Chiral Gold Nanoclusters: Atomic Level Origins of Chirality

Abstract

Chiral nanomaterials have received wide interest in many areas, but the exact origin of chirality at the atomic level remains elusive in many cases. With recent significant progress in atomically precise gold nanoclusters (e.g., thiolate-protected Au (SR) ), several origins of chirality have been unveiled based upon atomic structures determined by using single-crystal X-ray crystallography. The reported chiral Au (SR) structures explicitly reveal a predominant origin of chirality that arises from the Au-S chiral patterns at the metal-ligand interface, as opposed to the chiral arrangement of metal atoms in the inner core (i.e. kernel). In addition, chirality can also be introduced by a chiral ligand, manifested in the circular dichroism response from metal-based electronic transitions other than the ligand's own transition(s). Lastly, the chiral arrangement of carbon tails of the ligands has also been discovered in a very recent work on chiral Au (SR) and Au (SR) nanoclusters. Overall, the origins of chirality discovered in Au (SR) nanoclusters may provide models for the understanding of chirality origins in other types of nanomaterials and also constitute the basis for the development of various applications of chiral nanoparticles.

Amplified vibrational circular dichroism as a manifestation of the interaction between a water soluble gold nanocluster and cobalt salt

“…Chirality in nanoclusters is often observed and can be attributed to different reasons: (1) capping of the cluster by chiral ligands, (2) dissymmetric distribution of ligands (chiral arrangement of ligands around the metal core), and (3) inherent chirality of the metal core of the cluster. 4,5 Chiral metal nanoclusters have properties that make them attractive for applications in different domains like enantiomeric separation, enantioselective detection, asymmetric catalysis, pharmaceutical applications and others. [6][7][8][9][10][11] The chirality of metal nanoclusters can be probed by electronic circular dichroism (CD).…”

Functionalization, Modification, and Transformation of Platinum Chini Clusters

“…The resulting platinum browns may be viewed as molecular ultra‐small nanoparticles (atomically precise nanoclusters), whose structures and compositions are perfectly defined. It is noteworthy that these molecular nanoclusters may present pp, bcc, ccp, hcp or twinned hcp/ccp structures without any clear structure/size relationship, as found also in the case of Au‐thiolate nanoclusters , . Indeed, within this size regime (0.5–2 nm) M–L (L = surface ligand) interactions are as important as M–M ones in order to determine the geometric and electronic structures of these nanoclusters .…”

“…In all cases, the heteroelement, which retains its positive oxidation state, is segregated on the surface of a low valent Pt‐CO core cluster. Such decorations are reminiscent of the staple motives present on the surface of gold nanoclusters …”

“…The main difference between the Pt‐Cd and Pt‐Sn clusters consists in the fact that the Cd II fragments act as Lewis acids toward the Pt cage of the cluster that behaves as a Lewis base, whereas the opposite behavior is observed for Pt‐Sn carbonyl clusters (see above). Thus, [Pt 13 (CO) 12 Cd 10 Br 14 (dmf) 6 ] 2– and [Pt 19 (CO) 17 Cd 10 Br 14 (dmf) 6 ] 2– are composed of icosahedral [Pt 13 (CO) 12 ] 8– and bis‐icosahedral [Pt 19 (CO) 17 ] 8– cores decorated on the surface by {Cd 5 (µ‐Br) 5 Br 2 (dmf) 3 } 3+ , {Cd 5 (µ‐Br) 5 Br 3 (Me 2 CO) 2 } 2+ and {Cd 5 (µ‐Br) 5 Br(Me 2 CO) 4 } 4+ moieties, which are reminiscent of the staple‐motives present in Au‐thiolate nanoclusters and Au‐Fe‐CO low valent organometallic nanoclusters (Figure ) , , , , . Conversely, [H 2 Pt 26 (CO) 20 (CdBr) 12 ] 8– possesses a cubic close packed Pt 26 Cd 12 metal frame, closely related to that of [Pt 38 (CO) 44 ] 2– , decorated by CO and Br ligands.…”

“…Over the years, homoleptic Chini anions have been employed for the synthesis of globular platinum molecular nanoclusters (platinum browns) and bimetallic clusters, as precursors of platinum nanoparticles and nanowires, for the preparation of conductive materials and catalysts . A renewed interest for molecular (atomically precise) metal nanoclusters, including platinum ones, has recently appeared because of their relevance to nanochemistry, nanotechnologies and nanoscience . An attractive feature of Pt nanoclusters is their enhanced catalytic activity in several chemical and electrochemical reactions compared to larger Pt nanoparticles .…”