Chalcogens-Induced Ag6Z4@Ag36 (Z = S or Se) Core-Shell Nanoclusters: Enlarged Tetrahedral Core and Homochiral Crystallization.

Control over core structure is much more challenging than that over shell structure in core-shell silver nanoclusters. Herein, two isostructural chalcogen-mediated [Ag6Z4@Ag36] (Z = S or Se) nanoclusters (SD/Ag42a and SD/Ag42b) caging tetrahedral [Ag6Z4] as cores were synthesized by introducing Ph3CSH or Ph3PSe as slow-release source of S2- or Se2-, respectively, and characterized by single-crystal X-ray diffraction (SCXRD). As compared to the previously reported [AgS4@Ag36] cluster (Ag37), we found that introducing additional S2- or Se2- ions can effectively enlarge the inner core from tetrahedral AgS4 to Ag6Z4, which is a regular octahedron of silver with four Z2- capping on one tetrahedral set of four faces. More interestingly, the molecular enantiomers of SD/Ag42a and SD/Ag42b segregate into different crystals (P212121), while those of Ag37 form racemic crystals (I41/acd). The larger Ag6Z4 core in Ag42 clusters also extends their emission to the near-infrared region (∼760 nm). The study confirms that chalcogenide can enlarge the nuclearity of nanoclusters by altering the inner core structure and affords a new strategy to synthesize chiral core-shell silver nanoclusters of higher-order in controlled fashion.

Carboxylic acid stimulated silver shell isomerism in a triple core-shell Ag84 nanocluster.

Isomerization is highly important in all aspects of science, yet it is rarely observed in nanoscience. Here, we synthesized a unique triple core-shell Ag84 nanocluster displaying isomerism, which is controlled by different carboxylic acids and a one-way transformation (SD/Ag84a → SD/Ag84b). The innermost core is a rare Ag10 nanocluster which comprises an Ag6 octahedral unit as seen in face-centred cubic (fcc) silver metal and four capped Ag atoms. It templates two crescent-shaped polyoxometalate (W7O26)10- shells which are then enclosed in a shell of silver shaped as rugby balls. The organic ligands (iPrS-, n PrCOO- and PhCOO-) finally shield the metallic clusters. Due to slight differences in structure at two poles and the steric hindrance of n PrCOO- and PhCOO-, SD/Ag84a and SD/Ag84b adopt the shapes of flat-headed and cuspidal prolate spheres, respectively. Interestingly, PhCOOH is dominant over n PrCOOH whereby crystals of SD/Ag84b were isolated if PhCOOH is added during the synthesis of SD/Ag84a. This demonstrates that PhCOOH not only alters the organic coats but also induces metal shell re-organization. This work reveals carboxylate-controlled skeletal isomerism in silver nanoclusters for the first time, thus deepening the understanding of silver nanocluster assembly, flexibility and reactivity.

Unusual fcc-structured Ag10 kernels trapped in Ag70 nanoclusters.

Controlled trapping atom-precise ultrasmall silver nanoparticles into silver nanoclusters is challenging; thus only limited progress has been made in this area. We are therefore inspired to isolate two novel silver nanoclusters, Ag10@Ag70 (SD/Ag80a and SD/Ag80b; SD = SunDi), where a novel fcc-structured Ag10 kernel built from two single-edge opened Ag6 octahedra by sharing one edge is trapped. The bioctahedral Ag10 kernel is locked by a pair of Mo7O26 10- anions to form an inner Ag10@(Mo7O26)2 core which is further encapsulated by an outer Ag70 shell to form three-shell Ag10@(Mo7O26)2@Ag70 nanoclusters. Notably, the bioctahedral Ag10 kernel has not been observed in silver nanoclusters ever before, thus representing a new embryo state of silver nanoparticles. SD/Ag80a emits in the near infrared (NIR) region (λ em = 730 nm) at low temperature. This work will deepen our understanding on the atomic-level growth of silver nanoparticles and complicated three-shell self-assembly involving polyoxometalate (POM) and two different silver nanoclusters.

[Au18(dppm)6Cl4]4+: a phosphine-protected gold nanocluster with rich charge states.

A diphosphine-protected 18-gold-atom nanocluster was isolated via a facile reduction of an AuI precursor by NaBH4. Its composition was identified as {[Au18(dppm)6Cl4]·C6H6·3Cl·PF6} (SD/Au18, SD = SunDi; dppm = bis-(diphenylphosphino)methane) by X-ray single crystal structural analysis. This nanocluster possesses a prolate shape and is built from an Au10 kernel (bi-octahedral Au6 units sharing one edge) fused with two Au7 caps via sharing six gold atoms. The identity of the Au18 cluster is further demonstrated by ESI-MS. The number of valence electrons of [Au18(dppm)6Cl4]4+ is 10 (n* = 18-4-4), which does not match with the known magic numbers according to the spherical jellium model, and elongated models must be considered. The special stability of the Au18 cluster likely arises from geometrical factors in the metallic core. Two charge states are reported for this system. This work not only presents the structure elucidation of a diphosphine-protected Au18 nanocluster, but also provides an important insight into the growth pattern of gold nanoclusters and the charge states they can achieve.

Core Modulation of 70-Nuclei Core-Shell Silver Nanoclusters.

The reaction of {(HNEt3 )2 [Ag10 (tBuC6 H4 S)12 ]}n , Ag2 O, Na2 MoO4 , and m-methoxybenzoic acid (Hmbc) in CH3 OH/CH2 Cl2 led to yellow crystals of [Ag4 S4 (MoO4 )5 @Ag66 ] (SD/Ag70b; SD=SunDi) only, while in the presence of DMF, additional dark-red crystals of [Ag10 @ (MoO4 )7 @Ag60 ] (SD/Ag70a) were obtained. SD/Ag70b consists of five MoO4 2- ions wrapped by a shell of 66 Ag atoms, while SD/Ag70a contains a rare Ag10 kernel consisting of five tetrahedra sharing faces and edges, surrounded by seven MoO4 2- ions enclosed in a shell of 60 Ag atoms. The formation of the Ag10 kernel originates from a reduction reaction during the self-assembly process that involves DMF. This work provides the structural information of a unique Ag10 kernel (five fused Ag4 tetrahedra) and paves an avenue to trap elusive silver species with hierarchical multi-shell silver nanocluster assemblies with the help of anion templates.

Different Silver Nanoparticles in One Crystal: Ag210 (i PrPhS)71 (Ph3 P)5 Cl and Ag211 (i PrPhS)71 (Ph3 P)6 Cl.

Two pure silver nanoparticles (Ag210 (i PrPhS)71 (Ph3 P)5 Cl and Ag211 (i PrPhS)71 (Ph3 P)6 Cl labeled as SD/Ag210 and SD/Ag211 (SD=SunDi), were found to co-crystallize in forming compound 1. Single-crystal X-ray diffraction (SCXRD) revealed that they differ by only one Ag(PPh3 ). Their four-shell nanoparticles consist of three pure Ag metal shells (Ag19 @Ag52 @Ag45 ) shielded by a silver-organic Ag89 (i PrPhS)71 Cl[Ag(Ph3 P)]n outermost shell. The number (n) of Ag(Ph3 P) is five for SD/Ag210 and six for SD/Ag211. The pseudo-fivefold symmetric Ag nanoparticles exhibit surface plasmon absorption similar to a true metallic state but at the nanoscale. This work exemplifies the important effects of phosphine in stabilizing large silver nanoparticles; and offers a platform to investigate the origin of differences in nanoscale metal materials, even differing by only one metal atom; it also sheds light on the regioselective binding of auxiliary Ph3 P on the surface of silver nanoparticles.

Three Silver Nests Capped by Thiolate/Phenylphosphonate.

Introducing phenylphosphonic acid (H2 PPA) into the Ag/tBuSH assembly system has produced a family of nanoscale-sized, high-atom number, silver thiolate/PPA nests (SD/Ag45 a, SD/Ag66 a, and SD/Ag73 a) with impressive core-shell features. SD/Ag45 a is a 45-atom ellipsoid comprised of an Ag36 shell trapping an Ag9 S2 three-bladed rotor inside. SD/Ag66 a comprises an inner rod-like Ag20 core and an outer Ag44 shell, giving a 64-atom nest. These Ag64 nests are further extended by Ag(CN)2 linkers to form a one-dimensional chain structure. SD/Ag73 a is a three-shell 73-nucleus silver nest with a central silver atom enclosed in a rhombicuboctahedron of 24 silver atoms, which is itself enclosed in the outermost shell of a rectified version of a 48-Ag octahedral Goldberg 2,0 cage. The solution behaviors and optical absorption properties of the three nests are described in detail. Of note, SD/Ag45 a and SD/Ag73 a emit in the near-infrared region and show different luminescent thermochromic behavior. This work demonstrates that the participation of H2 PPA strongly influences the structures of silver thiolate nests, thus providing a new route to fabricate and modify them in a more rational way.

Diphosphine-protected ultrasmall gold nanoclusters: opened icosahedral Au13 and heart-shaped Au8 clusters.

Due to distinctive quantum confinement effects, ultrasmall gold nanoparticles usually exhibit interesting electronic structure and molecular-like properties. However, the lack of atomically-precise structural information makes the understanding of them almost impossible, such as understanding the relationships between their compositions and unique properties. Herein, by reducing a diphosphine AuI precursor (Au2(dppm)2Cl2; dppm = Ph2PCH2PPh2) with or without a S2- releasing reagent, we enriched our knowledge of the members in the families of Au13 and Au8 by the structural determinations of two new dppm-protected gold nanoclusters, [Au13(dppm)6]5+ (SD/Au1) and [Au8(dppm)4S2]2+ (SD/Au2), respectively. Within SD/Au1, the Au13 kernel significantly deviates from the ideal Ih icosahedron by the elongation of three surface Au-Au bonds to ∼3.5 Å, giving it C3 symmetry, whereas SD/Au2 has a novel heart-shaped C2 symmetric Au8S2 core (central Au4 tetrahedron + two Au2S units) protected by four µ2-dppm ligands in the outer shell. Of note, SD/Au1 represents a rare Au13 nanocluster with an opened icosahedral geometry, and SD/Au2 shows a new edge-shared "core + 4exo" structure type that has never been observed before. The electronic structures and optical absorption spectra of these systems are correlated with time-dependent density functional theory (TDDFT) calculations. Based on the spherical jellium model, the stability of the Au13 and Au8 nanoclusters can be ascribed to 8- and 2-electron superatoms with 1S21P6 and 1S2 configurations, respectively. Interestingly, the cluster SD/Au2 exhibits bright yellow luminescence with an emission maximum at 591 nm that slightly hypsochromically shifts to 581 nm upon cooling to 93 K. Our findings not only enrich the family of diphosphine-protected ultrasmall gold nanoclusters, but also demonstrate the rich variations of gold kernels during the transformation from a simple AuI precursor to Au nanoclusters.

A giant 90-nucleus silver cluster templated by hetero-anions.

A 90-nucleus silver cluster (SD/Ag38) cocapped by tBuC6H4S- and PhCOO- ligands was synthesized using hetero-anion template method. Single-crystal X-ray diffraction (SCXRD) revealed a 90-nucleus metallic dumbbell-like core constructed by two large W5O19@Ag38 heads sandwiching one slender (SO4)2@Ag14 waist. Both W5O198- and SO42- templates were in situ generated and synergistically induced the formation of the largest known anion-templated silver cluster. Although SD/Ag38 is emission-silent at room temperature, increasingly brighter near-infrared (NIR) emission at ca. 742 nm was detected on cooling from 293 to 93 K.

Benzoate-Induced High-Nuclearity Silver Thiolate Clusters.

Compared with the well-known anion-templated effects in shaping silver thiolate clusters, the influence from the organic ligands in the outer shell is still poorly understood. Herein, three new benzoate-functionalized high-nuclearity silver(I) thiolate clusters are isolated and characterized for the first time in the presence of diverse anion templates such as S2- , α-[Mo5 O18 ]6- , and MoO42- . Single-crystal X-ray analysis reveals that the nuclearities of the three silver clusters (SD/Ag28, SD/Ag29, SD/Ag30) vary from 32 to 38 to 78 with co-capped tBuS- and benzoate ligands on the surface. SD/Ag28 is a turtle-like cluster comprising a Ag29 shell caging a Ag3 S3 trigon in the center, whereas SD/Ag29 is a prolate Ag38 sphere templated by the α-[Mo5 O18 ]6- anion. Upon changing from benzoate to methoxyl-substituted benzoate, SD/Ag30 is isolated as a very complicated core-shell spherical cluster composed of a Ag57 shell and a vase-like Ag21 S13 core. Four MoO42- anions are arranged in a supertetrahedron and located in the interstice between the core and shell. Introduction of the bulky benzoate changes elaborately the nuclearity and arrangements of silver polygons on the shell of silver clusters, which is exemplified by comparing SD/Ag28 and a known similar silver thiolate cluster. The three new clusters emit luminescence in the near-infrared (NIR) region and show different thermochromic luminescence properties. This work presents a flexible approach to synthetic studies of high-nuclearity silver clusters decorated by different benzoates, and structural modulations are also achieved.

Anisotropic Assembly of Ag52 and Ag76 Nanoclusters.

Although there has been an upsurge of interest in anisotropic assembly of inorganic nanoparticles, atomically precise self-assembly of anisotropic metal clusters is extremely rare. Herein, we presented two novel silver nanoclusters, Ag52 (SD/Ag23) and Ag76 (SD/Ag24), which are interiorly templated by five MoO42- and a pair of Mo6O228- anions, respectively, and coprotected by bridging RSH and terminal diphosphine ligands exteriorly. Regiospecific distribution diphosphine ligands on the surface and the arrangement of multiple molybdate templates within the nanoclusters synergetically tailor their shapes to anisotropic oblate spheroid and elongated rod, respectively. This work not only open up new avenues for the synthesis of silver nanoclusters with novel metal skeleton shapes and anisotropic surface structures but also give important insights for the anisotropic growth of silver nanoclusters through surface modifications or/and template organizations.

Elimination-Fusion Self-Assembly of a Nanometer-Scale 72-Nucleus Silver Cluster Caging a Pair of [EuW10 O36 ]9- Polyoxometalates.

The largest known polyoxometalate (POM)-templated silver-alkynyl cluster, [(EuW10 O36 )2 @Ag72 (tBuC≡C)48 Cl2 ⋅4 BF4 ] (SD/Ag20), was isolated under solvothermal conditions and structurally characterized. It was confirmed by single-crystal X-ray diffraction (SCXRD) as a {EuW10 }2 -in-{Ag72 } clusters-in-cluster rod-like compound. The high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) shows that such a double anion-templated cluster is assembled from a crucial single anion-templated Ag42 intermediate in the solution. The crystallization of Ag42 species (SD/Ag21), followed by SCXRD, gave an important clue about the assembly route of SD/Ag20 in solution: the Ag42 cluster eliminates six silver atoms laterally, then fuses together at the vacant face to form the final Ag72 cluster (elimination-fusion mechanism). The characteristic emission of [EuW10 O36 ]9- is well maintained in SD/Ag20. This work not only provides a new method for the synthesis of larger silver clusters as well as the functional integration of the silver cluster and POMs, but also gives deep insights about the high-nuclear silver cluster assembly mechanism.

Johnson Solids: Anion-Templated Silver Thiolate Clusters Capped by Sulfonate.

Sulfonates were incorporated into six novel high-nuclearity silver(I) thiolate clusters under the guidance of anion templates varied from S2- , SO42- , α-[Mo5 O18 ]6- , ß-[Mo5 O18 ]6- , [Mo2 O8 ]4- , to [Mo4 O14 (SO4 )]6- . Single crystal X-ray analysis revealed that SD/Ag1, SD/Ag3, SD/Ag5, and SD/Ag6 are discrete [S@Ag60 ], [α-Mo5 O18 @Ag36 ], [Mo2 O8 @Ag30 ]2 , and [Mo4 O14 (SO4 )@Ag73 ] clusters, respectively, whereas SD/Ag2 and SD/Ag4 are one-dimensional (1D) chains based on the [SO4 @Ag20 ] and [ß-Mo5 O18 @Ag36 ] cluster subunits, respectively. Their silver skeletons are protected exteriorly by thiolates and sulfonates and interiorly supported by diverse anions as templates. Structurally, cluster SD/Ag1 is a typical core-shell structure comprised of an inner Ag12 cuboctahedron and an outer Ag48 shell. The sulfate-templated drum-like Ag20 cluster subunits are bridged by PhSO3- to give a 1D chain of SD/Ag2. Complex SD/Ag3 and SD/Ag4 are spindle-like Ag36 clusters with isomeric [Mo5 O18 ]6- inside, and the latter is further extended to a 1D chain through PhSO3- bridges. A pair of [Mo2 O8 ]4- templated gourd-like Ag30 clusters are dimerized in a head-to-head fashion to form SD/Ag5. Complex SD/Ag6 is the largest cluster in this family and doubly templated by unprecedented [Mo4 O14 (SO4 )]6- anions. Geometrically, the silver shells of SD/Ag1-SD/Ag5 show the polyhedral features of Johnson solids, instead of the usual Platonic or Archimedean solids. Solution behaviors and luminescent properties were also investigated in detail.

Multifunctional Triple-Decker Inverse 12-Metallacrown-4 Sandwiching Halides.

A family of six triple-decker complexes, {(MX)2[(pz)4]3} (Hpz = 4-nitropyrazole, MX = NaCl, 1; NaBr, 2; NaI, 3; KCl, 4; KBr, 5, and KI, 6), exhibiting inclusion of halides into inverse 12-metallacrown-4 [inv-(12-MCCu(I),pz-4)] array has been realized. Single-crystal X-ray crystallography of each compound reveals a common structural feature consisting of four CuI ions bonded by four pz to form a square metallomacrocycle comprising four metal centers and eight N atoms, thus giving an inv-[12-MCCu(I),pz-4] motif. Two halides are sandwiched by three inv-[12-MCCu(I),pz-4] to form triple-deckers that are further extended in an offset stacking mode by ligand-unsupported cuprophilicity interactions to form a one-dimensional chain structure. Halides are attached to six CuI centers with weak CuI···halogen interaction, resembling anion templates. High-resolution electrospray ionization mass spectrometry reveals that the predominant fragments corresponding to a half of the triple-decker structures of 1-3 exist in solution. Compounds 4, 5, and 6 showed excellent electrocatalytic activities toward the reduction of nitrite and can also be used as selective "turn-off" sensors for Ag(I) in water. The present results will be helpful for the future design and synthesis of functional inverse metallacrowns and their multiple-decker complexes.

Anion-Templated Nanosized Silver Alkynyl Clusters: Cluster Engineering and Solution Behavior.

Assembly of nanosized polynuclear metal clusters from simple building blocks usually involves complicated self-organization processes and thus is a long-standing challenge. Here, we demonstrate the controllable assembly, single-crystal structures and solution behaviors of four molecular assemblies based on nanosized silver alkynyl clusters, formulated as {[(CrO4 )2 Cl@Ag42 (PhC≡C)34 (CF3 COO)2 ]⋅CF3 COO} (1), {(NH4 )[(CrO4 )2 Cl@Ag42 (PhC≡C)34 (CrO4 )(H2 O)2 ]⋅2BF4 ⋅CH3 OH}n (2), [(CrO4 )@Ag22 (PhC≡C)16 (CF3 SO3 )4 ]n (3), and {[(CrO4 )2 @Ag31 (PhC≡C)22 (CF3 SO3 )4 ]⋅CF3 SO3 ⋅2CH3 OH⋅H2 O}n (4). In the presence of concomitant CrO42- and Cl- templates, we could isolate a discrete cluster 1 and a polymeric chain-like compound 2 by using different silver salts. Both 1 and 2 have a similar 42-metallic cage, which traps two CrO42- and one Cl- as anion templates. Using sole CrO42- template, 3 and 4 were simultaneously isolated in a one-pot reaction. Both of them are 1D chain structures based on single CrO42- templated Ag18 and double CrO42- templated Ag30 clusters, respectively. HR-ESI-MS was used to study the solution behaviors of 1-4. This work has the following purposes: i) it presents the cluster engineering concept used in the assembly of polynuclear silver alkynyl clusters; ii) it exemplifies template effects from hetero and homo anions; and iii) it provides a controllable way to achieve assembly of silver alkynyl clusters.

[Reaction mechanism of cefotaxime with human serum albumin].

The reaction mechanism of cefotaxime with human serum albumin (HSA) and the affinity between cefotaxime and beta-lactamase were investigated by spectrometry and spectrofluorimetry. The interaction dissociation constants of human serum albumin and cefotaxime were determined from a double reciprocal Lineweaver-Burk plot. The binding distance and transfer efficiency between cefotaxime and HSA were also obtained according to the theory of Förster non-radiation energy transfer. The result suggested that the main binding force between cefotaxime and HSA is electrostatic force interaction. The high beta-lactamase stability of cefotaxime may be correlative with its molecular structure. The antibiotic activity and valence are connected with transfer efficiency and dissociation constant. The effect of cefotaxime on the conformation of HSA was also analyzed using synchronous fluorescence spectrometry.