An Intermetallic Au 24 Ag 20 Superatom Nanocluster Stabilized by Labile Ligands

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1 Supporting information for An Intermetallic Au 24 Ag 20 Superatom Nanocluster Stabilized by Labile Ligands Yu Wang, 1 Haifeng Su, 1 Chaofa Xu, 1 Gang Li, 2,3 Lars Gell, 4 Shuichao Lin, 1 Zichao Tang, 2 Hannu Häkkinen, 4 Nanfeng Zheng 1 1 State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen , China 2 State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian , China 3 State Key Laboratory of Fine Chemicals, Institute of Coal Chemical Engineering, School of Chemical Engineering, Dalian University of Technology, 129 Street, Dalian , China 4 Departments of Physics and Chemistry, Nanoscience Center, University of Jyväskylä, FI Jyväskylä, Finland Experimental Details Reagents: Silver acetate (AgOAc, purity 98%), Pyridine-2-thiol (C 5 NH 5 S, purity 99%), 6-Mercaptonicotinic acid (C 6 H 5 NO 2 S, purity 98%), Mercaptosuccinic acid (C 4 H 6 O 4 S, purity 99%), Borane-tert-butylamine complex [(CH 3 ) 3 CNH 2 BH 3, purity 97%], Phenylacetylene (PhC CH, purity 98%) were purchasedfrom Alfa Aesar Chemical Reagent Co. Ltd. (Tianjin, China), Sodium hydroxide (NaOH, purity 99%), Chloroform (CHCl 3, A.R.), Methanol (CH 3 OH, A.R.) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). The water used in all experiments was ultrapure. All reagents were used as received without further purification. AuSMe 2 Cl was prepared according to a literature method. 1 Synthesis of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2, PA=PhC C -. 6mg AuSMe 2 Cl and 3mg AgCH 3 COO were first dissolved in the mixture solution of chloroform and methanol. The suspension was then cooled to 0 C in an ice bath. After 2.2µL phenylacetylene, and 0.22mg 2-pyridinethiol were added and stirred for 5 min, the reducing agent, tert-butylamine borane (3.6mg), was added to the mixture under vigorous stirring. The reaction was aging for 12 hr at 0 C. Solvents were removed through rotary evaporation and the obtained products were re-dissolved into chloroform for crystallization. Black block crystals were obtained through slow solvent evaporation in a yield of ~40% (based on Au). Preparation of alcohol soluble Au 24 Ag 20. During the synthesis of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2, pyridine-2-thiol was substituted by the same amount of 6-mercaptonicotinic acid while keeping other conditions the same. Solvents were removed through rotary evaporation and the obtained products were re-dissolved into S1

2 methanol and centrifuged for 3 min at 8000 r/min. The supernatant solution was subject to rotary evaporation again to afford block solids. Synthesis of phenylalkynyl stabilized Au 24 Ag 20. During the synthesis of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2, no pyridine-2-thiol was added while keeping other conditions the same. Black tiny crystals were obtained through slow solvent evaporation. Ligand exchange with mercaptosuccinic acid. To 1mL water suspension of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 (10mg), mercaptosuccinic acid ( mmol) and NaOH aqueous solution (1mL, M) were added. After being stirred overnight at room temperature, the solution became clear, indicating the cluster had been water soluble. Ligand exchange with pyridine-2-thiol. 3mg Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 were first dissolved in 1mL CH 2 Cl 2, then 0.66 mg pyridine-2-thiol were added. The solution was stirred overnight and diluted for ESI-MS characterization. Physical measurements. UV-Vis absorption spectra were recordedon a Varian Carry 5000 spectrophotometer. Mass spectrum was recorded on an Agilent Technologies ESI- TOF- MS. TGA- DSC was measured on STA449. TEM studies were performed on a TECNAI F-30 transmission electron microscope operating at 300 kv. Single-Crystal Analysis. The diffraction data were collected on an Agilent SuperNova X-Ray single crystal diffractometer using Cu Kα (λ= Å) micro-focus X-ray sources at 100 K. The data were processed using CrysAlisPro. 2 The structure was solved and refined using Full-matrix least-squares based on F 2 with program SHELXS-97 and SHELXL-97 within OLEX2. 3,4 Crystallographic data for Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 : monoclinic P2/n, a = (5) Å, b = (5) Å, c = (4) Å, α = 90, β = (3), γ = 90, V = (5) Å 3, Z = 2, Cu Kα, T= 100 K, 2θ = reflections were measured, of which were unique with R int = Final R 1 = 6.96%, wr 2 = for 934 parameters and reflections with I > 2σ(I). Computational Methods: We used density-functional theory (DFT) with projector augmented waves (PAW) as implemented in the real-space grid code-package GPAW. 5,6 Scalar relativistic effects for gold and silver are included in the used PAW setup. Total energy calculation and structure optimization was carried out by using the PBE 7 exchange correlation functional, real space grid spacing of 0.2 Å, and 0.05 ev/ Å convergence criteria for the residual forces acting on atoms. Angular momentum resolved projected density of state analysis was performed by projecting the Kohn-Sham orbitals to the center of mass of the full cluster (PDOS). The optical absorption spectrum for the optimized structure was calculated by using the linear response time-dependent DFT (LR-TDDFT) as implemented in GPAW. 8 The PBE functional was used for the exchange-correlation kernel, and the spacing in the real space grid was 0.25 Å. For plotting the spectra, the individual absorption lines were S2

3 folded with a Gaussian broadening of 0.05 ev. TPD-MS studies of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 : The TPD-MS experiment was performed on a home-made TPD-TOF analyzer. 3 mg of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 sample was pyrolyzed in a small tube heated by heating coil. A K-type thermocouple was put inside the sample tube and insulated from samples to measure the temperature. The heating coil was powered by a precise electric source and adjusted at interval of 10mV. The temperature of sample tube was ramping from room temperature to 400 C smoothly at speed of 5 K/min controlled by computer. The desorbed spices were ionized by a UV lamp at position very close to the sample tube with phonon energy of 10.6 ev, and then transferred to TOF analyzer by an ion optical system. The TOF analyzer had a resolution of more than 5000, and the sensitivity of ppb level. All those steps were processed in high vacuum of about Pa. The mass spectrum and sample temperature were acquired and recorded every second. Each spectrum is an accumulation of spectra gathered at interval of 100 s. An electron beam ion source (EBIS) was also used for the detection of Cl. During the temperature ramping from room temperature to 400 C, five major decomposition products [i.e., PhC CH (m/z =102), PySH (m/z =111), PySSPy (m/z = 220) and Cl (m/z = 35) were detected (Figure S5). The intensity-temperature profiles reveal that Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 underwent a rather complicated degradation process during the thermal treatment under vacuum. PhCCH started to come out from the cluster at 60 C and most of PhC CH had released before 120 C. Cl started to release at 108 C. Thiolate started to decompose at 100 C mainly into disulfide [i.e., PySSPy] with two maximum intensity observed at 120 C and 160 C. Upon the thermal treatment up to 250 C, only a trace amount of PySSPy was yielded. Reference: 1) Nishina, N.; Yamamoto, Y. Synlett 2007, 11, ) CrysAlis Pro Version (2011). Agilent Technologies Inc. Santa Clara, CA, USA. 3) Sheldrick, G. M. Acta Crystal. A 2008, 64, ) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Cryst. 2009, 42, ) Mortensen, J. J.; Hansen, L. B.; Jacobsen, K. W. Phys. Rev. B 2005, 71, ) Enkovaara, J.; Rostgaard, C.; Mortensen, J. J.; Chen, J.; Dulak, M.; Ferrighi, L.; Gavnholt, J.; Glinsvad, C.; Haikola, V.; Hansen, H. A.; Kristoffersen, H. H.; Kuisma, M.; Larsen, A. H.; Lehtovaara, L.; Ljungberg, M.; Lopez-Acevedo, O.; Moses, P. G.; Ojanen, J.; Olsen, T.; Petzold, V.; Romero, N. A.; Stausholm-Moller, J.; Strange, M.; Tritsaris, G. A.; Vanin, M.; Walter, M.; Hammer, B.; Häkkinen, H.; Madsen, G. K. H.; Nieminen, R. M.; Norskov, J. K.; Puska, M.; Rantala, T. T.; Schiotz, J.; Thygesen, K. S.; Jacobsen, K. W. J. Phys.: Cond. Matter 2010, 22, ) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev.Lett. 1996, 77, ) Walter, M.; Häkkinen, H.; Lehtovaara, L.; Puska, M.; Enkovaara, J.; Rostgaard, C.; Mortensen, J. J. J. Chem. Phys.2008, 128, S3

4 Figure S1. The packing structure of Au 24 Ag 20 (PA) 20 (SPy) 4 Cl 2 clusters in their single crystals. Color legend: gold and pink sphere, Au; green sphere, Ag; yellow sphere, S; blue sphere, N; cyan sphere, Cl; grey sphere, C. All hydrogen atoms are omitted for clarity. Figure S2. The detailed bonding structure -Au-L staple units on Ag 5 faces of the Ag 20 shell. The color legend: gold sphere, Au; green sphere, Ag; yellow sphere, S; blue sphere, N; grey sphere, C. All hydrogen atoms are omitted for clarity. S4

5 Abs(a.u.) Abs(a.u.) 2.0 Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 made without HSPy Wavelength(nm) Figure S3. UV-Vis spectra of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 (black trace) and cluster synthesized without the use of thiolates (red trace) in CHCl Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 made with HSPy replaced by HSPyCOOH Wavelength(nm) Figure S4. UV-Vis spectra of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 in CHCl 3 (black trace) and 6- mercaptonicotinic acid and phenylacetylene stabilized water-soluble Au 24 Ag 20 cluster in H 2 O (red trace). S5

6 Figure S5. Electrospray ionization (ESI) mass spectrum of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 after exchange with 2-HSPy. The two surface chloride anions on the cluster were replaced by two SPy -. Figure S6. Photographs and optical absorption spectra of the solutions of Au 24 Ag 20 nanocluster before and after ligand-exchange with mercaptosuccinic acid. S6

7 Figure S7. The accumulative ionization intensity of all decomposition products of Au 24 Ag 20 (SPy) 4 (PA) 20 Cl 2 from room temperature to 350 C. Figure S8. TEM images of the cluster before (a) and after (b) being heated in the solid-state form at 100 C for 1 hr. The solids were redissolved in CH 2 Cl 2 for the preparation of TEM samples. S7