Anion-Templated Syntheses of Rhombohedral Silver-Alkynyl Cage Compounds

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.

Asymmetrically fused polyoxometalate-silver alkynide composite cluster

We demonstrate that an asymmetric composite cluster, [Ag25{C≡CC(CH3)3}16(CH3CN)4(P2W15Nb3O62)] (1), consisting of directly fused polyoxometalate and silver alkynide moieties can be facilely synthesized by a one-pot reaction between a Nb-substituted Dawson-type polyoxometalate, H4[α-P2W15Nb3O62](5-), and the mixture of (CH3)3CC≡CAg and CF3SO3Ag. Single-crystal X-ray diffraction revealed the structure of 1, where Ag atoms are selectively attached to the Nb-substituted hemisphere of the pedestal Dawson anion. Its structural integrity in the solution was demonstrated by (31)P NMR spectroscopy and analytical ultracentrifugation. The latter method also unveiled the stepwise formation mechanism of 1.

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⁻.

Anion complexation with cyanobenzoyl substituted first and second generation tripodal amide receptors: crystal structure and solution studies

Solid and solution state anion binding via a side cleft and pseudocapsular fashion by two cyanophenyl substituted first (L1) and second (L2) generation tripodal amides has been demonstrated along with a selective anion induced conformational change of L2 from open C_2v to folded C_3v symmetry.

An organic anion template: a 24-nucleus silver cluster encapsulating a squarate dimer

An unprecedented organic anion templated silver cluster has been isolated, leading to unusual π–π interaction within the encapsulated squarate dimer.

Shedding light on the photochemistry of coinage-metal phosphorescent materials: a time-resolved Laue diffraction study of an Ag(I)-Cu(I) tetranuclear complex

The triplet excited state of a new crystalline form of a tetranuclear coordination d(10)-d(10)-type complex, Ag2Cu2L4 (L = 2-diphenylphosphino-3-methylindole ligand), containing Ag(I) and Cu(I) metal centers has been explored using the Laue pump-probe technique with ≈80 ps time resolution. The relatively short lifetime of 1 μs is accompanied by significant photoinduced structural changes, as large as the Ag1···Cu2 distance shortening by 0.59(3) Å. The results show a pronounced strengthening of the argentophilic interactions and formation of new Ag···Cu bonds on excitation. Theoretical calculations indicate that the structural changes are due to a ligand-to-metal charge transfer (LMCT) strengthening the Ag···Ag interaction, mainly occurring from the methylindole ligands to the silver metal centers. QM/MM optimizations of the ground and excited states of the complex support the experimental results. Comparison with isolated molecule optimizations demonstrates the restricting effect of the crystalline matrix on photoinduced distortions. The work represents the first time-resolved Laue diffraction study of a heteronuclear coordination complex and provides new information on the nature of photoresponse of coinage metal complexes, which have been the subject of extensive studies.

Dual templated synthesis of silver acetylide cluster-encapsulated supramolecular boxes

A dual-templated approach for the controllable synthesis of metal cluster complexes is described. By using an acetylide-containing anion with specific geometry as a central template and a macrocyclic coordinative compound as a peripheral one, two multinuclear silver-acetylide cluster-encapsulated supramolecular boxes were synthesized.