Hexanuclear Silver Research Articles

Atomically precise chiral silver clusters based on non-chiral ligands for acid/base stimulated luminescence response.

Chiral metal nanoclusters synthesized by non-chiral ligands are usually in the form of racemates. Thus, resolving racemic compounds continues to be a great challenge. Herein, we report a case of the racemic compound hexanuclear silver cluster (Ag6-Rac) protected by the non-chiral sulfhydryl ligand sodium 1H-1,2,3-triazole-5-thiolate (SHTT) and 2,6-bis(diphenylphosphino)pyridine (dpppy). The homochiral clusters in Ag6-Rac are able to spontaneously crystallize and undergo chiral resolution to obtain a racemic conglomerate (Ag6-S/Ag6-R) by solvent-induced crystallization. Interestingly, the Ag6-Rac clusters exhibit strong luminescence in solid and solution, which can respond to trifluoroacetic acid (TFA) and reversible cycling over five times using diethylamine (DEA). This work provides a new research model for resolving racemic clusters and constructing stimulus-responsive clusters.

Synthesis and Structural Characterization of a Silver(I) Pyrazolato Coordination Polymer.

Coinage metal(I)···metal(I) interactions are widely of interest in fields such as supramolecular assembly and unique luminescent properties, etc. Only two types of polynuclear silver(I) pyrazolato complexes have been reported, however, and no detailed spectroscopic characterizations have been reported. An unexpected synthetic method yielded a polynuclear silver(I) complex [Ag(μ-L1Clpz)]n (L1Clpz− = 4-chloride-3,5-diisopropyl-1-pyrazolate anion) by the reaction of {[Ag(μ-L1Clpz)]3}2 with (nBu4N)[Ag(CN)2]. The obtained structure was compared with the known hexanuclear silver(I) complex {[Ag(μ-L1Clpz)]3}2. The Ag···Ag distances in [Ag(μ-L1Clpz)]n are slightly shorter than twice Bondi’s van der Waals radius, indicating some Ag···Ag argentophilic interactions. Two Ag–N distances in [Ag(μ-L1Clpz)]n were found: 2.0760(13) and 2.0716(13) Å, and their N–Ag–N bond angles of 180.00(7)° and 179.83(5)° indicate that each silver(I) ion is coordinated by two pyrazolyl nitrogen atoms with an almost linear coordination. Every five pyrazoles point in the same direction to form a 1-D zig-zag structure. Some spectroscopic properties of [Ag(μ-L1Clpz)]n in the solid-state are different from those of {[Ag(μ-L1Clpz)]3}2 (especially in the absorption and emission spectra), presumably attributable to this zig-zag structure having longer but differently arranged intramolecular Ag···Ag interactions of 3.39171(17) Å. This result clearly demonstrates the different physicochemical properties in the solid-state between 1-D coordination polymer and metalacyclic trinuclear (hexanuclear) or tetranuclear silver(I) pyrazolate complexes.

Cover Feature: A Sandwich‐Shaped Hexanuclear Silver Complex with a Giant Cavity Constructed from a Macrocycle with Inward Chelating Units (Eur. J. Inorg. Chem. 4/2021)

Cover Feature: A Sandwich‐Shaped Hexanuclear Silver Complex with a Giant Cavity Constructed from a Macrocycle with Inward Chelating Units (Eur. J. Inorg. Chem. 4/2021)

A Sandwich‐Shaped Hexanuclear Silver Complex with a Giant Cavity Constructed from a Macrocycle with Inward Chelating Units

AbstractThe formation of a macrocyclic hexanuclear silver complex with a giant cavity (diameter ∼16.5 Å) is reported. Six silver centers are sandwiched by two molecules of a macrocyclic ligand possessing six pap (2‐[(pyridin‐2‐ylmethylene)amino]phenol) chelating units, and the metals are arranged on the wall of the internal cavity. Various analytical techniques revealed that each pap binds to the silver as an NN bidentate ligand.

Synthesis, crystal structure, DFT analyses and properties of a sub-nanometer sized hexanuclear silver(I) cluster

The ambient solution reaction of silver salt (CF3COOAg) with a heterolytic thiolate gave rise to the isolation of an air-stable sub-nanometer sized hexanuclear silver(I) cluster, Ag6(dmmp)6‧6CH3OH (1, Hdmmp = 4,6-dimethyl-2-mercaptopyrimidine). X-ray single-crystal structural analysis shows that the Ag66+ core in 1 is a distorted octahedron surrounded by six depronated dmmp ligands as protecting units with each through a simple μ3-bridging coordinating motif. The shortest Ag–Ag bond distance of 2.835 Å in the Ag66+ unit, suggests a closed shell d10‧‧‧d10 argentophilic interactions. DFT studies indicate that the HOMO in 1 is largely composed of d orbitals of AgI ions, while the LUMO mainly consists of s orbitals of AgI ions and p orbitals of S atoms. Hirshfeld surface analysis was also performed to analyze the nature of intermolecular interactions of 1. Complex 1 shows a yellow emission at λmax = 566 nm in the solid state upon excited at 395 nm and antibacterial activity.

A new silver cluster that emits bright-blue phosphorescence.

A new hexanuclear silver(i) cluster (NC-Ag6) that emits bright-blue phosphoresce with a lifetime of 22.4 μs and a quantum yield (QY) of 22% under ambient conditions was synthesized. A film combining NC-Ag6 with yellow cerium(iii)-doped yttrium aluminum garnet phosphors (YAG:Ce3+) displays "chameleon"-like emission (including white), which is related to excitation-dependent Förster resonance energy transfer (FRET) between dual phosphors. The mechanoresponsive luminescence colour of this silver cluster ranges from blue to green virtually without loss of QY.

Synthesis, structures and urease inhibitory activities of three silver(I) complexes derived from 2,6-dichlorophenylacetic acid

Three new silver complexes based on 2,6-dichlorophenylacetate (dcpa), namely [Ag2(dcpa)2]n (1), [Ag(NH3)2](dcpa) (2), and [Ag3(N,N-eten)(dcpa)3]2 (3) (N,N-eten = N,N-diethylethylenediamine), were synthesized and structurally characterized. The dcpa ligand adopts a µ2-η1:η1 bridging coordination mode in silver complexes 1 and 3, whereas it is a non-coordinating counter anion in silver complex 2. Complex 1 shows a two-dimensional sheet polymer in which the dimeric [Ag(dcpa)]2 units with a short Ag···Ag separation of 2.783 Å are linked to each other by weak Ag···O and Ag···Cl interactions. Complex 2 contains a linear [Ag(NH3)2]+ cation and a dcpa anion, which constructs a two-dimensional sheet structure via intermolecular N–H···O interactions. Complex 3 features an unusual discrete hexanuclear silver(I) dimer, [Ag3(N,N-eten)(dcpa)3]2, formed by Ag···O and argentophilic interactions (Ag3···Ag3# = 3.335 Å), which are further connected by intermolecular N–H···O interactions to offer a one-dimensional ladder-like chain. The urease inhibitory activities of the obtained silver complexes 1, 2 and 3 were investigated and complex 3 was proven to be a potent inhibitor against jack bean urease.

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.

A novel hexanuclear silver(I) complex with photoluminescence properties

A hexanuclear complex of d10–d10 transition metal with organosulfur ligand, Ag6(py2t)6 (py2t=pyrazine-2-thiol), has been synthesized using diffusion methodology at room temperature. Crystal structure was revealed using single crystal X-ray diffraction and data indicate that the complex synthesized containing Ag–Ag bonds in the silver cluster. The density function theory (DFT) calculation was performed to investigate the molecular orbital and photoluminescence potential. The photoluminescence properties of the complex have been further investigated, and a favorable fluorescence property was observed from the complex.

Synthesis, characterization, photophysics and electrochemistry of hexanuclear silver(I) alkynyl phosphine complexes

Hexanuclear silver(I) alkynyl phosphine complexes with anthryl (An) and naphthyl (Np) moieties, [{Ag3(μ-dppm)3(μ3-η1-CC)}2An-9,10](BF4)4 and [{Ag3(μ-dppm)3(μ3-η1-CC)}2Np-1,5](BF4)4, have been synthesized. X-Ray crystallography has been used to study the single crystal structure of one of the complexes. This class of silver(I) complexes was found to be emissive at both room and low temperatures in various media, showing green to orange luminescence at ca. 524–593 nm. The electrochemical properties have also been studied by cyclic voltammetry, and an irreversible anodic wave for the alkynyl-centered oxidation was observed. A computational study has been performed to provide further insight into the spectroscopic origin.

Template Synthesis of Tetrakis-triazolylthiacalix[4]arene in the Cone Conformation and Supramolecular Structure of Its Hexanuclear Complex with Ag(I)

A stereoselective synthesis of the cone stereoisomer of thiacalix[4]arene bearing four triazolyl coordinating sites at the lower rim, 2, has been achieved by the 1,3-dipolar cycloaddition of p-nitrophenylazide to tetrakis-(propargyloxy) thiacalix[4]arene, 1, in presence of copper(I) iodide. A combination of 2 with AgNO3 leads to the formation of hexanuclear silver(I) complex with M:L ratio of 6:2. The latter forms a 3D π-bonded molecular network in the crystalline phase.

A novel hexanuclear silver(i) cluster containing a regular Ag6 ring with short Ag–Ag distances and an argentophilic interaction

The hexanuclear complex [HQ][Ag(p-mpspa)] (H2-p-mpspa = 3-(4-methoxyphenyl)-2-sulfanylpropenoic acid) was prepared by reacting the precursor [Ag(H-p-mpspa)] with diisopropylamine (Q). The complex was characterized by spectroscopic techniques and the structure was solved by a single crystal X-ray diffraction study. The crystal contains hydrogen-bonded diisopropylammonium cations and [Ag6(p-mpspa)6](6-) anions that are based on a regular Ag6 ring with each S-donor atom of the sulfanylcarboxylate ligand bridging two Ag atoms. The Ag-Ag bond distances, 2.8036(6) Å, are very short and suggest a closed shell d(10)···d(10) argentophilic interaction. To analyze the relative role of this interaction and that of the S-bridging atom the anionic [Ag6(p-mpspa)6](6-) moiety has been studied theoretically at the Hartree-Fock (HF) and 2(nd) order Møller-Plesset perturbation theory (MP2) levels on a very simple [Ag6(SH)6] A model system. A large model system [Ag6(p-mpspa)6](6-)B has also been studied by applying the ONIOM (QM/MM) approach using HF/UFF and MP2/UFF combinations as levels of theory. The six experimentally observed Ag(I)···Ag(I) supported interactions are reproduced when dispersion-type interactions are considered in the theory levels MP2 and ONIOM MP2/UFF for models A and B, respectively. The use of HF and ONIOM HF/UFF levels led to a similar hexanuclear structure but displayed a large hexagonal disposition without argentophilic contacts for both models A and B. The steric hindrance exerted by the ligands did not preclude the formation of argentophilic interactions, as observed experimentally.

Bright-yellow to orange-red thermochromic luminescence of an AgI6–ZnII2 heterometallic aggregate

A novel octanuclear Ag(I)(6)-Zn(II)(2) heterometallic aggregate, (NH(4))(2){[Zn(2)(phen)(2)(H(2)O)(4)][Ag(6)(mna)(6)]}·2H(2)O·2CH(3)CH(2)OH (1, H(2)mna = 2-mercaptonicotinic acid, phen = 1,10-phenanthroline), was stepwisely obtained based on a hexanuclear silver(i) metalloligand using a liquid-liquid diffusion method. It is an exceedingly rare example that exhibits interesting temperature dependent photoluminescence behaviors, including gradual changes in energy and intensity upon cooling.

Nonamer Water Cluster Encapsulated in a Heterometallic Supramolecular Complex

A crownlike nonamer water cluster has been observed in the heterometallic supramolecular complex {[Cu(eda)2(H2O)2]3·[Ag6(mna)6]·9H2O} (1), which is built from one anionic hexanuclear silver cluster [Ag6(mna)6]6− and three mononulear [Cu(eda)2(H2O)2]2+ cations (H2mna = 2-mercaptonicotinic acid, eda = ethylenediamine). Moreover, the thermogravimetric curve, UV−vis absorption, and photoluminescence spectra of 1 were discussed.

Synthesis, crystal structures, and biological activities of 2-thiophene N(4)-methylthiosemicarbazone and its unusual hexanuclear silver(I) cluster

Abstract 2-Thiophene N(4)-methylthiosemicarbazone (HL) and its Ag(I) complex of formula [Ag6(L)6⋅ 4DMF] 1 have been synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction studies. The silver(I) complex 1 with a 1:1 metal–ligand molar ratio is an unusual hexanuclear cluster with 6 silver atoms in different environments: four silver atoms of them are considered to be 3-coordinate form, which are coordinated by two thiolate sulfur atoms and one imine nitrogen and the other two silver atoms are considered to be 4-coordinate form, which are coordinated by three thiolate sulfur atoms and one imine nitrogen, with four thiolate sulfur bridging two silver atoms and two thiolate sulfur bridging three silver atoms. Biological studies, carried out in vitro against bacteria, fungi and SMMC-7721 liver cancer cell line, respectively, have shown that the free ligand and the title complex show distinct difference in the biological property.

Synthesis of Silver(I) and Gold(I) Complexes with Cyclic Tetra‐ and Hexacarbene Ligands

Cyclic polyimidazolium salts have been investigated with respect to their function as anion receptors and cyclophanelike tetraimidazolium tetracations have been shown to bind anions inside the ring cavity. Cyclic polyimidazolium cations can also serve as precursors for N-heterocyclic carbenes (NHCs) and their complexes. Complexes of cyclic di-NHC ligands have been generated from bisazolium cyclophanes like A. However, such dicarbene ligands coordinate in a cisfashion to the metal center. They act as classical bidentate ligands rather than encapsulating the metal in a manner typical for macrocyclic ligands. Only one cyclic tetradentate dicarbene ligand is known to form a saddle-shaped macrocyclic complex B with nickel(II). We have described the first complex with a macrocyclic tetracarbene ligand C. The rhenium complex of a tridentate, facially coordinated [11]ane-P2C NHC macrocycle has also been reported. Since the preparation of complex C in a metal-template controlled domino-reaction is cumbersome we became interested in the preparation of complexes with macrocyclic poly-NHC ligands from cyclic polyimidazolium cations. This approach has previously been applied successfully for the preparation of some mono (Pd) and dinuclear (Cu, Ag) carbene complexes from the cyclic tetraimidazolium salt D. We became particularly interested in the lutidine-bridged tetraimidazolium salt H4-1 ACHTUNGTRENNUNG(Br4)[8] which upon C deprotonation would yield a potentially hexadentate ligand possessing two C-N-C pincer-type binding sites. Here we describe the mono and dinuclear silver(I) complexes with the carbene ligands derived from H4-1(Br)4 and the transfer of the carbene ligand to yield the mono and dinuclear gold(I) complexes (Scheme 1). A slight modification in the synthesis protocol employed for the preparation of H4-1(Br)4 yields the cyclic hexaimidazolium salt H6-6Br ACHTUNGTRENNUNG(BPh4)5 (Scheme 2). The preparation and molecular structure of the hexanuclear silver(I)-NHC complex derived from this ligand is also ACHTUNGTRENNUNGdescribed. The tetraimidazolium salt H4-1(Br)4 is soluble in water. [8]

A grid-like two-dimensional AgIcoordination polymer: poly[[[μ3-N′-(4-cyanobenzylidene)isonicotinohydrazide]silver(I)] perchlorate

This study presents new coordinating modes of a Schiff base with three coordinating groups and an interesting two-dimensional framework based on two types of constructing units. In the title compound, {[Ag(C(14)H(10)N(4)O)]ClO(4)}(n), the Ag(I) ion is coordinated by three N atoms and one O atom from three different N'-(4-cyanobenzylidene)isonicotinohydrazide (L) ligands, forming a primary distorted square-planar coordination geometry. Two ligands each bridge two metal centres through one carbonitrile N atom in a monodentate mode and the hydrazide N and O atoms in a bidentate mode to form a small centrosymmetric (2+2)-Ag(2)L(2) ring as a principal constructing unit. The pyridyl N atoms from four ligands in four of these small rings coordinate to Ag atoms in adjacent rings to form a large hexanuclear silver grid. A two-dimensional framework of rectangular grids is constructed from these small rings and large grids. Two perchlorate anions are located in each large grid and are bound to the grid by N-H...O hydrogen bonding. Crosslinking between the layers is achieved through long Ag...O interactions between the perchlorate anions and Ag atoms in adjacent layers.

A photoluminescent hexanuclear silver(I) complex exhibiting C–H⋯Ag close interactions

The reaction of AgNO 3 with bulky anthracene-9-carboxylic acid (H L 1) in the presence of 2,6-dimethylpyridine ( dmp) afforded a photoluminescent hexanuclear discrete Ag I complex [Ag 6( L 1) 6( dmp) 2] exhibiting C–H⋯Ag interactions whose total interaction energy were further estimated by DFT calculations. The relevant results reveal that the steric bulk of the anthracene ring skeleton of L 1 may play important roles in the formation of the final structure.

Synthesis, characterization and DFT calculations of a novel hexanuclear silver(I) cluster-complex containing 4-ethyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazol-3-thione as a result from the cyclization of 2-pyridinformamide N-4-ethylthiosemicarbazone

Reaction of 2-pyridine N-4 ethylthiosemicarbazone, HAm4E, with AgNO 3 leads to the hexanuclear compound [Ag(E124tazt)] 6 ( 1) (HE124tazt = 4-ethyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazol-3-thione), the result of an oxidative cyclization of the starting thiosemicarbazone. All Ag atoms of [Ag(E124tazt)] 6 are bridged through the six S atoms of the deprotonated E124tazt ligand to form two bridged Ag 3S 3 rings. Each silver atom exhibits a trigonal planar coordination geometry bonded to two thiolate S atoms and one N atom from the bidentate E124tazt ligand. The Ag⋯Ag distances are much shorter than the van der Waals’ radius sum for silver(I), suggesting binding interactions between the silver atoms, which were confirmed by means of DFT calculations. The X-ray single-crystal structural analysis reveals the arrangement of 1 as a two-dimensional (2D) network via π–π stacking interactions. Preliminary luminescence measurements have been carried out.

Solid channel structure and nanoscale drum-like Ag 6 cluster constructed with pentafluorobenzenethiolate and triphenylphosphine ligands: The use of water-soluble silver(I) carboxylate as silver(I) source

A nanoscale drum-like hexanuclear silver(I) cluster [Ag(pfbt)(PPh 3)] 6 1 (Hpfbt = pentafluorobenzenethiol), which showed the arrays of channels based on its self-assembly in the solid, was obtained by the 1:1 molar-ratio reaction of the insoluble polymeric precursor ∞[Ag(pfbt)] 2 and PPh 3 in chloroform. Synthetic yield and purity of 1 were strongly dependent on the purity of 2. Compound 2 with higher purity was prepared in good yield using light-stable and water-soluble silver(I) carboxylate [Ag(Hpyrrld)] 2 (H 2pyrrld = 2-pyrrolidone-5-carboxylic acid) as the silver(I) source.