The cyclic "silver-diphos" motif [Ag2(mu-diphosphine)2]2+ as a synthon for building up larger structures

The dinuclear, cyclic structural motif [Ag2(diphosphine)2](2+), here termed the "silver-diphos" motif, previously observed in many diphosphine-silver complexes, has been investigated as a synthon for building up larger structures such as coordination cages and polymers. A series of ligands containing one to four meta-substituted diphosphine groups, attached via a central core, has been synthesized from the corresponding fluoroarenes by reaction with KPPh2. Upon reaction with silver salts, the target synthon is adopted by meta-substituted diphosphines 1,3-bis(diphenylphosphino)benzene (L1), 2,6-bis(diphenylphosphino)benzonitrile (L2), and 3,5-bis(diphenylphosphino)benzamide (L3), each of which gives a single species in solution consistent with the expected dimeric complexes [Ag2L2(anion)2]. X-ray crystal structures of [Ag2(L1)2(OTf)2] and [Ag2(L2)2(SbF6)2] confirm the adoption of the silver-diphos motif in the solid state. Amide-functionalized diphosphine L3 forms a hydrogen-bonded chain structure in the solid state via the amide group. A discrete boxlike cage [Ag4(L4)2][SbF6]4 based on two silver-diphos synthons is formed when the tetraphosphine Ph2Sn{3,5-bis(diphenylphosphino)benzene}2 (L4) reacts with silver(I). Its single-crystal X-ray structure reveals a central cavity of minimum diameter, ca. 5.0 A, which contains a single SbF6(-) counterion disordered over two sites. In contrast to the highly selective behavior of the di- and tetra-phosphines L1-L4, the heptaphosphine P{3,5-bis(diphenylphosphino)benzene}3 L5 and the hexaphosphine PhSn{3,5-bis(diphenylphosphino)benzene}3 L6 give dynamic mixtures upon reaction with silver salts in solution. This nonspecific behavior is rationalized by the fact that their diphosphine groups are not appropriately disposed to form stable discrete structures based on the silver-diphos synthon. By contrast, the octaphosphine Sn{3,5-bis(diphenylphosphino)benzene}4 L7 does selectively form a single, discrete, highly symmetrical product in solution, [Ag4(L7)(OTf)4]. In this case, the ligand unexpectedly adopts an interarm tetra-chelating coordination mode, resulting in a continuous 24-membered ring around the periphery of the molecule. To understand the adoption of this unusual coordination mode, the alternative diphosphine Ph2Sn(3-diphenylphosphinobenzene)2 L8, which models a single interarm chelating site of L7, was also investigated. By contrast to L7, its coordination was nonspecific, giving mixtures of silver complexes upon reaction with AgOTf. The selective interarm chelation by L7 may therefore be stabilized by the continuous coordination ring in [Ag4(L7)(OTf)4]; that is, the four chelating sites can be thought of as acting in a cooperative manner. Alternatively, interarm steric repulsions between phenyl groups may favor interarm chelation. Overall, we conclude that, if the diphosphine groups are appropriately articulated to act independently (i. e., they are adequately separated and oriented), the silver-diphos synthon can be a useful tool for the coordination-based self-assembly of larger structures.     

Silver(I) 3-aminomethylpyridine complexes, part 2: effect of ligand ratio, hydrogen bonding, and pi-stacking with an interacting anion

Reaction of 3-aminomethylpyridine (3-amp) with silver(I) salts of triflate (OTf-) and trifluoroacetate (tfa-) produce a variety of multidimensional coordination networks whose structures depend on the stoichiometry of the components present. A 1:1 ratio of 3-amp to AgX produces a linear polymer, 1, when X = tfa- and a planar sheet, 2, when X = OTf-. Addition of a second equivalent of ligand increases the dimensionality of both structures by one to form a two-dimensional sheet, 3, and a three-dimensional system, 4, for their respective anions. Addition of 2,2'-bipyridine (bipy) to solutions of any of the previous compounds produces the fixed-ratio complexes 5 (tfa- salt) and 6 (OTf- salt). The bipyridyl ligand halts the polymerization of compounds 1-4 by cutting the chain after each silver(I) link and forcing a 1:2:2 ratio of 3-amp to AgX to bipy. Compound 5, however, remains polymeric in nature due to the closed-shell Ag-Ag interactions of the planar metals holding the monomers together. Differences between structures of each ratio stem from the differences in basicity and in the extra degree of H-bonding ability that the OTf- anion has over tfa-.     

Gold(I)‐Catalyzed Asymmetric Desymmetrization of meso‐Alkynyl Diols and Kinetic Resolution of the Corresponding dl‐Diols: Effects of Celite Filtration and Silver Salts

The asymmetric desymmetrization of meso‐2‐alkynylbenzenediols through the use of a combination of axially chiral diphosphine(AuCl)₂ precatalysts and silver salt co‐catalysts gave optically active isochromene compounds with high enantioselectivities in good yields. The corresponding dl ‐diol isomers underwent efficient kinetic resolution to give the cyclized isochromenes and recovered diols with high enantioselectivities under similar conditions. The high reactivity and selectivity in the desymmetrization of the meso‐diols is independent of the combination of axially chiral diphosphine(AuCl)₂ precatalyst and silver salt co‐catalyst, whereas the corresponding tricarbonylchromium complexes of alkynylbenzenediols were affected by the combination of the diphosphine(AuCl)₂ and silver salt. The reactivity was largely dependent on the nature of the gold(I) species.     

X-ray crystal structures of discrete and polymeric chiral silver complexes of monoterpenoid alkenes

X-ray crystal structures are reported for five silver(I) complexes of four monoterpenoid alkenes. Discrete mononuclear complexes of the chiral alkenes (1S)-(−)-α-pinene and (1S)-(−)-β-pinene with silver perchlorate and silver hexafluorophosphate are described. The achiral diene γ-terpinene forms a discrete mononuclear adduct with silver hexafluorophosphate and a two-dimensional polymeric network structure with silver triflate. The chiral diene (R)-(+)-limonene forms a one-dimensional chiral coordination polymer with silver hexafluorophosphate. In all structures the silver atom is η²-bonded to the carbon-carbon bond(s) of the monoterpene with slightly longer bond distances to the more substituted carbon of the alkene moiety.     

A variable temperature 31P NMR study of 9-30 atom macrocylic rings of silver(I) with long chain diphosphines

The coordination chemistry of equimolar amounts of silver(I) with the long chain diphosphine ligands Ph₂P(CH₂) _n PPh₂ (where n?=?6, 8, 10, or 12) has been studied by variable temperature ³¹P{¹H} NMR. In all cases two silver(I)/diphosphine complexes were observed in solution at ambient temperature with ¹ J(¹⁰⁷Ag–P) values of ca 500?Hz indicating silver(I) coordinated to two phosphorus atoms in a linear mode. A van’t Hoff study on the variable temperature ³¹P{¹H} NMR data has been used to assign monomeric and dimeric species.     

Gold(I)-catalyzed asymmetric synthesis of planar chiral arene chromium complexes

Gold(I)-catalyzed asymmetric cyclization of 1,3-dihydroxymethyl-2-alkynylbenzene chromium complexes gave planar chiral isochromene chromium complexes with high enantioselectivity. Enantiomeric excess of the cyclization products was largely affected by a combination of axially chiral diphosphine(AuCl)(2) precatalysts and silver salts. A system of segphos(AuCl)(2) with AgBF(4) resulted in the formation of the corresponding antipode.     

A simple two-phase route to silver nanoparticles/polyaniline structures

Novel silver nanoparticles/polyaniline composites were obtained through a two-phase water/toluene interfacial reaction. We show that by rigorously controlling the reaction time, different structures of the nanocomposites can be obtained, such as a thin sheet of polyaniline around the silver nanoparticles or a polymer mass with nanoparticles homogeneously embedded within it. Samples were characterized by FT-IR, UV-vis-NIR and Raman spectroscopy, X-ray diffraction, cyclic voltammetry, TEM, and HRTEM. Conductivity and current-voltage characteristics of the nanocomposites were measured, and the results indicate that different properties result from the different structures in which the nanocomposites were formed.     

Synthesis and characterization of novel S,N and Se,N homodimetallic Ag(I)-complexes

Novel C2-symmetric doubly bidentate Se,N and S,N-ligands based on a readily available Tr?ger's base backbone were synthesized and fully characterized. Their coordination properties were studied in dinuclear Ag(I)-complexes employing (1)H, (77)Se and (1)H-(15)N HETCOR NMR spectroscopy as well as X-ray diffraction crystallography. In solution, a single ligand can accommodate two silver atoms by coordination to nitrogen and sulfur or selenium. The investigations in the solid state revealed the presence of a pentacoordinated silver atom (NSO(3) and N(3)Se(2) donor sets are influenced by the solvent employed during the crystallization). In the solid state, the Ag(I)-complex with the S,N-ligand 2b forms dimeric structures bridged by the two perchlorate counterions. The analogous Se,N-ligand 2c coordinates to Ag(I) and forms polymeric enantiomerically pure helices, although the crystal is racemic.     

Homochiral and heterochiral coordination polymers and networks of silver(I)

The self-assembly of racemic and enantiopure binaphthylbis(amidopyridyl) ligands 1,1'-C(20)H(12){NHC(O)-4-C(5)H(4)N}(2), 1, and 1,1'-C(20)H(12){NHC(O)-3-C(5)H(4)N}(2), 2, with silver(I) salts (AgX; X = CF(3)CO(2), CF(3)SO(3), NO(3)) to form extended metal-containing arrays is described. It is shown that the self-assembly with racemic ligands can lead to homochiral or heterochiral polymers, through self-recognition or self-discrimination of the ligand units. The primary polymeric materials adopt helical conformations (secondary structure), and they undergo further self-assembly to form sheets or networks (tertiary structure). These secondary and tertiary structures are controlled through secondary bonding interactions between pairs of silver(I) centers, between silver cations and counteranions, or through hydrogen bonding involving amide NH groups. The self-assembly of the enantiopure ligand R-1 with silver trifluoroacetate gave a remarkable three-dimensional chiral, knitted network composed of polymer chains in four different supramolecular isomeric forms.     

Silver(I) coordination chemistry of 2,6-diarylpyrazines. Pi-stacking,anion coordination,and steric control

The silver(I) coordination chemistry of 2,6-diarylpyrazines is reported. Discrete coordination complexes and two-dimensional coordination networks were characterized. The substitution pattern on the pendant aryl groups controlled the type of coordination chemistry involved. Thus, o-methyl-substituted aryl groups held the aryl groups orthogonal to the central pyrazine ring, opening the "hindered" nitrogen atoms to complexation, and polymeric networks were characterized. In the absence of the o-methyl groups, discrete coordination complexes were characterized. Thus, a dimeric 2:1 ligand-silver(I) complex was isolated and characterized on reaction of 2,6-bis(3',5'-dimethylphenyl)pyrazine with silver(I) trifluoroacetate in acetonitrile solvent, while a 2:2 complex was isolated from dichloromethane solvent. Two trifluoroacetate ligands bridge two silver cations in both complexes. Reaction of the same pyrazine ligand with silver(I) tetrafluoroborate yielded a discrete 2:1 complex. A 2:1 complex was isolated on reaction of 2,6-diphenylpyrazine with silver(I) nitrate. These complexes were interlinked by weakly coordinating nitrate anions to form interwoven one-dimensional ribbons. Two-dimensional networks were obtained on reaction of silver(I) trifluoroacetate with either 2,6-bis(2',6'-dimethylphenyl)pyrazine or 2-(2',6'-dimethylphenyl)-6-(3',5'-dimethylphenyl)pyrazine. The networks comprised pyrazine-silver(I) strands cross-linked with complex bridged silver(I) trifluoroacetates.     

Polynuclear Silver(I) Triazole Complexes: Ion Conduction and Nanowire Formation in the Mesophase

Examples of polynuclear metallomesogens are few. Herein,1,2,4‐triazole ligands were used to prepare mono‐ and polynuclear silver(I) triazole metallomesogens. Besides showing an SmA phase in the mesophase, two interesting properties were observed. First, higher ion conductivity is always found for the polynuclear complexes than for the mononuclear complexes with the same anion, an observation contrary to the knowledge that migration of a monomeric cation should be faster than that of a polymeric cation. Second, thermolysis of the polynuclear silver(I) triazole complexes in the assembled mesophase yielded Ag nanowires, in an excellent demonstration of the assembled nature of the polynuclear silver(I) ions in the thermolysis process.     

Spiral, herringbone, and triple-decker silver(I) complexes of benzopyrene derivatives assembled through eta(2)-coordination

Three novel silver(I) complexes with benzopyrene derivatives were synthesized and characterized in this paper. Treatment of AgClO(4)*H(2)O with 7-methylbenzo[a]pyrene (L(1)) afforded [Ag(2)(L(1))(toluene)(0.5)(ClO(4))(2)](n)() (1) which exhibits a 2-D sheet structure with double-stranded helical motifs. Reaction of AgCF(3)SO(3) with dibenzo[b,def ]chrysene (L(2)) gave rise to an unprecedented cocrystallization structure, ([Ag(2)(L(2))(CF(3)SO(3))(2)][Ag(2)(toluene)(2)(CF(3)SO(3))(2)])(n)() (2), formed by a 2-D neutral lamellar polymer and a 1-D neutral rodlike one. The ligand benzo[e]pyrene (L(3)) coordinated to silver(I) ions generating a closed triple-decker tetranuclear complex [Ag(4)(L(3))(4)(p-xylene)(ClO(4))(4)] (3) which can be regarded as a stacking polymer owing to existing intermolecular pi-pi stack interactions. The structural diversity of the silver(I) coordination polymers with polycyclic aromatic hydrocarbons is not only related to the stacking patterns of free polycyclic aromatic hydrocarbons in the crystalline state, but also the geometric shapes of the molecules for these free ligands. In addition, the coordination of solvents to metal ions plays a crucial role in the formation of the unprecedented coordination polymeric architectures. The ESR spectroscopic results, conductivity, and synthesis properties are also discussed.     

Ag(I)-based tectons for the construction of helical and meso-helical hydrogen-bonded coordination networks

The new ligand 4-(3-(2-pyridyl)pyrazol-1-ylmethyl)benzoic acid (L) has been prepared and characterized. This bifunctional ligand incorporates both a chelating region, with two nitrogen donors, suitable for chelating to soft transition metal ions, and a self-complementary hydrogen-bonding region which can facilitate intermolecular association of ligands or ligand-based complexes. X-ray structural analysis of the ligand shows it to adopt a one-dimensional helical polymeric structure, with adjacent ligands hydrogen bonded to each other. Reaction of L with silver(I) salts (AgOTf (1, 1.1.5H(2)O), AgNO(3) (2), AgPF6 (3.CH(3)OH), and AgClO(4) (4.CH(3)OH)) results in the formation of complexes with 2:1 stoichiometries. X-ray structural analysis of these complexes shows that, in each case, one-dimensional chain structures are obtained where chiral AgL(2) tectons are hydrogen bonded together, either directly or mediated by anions or solvent. Structures with either helical or meso-helical structures are observed.     

Variability in the structures of [4-(aminomethyl)pyridine]silver(I) complexes through effects of ligand ratio, anion, hydrogen bonding, and pi-stacking

The reaction of the asymmetric 4-(aminomethyl)pyridine (4-amp) ligand with silver(I) salts of trifluoromethanesulfonate (triflate, OTf(-)), trifluoroacetate (tfa(-)), or tetrafluoroborate (BF(4)(-)) have produced a variety of one- and two-dimensional structural motifs depending upon the ratio in which the components are mixed. When the proportion of ligand to metal is 1:1, linear coordination polymers are formed with silver(I) OTf(-) (1) and tfa(-) (2). Altering the ratio to 2:1, a linear polymer of corner-shared boxes (3) is formed with tfa(-), a linear box-in-box "chain link" polymer (4) is formed with OTf(-), and a two-dimensional sheet (5) is constructed with BF(4)(-). Addition of 5,5'-dimethyl-2,2'-bipyridine to a solution of 4-ampAgBF(4) disrupts the polymerization of the previous structure and results in the construction of the infinite metal-metal bound strings of 6a regardless of ratio of amp to silver present. H-bonding, pi-stacking, and closed-shell Ag-Ag interactions are all involved in the overall conformations of the final structures.     

Using ligand bite angles to control the hydricity of palladium diphosphine complexes

A series of [Pd(diphosphine)(2)](BF(4))(2) and Pd(diphosphine)(2) complexes have been prepared for which the natural bite angle of the diphosphine ligand varies from 78 degrees to 111 degrees. Structural studies have been completed for 7 of the 10 new complexes described. These structural studies indicate that the dihedral angle between the two planes formed by the two phosphorus atoms of the diphosphine ligands and palladium increases by over 50 degrees as the natural bite angle increases for the [Pd(diphosphine)(2)](BF(4))(2) complexes. The dihedral angle for the Pd(diphosphine)(2) complexes varies less than 10 degrees for the same range of natural bite angles. Equilibrium reactions of the Pd(diphosphine)(2) complexes with protonated bases to form the corresponding [HPd(diphosphine)(2)](+) complexes were used to determine the pK(a) values of the corresponding hydrides. Cyclic voltammetry studies of the [Pd(diphosphine)(2)](BF(4))(2) complexes were used to determine the half-wave potentials of the Pd(II/I) and Pd(I/0) couples. Thermochemical cycles, half-wave potentials, and measured pK(a) values were used to determine both the homolytic ([HPd(diphosphine)(2)](+) --> [Pd(diphosphine)(2)](+) + H*) and the heterolytic ([HPd(diphosphine)(2)](+) --> [Pd(diphosphine)(2)](2+) + H(-)) bond-dissociation free energies, Delta G(H*)* and Delta G(H-)*, respectively. Linear free-energy relationships are observed between pK(a) and the Pd(I/0) couple and between Delta G(H-)* and the Pd(II/I) couple. The measured values for Delta G(H*)* were all 57 kcal/mol, whereas the values of Delta G(H-)* ranged from 43 kcal/mol for [HPd(depe)(2)](+) (where depe is bis(diethylphosphino)ethane) to 70 kcal/mol for [HPd(EtXantphos)(2)](+) (where EtXantphos is 9,9-dimethyl-4,5-bis(diethylphosphino)xanthene). It is estimated that the natural bite angle of the ligand contributes approximately 20 kcal/mol to the observed difference of 27 kcal/mol for Delta G(H-)*.     

Cellulose/cysteine based thiol-ene UV cured adsorbent: removal of silver (I) ions from aqueous solution

Cellulose - In the present study, a novel, eco-friendly, and simple polymeric adsorbent was obtained from cellulose acetate butyrate (CAB) and cysteine (Cys) to remove silver (I) ions in the...     

Ring-opening polymerization of coordination complexes: silver(I) complexes with bis(amidopyridine) ligands derived from thiophene

The thiophene-based bis(N-methylamido-pyridine) ligand SC4H2-2,5-{C(=O)N(Me)-4-C5H4N}2 reacts with silver(I) salts AgX to give 1 : 1 complexes, which are characterized in the solid state as the macrocyclic complexes [Ag(2){SC4H2-2,5-(CONMe-4-C5H4N)2}2][X]2, which have the cis conformation of the C(=O)N(Me) group, when X = CF3CO2, NO3, or CF3SO3 but as the polymeric complex [Ag(n){SC4H2-2,5-(CONMe-4-C5H4N)2}n][X]n, with the unusual trans conformation of the C(=O)N(Me) group, when X = PF6. The bis(amido-pyridine) ligand SC4H2-2,5-{C(=O)NHCH2-3-C5H4N}2 reacts with silver(I) trifluoroacetate to give the polymeric complex [Ag(n){SC4H2-2,5-(CONHCH2-3-C5H4N)2}n][X]n, X = CF3CO2. The macrocyclic complexes contain transannular argentophilic secondary bonds. The polymers self assemble into sheet structures through interchain C=O...Ag and S...Ag bonds in [Ag(n){SC4H2-2,5-(CONMe-4-C5H4N)2}n][PF6]n and through Ag...Ag, C=O...Ag and Ag...O(trifluoroacetate)...HN secondary bonds in [Ag(n){SC4H2-2,5-(CONHCH2-3-C5H4N)2}n][CF3CO2]n.     

One- and two-dimensional silver-coordination networks containing pi-sandwiched silver-silver interactions

The self-assembly of coordination networks from reaction of 2,4,6-trimesityl-1,3,5-triazine and silver(I) trifluoroacetate is described. A one-dimensional linear polymer is formed from solutions deficient in silver while a two-dimensional, graphite-like sheet is formed from solutions containing 3 equiv of silver per triazine. The structurally similar networks both contain triazine rings separated by two trifluoroacetate-bridged silver atoms. The two silver atoms are effectively sandwiched between two mesityl rings with intermediate arene-silver interactions. The silver-silver bond lengths are 2.9731(4) and 2.9246(5) A in the one-dimensional network and 2.8842(4) A in the two-dimensional network.     

Antibacterial Effects of Silver Doped Polyethyleneglycol Based Polyamidoamine Side Chain Dendritic Polyurethane

Antibacterial activity was imparted with polyamidoamine (PAMAM) side chain dendritic polyurethane (SCDPU‐PEG) by doping of silver particles. Antibacterial activities of both the polyurethane (SCDPU‐PEG) and its silver doped structures were investigated against Escherichia coli bacteria. The silver doped polymeric structures were found to exhibit antibacterial activity while the polymer without silver loading showed no antibacterial activity. Formation of silver doped side chain dendritic polymers was investigated from the UV‐vis plasmon absorption band of silver particles.     

Patterning Flexible Substrates Using Surface Relief Structures in Azobenzene Functionalized Polymer Films

A novel method for maskless micro-patterning of polymeric substrates is presented. First, an azobenzene functionalized polymer film is spin-coated on a Poly (ethylene terephthalate) (PET) sheet. Then surface relief structures are optically inscribed on the polymer film by interference of laser beams. The patterned azobenzene functionalized film is then etched in the plasma chamber such that the gratings are transferred to the PET substrate. Finally, any remaining azobenzene functionalized polymer is dissolved away using an appropriate solvent. This method of patterning can be broadly applied to a variety of flexible/polymeric substrates and the resolution is not limited by the substrate thermo-mechanical properties.