Understanding and designing one-dimensional assemblies of ligand-protected metal nanoclusters

aDepartment of Applied Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku−ku, Tokyo 162−8601, Japan bRicoh Company, Ltd., Izumi−ku, Ebina, Kanagawa 243−0460, Japan cDepartment of Liberal Arts, Faculty of Engineering, Tokyo University of Science, Katsushika−ku, Tokyo 125−8585, Japan dResearch Institute for Science & Technology, Tokyo University of Science, Shinjuku−ku, Tokyo 162−8601, Japan


[Au4Pt2(SCH2Ph(CH3)3)8] 0 (b)
.5 mg (0.40 mmol) of HAuCl44H2O, 22.5 mg (0.10 mmol) of H2PtCl66H2O, and 317 mg (0.58 mmol) of (C8H17)4NBr was dissolved in 15 mL of THF. After stirring of 30 min, 433 mg (2.6 mmol) of (CH3)3PhCH2SH was added to the solution. After 2 h of reaction at room temperature, methanol was added in the reaction system to remove excess (CH3)3PhCH2SH. When methanol was added, precipitation was confirmed. This process was continued at least 3 times. After that, the product was extracted by toluene. Crystals was grown by vapor diffusion ( Figure S4). Toluene was used as good solvent and methanol was used as poor solvent.
[Au4Pt2(SCH2Ph t Bu)8] 0 (c) 164.5 mg (0.40 mmol) of HAuCl44H2O, 22.5 mg (0.10 mmol) of H2PtCl66H2O, and 317 mg (0.58 mmol) of (C8H17)4NBr was dissolved in 15 mL of THF. After 30 min of stirring, 468 mg (2.6 mmol) of t BuPhCH2SH was added to the solution. After 45 min of stirring, 6 mL of ice water containing 190 mg (5.0 mmol) of NaBH4 was added to the solution. This reaction was continued for 5 h under strong stirring at room temperature. Excess NaBH4 was removed by 1−2 times of water wash. Excess t BuPhCH2SH was removed by methanol wash at least 3 times. After that, the product was extracted by toluene. Expected product was separated by two times of GPC. In first time GPC, the second fraction was collected (first fraction, which included the large cluster, was removed) and in second time GPC, only the top of the first fraction was collected. Crystals was grown by vapor diffusion ( Figure S4). Toluene was used as good solvent and ethanol was used as poor solvent.
[Au4Pt2(SCH2PhCl)8] 0 (d) 164.5 mg (0.40 mmol) of HAuCl44H2O, 22.5 mg (0.10 mmol) of H2PtCl66H2O, and 317 mg (0.58 mmol) of (C8H17)4NBr was dissolved in 15 mL of THF. After 30 mins stirring, 413 mg (2.6 mmol) of ClPhCH2SH was added to the solution. After 1 h of stirring, 6 mL of ice water containing 190 mg (5.0 mmol) of NaBH4 was added to solution. This reaction was continued for 1 h under strong stirring at room temperature. Excess NaBH4 was removed by 1−2 times of water wash. Excess ClPhCH2SH was removed by methanol wash at least 3 times. After that, product was extracted by toluene. After the complete removal of ClPhCH2SH, the product was separated by gel permeation chromatography (GPC) and second peak from light side was collected. After GPC, the product was purified by an open column that was loaded with silica gel and a mixture of solvent (dichloromethane:hexane = 1:19) as starting eluent and slowly solvent polarity was increased (maximum 1:4). The first fraction was collected. Crystals was grown by vapor diffusion ( Figure S4). Toluene was used as good solvent and ethanol was used as poor solvent.
[Au4Pt2(SC2H4Ph)8] 0 (e) 164.5 mg (0.40 mmol) of HAuCl44H2O and 22.5 mg (0.10 mmol) of H2PtCl66H2O, and 317 mg (0.58 mmol) of (C8H17)4NBr was dissolved in 15 mL of THF. After 30 min of stirring, 180 μL (1.3 mmol) of PhC2H4SH was added to the solution. After 30 min of stirring, 6 mL of ice water containing 190 mg (5.0 mmol) of NaBH4 was added to the solution. This reaction was continued for 3 h under strong stirring at room temperature. After reaction, THF was removed by rotary evaporator. Excess NaBH4 was removed by 1−2 times of water wash. Excess PhC2H4SH was removed by methanol wash at least 3 times. Then, the product was extracted by toluene. The product was purified by an open column that was loaded with silica gel and a mixture of solvent (toluene:hexane = 3:2) as eluent, and the first fraction was collected. Crystal was got by vapor diffusion ( Figure S4). Toluene was used as good solvent and ethanol was used as poor solvent.
[Au4Pt2(SC3H7)8] 0 (f) 164.5 mg (0.40 mmol) of HAuCl44H2O, 22.5 mg (0.10 mmol) of H2PtCl66H2O, and 317 mg (0.58 mmol) of (C8H17)4NBr was dissolved in 15 mL of THF. After 30 min stirring, 118 μL (1.3 mmol) of C3H7SH was added to the solution. After 30 min of stirring, 6 mL of ice water containing 190 mg (5.0 mmol) of NaBH4 was added to the solution. This reaction was continued for 5 h under strong stirring at room temperature. After reaction, THF was removed by rotary evaporator. Excess NaBH4 was removed by 1−2 times S3 of water wash. Excess C3H7SH was removed by methanol wash at least 3 times. After that, the product was extracted by toluene. The product was purified by an open column that was loaded with silica gel and a mixture of solvent (dichloromethane:hexane = 1:19) as eluent at first time, after that increase the ratio slowly (maximum 1:4). The first fraction was collected. Crystal was got by vapor diffusion ( Figure S4). Toluene was used as good solvent and ethanol was used as poor solvent.

Characterization
Matrix assisted laser desorption/ionization (MALDI) mass spectra were collected by a spiral time-of-flight mass spectrometer (JEOL, JMSS3000) with a semiconductor laser (λ = 349 nm). DCTB 1 was used as the MALDI matrix. To minimize dissociation of the cluster induced by laser irradiation, the cluster-to-matrix ratio was fixed to 1:1000.
Electrospray ionization (ESI) mass spectrometry was performed using a time-of-flight mass spectrometer (Bruker, micrOTOF II). In these measurements, a cluster solution with a concentration of 1 mg/mL in dichloromethane/methanol (1:1 = v:v) containing CH3COOCs was electrosprayed at a flow rate of 1800 μL/h. Diffraction data for the crystals (b−e) was collected on a SMART APEX 2 Ultra equipped with an Apex II CCD diffractometer whereas for crystal a, it was collected in a SMART APEX fitted with SMART APEX I CCD diffractometer. From the collected data, unit cell, integration, absorption correction (multi-scan), and space group (based on intensity statistics and systematic absences) were determined using the Bruker APEX 3 software package. 3 Crystal structures were solved by the intrinsic phasing method in APEX 3. 2 Final refinements were performed by SHELXL-2018/3 4 using the Olex 2 platform 5 (Table S7−S9). X-ray photoelectron spectroscopy (XPS) analysis was performed using a JEOL JPS-9010MC electron spectrometer equipped with a chamber at a base pressure of ∼2 × 10 −8 Torr. X-rays from the Mg Kα line (1253.6 eV) were used for excitation. Binding energies were corrected using the binding energy of C 1s (284.6 eV).
Optical absorption spectra of the cluster dichloromethane-solution, solid sample and crystal sample were obtained at room temperature with a spectrometer (JASCO, V-670). Solid sample was prepared by just drying the solution sample. Thus, the solid sample should be the amorphous film. In the measurements of the crystal sample, we used many crystals for one measurement.

Stability of Clusters
All the [Au4Pt2(SR)8] 0 were stable in toluene solution. The formed crystals were also stable in toluene and in air. However, in dichloromethane solution, [Au4Pt2(SC2H4Ph)8] 0 deteriorated gradually and the precipitate was formed after a long time. The formed precipitate was not dissolved in solvent.

Theoretical Section
The electronic structures of [Au4Pt2(SC2H4Ph)8] 0 and [Au4Pt2(SCH2PhCl)8] 0 were calculated using firstprinciples calculations based on DFT. The ligand structures were optimized with gold, platinum and sulfur atoms fixed on the coordinates obtained by SCXRD ( Figure 3). Calculations were performed using QuantumATK 2018.06 package, 6,7 which is a commercial software for atomic scale simulation based on DFT using atomic orbital basis sets. The generalized gradient approximation (GGA) was used with the Perdew-Burke-Ernzerhof (PBE) functional (GGA.PBE) and a mesh cut-off energy of 80 Hartree. Convergence is taken to have been achieved when the force on each atom reaches 0.01 eV/Å.    Figure S6 and S7. b Å. c Enantiomer (see Figure S16). d Enantiomer of these clusters have same bond lengths for both R and S enantiomers.  Figure S6 and S7. b Å. c Enantiomer (see Figure S16). d Enantiomer of these clusters have same bond lengths for both R and S enantiomers.  Figure 3. b See Figure S10 and S11. c See Figure 2.  Figure S20.  Table  S2.       11 For a, b and e, Au 4f peak was fitted with two peaks, indicating that two kinds of Au atoms exist in these clusters (Table S5). In these clusters, the ligands are distributed in a comparatively isotopic manner in contract to the other clusters (c and d).

Additional Tables
Thus, the stress in the metal core, caused by the formation of this [Au4Pt2(SR)8] 0 structure, might be a little in the metal core of this group (a, b, and e) compared with the cases of other clusters (c and d). This little stress might lead to the generation of the two kinds of Au and Pt atoms in these clusters.         . These results demonstrate that the band gap increases with the decrease of inter-cluster distance, namely, the expansion of band gap is caused by the decrease of inter-cluster distance.

Structure Quality Indicators and Refinement Details
First initial model of each structure of all the clusters containing heavy atoms (metal and sulfur) and few carbon atoms of thiolates were solved by Shelxt using intrinsic phasing method. 3 Total structures of all the clusters were refined by full-matrix least-squares method against F 2 by SHELXL-2018/3 4 using Olex2 software. 5 Electron density corresponding to disordered solvent molecule of cluster e was SQUEEZED by PLATON 12 in Olex2 platform (Details is appended in cif file). Cluster a has positional disorder in its structure which was refined using PART command in SHELXL 2018/3 and ratio of PARTS is 0.89/0.11. Some high Q peaks appearing inside near to cluster cores are due to similar positional disorder which, however, could not be refined due to very low electron density (~4 for metal positions). Diffraction data of cluster d lack higher angle data (resolution below 1.1 Å) which were collected at very high exposure time (360 sec.). Even after repeated attempt, we could not get diffraction data having higher angle data for the same cluster. Except cluster a and d, the hydrogen atoms were placed at calculated positions with the exception of disordered H atoms, and their positions were refined with a riding model. During overall refinement, several restrain and constrain (ISOR, RIGU, SIMU, DFIX, AFIX 66 and EADP) have been used.