystal at 80 GPa (C₂H₅ omitted for clarity): (a) viewed along the c-axis; (b) zoom-in view of the intercluster Au–S and S–S bonds along the b-axis; (c) viewed along the c-axis in a different perspective; (d) zoom-in view of the intercluster Au–S bonds along the a-axis.

Figure 6

Au₂₅(SC₂H₅)₁₈ crystal at 110 GPa (C₂H₅ omitted for clarity): (a) viewed along the c-axis; (b) zoom-in view of the intercluster Au–S and Au–Au bonds along a + b direction; (c) zoom-in view of the intercluster Au₄ parallelogram along the a-axis.

Figure 7

Packed structure of the Au₂₅(SC₂H₅)₁₈ crystal at various pressures showing also the C₂H₅ groups.

Figure 8

Variation of intracluster Au–Au distances of Au₂₅(SC₂H₅)₁₈ with pressure: Center-Shell, average distance from the central Au to the 12 Au atoms of the the icosahedral shell; Shell-Shell, average nearest-neighbor distance among the 12 Au atoms of the icosahedral shell; Shell-Staple, average nearest-neighbor distance between staple Au atoms and the icosahedral-shell Au atoms.

Figure 9

Structure of the Au₂₅(SC₂H₅)₁₈ cluster (left) and its Au–S framework (right) in the crystal at various pressures: (a) ambient; (b) 10 GPa; (c) 25 GPa; (d) 50 GPa; (e) 80 GPa; (f) 110 GPa.

Figure 10

Structural change of the Au₁₃ core with pressure. Note that 3.1 Å is used as the cutoff for drawing a bond between two Au atoms.

Figure 11

Band structure and density of states of Au₂₅(SC₂H₅)₁₈ crystal at various pressures: (a) ambient; (b) 10 GPa; (c) 25 GPa; (d) 50 GPa; (e) 80 GPa; (f) 110 GPa. The Fermi level is set as zero and denoted by the dashed red line.