Mercedes Marcos

Dendromesogens: liquid crystal organizations of poly(amidoamine) dendrimers versus starburst structures.

A new series of liquid crystalline poly(amidoamine) (PAMAM) dendrimers is described. These dendrimers are made by attaching to the 0-, 1-, 2-, 3-, and 4-generation of PAMAM-terminal promesogenic units that carry two decyloxy chains in the 3- and 4-positions of their peripheral aromatic ring. X-ray diffraction studies show that all the compounds display a hexagonal columnar mesophase. A high density of aliphatic chains imposes a curved interface with the promesogenic units that forces the molecules to adopt a radial conformation, and therefore, the columnar structure. A model for the supramolecular organization of the different generations within the columnar mesophase is proposed based on the variation of some of the structural parameters.

Dendromesogens: Liquid Crystal Organizations versus Starburst Structures

Poly(amidoamine) starburst dendrimers which contain peripheral mesogenic ester units were found to exhibit a smectic A mesophase. A structural model is proposed that is valid for several generations of dendrimers. The mesogenic units form parallel aggregations that give rise to the smectic structure (shown schematically).

Mesogenic Transition Metal Complexes Liquid Crystal Phase Behaviour and Crystal and Molecular Structure of Some Nitrile Complexes of the Platinum Metals

Abstract A new range of transition metal-containing liquid crystals is formed by complexing classical organic mesogens directly to a metal. Thus, reaction of [PdCl2(PhCN)2] with 4-n-pentyl-4′-cyanobiphenyl (5CB) leads to [PdCl2(5CB)2] which exhibits a monotropic nematic phase. Complexes of long chain 4-alkyloxy-4′-cyanobiphenyls show enantiotropic mesophases. Analogously, reaction of [PtCl2(PhCN)2] or [Rh2Cl2(CO)4] with 4-alkyl-4′-cyanobiphenyls (L) yields mesogenic [PtCl2L2] or cis-[RhCl(CO)2 L] respectively. The crystal and molecular structure of [PdCl2(5CB)2] and [PtCl2(8CB)2] are also reported and show different packing in the solid state.

Self-organization of nanostructured functional dendrimers

In this article, we review some of our recent work on the development and study of the properties of self-organizing supermolecular liquid crystalline dendritic materials. Prior to this purpose, the state of the art in the field of molecular design, structure and properties of liquid-crystalline dendrimers (LCDs) will be briefly reviewed, and illustrated by a selection of pioneering examples. The first type of LC dendrimer takes into account the location of their functional elements (mesogens) in the periphery of the macromolecules and its topology of attachment, and the nature of the mesogen. We will show how functionality can be in-built into such materials so that self-organising functional systems can be created. Side-chain liquid-crystalline dendrimers exhibiting lamellar, columnar and nematic phases are shown. The mechanism of mesophase formation (mesogen interaction versus microphase separation) is also discussed in relation to the molecular structure (the nature of the mesogen and of the dendritic matrix, dendritic generation number). The second type of LC dendrimer introduced presents a different topology in that the mesogens are now inserted within the dendritic matrix and in the periphery. Owing to their particular constitution, it will be shown that the mesophases of the lamellar and columnar types possess unusual morphologies.

X-ray diffraction study of some mesogenic copper, nickel and vanadyl complexes

Abstract We present a comparative study of various metallomesogenic complexes, using X-ray diffraction methods. For a given ligand linked to different metal atoms (Cu, Ni, VO), the nature of this central atom influences mainly the magnetic susceptibilities of the mesophases. With different ligands, which keep the close neighbourhood of the metal atom unchanged, the apparent length of the mesogenic unit is longer for short ligands than for longer ones. This unexpected behaviour is qualitatively well explained by taking into account the global shape of the different complexes.

Copper-containing dendromesogens: the influence of the metal on the mesomorphism

The synthesis and liquid crystalline behaviour of the first and second generations of a dendrimeric structure based on poly(propyleneimine)(DAB-dendr(NH2)x) are reported. 4-(4-n-Alkoxybenzoyloxy)salicylaldehydes are used as mesogenic moieties attached at the peripheral amino groups of the dendrimers giving rise to dendromesogens with four and eight mesogenic branches. From these dendromesogens, considered as organic ligands, were prepared six metal-containing dendrimers which incorporate two or four copper atoms in their structures. All the dendrimeric ligands and three of the metal-containing dendrimers exhibit liquid crystalline properties which were studied by optical microscopy, DSC, X-ray diffraction and EPR spectroscopy.

Bis(salicylaldiminate) copper(II) and palladium(II) complexes: towards columnar mesophases

Copper and palladium complexes of new salicylaldimines derived from 3,4,5-tridecyloxyaniline, 2,3,4-tridecyloxyaniline and 4-decyloxyaniline have been synthesized and characterized. All the ligands bear four or more aliphatic chains with the aim of inducing columnar mesophases at low temperatures. In particular, metal complexes derived from 4-(3,4,5-tridecyloxybenzoyloxy)-salicyliden-3,4,5-tridecyloxyaninile display rectangular columnar mesophases at (or near) room temperature. These mesophase assignments have been confirmed by X-ray diffraction. A significant decrease of the melting points of the compounds is observed in the tridecyloxyaniline derivatives compared with those of similar complexes derived from mono- or di-decyloxyaniline.

Novel liquid-crystalline derivatives of transition metals. The effect of the molecular geometry of the ligands on the mesogenic properties of tetracoordinated copper(II) complexes

Abstract The synthesis, characterization and thermal behaviour of several new series of copper(II) complexes derived from carbonylic compounds and their Schiffs bases are reported. The complexes are of two types; [Cu(C6H3O(R)-C(X) = O)2], (type I) and [Cu(C6H3O(R)-C(X) = N-R′)2] (type II) where R = - OOC-C6H4OC10H21-p, and the position of R is 4 or 5; R′ = CH3, n-C10H21, p-n-C10H21O(C6H4)-; X [dbnd] H, CH3. In type I complexes, only the compound with X [dbnd] H and R in position 5 showed mesomorphism. For type II complexes, all the Schiffs bases complexes of copper(II) derived from 2,4-dihydroxybenzaldehyde showed thermotropic mesophases (smectic C and nematic), whereas the complexes derived from 2,5-dihydroxybenzaldehyde were only mesogenic when the imine was derived from methylamine. None of the complexes derived from the ketone (2,4 or 2,5-dihydroxy derivatives) showed liquid-crystalline properties. X-ray studies of four complexes of type II were carried out. The anisotropy of the magnetic susceptibi...

Liquid Crystal Derivatives of Transition Metals (I): Tetracoordinated Copper (II) Complexes Derived From Schiffs Bases

Abstract The synthesis, characterization and thermal behavior of several new series of Copper (II) complexes derived from Schiffs bases are reported. The complexes are of the type: [Cu{C6H3O(OR)‒C(Z)=N‒R′}2] (R=n‒C n H2n+1+, R′=p-n-alkoxy-(C6H4)‒, p-n-alkyl‒(C6H4)‒, n-alkyl; Z˭H, CH3). Sehiffs base complexes of Copper (II) derived from an aldehyde show thermotropic mesophases (smectic discotic polymorphism), whereas complexes derived from a ketone do not. When the amine forming the imine ligand is an aromatic amine the complexes form liquid crystals, whereas if the amine is aliphatic the complexes do not give liquid crystals.

Structural study of metallomesogens derived from tris-[2-(salicylideneamino)ethyl]amine. A molecular meccano

The synthesis of new metal complexes based on imines derived from tris-(2-aminoethyl)amine (TREN) which exhibit different geometries depending on the metal [Cu(II), VO(IV), Pd(II), Ni(II), Ln(III)] has been carried out. TREN has three coordination positions which allow us to obtain different coordination complexes involving one, two or three metallic centres. The molecular structure and purity of these novel compounds have been verified by IR, 1H and 13C NMR and elemental analysis and electro-spray mass spectrometry. The phase behaviour was studied by polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction techniques. It was found that the transition metal complexes display a smectic C mesophase whereas the lanthanide complexes display an unidentified smectic mesophase.