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.     

Columnar metallomesogens based on vanadyl(VI) and cobalt(II) complexes of N,N'-bis[3-(3,4-dialkoxyphenyl)3-oxopropenyl]ethylenediamines

The preparation, characterization and mesomorphic properties of vanadyl(VI) and cobalt(II) complexes derived from N , N -bis[3-(3,4-dialkoxyphenyl)-3-oxopropenyl]ethylenediamines are described. These half-disk-shaped molecules exhibited columnar mesophases over a wide range of temperature, as characterized by DSC analysis and polarizing optical microscopy. The structure of the mesophases was also confirmed as columnar hexagonal (Col_ho) by powder XRD. The vanadyl complexes were found to have substantially higher clearing temperatures and wider mesophase temperatures than the analogous cobalt complexes. The influence of the metal centres on the mesomorphic temperatures may be attributed to better intermolecular dative association in the vanadyl complexes than in the cobalt complexes.     

Columnar metallomesogens based on vanadyl(VI) and cobalt(II) complexes of N,N'-bis[3-(3,4-dialkoxyphenyl)3-oxopropenyl]ethylenediamines

The preparation, characterization and mesomorphic properties of vanadyl(VI) and cobalt(II) complexes derived from N, N -bis[3-(3,4-dialkoxyphenyl)-3-oxopropenyl]ethylenediamines are described. These half-disk-shaped molecules exhibited columnar mesophases over a wide range of temperature, as characterized by DSC analysis and polarizing optical microscopy. The structure of the mesophases was also confirmed as columnar hexagonal (Col_ho) by powder XRD. The vanadyl complexes were found to have substantially higher clearing temperatures and wider mesophase temperatures than the analogous cobalt complexes. The influence of the metal centres on the mesomorphic temperatures may be attributed to better intermolecular dative association in the vanadyl complexes than in the cobalt complexes.     

Binuclear mesogenic copper(i) isocyanide complexes with an unusual inorganic core formed by two tetrahedra sharing an edge

The preparation of binuclear mesogenic copper(I) isocyanide complexes [CuX(CNR)(2)](2) (X = halogen; R = C(6)H(4)C(6)H(4)OC(10)H(21) (L(A)), C(6)H(4)COOC(6)H(4)OC(n)H(2n+1)((L(B)), C(6)H(2)(3,4,5-OC(n)H(2n+1))(3) (L(C))) with an unusual tetrahedral core is described. The copper complexes with L(A) are not liquid crystals, but the Cu-L(B) complexes show SmA mesophases and the Cu-L(C) derivatives display hexagonal columnar mesophases, some of them at room temperature. The relationship between the molecular structure of the complexes and their thermal behavior is discussed.     

Columnar mesomorphism of bi- and trinuclear Ni(II), Cu(II), and VO(II) cis-enamonoketone complexes with low symmetry

New enaminoketone tetradentate bi- and trinuclear complexes creating columnar mesophases are reported. Various combinations of nickel, copper, or vanadyl ions were applied as metallic centers. Because of the bowlike structure of chelating centers and the low molecular symmetry (Cs) the bivanadyl complexes form two diastereoisomers, which were separated. The superexchange coupling of the electron spins of paramagnetic centers copper-copper and vanadyl-vanadyl was found for binuclear complexes in ESR studies.     

Liquid crystalline salen manganese(III) complexes. Mesomorphic and catalytic behaviour

Several salen manganese(III) complexes displaying stable columnar mesophases in a wide range of temperatures have been synthesized. In condensed phases the molecules are assembled into dimers through intermolecular manganese-oxygen interactions and the columnar structure of the mesophases consist of the stacking of supramolecular discs formed by the association of two or three dimers, depending on the number and location of alkoxy chains in the complex. The catalytic activity of the complexes in solution has been studied, and they behave as efficient homogeneous catalysts in the epoxidation of styrene with iodosylbenzene as oxidant.     

On the Structure and Chiral Aggregation of Liquid Crystalline Star-Shaped Triazines H-Bonded to Benzoic Acids

The ability of a star-shaped tris(triazolyl)triazine derivative to hierarchically build supramolecular chiral columnar organizations through the formation of H-bonded complexes with benzoic acids was studied from a theoretical and experimental point of view. The combined study has been done at three different levels including the study of the structure of the triazine core, the association with benzoic acids in stoichiometry 1:3, and the assembly of 1:3 complexes in helical aggregates. Although the star-shaped triazine core crystallizes in a non-C₃ conformation, the C₃-symmetric conformation is theoretically predicted to be more stable and gives rise to a favorable C₃ supramolecular 1:3 complex upon the interaction with three benzoic acids in their voids. In addition, calculations at different levels (DFT, PM7, and MM3) for the 1:3 host-guest complex predict the formation of large stable columnar helical aggregates stabilized by the compact packing of the interstitial acids by π–π and CH⋅⋅⋅π interactions. The acids restrict the movement of the the star-shaped triazine cores along the stacking axis causing a template effect in the self-assembly of the complex. Theoretical predictions correlate with experimental results, since the interaction with achiral or chiral 3,4,5-(4-alkoxybenzyloxy)benzoic acids gives rise to supramolecular complexes that organize in bulk hexagonal columnar mesophases stable at room temperature with intracolumnar order. The existence of supramolecular chirality in the mesophase was determined for complexes formed by acids derived from (S)-2-octanol. Chiral aggregation was also evidenced for complexes formed in dodecane.     

Synthesis and characterization of tris-methacrylated 3,4,5-tris

The synthesis of liquid crystalline 3,4,5-tris(11-methacryloylundecyl-1-oxybenzyloxy)benzoic acid, 2-methyl-(1,4,7,10,13-pentaoxacyclopentadecane)-3,4,5-tris[4-(11-methacryloylundecyl-1-oxy)benzyloxy] benzoate and its 1:1 complex with sodium triflate is described. The observed mesophases were identified, by polarized optical microscopy and contact preparation techniques, to be of hexagonal columnar disordered structure. The amphiphiles form lyotropic columnar phases in concentrated methacrylate solvents, while at low solute contents supramolecular organogels emerge.     

Hydrogen-bonded block mesogens derived from semiperfluorinated benzoic acids and the non-mesogenic 1,2-bis(4-pyridyl)ethylene

Thermal properties of benzoic acids carrying one or two semiperfluorinated alkoxy tails on the aromatic core have been investigated in binary mixtures with the non-liquid crystalline bidirectional trans-1,2-bis(4-pyridyl)ethylene. The hydrogen bonded complexes built from the complementary molecular species show a significantly enhanced mesophase stability compared with the fluorinated acids in their pure states. The mesophase morphologies of the complexes are governed mainly by the number of the partially fluorinated chains grafted to the acid component. Mixed systems comprising the one-chain acids exhibit a smectic C phase followed by a smectic A phase at more elevated temperatures. Incorporation of a second semiperfluorinated chain into the acid leads to the formation of columnar mesophases. These columnar phases of the H-bonded complexes should represent ribbon phases resulting from the collapse of the smectic layers.     

Calamitic or columnar mesomorphism determined by number and position of substituents in enaminoketone Cu(II), Ni(II) and Co(II) complexes

New enaminoketone metalomesogens with an almost equilateral triangular shape of the mesogenic core have been synthesized. They form either calamitic or columnar mesophases depending on the number and position of the substituted chains. The stability of the columnar as well as of the calamitic phases depends substantially on the central metallic ion.     

The synthesis and mesomorphism of a new series of silver(I) complexes showing glassy mesophases

Reaction of 3,4-dialkoxystilbazoles (n-3,4-OPhVPy) with silver dodecylsulphate (AgDOS) leads to complexes of the formula [Ag(n-3,4-OPhVPy)₂][DOS]. These complexes are polycatenar liquid crystals and show mesophases which are characteristic of this structural type, namely, hexagonal, columnar and cubic. On cooling, some of the materials do not crystallize, but form stable glasses instead. All the mesophases have been fully characterized by small angle X-ray diffraction.     

Columnar mesophases and phase behaviors of novel polycatenar mesogens containing bi-1,3,4-oxadiazole

A new series of liquid-crystalline bi-1,3,4-oxadiazole derivatives (2,2′-bis(3,4,5-trialkoxyphenyl)-bi-1,3,4-oxadiazole, BOXD-Tn, n=3, 4, 5, 6, 7, 8, 10, 14) were designed and synthesized. They have been confirmed to give rise to columnar mesophases. The columnar mesophases for BOXD-Tn (n=5, 6, 7, 8, 10) could be supercooled to −20 °C on the cooling runs. A room temperature Col_ho phase was obtained for BOXD-T14. All BOXD-Tn exhibit good fluorescence properties either in cyclohexane or in solid state.     

Columnar mesomorphism from hemi-disklike metallomesogens derived from 2,6-bis[3',4',5'-tri(alkoxy)phenyliminomethyl]pyridines (L): crystal and molecular structures of [M(L)Cl2] (M=Mn,Ni, Zn)

Four new series of non-disklike complexes of general formula [MCl(2)(L(n))] based upon substituted 2,6-bis(3',4',5'-trialkoxyphenyliminomethyl)pyridine ligands (L(n)) and with M=Zn(II), Co(II), Mn(II), and Ni(II) have been prepared and examined for liquid crystallinity. A complete analysis of the thermal behavior by polarized-light optical microscopy, differential scanning calorimetry, and small-angle Xray scattering revealed a rich and varied mesomorphism. Moreover, the high thermal stability of the compounds leads to rather extended mesomorphic ranges. The nature and thermal stability of each mesophase depend on both the length of the six terminal alkoxy chains, n (n=8, 10, 12, 14, 16), and on the metal ions. As demonstrated by small-angle Xray diffraction experiments, the mesomorphism of these complexes is solely of the columnar type. One compound shows an oblique columnar phase, while most of them show a hexagonal columnar phase, Col(h), and several types of rectangular columnar phase, Col(r). Xray single-crystal structures obtained for three methoxy derivatives confirm the 1:1 metal-ligand stoichiometry of the complexes, in which the metal is pentacoordinate with a distorted, trigonal bipyramidal geometry. The crystalline structures also reveal the existence of some columnar organization in the solid state, the columns resulting from an alternated stacking of the complexes in one direction. By combining these results with those obtained from dilatometry experiments, a model for the molecular organization within the mesophases is proposed in which an antiparallel arrangement of the metallomesogens is retained in the mesophase.     

Self‐organized liquid‐crystalline polyethers obtained by grafting tapered mesogenic groups onto poly(epichlorohydrin): Toward biomimetic ion channels 2

A set of high‐molecular‐weight, new, side‐chain liquid‐crystalline polyethers was obtained by chemical modification of poly(epichlorohydrin) with potassium 3,4,5‐tris[4‐(n‐dodecan‐1‐yloxy)benzyloxy]benzoate. The degree of modification depended on the reaction conditions and ranged from 39 to 58%. The highest value was an apparent modification plateau. NMR characterization indicated no side reactions of any kind (e.g., deshydrohalogenation). All random‐grafted copolymers had hexagonal columnar mesophases with the exception of the least modified copolymer, which had a nematic columnar mesophase. X‐ray diffraction experiments performed on mechanically oriented samples showed that tapered groups were tilted with respect to the column axes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 326–340, 2004     

Heterocyclic 1,3,4-oxadiazole as columnar core

The synthesis, characterization and mesomorphic properties of a new type of liquid crystalline compound, the 2,5-bis(3,4,5-trialkoxyphenyl)-1,3,4-oxadiazoles, 3a-3h, are reported. These heterocyclic compounds are derived from unsaturated 1,3,4-oxadiazole as the core group, and obtained by the condensation reaction of 3,4,5-trialkoxybenzoic acid N-(3,4,5-trialkoxybenzoyl)-hydrazides and phosphorus oxychloride in toluene under reflux. All compounds were characterized by ¹H and ¹³C NMR spectroscopy, and elemental analysis. The mesomorphic properties of these and the related compounds 1, 2 were characterized and studied by differential scanning calorimetry and polarizing optical microscopy. The formation of columnar mesophases was found to be dependent on the numbers of alkoxy sidechains. The compounds 3 exhibited hexagonal columnar (Col_h) phases, however compounds 1, 2 formed crystalline phases. Compounds 3b-3e with shorter carbon chains were room temperature liquid crystals. Polar induction by nitrogen and/or oxygen atoms on the heterocyclic core ring might be responsible for the formation and better observed mesomorphic properties in this type of compound.     

Discotic Metallomesogens: Effects of Sidechains Density in Transition Metal Bis(β-Diketonate) Complexes

The preparation and mesogenic properties of a series of discotic β-diketonate metal complexes are reported. The results show that the density of side chains, positions of side chains, and the geometries of the metal centers play important roles in determining the mesomorphic behaviors and thermodynamic stability of these complexes. In the series of copper complexes 3, all these disc-like molecules with eight alkoxy side chains exhibit columnar hexagonal disordered (D_hd) mesophases. In the series of copper complexes 2 with six side chains, only compounds substituted with longer alkoxy chains (n = C₁₄ or C₁₆) exhibit discotic columnar mesophase. However, in the series of complexes 1, only crystal-to-isotropic transitions were observed. The results showed that induction of liquid crystallinity not only depends on the numbers of side chains (i.e. side chain density), but also on the degree of distribution over the central core. Palladium complexes analogs exhibit similar discotic mesophases, and due to their greater core-core organization, they also have higher clearing points and wider temperature range of mesophases than copper complexes.     

Structural study of crystalline and columnar copper (II) soaps

A homologous series of binuclear copper (II) linear chain alkanoates together with two branched chain and one aromatic substituted copper (II) alkanoates have been synthesized and studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. All of these are crystalline at room temperature, they are mesomorphic in nature above c. 100°C, with the exception of copper propionate which remains crystalline up to its thermal decomposition above 200°C. A systematic study has shown that the linear chain alkanoates, starting from the pentanoic derivative, produce columnar mesophases with hexagonal symmetry. Columns of polar copper carboxylate groups are surrounded by disordered aliphatic chains, and form a two dimensional hexagonal lattice. The repeat unit in a column is a binuclear dicopper tetracarboxylate complex. Two transition regimes have been detected leading from the crystal to the columnar mesophase: one dominated by the interactions between the polar heads, the other by the interactions between aliphatic chains. In the special case of the butyric derivative, the columnar mesophase obtained is rectangular in symmetry. Instead of being oriented perpendicular to the columnar axis and superposed in a four fold helicoidal fashion, the repeat units in the columns are tilted and all shifted in the same direction with respect to one another.     

Rod-like phases formed by Ni(II) and VO(II) complexes of tetradentate enaminoketone ligands

Most of the nickel(II) complexes of tetradentate enaminoketone ligands obtained, although not strictly calamitic and with a rather low length to width ratio, form enantiotropic rod-like nematic and smectic A phases. Corresponding vanadyl(II) complexes exhibit only monotropic mesophases. The vanadyl complexes, due to their non-planar structure, are chiral with an asymmetry centre placed at the metal ion.     

Tetrahedral zinc complexes with liquid crystalline and luminescent properties: interplay between nonconventional molecular shapes and supramolecular mesomorphic order

Novel metallomesogens with luminescent properties and liquid crystalline behavior at room temperature have been achieved by the preparation of zinc complexes with polycatenar pyrazole and bis(pyrazolyl)methane ligands. Their molecular structures do not have a conventional shape in that they are far from the typical rod-like and flat disc-like geometries of common liquid crystals. They consist of a nonplanar nucleus due to the methylene spacer and/or the coordination to the tetrahedral center, as confirmed by single crystal analysis of the cores. The different numbers and positions of side chains in the pyrazole ligand enabled us to access lamellar and columnar mesophases and, of particular interest, to obtain columnar arrangements at room temperature. Supramolecular models for the organization of the molecules in the mesophases are proposed on the basis of the small-angle XRD diffractograms. The zinc complexes display luminescence in the near UV-blue region with large Stokes shifts. An interplay between non-conventional molecular shapes (due to the tetrahedral core) and the supramolecular mesomorphic order (due to the ligand design) led to materials that interestingly embody two rather opposite properties, a columnar self-organizational ability and luminescence with weak intermolecular interactions.