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.     

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.     

Liquid-crystalline oxovanadium(IV) complexes accessed from bidentate [N,O] donor salicylaldimine Schiff-base ligands

A series of bis[4-(n-alkoxy)-N-(4′-R-phenyl)salicylideneiminato]oxovanadium(IV) complexes (n?=?6,?10,?14,?16,?18 and R?=?C₃H₇) were prepared and their mesogenic properties were investigated. The mesomorphic behaviors of the compounds were studied by polarized optical microscopy and differential scanning calorimetry. Ligands display SmA/SmC and unexpected nematic mesophases. The complexes bearing longer alkoxy carbon chain (n?=?10,?14,?16, and 18) showed both monotropic or enantiotropic transitions with smectic A and high ordered smectic E phases. However, the complex with shorter carbon chain length (n?=?6) showed monotropic transition with an unprecedented nematic (N) phase. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimized structure. A square-pyramidal geometry for the vanadyl complexes has been suggested. A ν_V=O stretching value of ～970?cm^?1 corroborated absence of any V?=?O?···?V?=?O interactions. Cyclic voltammetry revealed a quasireversible one-electron response at 0.61?V for the VO(IV)–VO(V) redox couple. Variable temperature magnetic susceptibility measurements of the vanadyl complexes suggested absence of any exchange interactions among the vanadyl spin centers.     

Synthesis and properties of hexakis(6-octyl-2-azulenyl)benzene as a multielectron redox system with liquid crystalline behavior

[structure: see text] This paper describes the cyclotrimerization reaction of di(2-azulenyl)acetylenes (2a,b) catalyzed by Co2(CO)8 to produce hexa(2-azulenyl)benzene derivatives (1a,b). The cyclooligomerization of 2a and 2b utilizing CpCo(CO)2 as a catalyst produced (eta5-cyclopentadienyl)[tetra(2-azulenyl)cyclobutadiene]cobalt complexes (3a,b). The redox behavior of hexakis(6-octyl-2-azulenyl)benzene (1b), bis(6-octyl-2-azulenyl)acetylene (2b), and the cobalt complexes 3a and 3b along with 6-octyl-2-phenylazulene (19) was examined by cyclic voltammetry (CV). The reduction of compound 1b exhibited multiple-electron transfers in one step upon CV with a reduction potential similar to that of compound 19. However, the CVs of compounds 2b, 3a, and 3b were characterized by stepwise waves because of the reduction of each azulene ring. The mesomorphic behaviors of 1b, 2b, and 19 were also studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques. A new series of azulene derivatives, 1b, 2b, and 19, substituted by a long alkyl chain at the 6-position shows mesomorphism with crystalline polymorphs. Compound 1b showed a large temperature range of hexagonal columnar mesophases (Col(ho)) from 115.5 to 199.9 degrees C. Compound 2b has rectangular columnar (Col(ro)), smectic E (S(E)), and nematic (N) mesophases. Compound 19 exhibited an S(E) mesophase.     

Discotic metallomesogens: Synthesis and properties of square planar metal bis(β-diketonate) complexes

Discotic β-diketonate liquid crystals containing palladium(II), and oxovanadium(IV), (V≡0), analogous to known copper complexes (which display discotic lamellar and columnar mesophases), have been prepared and characterized. These are the first enantiotropic discotics containing Pd(II) and among the earliest examples containing VO(IV). The best-behaved Pd(II) complex is [Pd(DK 10, 10)₂], and it also is probable that the complexes [Pd(DKn,n)₂] (n = 7-9) are mesomorphic, however their characterization is difficult due to decomposition in the isotropic phase. The mesophase of [Pd(DK 10²,10²)₂], which appears below 100°C, is suggested to be an example of the rare N_d phase on the basis of optical microscopy. The complex [VO(DK8,8)₂] is an enantiotropic discotic vanadyl complex; the monotropic behaviour of [VO(DK 10,10)₂] was also confirmed. It is suggested that the discotic phase which occurs for [VO(DK 8,8)₂] is more organized than that of [Cu(DK 8,8)₂].     

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.     

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 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.     

Synthesis and spectral studies of copper(II), nickel(II), cobalt(II) and vanadyl(II) complexes of tridentate Schiff bases of 1,2,3,5,6,7,8,8a-octahydro-3-oxo-N,1-diphenyl-5-(phenylmethylene)-2-naphthalenecarboxamide

Summary Metal(II) chelates of Schiff bases derived from the condensation of 1,2,3,5,6,7,8,8a-octahydro-3-oxo-N,1-diphenyl-5-(phenylmethylene)-2-naphthalenecarboxamide with o-aminophenol (KAAP), o-aminothiophenol (KAAT) or o-aminobenzoic acid (KAAB) have been prepared and characterized. The complexes are of the type [M(N₂X)]₂ for M = Cu^II and M(NX)₂·nH₂O for M = Ni^II, Co^II and VO^II (X = phenolic oxygen, thiophenolic sulphur or carboxylic oxygen; n = 0 or 2). Conductivity data indicate that the complexes are non-ionic. The Schiff bases behave as dibasic tridentate ligands in their copper(II) complexes and as monobasic bidentate ligands in their nickel(II), cobalt(II) and vanadyl(II) complexes. The subnormal magnetic moments of the copper(II) complexes are ascribed to an antiferromagnetic exchange interaction arising from dimerization. Nickel(II) and cobalt(II) complexes are trans octahedral whereas vanadyl(II) complexes are square pyramidal     

Discotic metallomesogens: Synthesis and properties of square planar metal bis(β-diketonate) complexes

Abstract

Discotic β-diketonate liquid crystals containing palladium(II), and oxovanadium(IV), (V[tbnd]0), analogous to known copper complexes (which display discotic lamellar and columnar mesophases), have been prepared and characterized. These are the first enantiotropic discotics containing Pd(II) and among the earliest examples containing VO(IV). The best-behaved Pd(II) complex is [Pd(DK 10, 10)₂], and it also is probable that the complexes [Pd(DKn,n)₂] (n = 7–9) are mesomorphic, however their characterization is difficult due to decomposition in the isotropic phase. The mesophase of [Pd(DK 10²,10²)₂], which appears below 100°C, is suggested to be an example of the rare N_d phase on the basis of optical microscopy. The complex [VO(DK8,8)₂] is an enantiotropic discotic vanadyl complex; the monotropic behaviour of [VO(DK 10,10)₂] was also confirmed. It is suggested that the discotic phase which occurs for [VO(DK 8,8)₂] is more organized than that of [Cu(DK 8,8)₂].     

Liquid crystalline behaviour of hydrogen bonded complexes of a non-mesogenic anil with p-n-alkoxybenzoic acids

Phase diagrams of binary mixtures of the non-mesogenic N -( p -methoxy- o -hydroxybenzylidbe ene)- p -aminopyridine with a series of p - n -alkoxybenzoic acids ranging from methoxy to hexadecyloxy were established using differential scanning calorimetry and polarising optical microscopy. The key results obtained are: (1) the formation of 1 1 hydrogen bonded complexes between the pyridine derivative and the alkoxybenzoic acids, (2) the stability of the alkoxybenzoic acid mesophases over a wide range of compositions (up to slightly over 50 mol% of the pyridine derivative), (3) the absence of additional mesophases corresponding specifically to the 1 1 complexes, and (4) the complete miscibility of the acids with the complexes in the mesomorphic state. With alkoxy chains from methoxy to heptyloxy, mixtures produce only nematic phases; they produce both nematic and smectic phases with chains from octyloxy to dodecyloxy, and only smectic phases with chains from tetradecyloxy to hexadecyloxy. The formation of hydrogen bonded complexes was investigated at various temperatures using FTIR spectroscopy. Molecular ordering was studied by X-ray diffraction as a function of temperature and composition both for the crystalline and the mesomorphic states.     

Photoluminescent nickel(II)-metallomesogens derived from salphen ligands: influence of halogens at the spacer on mesomorphism and emission properties

Three new series of photoluminescent nickel(II) metallomesogens, [NiL]; H₂L = N,N′-Bis(4-n-alkoxysalicylidene)-4-fluoro/bromo/chloro-1,2-diaminobenzene (n = 12, 14, 16) based on ‘salphen’ ligands have been synthesised and their mesomorphic and photophysical properties explored. The complexes, isolated as orange microcrystalline solids were characterised by elemental analyses, FT-IR, ¹H NMR and UV-visible spectroscopy. Thermal studies show all the compounds to be enantiotropic liquid crystals displaying columnar mesophase over a wide temperature range. Electronegativity and steric requirement of the halogen substituent at the ligand’s spacer remarkably influence the 2-D packing of the columns in the lattice in these complexes controlling the supramolecular mesomorphic order and photoluminescence. The mesophase behaviour of the fluoro-substituted complex is characterised by a transition from a columnar oblique (p1) to columnar rectangular (p2mm) phase, former stable till ambient temperature. The chloro and bromo analogues, on the other hand, displayed exclusively columnar rectangular (p2mm) mesophase with the former transforming into a glassy state and latter into a crystalline phase during cooling to ambient temperature. Molecular model based on interdigitated anti-parallel and back to back arrangements in the different columnar mesophase are proposed on the basis of X-ray diffraction (XRD) studies. The complexes emit in the blue region when excited with near UV wavelength.     

Ionic hexagonal columnar metallomesogens derived from tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine

A series of transition metal (Ni, Cu, Pd) complexes derived from macrocyclic tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine (TAAB) was synthesized and their mesomorphic properties studied by differential scanning calorimetry, polarized optical microscopy and X-ray powder diffraction (XRD). These compounds have eight alkoxy side chains attached around the central molecular core and form disc-like molecules. All the derivatives exhibited columnar mesophases over a wide range of temperature. The mesomorphic behaviour was found to be dependent on the incorporated metal and the carbon length of the alkoxy side chains. The clearing temperatures decreased in the order M = Ni > Pd > Cu; this decrease was probably due to the size of the metal ions. Some derivatives with shorter side chains (n = 10, 12) were room temperature liquid crystals. All compounds were found to exhibit hexagonal columnar (Col_h) phases which were confirmed by powder XRD.     

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.     

Steric effect on the formation of columnar phases in β-diketonate copper(II) complexes

A systematic study of the mesomorphic properties of three series of copper(II) complexes based on β-diketonate ligands containing branched side chains is reported. These disc-like compounds have four, six and eight flexible alkoxy side chains appended to the central core, in which two or four side chains were substituted by bulkier secondary alkoxy groups: 1-methylbutyloxy R ' = C₅(2°) or 1-methylheptyloxy R ' = C₈(2°). The mesomorphic results indicated that at least eight side chains are required to form stable columnar mesophases; other compounds with four or six side chains are not mesogenic regardless of the combination of the carbon length on the alkoxy or secondary alkoxy groups of the side chains. The compounds 3 with shorter R ' = C₅(2°) side chains were all non-mesogenic regardless of the carbon length of three alkoxy side chains (R = C₈, C₁₀, C₁₂) used. However, when the longer 1-methylheptyloxy side chain R ' = C₈(2°) was substituted, the compounds 3b-3e with various alkoxy groups (R = C₆, C₇, C₈, C₁₀, C₁₂) exhibited columnar phases. The mesophases were characterized and identified as columnar hexagonal phases (Col_h), as expected, by thermal analysis and optical polarized microscopy. The presence of the introduced secondary alkoxy groups apparently appeared to influence the formation of columnar phases. The clearing points were relatively lower than other similar copper(II) compounds not substituted by secondary alkoxy side chains.     

Smectic bimetallomesogens: synthesis, characterization and mesomorphic properties and the crystal structure of bis[N-(3-hydroxypropyl)-4-octanoylsalicylaldiminato]copper(II) complex

The synthesis, characterization and mesomorphic properties of copper(II), palladium(II), vanadyl(IV) and iron(III) chloride complexes derived from salicylaldimine structures are reported. The copper and palladium complexes exhibited smectic A phases, however vanadyl and iron chloride complexes showed crystalline phase. The palladium complexes have lower melting and clearing points, and a wider temperature range of mesophase. This lowering in clearing points between M = Pd and M = Cu analogues was attributed to the weaker core-core interaction between palladium centres within layers in the mesophase. The crystal and molecular structures of bis[N-(3-hydroxypropyl)-4-octanoylsalicylaldiminato]copper(II) were determined by means of X-ray analysis. This complex crystallizes in the monoclinic space group p21/c, with a = 5.4908(23) A, b = 19.847(5) A, c = 16.636(4) A, beta = 96.87(3) degree, and Z = 2. The intramolecular separation of Cu-Cu atoms is 3.022(3)A. The structure shows that the molecular shape is nearly flat with two copper atoms lying 0.067(4)A above and below the plane of N1, O1a, O1 and O2 atoms.     

Plastic columnar mesomorphism in half-disc-shaped oxovanadium(IV) Schiff base complexes

A new series of non-disc-like oxovanadium(iv) Schiff base complexes of the type [VO((4-C _n H_2n+1O)₂salcn)], where n?=?14, 16 or 18 and salcn is N,N ^′-bis-salicylidene-1,2-cyclohexadiamine, containing 4-substituted alkoxy tails in the side aromatic rings, have been synthesised and their mesogenic properties investigated. The compounds were characterised by FT–IR, ¹H NMR, ¹³C NMR, UV–Vis and FAB mass spectrometry. The mesomorphic behaviour of the compounds was studied using polarised optical microscopy and differential scanning calorimetry. The molecular organisation in the mesophase was determined by X-ray diffraction. It was found that the ligands did not show mesogenic behaviour, but their complexes exhibited a thermally stable enantiotropic highly ordered three-dimensional plastic mesophase with a columnar structure in the extended temperature range 155–166°C. The clearing temperature of the complexes was found to be lower than in the structurally analogous copper complexes. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimised structure. A square pyramidal geometry for the vanadyl complexes has been proposed.     

Vanadyl(IV) complexes of 4-alkoxy substituted [N,O] donor salicylaldimine Schiff bases derived from chloro-/nitro-aniline: synthesis,mesomorphism, and DFT study

Oxovanadium(IV)-Schiff-base complexes, [VOL₂] {L?=?N,N′-bis-(4-X-amino phenyl (4′-n-alkoxy)-salicylaldiminato), n?=?10, 18; X?=?Cl, NO₂}, have been synthesized from the interaction of vanadyl (VO²⁺) and the bidentate [N,O] donor in methanol/ethanol. The compounds were characterized by FT–IR, ¹H- and ¹³C-NMR, FAB-mass spectra, elemental analyses, and solution electrical conductivity. Mesomorphic behavior of the ligands and their vanadyl complexes were probed by polarizing optical microscopy and differential scanning calorimetry. The compounds are thermally stable and exhibit enantiotropic smectic A mesomorphism over the temperature range of 57–231°C. The mesophase–isotropic transition temperatures for the complexes are much higher than the ligands. Melting and clearing points of the compounds did not show any definitive trend with regards to alkoxy chain length or electronegative substituent. Variable temperature magnetic susceptibility measurements of the vanadyl complexes clearly show the absence of exchange interactions among the vanadyl spin centers. Non-electrolytic natures of the complexes were shown by conductometric measurements. A ν(V=O) of ～970?cm^?1 corroborated the absence of any V=O?···?V=O interactions. Density functional theory study carried out using DMol3 at BLYP/DNP level to determine the energy-optimized structure revealed a distorted square pyramidal geometry for the vanadyl complexes.     

Mesomorphic structure peculiarities of two mix-substituted phthalocyanines of the A3B type

Mesomorphic properties and structures of two mix-substituted lipophilic phthalocyanine derivatives of the A₃B type, with a different ratio of electron-donating (hexadecyloxy-) and electron-withdrawing (Cl-) substituents on the isoindol fragments ‘A’ and ‘B’, correspondingly, were studied by polarising optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. Both compounds display columnar mesophases, and the type of organisation of the columns in the mesomorphic state was found to strongly depend on the number of peripheral chlorine substituents in the molecule. The di-chloro-substituted phthalocyanine forms a solid pasty lamellar phase at room temperature, which on heating undergoes successive transitions to two large-lattice columnar mesophases (2D-Col_h and 3D-M_Col) arising from the aggregation of several phthalocyanine-containing piles. On the contrary, aggregation of columns does not occur for the tetra-chloro-substituted phthalocyanine, which forms a nematic columnar mesophase of single phthalocyanine piles (1D-N_Col). While the di-chloro-compound partly crystallises on cooling, the nematic phase of the tetra-chloro-compound freezes at room temperature. The reasons for this different self-organisation behaviour are not yet fully understood, but some hints may be deduced from the proposed supramolecular models.