Atomically precise photothermal nanomachines.

Interfacing molecular machines to inorganic nanoparticles can, in principle, lead to hybrid nanomachines with extended functions. Here we demonstrate a ligand engineering approach to develop atomically precise hybrid nanomachines by interfacing gold nanoclusters with tetraphenylethylene molecular rotors. When gold nanoclusters are irradiated with near-infrared light, the rotation of surface-decorated tetraphenylethylene moieties actively dissipates the absorbed energy to sustain the photothermal nanomachine with an intact structure and steady efficiency. Solid-state nuclear magnetic resonance and femtosecond transient absorption spectroscopy reveal that the photogenerated hot electrons are rapidly cooled down within picoseconds via electron-phonon coupling in the nanomachine. We find that the nanomachine remains structurally and functionally intact in mammalian cells and in vivo. A single dose of near-infrared irradiation can effectively ablate tumours without recurrence in tumour-bearing mice, which shows promise in the development of nanomachine-based theranostics.

N-Heterocyclic Carbene-Stabilized Gold Nanoclusters with Organometallic Motifs for Promoting Catalysis.

The complexity of heterogeneous metal catalysts makes it challenging to gain insights into their catalytic mechanisms. Thus, there exists a huge gap between heterogeneous catalysis and organometallic catalysis. With the success in the preparation of highly robust atomically precise metal nanocluster catalysts (i.e., [Au16(NHC-1)5(PA)3Br2]3+ and [Au17(NHC-1)4(PA)4Br4]+, where NHC-1 is a bidentate NHC ligand, and PA is phenylacetylide) with surface organometallic motifs anchored on the metallic core, we demonstrate in this work how the metallic core works synergistically with the surface organometallic motifs to enhance the catalysis. More importantly, the discovery allows the development of highly stable and recyclable heterogeneous metal catalysts to achieve efficient hydroamination of alkynes with an extremely low catalyst dosage (0.002 mol %), helping bridge the gap between heterogeneous and homogeneous metal catalysis. The surface modification of metal nanocatalysts with organometallic motifs provides a new design principle of metal catalysts with enhanced catalysis.

Tertiary Chiral Nanostructures from C-H⋠⋠⋠F Directed Assembly of Chiroptical Superatoms.

We report the synthesis and structure of tertiary chiral nanostructures with 100 % optical purity. A novel synthetic strategy, using chiral reducing agent, R and S-BINAPCuBH4 (BINAP is 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl), is developed to access to atomically precise, intrinsically chiral [Au7 Ag6 Cu2 (R- or S-BINAP)3 (SCH2 Ph)6 ]SbF6 nanoclusters in one-pot synthesis. The clusters represent the first tri-metallic superatoms with inherent chirality and fair stability. Both metal distribution (primary) and ligand arrangement (secondary) of the enantiomers exhibited perfect mirror images, and unprecedentedly, the self-assembly driven by the C-H⋅⋅⋅F interaction between the phenyl groups of the superatom moieties and SbF6 - anions induced the formation of bio-mimic left- and right-handed helices, achieving the tertiary chiral nanostructures. DFT calculations revealed the connections between the molecular details and chiral optical activity.

An All-Alkynyl Protected 74-Nuclei Silver(I)-Copper(I)-Oxo Nanocluster: Oxo-Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation.

The hardness of oxo ions (O2- ) means that coinage-metal (Cu, Ag, Au) clusters supported by oxo ions (O2- ) are rare. Herein, a novel µ4 -oxo supported all-alkynyl-protected silver(I)-copper(I) nanocluster [Ag74-x Cux O12 (PhC≡C)50 ] (NC-1, avg. x=37.9) is characterized. NC-1 is the highest nuclearity silver-copper heterometallic cluster and contains an unprecedented twelve interstitial µ4 -oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH4 . The oxo ions induce the hierarchical aggregation of CuI and AgI ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw-puzzle-like cluster packing incorporating rare intermolecular C-H⋅⋅⋅metal agostic interactions and solvent molecules. This work not only reveals a new category of high-nuclearity coinage-metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage-metal clusters.

Highly Robust but Surface-Active: An N-Heterocyclic Carbene-Stabilized Au25 Nanocluster.

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface-active for liquid-phase catalysis without any pre-treatment. Now, an N-heterocyclic carbene-stabilized Au25 nanocluster with high thermal and air stabilities is presented as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au25 (i Pr2 -bimy)10 Br7 ]2+ (i Pr2 -bimy=1,3-diisopropylbenzimidazolin-2-ylidene) (1), was synthesized by direct reduction of AuSMe2 Cl and i Pr2 -bimyAuBr with NaBH4 in one pot. X-ray crystallization analysis revealed that the cluster comprises two centered Au13 icosahedra sharing a vertex. Cluster 1 is highly stable and can survive in solution at 80 °C for 12 h, which is superior to Au25 nanoclusters passivated with phosphines or thiols. DFT computations reveal the origins of both electronic and thermal stability of 1 and point to the probable catalytic sites. This work provides new insights into the bonding capability of N-heterocyclic carbene to Au in a cluster, and offers an opportunity to probe the catalytic mechanism at the atomic level.

Atomically Precise Bimetallic Au19Cu30 Nanocluster with an Icosidodecahedral Cu30 Shell and an Alkynyl-Cu Interface.

Bimetallic nanoclusters Au19Cu30 with chemical composition of [Au19Cu30(C≡CR)22(Ph3P)6Cl2](NO3)3 (where RC≡C is from 3-ethynylthiophene (H3C4S-3-C≡CH) or ethynylbenzene (PhC≡CH)) has been synthesized. Single X-ray structural analysis reveals that Au19Cu30 has a multishelled core structure of Au@Au12@Cu30@Au6, comprising a centered icosahedral Au13 (Au@Au12) surrounded by an icosidodecahedral Cu30 shell and an outmost shell of a chairlike hexagonal Au6. The alkynyl carbon is bound to the hollow sites on the Au19Cu30 nanocluster surface, which is a novel interfacial binding mode in alkynyl-protected alloy nanoclusters. The Cu30 icosidodecahedron is unprecedented and Au19Cu30 represents the first alkynyl-protected Au-Cu alloy nanocluster.

Microporous Cyclic Titanium-Oxo Clusters with Labile Surface Ligands.

By using ethylene glycol and monocarboxylic acid as surface ligands, a series of cyclic Ti-oxo clusters (CTOC) with permanent microporosity are successfully synthesized. With a cyclic {Ti32 O16 } backbone made of eight connected Ti4 tetrahedral cages that are arranged in a zigzag fashion, the clusters have a "donut" shape with an inner diameter of 8.3 Å, outer diameter of 26.9 Šand height of 10.4 Å. While both inner and outer walls of the "donut" clusters are modified by double-deprotonated ethylene glycolates, their upper and lower surfaces are bound by carboxylates and mono-deprotonated ethylene glycolates. The clusters are readily packed into one-dimensional tubes which are further arranged in two different modes into crystalline microporous solids with surface areas over 660 m2 g-1 , depending on the surface carboxylates. The solid with olefin-bearing carboxylates exhibits a superior CO2 adsorption capacity of 40 cm3 g-1 at 273 K under 1 atm. Moreover, the mono-deprotonated ethylene glycolates on the clusters are demonstrated to be highly exchangeable by other alcohols, providing a nice platform for creating microporous solids or films with a wide variety of surface functionalities.

Insights into Magnetic Interactions in a Monodisperse Gd12 Fe14 Metal Cluster.

The largest Ln-Fe metal cluster [Gd12 Fe14 (µ3 -OH)12 (µ4 -OH)6 (µ4 -O)12 (TEOA)6 (CH3 COO)16 (H2 O)8 ]⋅(CH3 COO)2 (CH3 CN)2 ⋅(H2 O)20 (1) and the core-shell monodisperse metal cluster of 1 a@SiO2 (1 a=[Gd12 Fe14 (µ3 -OH)12 (µ4 -OH)6 (µ4 -O)12 (TEOA)6 (CH3 COO)16 (H2 O)8 ]2+ ) were prepared. Experimental and theoretical studies on the magnetic properties of 1 and 1 a@SiO2 reveal that encapsulation of one cluster into one silica nanosphere not only effectively decreases intermolecular magnetic interactions but also significantly increases the zero-field splitting effect of the outer layer Fe3+ ions.

Cu28H20: a peculiar chiral nanocluster with an exposed Cu atom and 13 surface hydrides.

Reported herein is a racemate of a chiral nanocluster [Cu28H20(S2P(OiPr)2)9]-, which has a tetrahedral Cu4 core embedded in a peculiar Cu24 shell. The Cu28H20 framework conforms to idealized C3 symmetry. The positions of the hydrides were determined by a combinatorial use of 2H NMR and SC-XRD, revealing four different coordination modes: face-capping µ3-H, butterfly µ4'-H, tetrahedral µ4-H, and square-pyramidal µ5-H. These coordination modes were authenticated by DFT calculations. Simple empirical rules were developed for assigning the H NMR spectra. One exposed Cu atom from the Cu4 core and 13 exposed surface hydrides are easily accessible and thus may have catalytic functions.

Simple and Selective Synthesis of Copper-Containing Metal Nanoclusters Using (PPh3 )2 CuBH4 as Reducing Agent.

A simple and selective synthetic protocol, using (PPh3 )2 CuBH4 as reducing agent, for Cu-containing mixed metal nanoclusters (NCs) is reported. Representative NCs include alkynyl-protected [Ag25 Cu4 (PhCC)12 (PPh3 )12 Cl6 H8 ]3+ (1), thiolate-capped [AuCu14 (SR)12 (PPh3 )6 ]+ (R = 4-flurothiophenol) (2), and phosphine-stabilized [Au9 Cu2 (PPh3 )8 Cl2 ]+ (3), which are fully characterized by single-crystal X-ray diffraction analysis, electrospray ionization mass, nuclear magnetic resonance (1 H, 2 H, 13 C, and 31 P NMR), and optical measurements, respectively. This work demonstrates the advantages of using (PPh3 )2 CuBH4 as a reducing agent in the synthesis of Cu-containing heterometallic NCs in terms of versatility as well as high yield and high purity of the products. This work may open the door to utilizing functional metal borohydride, as a new generation of reducing agent for the simple and selective synthesis of metal NCs.

Dissection of bicapped octahedral copper hydride cluster to form two chiral tetrahedral copper hydride cluster series exhibiting auto deracemization and photoluminescence.

Three series of copper hydride clusters [Cu8H6L6]2+ (1), [Cu4HX2L4]+ where X- = Cl- (2a), Br- (2b), I- (2c), N3- (2d) and SCN- (2e), and [Cu4HX3L3] where X- = Br- (3b) and I- (3c) (L = 2-(diphenylphosphino)pyridine, dppy) were synthesized and characterized by single-crystal X-Ray crystallography and standard spectroscopic techniques. The metal core of 1, Cu8, can be described as a bicapped octahedron, while those of 2 and 3 series adopt tetrahedral structures. The hydride positions were deduced from difference electron density maps and corroborated by NMR and DFT calculations. For 1, there are two µ4-H-, one each in the two tetrahedral cavities of the two capping atoms and four µ3-H- on the six triangular faces around the waist of the octahedron. For [Cu4HX2L4]+ and [Cu4HX3L3] series, the single µ4-H- resides in the center of the Cu4 tetrahedron. It was found that these three series of copper clusters are intimately connected and can convert from one to another under specific reaction conditions. Their transformation pathways were investigated in detail. Spontaneous resolution to form optically pure enantiomeric single crystals was observed for [Cu4H(SCN)2L4]+ (2e) and [Cu4HBr3L3] (3b). Photoluminescence was observed for [Cu4HX2L4]+, as well as [Cu4HX3L3] with strong emissions from green to yellow regions.