Diphosphine-protected ultrasmall gold nanoclusters: opened icosahedral Au13 and heart-shaped Au8 clusters

Two ultrasmall gold clusters, Au13 and Au8, were identified as a distorted Ih icosahedral Au13 and edge-shared “core + 4exo” structure Au8S2 cores, respectively. They showed interesting luminescence and electrochemical properties.

1 Electronic Supplementary Material (ESI) for Chemical Science. This journal is © The Royal Society of Chemistry 2017

Experimental details
The precursor [Au 2 (dppm) 2 Cl 2 ] was synthesized via a literature procedure. 1 All reagents employed were commercially available and used as received without further purification. IR spectra were recorded on a PerkinElmer Spectrum Two in the frequency range of 4000-400 cm -1 . The elemental analyses (C and H) were determined on a Vario EL III analyzer. The diffuse-reflectance spectra were recorded on a UV/Vis spectrophotometer (Evolution 220, ISA-220 accessory, Thermo Scientific) using a built-in 10 mm silicon photodiode with a 60 mm Spectralon sphere. The excitation spectrum was recorded on a Lumina Fluorescence Spectrometer (Thermo Fisher) at the emission wavelength of 590 nm. Temperature-dependent photoluminescence measurements were carried out in an Edinburgh spectrofluorimeter (F920S) coupled with an Optistat DN cryostat (Oxford Instruments), and the ITC temperature controller and a pressure gauge were used to realize the variable-temperature measurement in the range of 80-300 K. Spectra were collected at different temperatures after a 5min homoiothermy. Time-resolved photoluminescence lifetime measurements were performed on the same instrument by using a time-correlated single-photon counting technique and the solid state quantum yields were determined on an Edinburgh FLS920 fluorescence spectrophotometer equipped with an integrating sphere. The highresolution electrospray mass spectrometry was performed on an Agilent 6510Q-TOF mass spectrometer. Differential pulse voltammetry (DPV) was conducted on an electrochemical work station model CHI-660 with a standard three-electrode system (glassy carbon working, Pt wire auxiliary, and Ag/Ag + reference); this study was performed on CH 2 Cl 2 solutions containing 0.1 M NBu n 4 PF 6 as supporting electrolyte in N 2 atmosphere. Inductively coupled plasma atomic emission spectroscopy was recorded in a Leeman ICP-AES Prodigy instrument for the elemental analysis of Au and P by digesting crystals in a 1:1 mixture of HNO 3

X-ray crystallography
Single crystals of SD/Au1·5Cl and SD/Au2·2Cl·2CH 2 Cl 2 with appropriate dimensions were chosen under an optical microscope and quickly coated with high vacuum grease (Dow Corning Corporation) to prevent decomposition. Intensity data and cell parameters were recorded at 173 K on a Bruker Apex II single crystal diffractometer, employing a Mo K α radiation ( = 0.71073 Å) and a CCD area detector.
The raw frame data were processed using SAINT and SADABS to yield the reflection data file. 5 The structure was solved using the charge-flipping algorithm, as implemented in the program SUPERFLIP 6 and refined by full-matrix least-squares techniques against F o 2 using the SHELXL program 7 through the OLEX2 interface. 8 Hydrogen atoms at carbon were placed in calculated positions and refined isotropically by using a riding model. Appropriate restraints or constraints were applied to the geometry and the atomic displacement parameters of the atoms in the cluster. All structures were examined using the Addsym subroutine of PLATON 9 to ensure that no additional symmetry could be applied to the models. Pertinent crystallographic data collection and refinement parameters are collated in Table S1. Selected bond lengths and angles are collated in Table S2.
A crystal of SD/Au2·2Cl·4CH 2 Cl 2 was attached to a nylon loop and mounted on a The intensity data were scaled and corrected for absorption, and final cell constants were calculated from the xyz centroids of strong reflections from the actual data S5 collections after integration. Space group was determined based on systematic absences and intensity statistics. The structure was solved using the charge-flipping algorithm, as implemented in the program SUPERFLIP 6 and refined by full-matrix least-squares techniques against F o 2 using the SHELXL program 7 through the OLEX2 interface. 8 Hydrogen atoms at carbon were placed in calculated positions and refined isotropically by using a riding model. Appropriate restraints or constraints were applied to the geometry and the atomic displacement parameters of the atoms in the cluster. Pertinent crystallographic data collection and refinement parameters are collated in Table S5.
Selected bond lengths and angles are collated in Table S6.
The computed optical absorption spectra for the two charge states demonstrates differences in the energy range of 450-800 nm. In SD/Au1 with the +5 charge state, the spectrum shows peaks around 757, 639, 594 and 505 nm while the +3 charge state demonstrates only one peak around 566 nm. The +5 charge state also gives high intensity and higher energy peaks with strong oscillator strengths in the wavelengths around 447, 427, 396 and 357 nm. The +3 charge state gives similar peaks in the higher energy range at 457, 425, 391 and 374 nm.