Silverio Coco

Luminescent Gold(I) Carbenes from 2-Pyridylisocyanide Complexes: Structural Consequences of Intramolecular versus Intermolecular Hydrogen-Bonding Interactions

Isocyanide [AuX(CNPy-2)] (X = Cl, C6F5, fluoromesityl, 1/2 octafluorobiphenyl) and carbene [AuX{C(NR1R2)(NHPy-2)}] (R1R2NH = primary or secondary amines or 1/2 primary diamine) gold(I) complexes have been synthesized and characterized. For X = Cl, the carbene complexes show aurophilic interactions. The fragment NHPy-2, formed in the carbenes, can give rise to intra- (for primary amines) or intermolecular (for secondary amines) hydrogen bonds, depending on the amine used. These bonds and contacts have been studied in the solid state and in solution. The intermolecular hydrogen bonds are split in an acetone solution, but the intramolecular ones, which close a six-membered ring, survive in solution. Except for the fluoromesityl derivatives, the carbene complexes display luminescent properties.

Liquid-Crystalline Self-Organization of Isocyanide-Containing Dendrimers Induced by Coordination to Gold(I) Fragments

Dendritic polyisocyanides can be considered as promising polytopic ligands to generate a great diversity of metallodendrimers due to the ability of the isocyanide moiety to bind to various transition metals. Here, new isocyanide-containing dendrimers and their corresponding polynuclear gold complexes have been prepared, [G(i)(NC)(Z)] and [G(i)(NCAuR)(Z)], respectively, where G(i) is a poly(phenyl ether) dendrimer, i is the generation number (i = 0, 1, or 2), Z is the number of peripheral groups (Z = 3 x 2(i)), and AuR are the surface groups ([R = Cl, C[triple bond]C-C(6)H(4)-OC(12)H(25), C[triple bond]CC(6)H(2)(OC(12)H(25))(3)]. The compounds are derived from a highly flexible phenyl ether-based dendritic core, G(i), having the general formula G(0) = C(6)H(3)(OC(11)H(22)OC(6)H(4)-)(3), G(1) = C(6)H(3)[OC(11)H(22)OC(6)H(3)(OC(11)H(22)OC(6)H(4)-)(2)](3), G(2) = C(6)H(3)[OC(11)H(22)OC(6)H(3){OC(11)H(22)OC(6)H(3)(OC(11)H(22)OC(6)H(4)-)(2)}(2)](3)), growing from the trivalent phloroglucinol and with undecylene aliphatic spacers between each branching benzene ring and end-functionalized by isocyanide groups. As in their monomeric model counterparts, stable liquid-crystalline phases are induced upon complexation of the AuR gold moieties at the branch termini. The nature of the anionic ligand R promotes the appearance of smectic or columnar mesophases, the formation of which are governed by steric and dipolar interactions. Based on X-ray diffraction experiments, models describing the supramolecular organization of these metallodendrimers into smectic and columnar mesophases are proposed: columnar phases result from the one-dimensional stacking of molecular disks made of self-assembled supermolecules in oblate cylindrical conformation, while the smectic phases form by the lateral two-dimensional registry of the supermolecules in antiparallel head-to-head prolate conformation.

Self‐Organization of Dendritic Supermolecules, Based on Isocyanide–Gold(I), –Copper(I), –Palladium(II), and –Platinum(II) Complexes, into Micellar Cubic Mesophases

First- and second-generation dendrimers with an isocyanide group as the focal functional point (CN-G(n); n: 1,2) and their corresponding organometallic complexes [MCl(CN-G(n))] (M: Au, Cu), [{CuCl(CN-G(n))2}2], and trans-[MI2(CN-G(n))2] (M: Pd, Pt) have been synthesized. The free ligands and the first-generation complexes do not show mesogenic behavior, but all of the second-generation complexes display a thermotropic micellar cubic mesophase, over a large temperature range, and some of them directly at room temperature. The structure of the mesophase consists of the packing of two, discrete polyhedral micellar aggregates in a three-dimensional cubic Im

Liquid crystals based on halogold(I) complexes with 4-isocyano-4′alkoxybiphenyl derivatives

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Alignment of Palladium Complexes into Columnar Liquid Crystals Driven by Peripheral Triphenylene Substituents

m lattice.

Room-Temperature Columnar Mesophases in Triazine-Gold Thiolate Metal-Organic Supramolecular Aggregates

Rod-like complexes [AuCl(CNC6H4C6H4OCnH2n+1-p)](n= 4, 6, 8, 10, 12) have been prepared by reaction of [AuCl(tht)](tht= tetrahydrothiophene) with the isonitriles CNC6H4C6H4OCnH2n+1-p. Metathetical reactions with KBr or KI afford the corresponding [AuX(CNC6H4C6H4OCnH2n+1-p)](X = Br, I). While the free isonitriles are liquid crystals displaying nematic and (some of them) smectic A phases with a short range of existence at moderate temperatures (40–85 °C), their coordination to AuX (X = Cl, Br, I) produces a marked increase in the melting points of the materials, and also an enormous expansion of the range of existence of the mesophase. The order in the mesophase also increases and only the smectic A phase is formed in most of the complexes (for X = Cl, Br and n= 4 a nematic phase is also formed). All the biphenyl halogold(I) derivatives are mesogenic (except for X = I and n= 4) and their melting points decrease in the order I > Br > Cl. Ranges of mesophase of nearly 140 °C are attained. Most of the complexes decompose to the isotropic state (above 220 °C), but seem thermally stable below 200 °C.

Alkynylisocyanide Gold Mesogens as Precursors of Gold Nanoparticles

A new triphenylene-imine (ImH) and its ortho-palladated complexes (μ-X)2[Pd2Im2] (X = CH3COO(-), Cl(-), Br(-)), (μ-Cl)(μ-SCnH2n+1)[Pd2Im2] (n = 6, 12), [PdIm(acac)] [PdIm Cl(CNC6H4OC12H25)], [PdImCl(CNC6H3(OC12H25)2)], and [PdImCl(CNC6H2(OC12H25)3)] have been prepared. The free imine ligand is not a liquid crystal, but most ortho-metalated dinuclear palladium complexes and the mononuclear trialkoxyphenyl isocyanide derivative display columnar mesophases at temperatures close to ambient. For the dimeric complexes the mesophase obtained is always columnar rectangular (Colr), with an uncommon structure: the dimeric triphenylene-Pd complex-triphenylene molecules give rise to a triple-column stacking consisting of two columns of stacked triphenylene groups connected to a central column formed by stacking of two ortho-palladated dimeric moieties. For the trialkoxyphenyl isocyanide derivative a related polymer-like arrangement of columns alternating stacking of triphenylenes with stacking of two ortho-palladated dimeric moieties is found. The mesophase structure is columnar oblique (Colob). The free imine and all palladium complexes exhibit fluorescence at room temperature in dichloromethane solution, associated with the triphenylene core.

Effects of isocyanide substituents on the mesogenic properties of halogeno(isocyanide)gold complexes : Calamitic and discotic liquid crystals

Supramolecular mono- and dinuclear liquid-crystalline gold(I) aggregates have been synthesized by means of hydrogen bond interactions of 2,4,6-triarylamino-1,3,5-triazine with thiolate moities of gold metalloacids [Au(PR3)(SC6H4COOH)] or [μ-(binap){Au(SC6H4COOH)}2], in 1:1 and 2:1 molar ratio, respectively. All of the supramolecular aggregates display a stable columnar hexagonal mesophase (Col(h)) at room-temperature. The supramolecular arrangement within the columns consists of the one-dimensional stacking of triazine units, with the core of the attached metallic thioacid fragments acting as the fourth branch. The phosphine-containing moieties of the metallic thioacid protrude out in the aliphatic continuum. These complexes do not show metallophilic interactions, but this strategy appears very promising for the future design of room-temperature LC mesophases containing interacting metallic fragments.

Mesomorphic trigonal bipyramidal iron(0) isocyanide complexes

Gold nanoparticles (Au NPs) have been synthesized using simple thermolysis, whether from the mesophase or from toluene solutions, of mesogenic alkynyl-isocyanide gold complexes [Au(C≡C-C(6)H(4)-C(m)H(2m+1))(C≡N-C(6)H(4)-O-C(n)H(2n+1))]. The thermal decomposition from the mesophase is much slower than from solution and produces a more heterogeneous size distribution of the nanoparticles. Working in toluene solution, the size of nanoparticles can be modulated from ~2 to ~20 nm by tuning the chain lengths of the ligands present in the precursor. Different experimental conditions have been analyzed to reveal the processes governing the formation of the gold nanoparticles. Experiments on the effect of adding ligands or bubbling oxygen support that the thermal decomposition is a bimolecular process that starts by decoordination of the isocyanide ligand, producing an oxidative coupling of the akynyl group to [R-C≡C-C≡C-R] and reduction of gold(I) to gold(0) as nanoparticles. The nanoparticles obtained behave as a catalyst in the oxidation of isocyanide (CNR) to isocyanate (OCNR), which in turn cooperates to catalyze the decomposition.

Pentafluorophenyl complexes of palladium and platinum containing chelating and bridging Fe(C5H4PPh2)2 or Fe(C5H4SPh)2

The liquid crystal behaviour of linear [AuX(CNC 6 H 4 OC n H 2n +1 )] (X=halogen) complexes is tuned by systematically changing the structure of the isocyanide ligand. The changes studied are lateral fluorination at the 2- and 3-positions of the phenyl ring and modification of the rod-like structure of the complexes by addition of two alkoxy chains at themeta positions. None of the free isocyanides used here are liquid crystals, but all the gold complexes prepared display mesomorphic properties, except iodo(2-fluoro-4-butoxyphenyl isocyanide)gold(i). The (2- and (3-fluorophenyl isocyanide)gold(i) complexes show smectic A mesophases, except the 2-fluoro derivative with n=6, which shows a nematic phase, while the (3,4,5-trialkoxyphenyl isocyanide)gold compounds display columnar hexagonal phases at room temperature.