Ligand- and Anion-Controlled Formation of Silver Alkynyl Oligomers from Soluble Precursors

The interesting luminescence behavior and rare nonlinear optical properties of the {Ag55Mo6} nanocluster

The remarkably reversible thermochromic luminescence behavior and the rare nonlinear optical (NLO) properties of the [Ag55(MoO4)6(C[triple bond, length as m-dash]C t Bu)24(CH3COO)18(CH3COO)]·2H2O ({Ag55Mo6} for short) nanocluster reported were investigated experimentally. The important contributions of Ag+, C[triple bond, length as m-dash]C- ions and MoO4 2- groups to the NLO properties were proved by further density functional theory (DFT) calculations.

First-principles exploration of the versatile configurations at an alkynyl-protected coinage metal(111) interface

Alkynyl groups (R-C[triple bond, length as m-dash]C-) have attracted intense interest recently as alternative ligands to thiolates to protect atomically precise coinage metal nanoclusters, and more than two dozen compositions have been structurally resolved. However, structure determinations indicated that the interface shows strong metal sensitivity, where a staple motif is the common structural feature at the interface of Au-alkynyl nanoclusters, while the bridging motif dominates at the RC[triple bond, length as m-dash]C-/Ag and RC[triple bond, length as m-dash]C-/Cu interface. To understand their interfacial differences, we employed density functional theory (DFT) calculations to examine the versatile interfacial structures between CH3C[triple bond, length as m-dash]C- and the coinage metal surface; both the (111) surface as well as a surface with a metal adatom are investigated. We find that the alkynyl/gold(111) interface does prefer to form the staple motifs, and a linear flat-lying staple motif is preferred. The adatom occupies the bridge position and two CH3C[triple bond, length as m-dash]C- ligands lie diagonally at the fcc hollow sites with the C[triple bond, length as m-dash]C bond interacting with the surface Au by both σ- and π-coordination modes. In contrast, the bridging motif is energetically more favored on Ag(111) and Cu(111). The alkynyl carbons form strong σ, π- or σ-only bonds with the surface Ag/Cu, forming μ3-bridge coordination over the fcc hollow site. The binding strengths have the order of Cu(111) > Ag(111) > Au(111). The difference in structural preference is attributed to the intrinsic metal attributes with the different gaps of energetic penalty for surface energy, adatom creation and vacancy formation. The other two reasons are the differences of alkynyl-metal bond character and vdW interaction. We further show that this structure preference is also the preferred bonding mode of CH3C[triple bond, length as m-dash]C- on M55 clusters and the CH3S-/M(111) interface. Our insights greatly facilitate the structural elucidation and provide useful guidelines for future structure predictions in alkynyl-protected metal nanosystems.

A one-dimensional infinite silver alkynyl assembly [Ag8(C[triple bond, length as m-dash]C t Bu)5(CF3COO)3(CH3CN)] n : synthesis, crystal structure and properties

A high-yield silver alkynyl assembly [Ag8(C[triple bond, length as m-dash]C t Bu)5(CF3COO)3(CH3CN)] n (1) constructed from [AgC[triple bond, length as m-dash]C t Bu] n ligand, CF3COOAg and CH3CN auxiliary ligands with a one-dimensional infinite chain structure has been obtained in one pot. Compound 1 has been well-defined and characterized. The photocurrent properties and the temperature-sensitive luminescent properties of 1 have been investigated.

Self-assembly of water-soluble silver nanoclusters: superstructure formation and morphological evolution

Supramolecular self-assembly, based on non-covalent interactions, has been employed as an efficient approach to obtain various functional materials from nanometer-sized building blocks, in particular, [Ag₆(mna)₆]^6-, mna = mercaptonicotinate (Ag₆-NC). A challenging issue is how to modulate the self-assembly process through regulating the relationship between building blocks and solvents. Herein, we report the controlled self-assembly of hexanuclear silver nanoclusters into robust multilayer vesicles in different solvents, DMSO, CH₃CN, EG and MeOH. Their unique luminescence enables them to be bifunctional probes to sense Fe³⁺ and dl-dithiothreitol (DTT). By protonating the Ag₆-NC to Ag₆-H-NC using hydrochloric acid (HCl), the multilayer vesicles survive in aprotic solvents, DMSO and CH₃CN, but are transformed to nanowires in protic solvents, water, EG and MeOH. Our results demonstrated that the solvent-bridged H-bond plays a key role in the evolution of the morphologies from vesicles to nanowires. Moreover, the nanowires could further hierarchically self-assemble in water into hydrogels with high water content (99.5%), and with remarkable mechanical strength and self-healing properties. This study introduces a robust cluster-based building block in a supramolecular self-assembly system and reveals the significance of aprotic and protic solvents for the modulation of the morphologies of cluster-based aggregates.

Silver(i)-organic frameworks constructed from silver(i) 3,6-pyrazyldiethynide and 3,8-1,10-phenanthrolyldiethynide complexes

Two diynes bearing functional groups with different binding modes, 3,6-diethynylpyrazine (H₂L1) and 3,8-diethynyl-1,10-phenanthroline (H₂L2), were utilized as ligands to synthesize two new organometallic units, Ag₂L1·3AgNO₃ (1) and Ag₂L2·6AgNO₃ (2), in order to investigate the effect of the bridging and chelating modes of the ligands on the structures of networks constructed from silver-ethynide compounds. Structural studies show that in 1, silver-ethynide cluster units aggregate to form chair-like organometallic slides through Ag-N coordination bonds. These slides are linked through argentophilic interaction to generate novel 2D ladder-like layers, and are further bridged by nitrate anions to afford a 3D network in the solid state. It is observed that all the Ag ions in one layer interact to afford a 2D silver network. However, in 2, the silver-ethynide cluster units only interact to generate unique sine wave-like organometallic chains through argentophilic interaction, which are further connected by nitrate anions to form a 3D network. In the solid state, both 1 and 2 are luminescent at room temperature.

A Silver(I)-Estrogen Nanocluster: GSH Sensitivity and Targeting Suppression on HepG2 Cell

A structure-determined silver nanocluster of [Ag₁₀ (Eth)₄ (CF₃ COO)₆ (CH₃ OH)₃ ]·3C-H₃ OH (Eth = ethisterone) (1), is firstly demonstrated by self-assembly of silver salt and ethisterone. Due to the thiophilicity of silver(I) ions, complex 1 shows reactivity with glutathione (GSH) molecules in solution and induces the fluorescence quenching behavior. Thus, complex 1 can be used as a fluorescent sensor for GSH. In consideration of the higher level of GSH in cancerous cells, complex 1 presents significant tumor suppression reactivity toward the human hepatocellular carcinoma (HepG2) cells with IC₅₀ value of 165 × 10^-9 m. Especially, complex 1 displays 3.4-fold higher in vitro cytotoxicity to HepG2 cells than that of the normal CCC-HEL-1 cells, which makes complex 1 a potential targeting suppression agent for cancerous cells. The molecular design of complex 1 not only generates a new medicine-silver(I) cluster family, but also opens a new avenue to the targeting anticancer organosilver(I) materials.

Role of Anions Associated with the Formation and Properties of Silver Clusters

Metal clusters have been very attractive due to their aesthetic structures and fascinating properties. Different from nanoparticles, each cluster of a macroscopic sample has a well-defined structure with identical composition, size, and shape. As the disadvantages of polydispersity are ruled out, informative structure-property relationships of metal clusters can be established. The formation of a high-nuclearity metal cluster involves the organization of metal ions into a complex entity in an ordered way. To achieve controllable preparation of metal clusters, it is helpful to introduce a directing agent in the formation process of a cluster. To this end, anion templates have been used to direct the formation of high nuclearity clusters. In this Account, the role of anions played in the formation of a variety of silver clusters has been reviewed. Silver ions are positively charged, so anionic species could be utilized to control the formation of silver clusters on the basis of electrostatic interactions, and the size and shape of the resulted clusters can be dictated by the templating anions. In addition, since the anion is an integral component in the silver clusters described, the physical properties of the clusters can be modulated by functional anions. The templating effects of simple inorganic anions and polyoxometales are shown in silver alkynyl clusters and silver thiolate clusters. Intercluster compounds are also described regarding the importance of anions in determining the packing of the ion pairs and making contribution to electron communications between the positive and negative counterparts. The role of the anions is threefold: (a) an anion is advantageous in stabilizing a cluster via balancing local positive charges of the metal cations; (b) an anion template could help control the size and shape of a cluster product; (c) an anion can be a key factor in influencing the function of a cluster through bringing in its intrinsic properties. Properties including electron communication, luminescent thermochromism, single-molecule magnet, and intercluster charge transfer associated with anion-directed silver clusters have been discussed. We intend to attract chemists' attention to the role that anions could play in determining the structures and properties of metal complexes, especially clusters. We hope that this Account will stimulate more efforts in exploiting new role of anions in various metal cluster systems. Anions can do much more than counterions for charge balance, and they should be considered in the design and synthesis of cluster-based functional materials.

Self-assembly of an unprecedented polyoxomolybdate anion [Mo20O66]12- in a giant peanut-like 62-core silver-thiolate nanocluster

A polyoxometalate-templated silver thiolate nanocluster, [Ag62(S(t)Bu)40(Mo20O66)(Mo6O19)3(CH3CN)2]·(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(S(t)Bu)40](22+) encapsulates an unprecedented [Mo20O66](12-) polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters.

Assembly of silver alkynyl compounds with various nuclearities

A series of silver alkynyl oligomers exhibiting nuclearities varying from 3 to 12 have been isolated. The new structural motifs are obtained by controlling the reactant ratios and using ligands/anions with different nature.

A silver-alkynyl cluster encapsulating a fluorescent polyoxometalate core: enhanced emission and fluorescence modulation

A fluorescent polyoxometalate-based silver(i)-alkynyl cluster exhibits sensitivity towards high energy UV irradiation and selectivity for detection of S²⁻.

High-nuclearity silver clusters templated by carbonates generated from atmospheric carbon dioxide fixation

Two high-nuclearity silver clusters have been prepared by reacting AgC(2)Bu(t) with AgBF(4) (or AgOTf) in the presence of TMEDA in air. The reaction takes up atmospheric CO(2) to give CO(3)(2-), which functions as a template for the formation of the cage compounds, whose nuclearities depend on the particular counteranions employed.