Au36(SR)22 Nanocluster and a Periodic Pattern from Six to Fourteen Free Electrons in Core Size Evolution.

An Au36(S-tBu)22 nanocluster (NC) is synthesized using the bulky tert-butyl thiol as the ligand. Single-crystal X-ray crystallography reveals that it has an Au25 core which evolves from the Au22 core in the previously reported Au30(S-tBu)18, and the Au25 core is protected by longer staple-like surface motifs. The new Au36 NC extends the members of the face-centered cubic structural evolution by adding an Au3 triangle and an Au4 tetrahedron unit. Additionally, it is found that Au36 emits near-infrared photoluminescence at 863 nm with a quantum yield (QY) of 4.3%, which is five times larger than that of Au30(S-tBu)18-the closest neighbor in the structural evolution pattern. The higher QY of Au36 is attributed to a larger radiative relaxation (kr), resulting from the structural effect. Finally, we find that the longer staple motifs lead to enhanced stability of Au36(S-tBu)22 relative to Au30(S-tBu)18.

Anomalous Structural Transformation of Cu(I) Clusters into Multifunctional CuAg Nanoclusters.

We report an anomalous structural transformation of a Cu(I) cluster into two different types of copper-silver (CuAg) alloy nanoclusters. Different from previous reports, we demonstrate that under specifically designed reaction conditions, the Ag-doping could induce a substantial growth of the starting Cu15 and a Ag13Cu20 nanocluster was obtained via the unexpected insertion of an Ag13 kernel inside the Cu(I)-S shell. Ag13Cu20 demonstrates high activity to initiate the photopolymerization of previously hard-to-print inorganic polymers in 3D laser microprinting. Interestingly, a slight modification of the reaction condition leads to the formation of another Ag18-xCuxS (8≤x) nanocluster templated by a central S2- anion, which possesses a unique electronic structure compared to conventional template-free CuAg nanoclusters. Overall, this work unveils the intriguing doping chemistry of Cu clusters, as well as their capability to create different types of alloy nanoclusters with previously unobtainable structures and multifunctionality.

Three-atom-wide gold quantum rods with periodic elongation and strongly polarized excitons.

Atomically precise control over anisotropic nanoclusters constitutes a grand challenge in nanoscience. In this work, we report our success in achieving a periodic series of atomically precise gold quantum rods (abbrev. Au QRs) with unusual excitonic properties. These QRs possess hexagonal close-packed kernels with a constant three-atom diameter but increasing aspect ratios (ARs) from 6.3 to 18.7, all being protected by the same thiolate (SR) ligand. The kernels of the QRs are in a Au1-(Au3)n-Au1 configuration (where n is the number of Au3 layers) and follow a periodic elongation with a uniform Au18(SR)12 increment consisting of four Au3 layers. These Au QRs possess distinct HOMO-LUMO gaps (Eg = 0.6 to 1.3 eV) and exhibit strongly polarized excitonic transition along the longitudinal direction, resulting in very intense absorption in the near-infrared (800 to 1,700 nm). While excitons in gapped systems and plasmons in gapless systems are distinctly different types of excitations, the strongly polarized excitons in Au QRs surprisingly exhibit plasmon-like behaviors manifested in the shape-induced polarization, very intense absorption (~106 M-1 cm-1), and linear scaling relations with the AR, all of which resemble the behaviors of conventional metallic-state Au nanorods (i.e., gapless systems), but the QRs possess distinct gaps and very long excited-state lifetimes (10 to 2,122 ns), which hold promise in applications such as near-infrared solar energy utilization, hot carrier generation and transfer. The observation of plasmon-like behaviors from single-electron transitions in Au QRs elegantly bridges the distinct realms of single-electron and collective-electron excitations and may stimulate more research on excitonics and plasmonics.

Tailoring Carbon Tails of Ligands on Au52(SR)32 Nanoclusters Enhances the Near-Infrared Photoluminescence Quantum Yield from 3.8 to 18.3.

One of the important factors that determine the photoluminescence (PL) properties of gold nanoclusters pertain to the surface. In this study, four Au52(SR)32 nanoclusters that feature a series of aromatic thiolate ligands (-SR) with different bulkiness at the para-position are synthesized and investigated. The near-infrared (NIR) photoluminescence (peaks at 900-940 nm) quantum yield (QY) is largely enhanced with a decrease in the ligand's para-bulkiness. Specifically, the Au52(SR)32 capped with the least bulky p-methylbenzenethiolate (p-MBT) exhibits the highest PLQY (18.3% at room temperature in non-degassed dichloromethane), while Au52 with the bulkiest tert-butylbenzenethiolate (TBBT) only gives 3.8%. The large enhancement of QY with fewer methyl groups on the ligands implies a nonradiative decay via the multiphonon process mediated by C-H bonds. Furthermore, single-crystal X-ray diffraction (SCXRD) comparison of Au52(p-MBT)32 and Au52(TBBT)32 reveals that fewer methyl groups at the para-position lead to a stronger interligand π···π stacking on the Au52 core, thus restricting ligand vibrations and rotations. The emission nature is identified to be phosphorescence and thermally activated delayed fluorescence (TADF) based on the PL lifetime, 3O2 quenching, and temperature-dependent PL and absorption studies. The 1O2 generation efficiencies for the four Au52(SR)32 NCs follow the same trend as the observed PL performance. Overall, the highly NIR-luminescent Au52(p-MBT)32 nanocluster and the revealed mechanisms are expected to find future applications.

Direct Observation of the Pressure-Induced Structural Variation in Gold Nanoclusters and the Correlated Optical Response.

The ability to gradually modify the atomic structures of nanomaterials and directly identify such structural variation is important in nanoscience research. Here, we present the first example of a high-pressure single-crystal X-ray diffraction analysis of atomically precise metal nanoclusters. The pressure-dependent, subangstrom structural evolution of an ultrasmall gold nanoparticle, Au25S18, has been directly identified. We found that a 0.1 Å decrease of the Au-Au bond length could induce a blue-shift of 30 nm in the photoluminescence spectra of gold nanoclusters. From theoretical calculations, the origins of the blue-shift and enhanced photoluminescence under pressure are investigated, which are ascribed to molecular orbital symmetry and conformational locking, respectively. The combination of the high-pressure in situ X-ray results with both theoretical and experimental optical spectra provides a direct and generalizable avenue to unveil the underlying structure-property relations for nanoclusters and nanoparticles which cannot be obtained through traditional physical chemistry measurements.

Crystal structures of two coordination isomers of copper(II) 4-sulfo-benzoic acid hexa-hydrate and two mixed silver/potassium 4-sulfo-benzoic acid salts.

A reaction of copper(II) carbonate and potassium 4-sulfo-benzoic acid in water acidified with hydro-chloric acid yielded two crystalline products. Tetra-aqua-bis-(4-carb-oxy-benzene-sulfonato)-copper(II) dihydrate, [Cu(O3SC6H4CO2H)2(H2O)4]·2H2O, (I), crystallizes in the triclinic space group P with the Cu2+ ions located on centers of inversion. Each copper ion is coordinated to four water mol-ecules in a square plane with two sulfonate O atoms in the apical positions of a Jahn-Teller-distorted octa-hedron. The carboxyl-ate group is protonated and not involved in coordination to the metal ions. The complexes pack so as to create a layered structure with alternating inorganic and organic domains. The packing is reinforced by several O-H⋯O hydrogen bonds involving coordinated and non-coordinated water mol-ecules, the carb-oxy-lic acid group and the sulfonate group. Hexa-aqua-copper(II) 4-carb-oxy-benzene-sulfonate, [Cu(H2O)6](O3SC6H4CO2H)2, (II), also crystallizes in the triclinic space group P with Jahn-Teller-distorted octa-hedral copper(II) aqua complexes on the centers of inversion. As in (I), the carboxyl-ate group on the anion is protonated and the structure consists of alternating layers of inorganic cations and organic anions linked by O-H⋯O hydrogen bonds. A reaction of silver nitrate and potassium 4-sulfo-benzoic acid in water also resulted in two distinct products that have been structurally characterized. An anhydrous silver potassium 4-carb-oxy-benzene-sulfonate salt, [Ag0.69K0.31](O3SC6H4CO2H), (III), crystallizes in the monoclinic space group C2/c. There are two independent metal sites, one fully occupied by silver ions and the other showing a 62% K+/38% Ag+ (fixed) ratio, refined in two slightly different positions. The coordination environments of the metal ions are composed primarily of sulfonate O atoms, with some participation by the non-protonated carboxyl-ate O atoms in the disordered site. As in the copper compounds, the cations and anions cleanly segregate into alternating layers. A hydrated mixed silver potassium 4-carb-oxy-benzene-sulfonate salt dihydrate, [Ag0.20K0.80](O3SC6H4CO2H)·2H2O, (IV), crystallizes in the monoclinic space group P21/c with the Ag+ and K+ ions sharing one unique metal site coordinated by two water mol-ecules and six sulfonate O atoms. The packing in (IV) follows the dominant motif of alternating inorganic and organic layers. The protonated carboxyl-ate groups do not inter-act with the cations directly, but do participate in hydrogen bonds with the coordinated water mol-ecules. (IV) is isostructural with pure potassium 4-sulfo-benzoic acid dihydrate.

Models for potential dendritic nitric oxide donors: crystal structures of two 2-nitroanilino precursors and nitric oxide-release behavior of the nitrosated derivatives.

Two molecular precursors to dendrimeric materials that could serve as slow and sustained NO-releasing therapeutic agents have been synthesized and characterized. N1,N4-Bis(2-nitrophenyl)butane-1,4-diamine, C16H18N4O4, (I), crystallizes in a lattice with equal populations of two molecules of different conformations, both of which possess inversion symmetry through the central C-C bond. One molecule has exclusively anti conformations along the butyl chain, while the other has a gauche conformation of the substituents on the first C-C bond. N2,N2-Bis[2-(2-nitroanilino)ethyl]-N1-(2-nitrophenyl)ethane-1,2-diamine, C24H27N7O6, (II), crystallizes with one unique molecule in the asymmetric unit. Neighboring pairs of molecules are linked into dimers via N-H...O amine-nitro hydrogen bonds. The dimers are assembled into layers that stack in an A-B-A-B sequence such that the repeat distance in the stacking direction is over 46 Å. Molecular NO-release agents N1,N4-bis(2-nitrophenyl)-N1,N4-dinitrosobutane-1,4-diamine, C16H16N6O6, (III), and N1-(2-nitrophenyl)-N2,N2-bis{2-[(2-nitrophenyl)(nitroso)amino]ethyl}-N1-nitrosoethane-1,2-diamine, C24H24N10O9, (IV), were prepared via treatment of (I) and (II), respectively, with NaNO2 and acetic acid. The release of NO from solid-phase samples of (III) and (IV) suspended in phosphate buffer was monitored spectroscopically over a period of 21 days. Although (IV) released a greater amount of NO, as expected due to it having three NO moieties for every two in (III), the (IV):(III) ratio of the rate and extent of NO release was significantly less than 1.5:1, suggesting that some combination of electronic, chemical, and/or steric factors may be affecting the release process.

Large-Scale Synthesis, Crystal Structure, and Optical Properties of the Ag146Br2(SR)80 Nanocluster.

Solving the atomic structure of large-sized metal nanoclusters is a highly challenging task yet critically important for understanding the properties and developing applications. Herein, we report a stable silver nanocluster-Ag146Br2(SR)80 (where SR = 4-isopropylbenzenethiolate)-with its structure solved by X-ray crystallography. Gram-scale synthesis with high yield has been achieved by a one-pot reaction, which offers opportunities for functionalization and applications. This silver nanocluster possesses a core-shell structure with a Ag51 core surrounded by a shell of Ag95Br2S80. The Ag51 core can be viewed as a distorted decahedron, endowing this nanocluster with quantized electronic transitions. In the surface-protecting layer, five different types of S-Ag coordination modes are observed, ranging from the linear Ag-S-Ag to S-Ag3 (triangle) and S-Ag4 (square). Furthermore, temperature-dependent optical absorption and ultrafast electron dynamics are conducted to explore the relationship between the properties and structure, demonstrating that the distorted metal core and "flying saucer"-like shape of this nanocluster have significant effects on the electronic behavior. A comparison with multiple sizes of Ag nanoclusters also provides some insights into the evolution from molecular to metallic behavior.

Sharp Transition from Nonmetallic Au246 to Metallic Au279 with Nascent Surface Plasmon Resonance.

The optical properties of metal nanoparticles have attracted wide interest. Recent progress in controlling nanoparticles with atomic precision (often called nanoclusters) provide new opportunities for investigating many fundamental questions, such as the transition from excitonic to plasmonic state, which is a central question in metal nanoparticle research because it provides insights into the origin of surface plasmon resonance (SPR) as well as the formation of metallic bond. However, this question still remains elusive because of the extreme difficulty in preparing atomically precise nanoparticles larger than 2 nm. Here we report the synthesis and optical properties of an atomically precise Au279(SR)84 nanocluster. Femtosecond transient absorption spectroscopic analysis reveals that the Au279 nanocluster shows a laser power dependence in its excited state lifetime, indicating metallic state of the particle, in contrast with the nonmetallic electronic structure of the Au246(SR)80 nanocluster. Steady-state absorption spectra reveal that the nascent plasmon band of Au279 at 506 nm shows no peak shift even down to 60 K, consistent with plasmon behavior. The sharp transition from nonmetallic Au246 to metallic Au279 is surprising and will stimulate future theoretical work on the transition and many other relevant issues.

Team Communication in the Operating Room: A Measure of Latent Factors From a National Sample of Nurse Anesthetists.

Medical errors more often result from miscommunication among providers than lack of medical knowledge. The consequences of miscommunication are well documented, but there is less information about factors contributing to communication errors among providers. In this study, surveys were administered to a national sample of 3,000 nurse anesthetists to measure variables associated with communication attitudes and behaviors. The specific variables measured in the survey were latent cultural factors that contribute to communication behaviors. Previous research found these latent variables contribute to miscommunication among operating room physicians, resulting in patient-related errors that could be avoided. The survey used for this study was based on an intercultural communication theory. Survey items were modified to reflect operating room culture, specifically nurse anesthetist communication. Exploratory factor analyses were used to analyze the survey data. The analyses found distinct patterns of latent cultural communication variables in the sample of 474 completed responses. The communication profiles that resulted from this study can be compared with previously collected physician data to help explain how miscommunication occurs among interprofessional groups of operating room providers, resulting in medical error. Knowledge of these latent variables can be translated to more effective communication training protocols in the future.

Reconstructing the Surface of Gold Nanoclusters by Cadmium Doping.

Atomically precise metal nanoclusters with tailored surface structures are important for both fundamental studies and practical applications. The development of new methods for tailoring the surface structure in a controllable manner has long been sought. In this work, we report surface reconstruction induced by cadmium doping into the [Au23(SR)16]- (R = cyclohexyl) nanocluster, in which two neighboring surface Au atomic sites "coalesce" into one Cd atomic site and, accordingly, a new bimetal nanocluster, [Au19Cd2(SR)16]-, is produced. Interestingly, a Cd(S-Au-S)3 "paw-like" surface motif is observed for the first time in nanocluster structures. In such a motif, the Cd atom acts as a junction which connects three monomeric -S-Au-S- motifs. Density functional theory calculations are performed to understand the two unique Cd locations. Furthermore, we demonstrate different doping modes when the [Au23(SR)16]- nanocluster is doped with different metals (Cu, Ag), including (i) simple substitution and (ii) total structure transformation, as opposed to surface reconstruction for Cd doping. This work greatly expands doping chemistry for tailoring the structures of nanoclusters and is expected to open new avenues for designing nanoclusters with novel surface structures using different dopants.

N-Benzylnicotinamide and N-benzyl-1,4-dihydronicotinamide: useful models for NAD+ and NADH.

3-Aminocarbonyl-1-benzylpyridinium bromide (N-benzylnicotinamide, BNA), C13H13N2O+·Br-, (I), and 1-benzyl-1,4-dihydropyridine-3-carboxamide (N-benzyl-1,4-dihydronicotinamide, rBNA), C13H14N2O, (II), are valuable model compounds used to study the enzymatic cofactors NAD(P)+ and NAD(P)H. BNA was crystallized successfully and its structure determined for the first time, while a low-temperature high-resolution structure of rBNA was obtained. Together, these structures provide the most detailed view of the reactive portions of NAD(P)+ and NAD(P)H. The amide group in BNA is rotated 8.4 (4)° out of the plane of the pyridine ring, while the two rings display a dihedral angle of 70.48 (17)°. In the rBNA structure, the dihydropyridine ring is essentially planar, indicating significant delocalization of the formal double bonds, and the amide group is coplanar with the ring [dihedral angle = 4.35 (9)°]. This rBNA conformation may lower the transition-state energy of an ene reaction between a substrate double bond and the dihydropyridine ring. The transition state would involve one atom of the double bond binding to the carbon ortho to both the ring N atom and the amide substituent of the dihydropyridine ring, while the other end of the double bond accepts an H atom from the methylene group para to the N atom.

Site-selective substitution of gold atoms in the Au24(SR)20 nanocluster by silver.

The synthesis and structure determination of atomically precise alloy nanoclusters have attracted much attention in recent research. Herein, we report a new alloy nanocluster Au24-xAgx(TBBM)20 (x∼1) synthesized via a ligand-exchange-induced size/structure transformation method. Its X-ray structure is obtained successfully and the dopant Ag is found to occupy three special positions in the kernel, rather than equivalently over all the kernel sites. This selective occupancy is interesting and DFT calculation results suggest that the relative oxidation state (rationalized as difference in the charge) of the Ag when doped into the cluster is likely determining the most favorable doping positions. This work provides a new strategy for controlled synthesis of new Au-Ag nanoclusters and also reveals a new scenario for the doping position of Ag atoms in Au-Ag bimetal nanoclusters.

Emergence of hierarchical structural complexities in nanoparticles and their assembly.

We demonstrate that nanoparticle self-assembly can reach the same level of hierarchy, complexity, and accuracy as biomolecules. The precise assembly structures of gold nanoparticles (246 gold core atoms with 80 p-methylbenzenethiolate surface ligands) at the atomic, molecular, and nanoscale levels were determined from x-ray diffraction studies. We identified the driving forces and rules that guide the multiscale assembly behavior. The protecting ligands self-organize into rotational and parallel patterns on the nanoparticle surface via C-H⋅⋅⋅π interaction, and the symmetry and density of surface patterns dictate directional packing of nanoparticles into crystals with orientational, rotational, and translational orders. Through hierarchical interactions and symmetry matching, the simple building blocks evolve into complex structures, representing an emergent phenomenon in the nanoparticle system.

Synthesis and Properties of "Sandwich" Diimine-Coinage Metal Ethylene Complexes.

Synthesis and full characterization of cationic isostructural "sandwich" diimine-coinage metal ethylene complexes are reported. Ethylene self-exchange kinetics proceeds by an associative exchange mechanism for Cu and Au complexes. The fastest ligand exchange was observed for Ag complex 8a. The upper limit of ΔG‡, assuming associative ligand exchange, was found to be ca. 5.0 kcal/mol. Ethylene self-exchange in Cu complex 7b proceeds with ΔG298‡ = 12.9 ± 0.1 kcal/mol, while the exchange is the slowest in Au complex 9, with ΔG298‡ = 16.7 ± 0.1 kcal/mol. Copper complex 7b is unusually stable and can survive in air for years.

Aluminum alkoxide, amide and halide complexes supported by a bulky dipyrromethene ligand: synthesis, characterization, and preliminary ε-caprolactone polymerization activity.

Aluminum halide, alkoxide and amide complexes 2-6 of the form (N,N)AlX2-nYn (n = 0, 1 and (N,N) = 1,9-dimesityl-5-phenyldipyrromethene (1)) were synthesized and characterized by NMR spectroscopy and X-ray crystallography. The in situ generated lithium salt of dipyrromethene 1 was reacted with AlX3 to afford aluminum halide complexes (N,N)AlX2 (X = Cl (2), I (3)) which were isolated as dichroic crystals. Salt metathesis reactions were employed to produce alkoxide complexes (N,N)Al(Cl)(O(t)Bu) (4) and (N,N)Al(O(t)Bu)2 (5) from compound 2. The dimethylamide complex (N,N)Al(NMe2)2 (6) was prepared by reaction of dipyrromethene 1 with [Al(NMe2)3]2. Crystallographic data revealed that the dipyrromethene is non-planar when bulky coligands are present as in compounds 3-6, while in the dichloride complex 2 the dipyrromethene is planar. Halide complexes 2 and 3 reacted with adventitious moisture in toluene to afford crystalline acid-base adducts (N,N)H·HX, (X = Cl (7), I (8)), which adopted structures reminiscent of anion receptors. Alkoxide and dimethylamide complexes 5 and 6 were also applied as precatalysts for the ring-opening polymerization of ε-caprolactone and preliminary results are reported.

Gold Quantum Boxes: On the Periodicities and the Quantum Confinement in the Au28, Au36, Au44 , and Au52 Magic Series.

Revealing the size-dependent periodicities (including formula, growth pattern, and property evolution) is an important task in metal nanocluster research. However, investigation on this major issue has been complicated, as the size change is often accompanied by a structural change. Herein, with the successful determination of the Au44(TBBT)28 structure, where TBBT = 4-tert-butylbenzenethiolate, the missing size in the family of Au28(TBBT)20, Au36(TBBT)24, and Au52(TBBT)32 nanoclusters is filled, and a neat "magic series" with a unified formula of Au8n+4(TBBT)4n+8 (n = 3-6) is identified. Such a periodicity in magic numbers is a reflection of the uniform anisotropic growth patterns in this magic series, and the n value is correlated with the number of (001) layers in the face-centered cubic lattice. The size-dependent quantum confinement nature of this magic series is further understood by empirical scaling law, classical "particle in a box" model, and the density functional theory calculations.

Heavily doped Au25-xAgx(SC6H11)18(-) nanoclusters: silver goes from the core to the surface.

We report a method for heavy doping of the Au25(SR)18 nanocluster (where R = C6H11) with silver through the Ag(I)-thiolate complex induced size/structure transformation of Au23(SR)16(-) into Au25-xAgx(SR)18(-). X-ray crystallographic analysis revealed that Ag dopants are distributed not only in the icosahedral core but also in the surface staple motifs; the latter was not achieved in earlier studies of alloy Au25-xAgx nanoclusters.

Structural patterns at all scales in a nonmetallic chiral Au133(SR)52 nanoparticle.

Structural ordering is widely present in molecules and materials. However, the organization of molecules on the curved surface of nanoparticles is still the least understood owing to the major limitations of the current surface characterization tools. By the merits of x-ray crystallography, we reveal the structural ordering at all scales in a super robust 133-gold atom nanoparticle protected by 52 thiolate ligands, which is manifested in self-assembled hierarchical patterns starting from the metal core to the interfacial -S-Au-S- ladder-like helical "stripes" and further to the "swirls" of carbon tails. These complex surface patterns have not been observed in the smaller nanoparticles. We further demonstrate that the Au133(SR)52 nanoparticle exhibits nonmetallic features in optical and electron dynamics measurements. Our work uncovers the elegant self-organization strategies in assembling a highly robust nanoparticle and provides a conceptual advance in scientific understanding of pattern structures.

Crystal Structure of Barrel-Shaped Chiral Au130(p-MBT)50 Nanocluster.

We report the structure determination of a large gold nanocluster formulated as Au130(p-MBT)50, where p-MBT is 4-methylbenzenethiolate. The nanocluster is constructed in a four-shell manner, with 55 gold atoms assembled into a two-shell Ino decahedron. The surface is protected exclusively by -S-Au-S- staple motifs, which self-organize into five ripple-like stripes on the surface of the barrel-shaped Au105 kernel. The Au130(p-MBT)50 can be viewed as an elongated version of the Au102(SR)44. Comparison of the Au130(p-MBT)50 structure with the recently discovered icosahedral Au133(p-TBBT)52 nanocluster (where p-TBBT = 4-tert-butylbenzenethiolate) reveals an interesting phenomenon that a subtle ligand effect in the para-position of benzenethiolate can significantly affect the gold atom packing structure, i.e. from the 5-fold twinned Au55 decahedron to 20-fold twinned Au55 icosahedron.