Angew. Chem. Int. Ed.2016, 55, 1 5 Published: 21 April 2016 Esma - PowerPoint PPT Presentation

Angew. Chem. Int. Ed.2016, 55, 1 – 5 Published: 21 April 2016 Esma Khatun 28-05-16 1

Introduction  Atomically precise nanoclusters (NCs) are missing link between small molecules and nanoparticles.  Investigation of size dependent properties of NCs is important step towards understanding their potential applications such as catalysis.  The relationship between the structure of NCs and the protecting ligand still remains elusive.  Ligand bulkiness influence the structure and sizes of NCs, whereas the aromaticity of ligands seems less critical.  It was also found that the substituted benzenethiolates provide an effective means for tailoring the size and structure of NCs. In this paper …  They have reported X-ray single crystal structure of Au 30 (S-Adm) 18 and compared this structure with previously reported Au 30 S(S- t Bu) 18 .  They have provided a method for the discovery of possibly overlooked clusters because of their anomalous solubility. 2

HAuCl 4 ·3 H 2 O methanol Further reduction Stirred over a period of one week + HS-Adm with NaBH 4 [(C 8 H 17 ) 4 N] + Br Single-crystal growth Pure Au 30 (S-Adm) 18 Washed the crude product with was performed by NCs were extracted methanol and dichloromethane vapor diffusion of with benzene three times cyclohexane into a benzene solution of the NCs UV-Vis spectra of (A) Au 30 (S-Adm) 18 and (B) Au 30 (StBu) 18 and Au 30 S(S-tBu) 18 3

Time course of UV-Vis spectra of crude Au 30 (S- Adm) 18 NC. Time course of MALDI-MS spectra of crude Au 30 (S-Adm) 18 NC. 4

MALDI mass spectrum of pure The effect of DCM washing monitored Au 30 (S-Adm) 18 . with MALDI-MS 5

Overall structure of the Au 30 (S-Adm) 18 NC : A) Unit cell with a FCC superlattice arrangement ; B) top view; C) side view. Labels: magenta=Au, yellow=S, gray=C, white=H. The carbon tails are in wireframe mode 6

Anatomy of the structure of Au 30 (S-Adm) 18 NC: A,B) Top view of the Au 18 kernel and the addition of six dimeric staple motifs in two steps (in blue and green, respectively); C,D) Side view of the kernel and addition of six staples; E) Four-layer structure of the Au 18 kernel in a HCP manner; F,G) Six Au 4 assembled pattern in top and side views. Color labels: magenta=Au in the kernel, 7 light blue=Au in the staple, yellow=S.

Au-Au bond length distribution in the Au 30 (S-Adm) 18 nanocluster 8

Comparison of the Au 30 (S-Adm) 18 and Au 30 S(S- t Bu) 18 structures (carbon tails omitted). A) Au 18 kernel and staples; B) Au 18 core only; C) Au 18 core of HCP arrangement in Au 30 (S-Adm) 18 ; and D) Au 22 core and staples; E) Au 22 core only; F) Au 22 core of FCC arrangement in Au 30 S(S- t Bu) 18 9

Conclusion  They reported first example of gold NCs packed into an FCC superstructure.  Structural control of the Au 30 NC is realized by exploring the bulky adamantanethiol ligand.  The new cluster was obtained in 20 % yield (Au atom basis) via spontaneous size focusing under mild conditions that do not lead to any sulfido ligand as in the previously reported Au 30 S(S t Bu) 18 and Au 38 S 2 (S-Adm) 20.  The newly obtained Au 30 (S-Adm) 18 nanocluster shows distinct optical absorption features and peculiar solubility.  The structure of Au 30 (S-Adm) 18 is rather different from the previously reported Au 30 S(S t Bu) 18 cluster and also the theoretical structures of Au 30 (SH) 18 and Au 30 (S t Bu) 18. 10

DOI:10.1021/acs.chemmater.5b05008 Chem. Mater. March 24, 2016, 28, 3292−3297 11

Introduction  The typical routes for metal NC synthesis are (i) direct reduction of metal precursors in the presence of desired ligands, (ii) postsynthetic ligand-exchange (LE), and (iii) metal- exchange.  LE has recently been widely adopted for preparing novel gold NCs, but the use of LE in silver is rare, and its mechanism remains unexplored and poorly understood.  Particularly in silver, LE is exclusively based on a biphasic approach, where the starting and the final products move between two immiscible phases.  In this paper they designed a single phase LE reaction to understand the step-by-step conversion of Ag 44 (SR) 30 NCs to Ag 25 (SR) 18 NCs, and vice versa.  The single phase LE of Ag 44 (SPhF) 30 clusters (SPhF: 4-fluorobenzenethiolate) with 2,4 dimethylbenzenethiol (HSPhMe 2 ) initially led to the partial LE and then complete LE. After complete LE, the Ag 44 experienced structural distortions to form Ag 25 (SPhMe 2 ) 18 and intermediate NCs of sizes larger than Ag 44.  The formation of Ag 44 (SPhF) 30 from the Ag 25 (SPhMe 2 ) 18 was observed to occur by dimerization of Ag 25 followed by rearrangements. 12

UV−vis of Ag 44 (SPhCOOH) 30 and its HSPhMe 2 - exchanged product (red trace). Negative mode ESI MS of (A) Ag 44 (SPhCOOH) 30 and (B) its ligand- exchange (LE) product with HSPhMe 2 . The assigned peak of [Ag 44 (SPhCOOH) 30 ] 4- is due to as synthesized product and the other [Ag 44 (SPhCOOH) 29 ] 4- is due to a fragment of UV-vis absorption spectra of Ag 25 (SPhMe 2 ) 18 and its 13 parent cluster. HSPhCOOH exchanged product Ag 44 (SPhCOOH) 30

Time - dependent absorption study of Ag 44 (SPhF) 30 LE with HSPhMe 2 Time - dependent ESI MS study of [Ag 44 (SPhF) 30 ] 4– LE with HSPhMe 2 . The numbers with black, red, and blue color correspond to the number of Ag atoms, SPhF, and SPhMe 2 ligands, respectively. The numbers in green represent the charge of the clusters. Sharp peaks labelled with “$” are unknown impurity artifacts in the mass spectrometer without silver isotopic pattern, which are also present in the spectrum of a pure HPLC-grade DCM control. Mass spectral data 14 reveal the conversion of Ag 44 to Ag 25 through intermediate NCs.

(B) UV−vis study of Ag 25 (SPhMe 2 ) 18 LE with HSPhF. Red asterisk in B (on blue curve) shows the appearance of Ag 44 features. Inset: photographs of Ag 25 (SPhMe 2 ) 18 LE as a (A) Time-dependent ESI MS. Sharp peaks labeled with“$” are unknown impurity artifacts in the function of time. Color change from orange mass spectrometer without silver isotopic pattern, Ag 25 to red indicates the formation of Ag 44 which are also present in the spectrum of a pure cluster HPLC-grade DCM control 15

All color spheres: Ag atoms. Left half cycle: stage 1, partial LE; stage2, nearly complete LE; stage3, disproportionation; and stage 4, size focusing. Right half cycle: stage 1, partial LE; stage 2, dimerization; stage 3, disproportionation; and stage 4, size focusing 16

Conclusion  They have successfully designed a single phase LE reaction to completely elucidate the step-by-step transformation of Ag 44 (SR) 30 NCs to Ag 25 (SR) 18 NCs, and vice versa.  They have done detailed investigations of the LE with unprecedented atomic detail reveal that the Ag 44 to Ag 25 transformation occurs via a disproportionation mechanism, whereas its reverse occurs through an uncommon dimerization prior to disproportionation. 17

Future plan  As adamentanethiol produce some unusual structure, so we can try ligand induced reaction of Ag 54 with this Ag 25 thiol. It may form new silver cluster 2 , Ag 44 4 - H of interesting structural properties. e 2 S M P h h C P l S 2 H , 4 - 4 - F , 2 T P Ag 54 1,3-BDT Ag 29 18

Bader charge analysis on the total structure of Au 30 S(S- t Bu) 18 (A) and the DFT-derived structure of Au 30 (S- t -Bu) 18 (B). The“19th sulfur ” is shown by the arrow in (A). Colors of atoms, t -Bu blue 19 sticks, sulfur yellow, gold in ranging colors from blue (negative) to red (positive)