[Ag115S34(SCH2C6H4 tBu)47(dpph)6]: synthesis, crystal structure and NMR investigations of a soluble silver chalcogenide nanocluster

The soluble 115 nuclear silver cluster [Ag115S34(SCH2C6H4 tBu)47(dpph)6] was synthesized and fully characterized in solution and in the solid state.


Experimental Section
General procedures: All manipulations were performed under rigorous exclusion of moisture and oxygen in Schlenk-type glassware.Hydrocarbon solvents (toluene, npentane, n-heptane) were dried using an MBraun solvent purification system (SPS-800).Elemental analyses were carried out with an ElementarVario EL or Micro Cube.
[AgSCH 2 C 6 H 4 t Bu] was synthesized following known procedures for silver thiolates from t BuC 6 H 4 CH 2 SH and AgNO 3 . 1Bis(diphenylphosphino)hexane (dpph) was obtained from Sigma-Aldrich and used as received.
Synthesis of [Ag 115 S 34 (SCH 2 C 6 H 4 t Bu) 47 (dpph) 6 ] (1): The silver thiolate [AgSCH 2 C 6 H 4 t Bu] (0.35 g, 1.21 mmol, 1.00 eq.) and dpph (0.30 g, 0.66 mmol, 0.55 eq.) were suspended in toluene (30 mL).To the suspension, S(SiMe 3 ) 2 (0.09 mL, 76 mg, 0.43 mmol, 0.35 eq.) was added dropwise and a colour change from yellow to dark red was observed.The resulting clear solution was stirred for 7 days yielding a dark green solution.The solvent was removed under vacuum and the dark residue was extracted with n-heptane.After filtration, the formation of dark green needle-shaped crystals was observed on the wall of the Schlenk tube, which were separated from the mother liquor by decantation and finally dried under high vacuum. 1

UV-Vis measurements
UV-Vis spectra were recorded in CH 2 Cl 2 using freshly prepared samples on a Varian Cary 50 spectrophotometer.UV-Vis measurements in the solid state were performed with a LAMBDA 900 spectrometer (Perkin-Elmer) from a suspension of grinded crystals in mineral oil between two quartz plates under air at room temperature.The absorption wavelength of the HOMO-LUMO gap was calculated by laying the tangent line through the inflection point of the first increase of the curve.The intersection point of the tangent with the abscissa was considered as wavelength of the HOMO-LUMO gap.

Diffusion-ordered NMR spectroscopy
1 H-NMR DOSY spectra were recorded on a Bruker Avance HD III WB 500 MHz spectrometer equipped with a broadband diffusion probe at Bruker, Rheinstetten.Pulsed field gradient echo was applied with a gradient duration of 2 ms, a diffusion time of 40 ms while varying the gradient amplitude.Both, 31 P and 1 H diffusion show same order of diffusion coefficients within the experimental error.Due to the better signal-to-noise ratio 1 H diffusion is shown here.
The viscosity was taken from www.knovel.com.

Analytical ultracentrifugation (AUC)
For all AUC experiments we used a Beckman Coulter (Proteomelab XL-A/XL-I) analytical ultracentrifuge equipped with an AN-50 rotor and an optical detection system.Equal aliquots (440 ml) of [Ag 115 S 34 (SCH 2 C 6 H 4 t Bu) 47 (dpph) 6 ] in toluene and appropriate reference solvent were injected into a two-sector cell (12 mm optical path length) comprising sapphire windows and an Epon charcoal-filled centerpiece.Data were collected in sedimentation velocity mode with the absorption optics set to a detection wavelength of 320 nm where the sedimentation process is monitored by scanning the concentration profile, c(r, t), with respect to the radial distance from the rotor (r) and time (t).All experiments were performed at 40,000 rpm with a radial resolution of 0.001 cm; scans were recorded every 10 min for 4 hrs.The numerical fitting software SEDFIT was used to fit the absorbance profiles with Lamm's equation solutions to calculate the distribution of sedimentation and diffusion coefficients.We have analyzed our sedimentation velocity data to yield distributions of diffusion (D) and sedimentation (s) coefficients -using the method recently applied by Carney et al. to characterize dissolved gold nanoparticles. 4This method numerically fits the experimental data using Lamm's equation and a two-dimensional (2D) model for s and D coefficient distributions.The approach does not require a priori knowledge of particle density but instead offers an independent way of estimating it in addition to the particle molecular mass and its hydrodynamic radius.This is particularly useful for the characterization of core-shell nanoparticles because particle composition (i.e.shell thickness) can be estimated from these three numbers by mass conservation.There are specific assumptions inherent in this approach: (i) diffusion and sedimentation coefficient distributions are independent and (ii) diffusion contributions are fully resolved experimentally.
Figure S9 shows the resulting best fit to the AUC data of diffusion (D) and sedimentation (s) coefficient distributions.From these we have determined the average mass of the species present in solution.The mass distribution is dominated by a single peak centered at 22790 ± 500 Da.Hence, the particle has a diffusion coefficient of 2.2 x 10 -10 m 2 s -1 , which corresponds to a hydrodynamic diameter of 3.8 nm.Note: AUC using methylene chloride or chloroform was not possible because of centrifugation tube incompatibility

Electron microscopy
All the transmission electron microscopy measurements were performed using an aberration corrected FEI Titan 80-300 operated at 80 kV.Samples were prepared by dissolving them in toluene and adding one drop (1.5 μL) onto a Cu 200 mesh TEM grid.The grid was washed three times with toluene (2 μL), dried on air and inserted into the microscope.

Thermogravimetric analysis
Thermogravimetric analysis was performed using a Netzsch STA 409 C/CD device.The sample (20.900 mg) was heated under N 2 (25 l/min) from 300 K to 1000K with a heating rate of 2 K/min.

Crystallographic information
Low temperature single crystal X-ray diffraction was performed on a STOE STADIVARI diffractometer using Cu-Kα-radiation (λ = 1.54178).Using Olex2, 5  5.63/-3.47CCDC number 1507868 Though many crystals of 1 were X-rayed, refinement of the datasets was problematic due to significant disorder in the cluster core (especially the Ag positions) as well as in the ligand shell.The positions of all non-carbon were found in the differential Fourier map but refinement was only possible with a significant number of constraints and restraints.Still there are high peaks of remaining electron density inside the cluster core indicating additional disorder of the silver atoms which was not further modelled.The contribution of the electron density of lattice bound toluene molecules in the voids between the cluster molecules was calculated using the SQUEEZE algorithm 8 and the hkl file was modified.GOF and R values in the table base on the modified data.

Figure S1 :
Figure S1: Representative picture of dried single crystals of 1 under air in a weighing boat.

Figure S3 :
Figure S3: UV-Vis spectrum of 1 in the solid state.

Figure S6 :
Figure S6: Stacked 31 P{ 1 H} NMR spectra of 1 measured every hour over a period of 21 hours in CDCl 3 .

Figure S7 :
Figure S7: Stacked 1 H NMR spectra of 1 measured every hour over a period of 21 hours.

Figure S11 :
Figure S11: Screenshot 2-D sedimentation and diffusion coefficient distribution as fitted by SEDFIT.

Figure S12 :
Figure S12: TGA analysis of 1.At 1000°C, the residual mass is 53.07% of the mass at the beginning of the measurement.

Figure S13 :
Figure S13: Extended solid state structure of 1.The cluster molecules are illustrated as dummy atoms with r = 1.3 nm which were positioned in the center of the original cluster.Their arrangement corresponds to a distorted hcp with ABAB… layers highlighted in red and blue.

Figure S14 :
Figure S14: Complete S-substructure of 1. S 2-(light brown), S in RS -(yellow).Lines between S atoms are nonbinding and solely illustrate the geometric arrangement.
the structures were solved with the ShelXD 6 structure solution program the using Dual Space method and refined with the ShelXL 7 refinement package using Least Squares minimization.Hydrogen atoms were calculated on idealized positions.CCDC 1507868 contains detailed crystallographic data of this article, which can be obtained free of charge from the Cambridge Cristallographic Data Centre, www.ccdc.cam.ac.uk/data-request/cif.