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.

Labile imidazolium salt protected palladium nanoparticles.

An imidazolium (Im) salt with two long alkyl substituents at N atoms is employed to prepare cubelike palladium nanoparticles (PdNPs). The bilayer nature of the capped Im salts is characterized by thermogravimetric analysis and NMR studies. These capped Im salts are labile, as evidenced by their displacement reaction with dimethylaminopyridine, and the observation of fast exchange between those free and capped Im salts on the NMR time scale. NMR results also show that these capped Im salts exhibit different diffusion rates, and interesting spinning rate dependent chemical shifts. These cubelike PdNPs could catalyze the Suzuki coupling of aryl chlorides and boronic acids with high yields in 10 min, even at room temperature.

Tetranuclear silver(I) clusters showing high ionic conductivity in a bicontinuous cubic mesophase.

The synthesis and characterization of tetranuclear silver triazole metallomesogens, [Ag4(L(4)-C(n))6][BF4]4 (L(4)-C(n) = 4-alkyl-1,2,4-triazoles where C(n) stands for C(n)H(2n+1) with n = 12, 14, 16, and 18), are reported. Upon heating, a phase transition sequence of Cr → SmC → Cub → SmA → isotropic liquid is observed for all of these compounds. Depending on the alkyl chain length, two types of cubic phases are found in this series of compounds. Those with shorter alkyl chains (n = 12 and 14) exhibit a micellar cubic phase, whereas long alkyl chains (n =16 and 18) show a bicontinuous cubic phase. Superior ionic conductivity at the bicontinuous cubic mesophase for [Ag4(L4-C16)6][BF4]4 is observed because of the presence of a three-dimensional ion-transporting channel. Doping a small amount of AgBF4 enhances the ionic conduction dramatically, presumably via promotion of the migration of Ag(I) ions in the channels.

Strong tendency of homeotropic alignment and anisotropic lithium ion conductivity of sulfonate functionalized zwitterionic imidazolium ionic liquid crystals.

Here, we report the first attempt to investigate the liquid crystal (LC) behavior of SO3(-) functionalized imidazolium zwitterionic (SO3(-)ImZI) salts, which display homeotropic alignment on a glass slide without the aid of any aligning approach. Doping lithium salt to ImZI salts lowers the melting temperatures and raises the clearing temperatures substantially to form room temperature ImZILCs. Excellent anisotropic lithium ion conductivity is achieved; which is strengthened by their tendency for homeotropic alignment.

Self-assembly of silver(I) and gold(I) N-heterocyclic carbene complexes in solid state, mesophase, and solution.

The assembly of silver(I) and gold(I) complexes of functionalized N-heterocyclic carbenes (NHCs) of the type [M(C(n),amide-imy)(2)][anion] were studied, in which C(n),amide-imy stands for an NHC of imidazol-2-ylidene having one N-alkyl substituent (C(n)H(2n+1)) and one N-acetamido substituent, while the anions are Br(-), NO(3)(-), BF(4)(-) or PF(6)(-). A single crystal X-ray diffraction study reveals that self-assembly of [Ag(C(10),amide-imy)(2)][PF(6)] through Coulombic, hydrogen bonding, and hydrophobic interactions gives a lamellar structure with tubular architecture around the metal ion head core. Self-assembly of these functionalized NHC complexes also leads to the formation of the first example of thermotropic liquid crystals of silver(I)-NHCs and gels of gold(I)-NHC. Results from an infrared spectroscopy study show that the degree of chain motion in the gel state is smaller than that in the mesophase, yet comparable to that in the solid state. In addition, the technique of nuclear magnetic resonance diffusion ordered spectroscopy was found for the first time to be a good tool to study the phase transition of gels. Xerogels of gold(I)-NHCs display fibers, oriental lantern-shaped bundles of belts and helical fibers when observed under scanning electron and transmission electron microscopes.

A triple helical structure supported solely by C-H···O hydrogen bonding.

A novel triple helical structure that is self-assembled by cationic molecules, 1-acetamido-3-(2-pyrazinyl)-imidazolium, is reported. The computational analysis underpins that the formation of the triple helix is driven by C-H···O hydrogen bonding.

Vertex and edge truncated octahedron gold crystals. N-alkylimidazole and silver(I) ion controlled morphology transformation.

Two interesting morphology transformations of Au crystals are observed through reacting a mixture of N-alkylimidazole (denoted as C(n)-im, where C(n) = C(n)H(2n+1), and n = 18 and 1), AgNO(3), and HAuCl(4) at 200 degrees C. The long chain C(18)-im with increasing AgNO(3) concentration leads to a progressive truncation of octahedrons at {100} vertices to produce cubes. On the other hand, increasing the concentrations of C(1)-im and AgNO(3), results in a progressive truncation of octahedrons at {110} edges to give rhombic dodecahedrons, which further transform to the unprecedented tetrahexahedrons. The phenomenon could be understood by considering that while both C(18)-im and C(1)-im function as a capping agent with preferential adsorption on Au {111} facets, Ag(+) adsorbs and is subsequently reduced to Ag on Au {110} facets for the sterically demanding C(18)-im, but on the Au {100} facets for C(1)-im. The competition between the growth of the facets protected by imidazole and Ag controls the morphology transformation via truncation of octahedrons at vertices or edges.

Liquid crystals of gold(I) N-heterocyclic carbene complexes.

Three types of Au(I) N-heterocyclic carbene (NHC) and imidazole (Im) complexes, namely [Au(NHC)Cl], [Au(NHC)(Im)][NO(3)], and [Au(NHC)(2)][NO(3)], with two-, three-, and four-N-long alkyl chains, respectively, were synthesized and their mesomorphic properties investigated. Only the [Au(NHC)(Im)][NO(3)] series of compounds, adopting an m-shaped conformation in the solid state, showed liquid crystalline properties. For the molecules with three alkyl chains in particular, the Coulombic and hydrogen bonding interactions between the cationic head core and anionic NO(3)(-), and the hydrophobic chain-chain interactions facilitate in sustaining the partially ordered motion, which is not observed for those with two and four arms. These complexes were employed for preparation of stable nanomaterials in organic solvents.

Au(i)-benzimidazole/imidazole complexes. Liquid crystals and nanomaterials.

Three series of Au(I)-imidazole complexes with stoichiometries of [Au(Cn-bim)Cl], [Au(Cn-im)Cl], and [Au(Cn-im)2][NO3] x 2H2O (Cn-bim = N-CnH2n+1 -substituted benzimidazole and Cn-im = N-CnH2n+1-substituted imidazole) together with the compound of [Au(C18-bim)2][NO3] are synthesiszed. Typical structures of each series are determined by single crystal X-ray diffraction. The last series of compounds, are liquid crystals, and exhibit a wider mesophase range than their Ag(I) analogues. These Au(I) complexes form Au nanostructures both through chemical reduction or thermolysis. For the first time, N-long chain imidazole is utilized to stabilize colloidal Au in solution. Also for the first time, unique examples of simple thermolysis to produce large Au plates of nanothickness are demonstrated. Formation of a plate-like morphology through fusion of sphere-like nanoparticles at an early stage is evidenced by TEM images.

Structural, photophysical, and catalytic properties of Au(I) complexes with 4-substituted pyridines.

Ionic gold(I) complexes with general formula of [Au(Py)2][AuCl2] and [Au(Py)2][PF6] (Py = 4-substituted pyridines) have been synthesized. Structures of five Au(I) complexes and a Ag(I) complex were determined by single crystal X-ray diffraction. Evidence for cationic aggregation of [Au(py)2][PF6] complexes in solution was obtained by conductivity measurements and by the isosbestic point observed from variable temperature UV-visible absorption spectra. All compounds were luminous in the solid state. Calculations employing density functional theory were performed to shed light on the nature of the electronic transitions. While the [Au(4-dmapy)2][AuCl2] (4-dmapy = 4-dimethylaminopyridine) and [Au(4-pic)2][AuCl2] (4-pic = 4-picoline) emissions were found to be mainly ligand in nature, their [PF6](-) counterparts involved a Au...Au-interaction imbedded in the highest occupied molecular orbital. [Au(4-dmapy)2][AuCl2] was found to be an efficient catalyst for Suzuki cross-coupling of aryl bromide and phenylboronic acid.

Probing C-H...X hydrogen bonds in amide-functionalized imidazolium salts under high pressure.

We have probed under high pressure the C-H hydrogen bonds formed by N,N(')-disubstituted imidazolium ions having PF(6) (-) and Br(-) counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N-H...F unit) in the infrared spectrum of the PF(6) (-) salt indicates that conventional N-H...O and N-H...N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C(2)-H...F interactions, combined with other weak hydrogen bonds, disturb the formation of N-H hydrogen bonds in the PF(6) (-) salt. This finding is consistent with the pressure-dependent results, which reveal that the C(2)-H...F interaction is enhanced upon increasing the pressure. In contrast to the PF(6) (-) salt, the imidazolium C-H bonds of the Br(-) salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br(-) and PF(6) (-) ions.

Liquid crystals of silver complexes derived from simple 1-alkylimidazoles.

A homologous series of silver complexes of 1-alkylimidazoles (R-im, R = CnH(2n+1), where n= 10, 12, 14, 16 and 18) was synthesized. All the CnH(2n+1)-im ligands are non-mesomorphic. Upon complexation, all the [Ag(CnH(2n+1)-im)2]-[NO3], except for n = 10, exhibit liquid crystalline properties. The crystal structure of [Ag(C12H25-im)2][NO3] shows that the silver center is two-coordinate and adopts a U-shaped conformation with bilayer packing. The non-mesomorphic [Ag(C16H33-bim)2][NO3](bim = benzimidazole) has a three-coordinate silver ion and has a chair conformation with monolayer stacking. Non-mesomorphic [Ag(C16H33-bim)2][BF4] has a linear geometry around the silver ion and also has a chair conformation. The mesophase for the Ag-(CnH(2n+1)-im) complexes has been identified as the smectic A (SmA) phase. [Ag(C16H33-im)2]+ with four different anions, NO3-, BF4-, PF6- and CF3SO3- were compared. Of the four Ag-im complexes, only that with the CF3SO3- anion does not show liquid-crystal behavior.

New hexatic liquid phase observed in lyotropic thin films.

An intermediate surface hexatic phase between the liquid and the crystalline phases has been found for the first time in a lyotropic lamellar liquid-crystal system. This phase is highly unusual in that it has long-range sixfold bond-orientational order but liquidlike nearest-neighbor positional correlations, and could represent a significant departure from our current understanding of defect-mediated melting in two dimensions.

C[bond]H- - -O hydrogen bonds in beta-sheetlike networks: combined X-ray crystallography and high-pressure infrared study.

Close interactions of the C(alpha)[bond]H- - -O type have been analyzed via X-ray crystallography and high-pressure infrared spectroscopy. The results demonstrate that the C(alpha)[bond]H- - -O interactions can offer an additional stability to the beta-sheet formation. X-ray structural data suggest that while 1-acetamido-3-(2-pyrimidinyl)-imidazolium bromide exhibits a bilayer stacking, the PF(6)(-) salt reveals a beta-sheetlike pattern. The appearance of the free-NH infrared absorption indicates that the conventional N[bond]H- - -O or N[bond]H- - -N hydrogen bonds do not fully dominate the packing for the PF(6)(-) salt. The high-pressure infrared study suggests that the C(alpha)[bond]H- - -O hydrogen bonds are the important determinants for the stability of the PF(6)(-) salt. This study also verifies that the imidazolium C[bond]H stretching frequency shifts to a longer wavelength upon the formation of the C[bond]H- - -O hydrogen bonds.

Molecular Aggregation of Annular Dinuclear Gold(I) Compounds Containing Bridging Diphosphine and Dithiolate Ligands.

A series of annular dinuclear Au(I) complexes containing diphosphine (R(2)P(CH(2))(n)()PR(2); R = Me, n = 1, dmpm; R = Me, n = 2, dmpe; R = Ph, n = 1, dppm; R = Ph, n = 2, dppe) and dithiolate (dtc = S(2)CNEt(2)(-), i-mnt = S(2)C(2)(CN)(2)(2)(-)) ligands were synthesized: [Au(2)(P-P)(S-S)]X (S-S = dtc: P-P = dmpm, X = Cl, 1; P-P = dppm, X = PF(6), 2; P-P = dppe, X = PF(6), 3; P-P = PPh(3), X = PF(6), 4) and [Au(2)(P-P)(S-S)] (S-S = i-mnt: P-P = dmpm,5; P-P = dppm, 6; P-P = dmpe, 7; P-P = dppe, 8). Crystal structures of two complexes are reported. Pertinent crystallographic data: [Au(2)(dmpm)(i-mnt)] (5), space group Fdd2, with a = 19.574(3) Å, b = 48.220(11) Å, and c = 15.273(2) Å, R = 0.0542; [Au(2)(dppe)(i-mnt)] (8), space group P2(1)/n, with a = 11.793(2) Å, b = 19.607(2) Å, and c = 15.349(2) Å, R = 0.0448. Each molecule has two gold atoms bridged by a dithiolate ligand on one side and a diphosphine ligand on the other side, thus forming an eight- or nine-membered ring digold complex. The tendency of the digold(I) compounds to aggregate through an intermolecular Au-Au interaction depends on the ligands. Among the structures determined, complex 5 forms a polymeric chain and compound 8 is monomeric. Molecular aggregation also occurs in solution. Concentration-dependent absorption spectra of Au-dtc compounds suggest that an equilibrium between the monomer and dimer exists. Equilibrium constants corresponding to the intermolecular Au-Au interaction range from 38 to 137 M(-)(1) with DeltaH values of approximately 15 kcal/mol and DeltaS values of approximately -35 to approximately -46 cal/(K mol). Concentration dependence of emission spectra of annular compounds in acetonitrile also supports association in solution. Emissions at approximately 400-440 nm assignable to spin-allowed metal-centered transitions from monomeric Au(2) at lower concentrations and dimeric Au(4) at higher concentrations are observed. Compounds 1-3 and 5-8 in the glass state having spin-forbidden dithiolate ligand to gold charge transfer ((3)LMCT) transitions give emission bands at approximately 550 nm. Compound 4 has a S --> Au (3)LMCT transition at 500 nm. (31)P variable-temperature NMR experiments were performed for 1-3. The dynamic process is attributed to molecular aggregation through an intermolecular Au-Au interaction in solution. The activation energies are approximately 9 kcal/mol for 1 and 2.