{'fraction_non_alphanumeric': 0.04488126349278491, 'fraction_numerical': 0.03499602317918418, 'mean_word_length': 4.656812339331619, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Synthesis and enantioseparation of chiral Au13 nanoclusters protected by bis-N-heterocyclic carbene ligands

A series of chiral Au13 nanoclusters were synthesized via the direct reduction of achiral dinuclear Au(i) halide complexes ligated by ortho-xylyl-linked bis-N-heterocyclic carbene (NHC) ligands. A broad range of functional groups are tolerated as wingtip substituents, allowing for the synthesis of a variety of functionalized chiral Au13 nanoclusters. Single crystal X-ray crystallography confirmed the molecular formula to be [Au13(bisNHC)5Cl2]Cl3, with a chiral helical arrangement of the five bidentate NHC ligands around the icosahedral Au13 core. This Au13 nanocluster is highly luminescent, with a quantum yield of 23%. The two enantiomers of the Au13 clusters can be separated by chiral HPLC, and the isolated enantiomers were characterized by circular dichroism spectroscopy. The clusters show remarkable stability, including configurational stability, opening the door to further investigation of the effect of chirality on these clusters.


Chiral high performance liquid chromatography
Chromatographic separation of cluster enantiomers was achieved on a Shimadzu LC-2010CHT HPLC system equipped with a Daicel CHIRALPAK IE-3 column (3µm, 250 mm×4.6 mm). A 10 mm path length UV-vis detector was used with the detection wavelength set to 350 nm. Analytes were eluted at a flow rate of 1.0 mL/min using MeOH/trifluoroacetic acid(TFA)/diethylamine(DEA) (100:0.1:0.1 volume ratio). For large-scale separations, a preparative scale Diacel CHIRALPAK IE-3 column (5µm, 250 mm×10.0 mm) was used with a flow rate of 2.0 mL/min and the same eluent system.

Circular dichroism spectroscopy
Circular dichroism (CD) spectra were recorded on a JASCO J-720WN CD-spectrometer using a 5 mm path length quartz cuvette. Samples were dissolved in dichloromethane, and a blank spectrum of solvent was subtracted from each sample spectrum. A scanning speed of 100 nm/min and data pitch of 0.1 nm was used to record four spectra, which were then averaged. All spectra were recorded at room temperature.

X-ray crystallography
Crystals of [3a]Cl3 of appropriate quality for X-ray diffraction studies were covered with a thin layer of hydrocarbon oil (Paratone-N). A suitable crystal was then selected, attached to a glass fiber or a microsampler, and quickly placed in a low-temperature stream of nitrogen. Data were collected at Nagoya University using a Rigaku FR-X with Pilatus 200K with fine-focus sealed tube Mo Ka radiation (l = 0.71073 Å), with the crystal cooled to −150 °C. The structure was solved using intrinsic phasing (SHELXT) and refined using SHELXL-2014. 11 2 Experimental procedures 2.1 Synthesis of dibenzimidazolium salts 1a-g General procedure for the synthesis of dibenzimidazolium salts 1a-e The following procedure for the preparation of dibenzimidazolium salts 1a-e was adapted from the literature. 12 A 25 mL glass pressure tube was charged with: (1) for salts 1a-c and 1e, the appropriate mono-alkylated benzimidazole (2.0 mmol) and 1,2-bis(chloromethyl)-or 1,2bis(bromomethyl)benzene (1.0 mmol); or (2) for salt 1d, 1,2-bis((1H-benzo[d]imidazol-1yl)methyl)benzene (1.0 mmol) and 1-(bromomethyl)-2,3,4,5,6-pentafluorobenzene (2.2 mmol). Acetonitrile (10 mL) was added, the tube was capped and the mixture was then heated in an 80 °C oil bath for 12 hours, and then cooled to room temperature. After cooling, the solvent was removed in vacuo to afford the crude solid. The crude solid was washed with EtOAc (3 x 10 mL) and dried in vacuo to afford the pure product as a white powder. Yields and characterization data for each compound are listed below.

General procedure for synthesis of gold nanoclusters [3a-e]X3
The synthesis of gold nanoclusters [3a-e]X3 was adapted from previously published procedures. 13 In a 50 mL round bottom flask, the appropriate gold complex 2a-e (ca. 40 mg, 0.04 mmol) was suspended in DCM/EtOH (2:1 v/v, 30 mL). The mixture was sonicated to form a homogenous suspension, then cooled to 0 °C in an ice bath. To the stirring solution was added a sonicated solution of sodium borohydride (3.0 mg, 0.08 mmol) in ethanol (99.5%, 10 mL). The mixture was stirred for 1 hour, then removed from the ice bath and stirred 2 hours at room temperature. Concentrated HCl (6.5 µL, 0.08 mmol) was added (see Figure S1 showing the positive effect of HCl treatment on cluster distribution), and the mixture was stirred for 1 hour at room temperature, then pumped to dryness in vacuo. The crude residue was extracted with EtOH (4 x 2 mL), and the supernatant solutions were filtered through celite, removing a beige to brown precipitate. The eluent from this filtration was dried in vacuo yielding the crude cluster mixture as a red-orange to dark red residue. The crude cluster mixtures were purified by silica gel column chromatography (Fuji Silysia Chromatorex PSQ60AB silica; 9:1 to 3:1 DCM/MeOH eluent; ~3x10 cm column size). The final red band on column yields the purified clusters [3a-e]X3 (cluster Rf (9:1 DCM/MeOH) = 0.3-0.4). See below for yields (based on Au) and characterization data.

Synthesis of [Au13(bisNHC Ph )5Br2]Br3 ([3b]Br3)
2b (41.7 mg, 0.04 mmol) afforded nanocluster [3b]Br3 as a red solid in 27 % yield after column chromatography (9.1 mg). The cluster was crystallized by dissolving the residue in DCM (~1 mL) and adding hexanes until a precipitate formed (~2 mL). The precipitate was redissolved by adding DCM dropwise, then the vial was capped and left at room temperature for 3 days, after which small red needles had formed. The crystals were washed with hexanes (2 x 0.5 mL) before being dried in vacuo for several hours (4.1 mg, 12 % crystal yield). 1 H NMR (CD2Cl2, 600 MHz): δ 7.91 (d, 3  Complexes 2f and 2g were reduced with sodium borohydride using the general method described above. The crude cluster mixtures were characterized by ESI-MS and showed only complicated mixtures of smaller gold complexes and some trace unidentifiable clusters, with no Au13 clusters present (see Figure S2). Attempts to purify the crude clusters by column chromatography yielded only mixtures, therefore further attempts at cluster synthesis using complexes 2f and 2g were not pursued.

Experimental procedure for large scale separation of racemic 3a by chiral HPLC
Cluster [3a]Cl3 (5.0 mg) was dissolved in 1.0 mL MeOH. Chromatographic separation of the cluster enantiomers was then carried out on a Shimadzu LC-2010CHT HPLC system equipped with a Diacel CHIRALPAK IE-3 column (5µm, 250 mm×10.0 mm) by direct injection of this solution. MeOH/TFA/DEA (1:0.1:0.1 volume ratio) was used as eluent with a flow rate of 2.0 mL/min. Once the first cluster peak started to elute, the column eluent was collected into a 50 mL vial. Due to partial peak overlap of the two enantiomers, the intermediate fractions at the tail end of the first enantiomer peak and the beginning of the second enantiomer peak were not collected in order to avoid significant mixing of the two enantiomers. The remainder of second enantiomer was then collected into a 50 mL vial. After separation, the solvents were removed in vacuo. To remove excess acid and amine impurities, the residues were dissolved in DCM and washed with water until the extracted aqueous phase was a neutral pH. The organic phase was then dried in vacuo to yield the cluster enantiomers as red residues (enantiomer 1: 2.0 mg; enantiomer 2: 1.5 mg). Each fraction was then re-evaluated by chiral HPLC to check the enantiomeric excess of the isolated fractions, as well as characterized by UV-vis spectroscopy ( Figure S3). ESI-MS and NMR spectroscopic data indicated partial anion exchange to the trifluoroacetate species [3a][CO2CF3]3 had most likely taken place, therefore each enantiomer was anion exchanged to the PF6 salt via the method described previously, which resulted in identical 1 H NMR spectroscopic peaks for each cluster enantiomer, which were consistent with independently prepared and isolated [3a][PF6]3 (see Figures S4-5). We have checked the separation of 3c-3e by chiral HPLC under the same conditions as 3a. Au13 nanoclusters 3c and 3d can be separated, while 3e can't be separated ( Figure S6).     Figure S6. Enantioseparation of 3c and 3d could be affected under the same conditions employed for 3a, however cluster 3e could not be resolved under these conditions.

Thermal stability of cluster 3a
Cluster [3a]Cl3 (0.3 mg) was dissolved in acetonitrile (3.0 mL). The sample was then transferred into a 1 cm 2 quartz cuvette fitted with a sealable screw cap top. The sample was heated at 60 o C in an oil bath, and changes to the UV-vis spectrum were monitored over time. The UV-vis spectrum showed no discernible changes over 3 days of heating (see Figure 6A in manuscript).