Total Structure, Electronic Structure and Catalytic Hydrogenation Activity of Metal-Deficient Chiral Polyhydride Cu57 Nanoclusters.

Accurate identifying and in-depth understanding of the defect sites in a working nanomaterial could hinge on establishing specific defect-activity relationships. Yet, atomically precise coinage-metal nanoclusters (NCs) possessing surface vacancy defects are scarce primarily owing to challenges in the synthesis and isolation of such defective NCs. Herein we report a mixed-ligand strategy to synthesizing an intrinsically chiral and metal-deficient copper hydride-rich NC [Cu57 H20 (PET)36 (TPP)4 ]+ (Cu57 H20 ). Its total structure (including hydrides) and electronic structure are well established by combined experimental and computational results. Crystal structure reveals Cu57 H20 features a cube-like Cu8 kernel embedded in a corner-missing metal-ligand shell of Cu49 (PET)36 (TPP)4 . Single Cu vacancy defect site occurs at one corner of the shell, evocative of mono-lacunary polyoxometalates. Theoretical calculations demonstrate that the above-mentioned point vacancy causes one surface hydride exposed as an interfacial capping µ3 -H- , which is accessible in chemical reaction, as proved by deuterated experiment. Moreover, Cu57 H20 shows catalytic activity in the hydrogenation of nitroarene. The success of this work opens the way for the research on well-defined chiral metal-deficient Cu and other metal NCs, including exploring their application in asymmetrical catalysis.

DppfCuBH4: new reducing agents for the synthesis of ferrocene-functionalized metal nanoclusters.

A facile synthesis of atomically precise metal nanoclusters, especially those decorated with functional groups, is the prerequisite for finding applications in special fields and studying structure-and-property relationships. The exploration of simple and efficient synthetic prototypes for introducing functional ligands (such as ferrocene) into cluster moieties is thus of high interest. In this work, a type of reducing agent of dppfCuBH4 (dppf is 1,1'-bis(diphenyphosphino)ferrocene) is introduced for the first time to prepare ferrocene-functionalized metal nanoclusters. Two new clusters of [Ag25Cu4(dppf)6(3-F-PhCC)12Cl6]3+ (1) and [Ag4(dppf)5Cl2]2+ (2) have been obtained from the simple synthetic method. The two compounds have been fully characterized by advanced techniques of electrospray ionization mass spectroscopy (ESI-MS), nuclear magnetic resonance (NMR), and ultraviolet-visible spectroscopy (UV-Vis). The total structure of the clusters, as determined by X-ray single-crystal diffraction, describes the Ag13@Ag12Cu4(dppf)6(3-F-PhCC)12Cl6 core-shell structure of 1 and [Ag2Cl(dppf)2]+-dppf-[Ag2Cl(dppf)2]+ polymeric structure of 2. This work opens the door to employing dppfCuBH4 as a functional reducing agent to discover many underlying metal nanoclusters and even other nanomaterials which feature ferrocene-groups.

Multi-layer 3D Chirality and Double-Helical Assembly in a Copper Nanocluster with a Triple-Helical Cu15 Core.

Conceptually mimicking biomolecules' ability to construct multiple-helical aggregates with emergent properties and functions remains a long-standing challenge. Here we report an atom-precise 18-copper nanocluster (NC), Cu18 H(PET)14 (TPP)6 (NCS)3 (Cu18 H) which contains a pseudo D3 -symmetrical triple-helical Cu15 core. Structurally, Cu18 H may be also viewed as sandwich type of sulfur-bridged chiral copper cluster units [Cu6 -Cu6 -Cu6 ], endowing three-layered 3D chirality. More importantly, the chiral NCs are aggregated into an infinite double-stranded helix supported by intra-strand homonuclear C-H⋅⋅⋅H-C dihydrogen contacts and inter-strand C-H/π and C-H/S interactions. The unique multi-layered 3D chirality and the double-helical assembly of Cu18 H are evocative of DNA. Moreover, the collective behaviours of the aggregated NCs not only exhibit crystallization-induced emission enhancement (CIEE) and aggregation-induced emission enhancement (AIEE) effects in the deep-red region, but also efficiently catalyze electron transfer (ET) reaction. This study thus presents that hierarchical assemblies of atomically defined copper NCs could be intricate as observed for important biomolecules like DNA with emergent properties arising from aggregated behaviours.

Controllable spontaneous resolution in ultrasmall Cu-Ag bimetallic cluster ion pairs from achiral components.

Bimetallic cluster ion pairs containing a quaternary phosphonium and an ultrasmall Cu2Ag3 anionic cluster protected by thiolates: (PPh3R'')[Cu2Ag3(SR')6] (R'SH = cyclohexylthiol (CySH), R'' = Ph, 1; Me, 2; Et, 3; Pr, 4; R'SH = tert-butylthiol (tBuSH) and R'' = Ph, 5) were reported. Without any chiral source, 1 crystallizes as conglomerate crystals with homochiral packings and spontaneous resolution occurs, while four other clusters 2-5 crystallize as racemic crystals with heterochiral packings. These results indicate that racemic and homochiral crystallization in the cluster system could be controlled through fine-tuning internal achiral structural components.

Observation of a bcc-like framework in polyhydrido copper nanoclusters.

Cu is well-known to adopt a face-centered cubic (fcc) structure in the bulk phase. Ligand-stabilized Cu nanoclusters (NCs) with atomically precise structures are an emerging class of nanomaterials. However, it remains a great challenge to have non-fcc structured Cu NCs. In this contribution, we report the syntheses and total structure determination of six 28-nuclearity polyhydrido Cu NCs: [Cu28H16(dppp)4(RS)4(CF3CO2)8] (dppp = 1,3-bis(diphenylphosphino)propane, RSH = cyclohexylthiol, 1; tert-butylthiol, 3; and 2-thiophenethiol, 4) and [Cu28H16(dppe)4(RS)4(CH3CO2)6Cl2] (dppe = 1,2-bis(diphenylphosphino)ethane, RSH = (4-isopropyl)thiophenol, 2; 4-tert-butylbenzenethiol, 5; and 4-tert-butylbenzylmercaptan, 6). Their well-defined structures solved by X-ray single crystal diffraction reveal that these 28-Cu NCs are isostructural, and the overall metal framework is arranged as a sandwich structure with a core-shell Cu2@Cu16 unit held by two Cu5 fragments. One significant finding is that the organization of 18 Cu atoms in the Cu2@Cu16 could be regarded as an incomplete and distorted version of 3 × 2 × 2 "cutout" of the body-centered cubic (bcc) bulk phase, which was strikingly different to the fcc structure of bulk Cu. The bcc framework came as a surprise, as no bcc structures have been previously observed in Cu NCs. A comparison with the ideal bcc arrangement of 18 Cu atoms in the bcc lattice suggests that the distortion of the bcc structure results from the insertion of interstitial hydrides. The existence, number, and location of hydrides in these polyhydrido Cu NCs are established by combined experimental and DFT results. These results have significant implications for the development of high-nuclearity Cu hydride NCs with a non-fcc architecture.

A Sodalite-Type Silver Orthophosphate Cluster in a Globular Silver Nanocluster.

The synthesis and structure of a giant 102-silver-atom nanocluster (NC) 1 is presented. X-ray structural analysis reveals that 1 features a multi-shelled metallic core of Ag6 @Ag24 @Ag60 @Ag12 . An octahedral Ag6 core is encaged by a truncated octahedral Ag24 shell. The Ag24 shell is composed of a hitherto unknown sodalite-type silver orthophosphate cluster (SOC) {(Ag3 PO4 )8 }, reminiscent of the Ag3 PO4 photocatalyst. The SOC is capped by six interstitial sulfur atoms, giving a unique anionic cluster [Ag6 @{(Ag3 PO4 )8 }S6 ]6- , which functions as an intricate polyhedral template with abundant surface O and S atoms guiding the formation of a rare rhombicosidodecahedral Ag60 shell. An array of 6 linear Ag2 staples further surround this Ag60 shell. [Ag6 @{(Ag3 PO4 )8 }S6 ]6- is an unusual Ag-based templating anion to induce the assembly of a SOC within silver NC. This finding provides molecular models for bulk Ag3 PO4 , and offers a fresh template strategy for the synthesis of silver NCs with high symmetry.

New protective ligands for atomically precise silver nanoclusters.

Atomically precise silver nanoclusters (NCs) have emerged as a hot topic attracting immense research interest. Protecting ligands are needed for direct capping on cluster surfaces in order to prevent aggregation and to stabilize NCs. It has been demonstrated that protective ligands are critical to determining the sizes, structures and properties of silver NCs. The past decades have witnessed conventionally used organic ligands (thiolates/selenols, phosphines and alkynyls) and inorganic ligands (chalcogens and halogens) being extensively used to passivate NC surfaces. However, only in the most recent years have new-type protecting ligands beyond the conventional ones begun to be introduced in the protecting sphere of new functional silver NCs. The present Frontier article covers the most recent examples of some new protective agents for well-defined silver NCs. We describe four classes of novel silver NCs stabilized by newly-developed surface ligands, namely, nitrogen-donor organic ligands, oxygen-donor inorganic ligands, metalloligands and macrocyclic hosts, paying attention to the synthesis, structures and properties of these silver NCs. This Frontier article will hopefully attract more cluster scientists to explore more freshly ligated atomically precise silver NCs with novel structures and properties in the years ahead. The literature survey in this review is based on publications up to February 2020. Some suggestions for future directions in this field are also given.

Combinatorial Identification of Hydrides in a Ligated Ag40 Nanocluster with Noncompact Metal Core.

No formation of bulk silver hydride has been reported. Until very recently, only a few silver nanoclusters containing hydrides have been successfully prepared. However, due to the lack of effective techniques and also poor stability of hydride-containing Ag nanoclusters, the identification of hydrides' location within Ag nanoclusters is challenging and not yet achieved, although some successes have been reported on clusters of several Ag atoms. In this work, we report a detailed structural and spectroscopic characterization of the [Ag40(DMBT)24(PPh3)8H12]2+ (Ag40H12) cluster (DMBT = 2,4-dimethylbenzenethiol). The metal framework consists of three concentric shells of Ag8@Ag24@Ag8, which can be described as (ν1-cube)@(truncated-ν3-octahedron)@(ν2-cube), respectively. The presence of 12 hydrides in each cluster was systematically identified by various techniques. Based on a detailed analysis of the structural features and 1H and 2H NMR spectra, the positions of the 12 hydrides were determined to be residing on the 12 edges of the cubic core. As a result, the electron count of the Ag40 cluster is a two-electron superatomic system instead of a 14-electron system. Moreover, based on our DFT calculations and experimental probes, it was demonstrated that the 12 hydrides play a crucial role in stabilizing both the electronic and geometric structure of the Ag40H12 cluster. The successful synthesis of stable hydride-containing Ag nanoclusters and the identification of hydride positions are expected to simulate research attention on both synthesis and application of hydride-containing Ag nanomaterials.

Atomically Precise, Thiolated Copper-Hydride Nanoclusters as Single-Site Hydrogenation Catalysts for Ketones in Mild Conditions.

Copper-hydrides are known catalysts for several technologically important reactions such as hydrogenation of CO, hydroamination of alkenes and alkynes, and chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols. Stabilizing copper-based particles by ligand chemistry to nanometer scale is an appealing route to make active catalysts with optimized material economy; however, it has been long believed that the ligand-metal interface, particularly if sulfur-containing thiols are used as stabilizing agent, may poison the catalyst. We report here a discovery of an ambient-stable thiolate-protected copper-hydride nanocluster [Cu25H10(SPhCl2)18]3- that readily catalyzes hydrogenation of ketones to alcohols in mild conditions. A full experimental and theoretical characterization of its atomic and electronic structure shows that the 10 hydrides are instrumental for the stability of the nanocluster and are in an active role being continuously consumed and replenished in the hydrogenation reaction. Density functional theory computations suggest, backed up by the experimental evidence, that the hydrogenation takes place only around a single site of the 10 hydride locations, rendering the [Cu25H10(SPhCl2)18]3- one of the first nanocatalysts whose structure and catalytic functions are characterized fully to atomic precision. Understanding of a working catalyst at the atomistic level helps to optimize its properties and provides fundamental insights into the controversial issue of how a stable, ligand-passivated, metal-containing nanocluster can be at the same time an active catalyst.

Ether-Soluble Cu53 Nanoclusters as an Effective Precursor of High-Quality CuI Films for Optoelectronic Applications.

An effective strategy is developed to synthesize high-nuclearity Cu clusters, [Cu53 (RCOO)10 (C≡CtBu)20 Cl2 H18 ]+ (Cu53 ), which is the largest CuI /Cu0 cluster reported to date. Cu powder and Ph2 SiH2 are employed as the reducing agents in the synthesis. As revealed by single-crystal diffraction, Cu53 is arranged as a four-concentric-shell Cu3 @Cu10 Cl2 @Cu20 @Cu20 structure, possessing an atomic arrangement of concentric M12 icosahedral and M20 dodecahedral shells which popularly occurs in Au/Ag nanoclusters. Surprisingly, Cu53 can be dissolved in diethyl ether and spin coated to form uniform nanoclusters film on organolead halide perovskite. The cluster film can subsequently be converted into high-quality CuI film via in situ iodination at room temperature. The as-fabricated CuI film is an excellent hole-transport layer for fabricating highly stable CuI-based perovskite solar cells (PSCs) with 14.3 % of efficiency.

Electrochemical CO2 Reduction at Glassy Carbon Electrodes Functionalized by MnI and ReI Organometallic Complexes.

The catalytic activities towards electrochemical CO2 reduction of two new rhenium and manganese complexes, namely fac-Mn(apbpy)(CO)3 Br (1) and fac-Re(apbpy)(CO)3 Cl (2) (apbpy=4-(4-aminophenyl)-2,2'-bipyridine), in both homogeneous and heterogeneous phases are compared. A glassy carbon electrode (GCE) surface has been functionalized with complexes 1 and 2 by two approaches: a) direct electrochemical oxidation of the amino group with formation of C-N bonds, and b) electrochemical reduction of the corresponding diazonium salts with formation of C-C bonds. The chemically modified GCEs show efficient conversion of CO2 into CO, with turnover numbers (TONs) about 60 times higher than those of the corresponding catalysts in homogeneous solutions, and in a much shorter time.

Electrocatalytic reduction of CO2 by thiophene-substituted rhenium(i) complexes and by their polymerized films.

Three novel thiophene substituted bipyridine ligands and their corresponding rhenium complexes were synthesized and tested for the electrocatalytic reduction of CO2. Two complexes underwent oxidative electropolymerization on a glassy carbon electrode (GCE) surface. The conductive polymers chemically deposited on the GCE allow electron transport from the surface to the polymer-attached rhenium catalytic center in contact with the solution. The chemically modified electrodes show significant catalytic activities for CO2 reduction, and moderate relative higher stabilities when compared with the homogeneous solution counterparts.

[Hydrothermal synthesis, crystal structure and luminescence property of 3D supermolecular compound [Zn(H2O)6].(C16H8O8)].

A supermolecular compound [Zn(H2O)6].(C16H8O8) was synthesized with 3,3', 4,4'-bipthenyltetracarboxylic acid (H4BPTC) and Zn(CH3COO)2.2H2O. Its structure was determined by single crystal X-ray diffraction, IR and element analysis. The crystal belongs to triclinic system with space group and the cell parameters are: a = 0.65484 (13) nm, b = 0.79388 (16) nm, c = 0.96812 (19) nm, alpha = 76.29 (3) degrees, beta = 87.75 (3) degrees, gamma = 86.43 (3) degrees, Z=1, R1 = 0.0665, wR2 = 0.1833, and GOF = 1.021. We have studied the luminescence property of compound 1, The compound 1 has blue-purple luminescence in solutions of DMSO and green luminescence in the solid state at room temperature. In the solid state, the emission frequencies for complex 1 are red-shifted compared with their emission maximum peaks in solutions of DMSO. This red-shift of emission energy from solution to solid is likely to be caused by the intermolecular interaction in the solid state that effectively decreases the energy gap.

Tetra-µ-acetato-κO:O';κO,O':O;κO:O,O'-bis-[(acetato-κO,O')(1,10-phenanthroline-κN,N')europium(III)].

In the title centrosymmetric dinuclear complex, [Eu(2)(CH(3)CO(2))(6)(C(12)H(8)N(2))(2)], the Eu(III) atom is nine-coordinated by two N atoms from a 1,10-phenanthroline ligand and seven O atoms from five acetate ligands (two bidentate, three monodentate). The crystal structure is stabilized by π-π stacking inter-actions between the pyridine and benzene rings of adjacent mol-ecules, with a centroid-centroid distance of 3.829 (2) Å.