Columnar/smectic metallomesogens derived from heterocyclic benzoxazoles

The synthesis, mesomorphic behavior, and optical properties of two new series of metal complexes 1a,b-M (M=Pd, Cu, Zn) derived from benzoxazoles 2a,b are reported. The crystal and molecular structures of mesogenic 5-decyloxy-2-(6-decyloxybenzooxazol-2-yl)phenol and nonmesogenic bis[5-octyloxy-2-(6-octyloxybenzooxazol-2-yl) phenol]Pd(II) were determined by means of X-ray structural analysis. Two benzoxazoles 2a exhibited monotropic SmA phases, and all benzoxazoles 2b were nonmesogenic. On the other hand, metal complexes 1a-M exhibited distinctly different mesomorphism from complexes 1b-M. Complexes 1a-Pd formed SmC phases; complexes 1a-Cu and 1a-Zn formed crystal phases. In contrast, complexes 1b-Zn exhibited columnar phases, and complexes 1b-Cu and 1b-Pd were nonmesogenic. The difference of the mesomorphism in 1a-M and 1b-M was probably attributed to the geometry and/or the overall molecular shape created by 2a and 2b. The electronic configuration of metal ion might play an important role in forming the mesophases. The fluorescent properties of these compounds were also examined.     

H-Bonded metallomesogens derived from salicyladiminates

A series of new mesogenic compounds 1a-b (n=8, 10, 12, 14, 16) derived from salicyladimines and their palladium 2a, 2b, vanadyl 2a, and copper complexes 3a, 3b were prepared and their mesomorphic properties investigated by optical microscopy, differential scanning calorimetry and powder X-ray diffractometry. Pd²⁺ and VO²⁺ ions formed mononuclear complexes, whereas, Cu²⁺ ion formed binuclear complexes due to the relative acidic strength of Schiff base. Single crystallographic analysis of non-mesogenic compound 2a (n=8) confirmed its coordination geometry at Pd²⁺ as square plane. It crystallizes in a triclinic space group P−1 with a Z=1. As expected, the Pd²⁺ was coordinated via a trans-N₂O₂ donor set of phenolic-O and imine-N atoms, leaving two hydroxyl groups intact and uncoordinated. The two alkoxy chains, pointing to the opposite direction were parallel, and the molecule was considered as twisted Z-shaped. Both hydroxyl-OH groups attached on C₁₇ and C₁₈-Schiff imines participate in the H-bonds in the lattice. Interestingly, a pseudo polymeric structure was observed, in which H-bonded dimer was continuously extended by another H-bonded dimer in the lattice. Compounds 1 exhibited smectic A phases, and Pd and VO complexes and Cu complexes 3b exhibited smectic A or/and smectic X phases, however, Cu complexes 3a formed crystal phases. Intermolecular H-bonds might be attributed to the difference observed on the mesomorphic properties in these compounds. Copper complexes 2b were not active on ESR spectroscopy.     

Columnar metallomesogens derived from unsymmetrical pyrazoles

The synthesis and mesomorphism for two series of unsymmetrical pyrazoles and their nickel(II) complexes were described. This is the first example of nickel complexes exhibiting columnar phase. The derivatives with two alkoxy chains exhibited smectic A or smectic C phases; however, all derivatives with four alkoxy chains formed hexagonal columnar phases. In contrast, all nickel(II) complexes 1a formed hexagonal columnar phases. The crystal and molecular structures of 1-(4-propyloxyphenyl)-2-(3-(4-propyloxyphenyl)-1H-pyrazol-5-yl)ethanone were determined, and it crystallizes in the triclinic space group P-1. The overall molecular shape is considered as rod-shaped. The pyrazole and one phenyl ring were coplanar, however, they were not coplanar with other phenyl ring by a dihedral angle of ca. 66.2°. A dimeric structure formed by an intermolecular H-bond (2.11 Å) and a weak π-π interaction (3.51 Å) was observed, which was probably attributed to the formation of the mesophase. The XRD experiments confirmed their structures of the mesophases.     

Calamitic metallomesogens derived from unsymmetric pyrazoles

Three series of copper(II) complexes 1a-1c derived from unsymmetric pyrazoles 2a-2c were prepared and their mesomorphic properties investigated. The mesomorphic behavior of compounds was studied by differential scanning calorimetry, polarizing optical microscopy, and powder X-ray diffractometry. The crystal and molecular structures of mesogenic copper complex (2a; n=10) of 3-[4-decyloxyphenyl]-1H-pyrazole were determined by means of X-ray structural analysis. It crystallizes in the triclinic space group P-1, with a=4.0890(1) Å, b=18.0167(2) Å, c=25.5015(5) Å, and Z=2. The geometry at copper center was not perfectly square planar. A weak intermolecular H-bond (d=2.36 Å) between Cl1 and H2 atoms and π-π interaction (ca. 3.45-3.55 Å) was also observed. All their precursors 2a-2c were not mesogenic. In contrast, copper complexes 1a formed nematic or smectic C phases and complexes 1b-1c formed crystalline phases. Powder X-ray diffraction experiments confirmed the presence of SmC phase.     

Symmetrical dimer liquid crystals derived from benzoxazoles

A series of dimeric twin liquid crystals derived from symmetric heterocyclic benzoxazoles 1a-1f exhibiting single smectic C phase are reported. All benzoxazoles were prepared by condensation of 2-aminophenols with benzaldehydes and then followed by subsequent intramolecular cyclization. The mesomorphic properties were investigated by DSC and POM, and the structure of the mesophases was confirmed as smectic C phases by powder XRD. The formation of mesophases was attributed to the weak dipole force induced by donor-acceptor interaction (D→A). A monolayer conformation was proposed based on the powder XRD data. A value of aspect ratio d/l=0.80-0.92 was calculated from d-spacings and the molecular lengths. By contrast, the odd-even effects by a value of entropy changes ΔS_SmC→I/R=2.00-6.50 showing odd-even effect for the transition of SmC→I phases were also associated in twin system.     

The effect of polar substituents on the heterocyclic benzoxazoles

The synthesis, characterization, and mesomorphic properties of a new type of heterocyclic compounds 1, 2 derived from benzoxazole are reported. In order to understand the relationship between the structure and the mesomorphic behavior, compounds containing a variety of polar substituents (i.e., X=H, F, Cl, Br, CH₃, CF₃, OCH₃, NO₂, CN, OH, NMe₂, COOCH₃) on the terminal end were prepared. The phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimetry (DSC) and polarization optical microscopy. The formation of mesophases was strongly dependent on the electronic and/or the steric factors of the substituents. In general, a mesophase was better induced by introduction of a polar substituent. Compounds (X=H) formed a crystalline phase, however, other compounds, except for X=OH, exhibited nematic or smectic A phases. Interestingly all compounds with electron-donating substituents (X=CH₃, OCH₃, NMe₂) exhibited nematic phases, however, other compounds with electron-withdrawing substituents (X=F, Cl, Br, CF₃, NO₂, CN, COOCH₃) formed smectic A phases. Compounds (X=NO₂, CN, COOCH₃) have higher clearing temperatures than those of other homologues, and the higher T_cl was attributed to an enhanced conjugative interaction. However, no linear correlation between the clearing temperature or the temperature range of mesophases with Hammett σ_p constants was found. The fluorescent properties of the compounds were examined. All λ_max peaks of the absorption and photoluminescence spectra of compounds occurred at ca. 348-381 and 389-478 nm, respectively. Whereas, the quantum yields of some compounds were relatively low.     

Copper chelates derived from heterocyclic thioureas

Summary Some potential pesticidal complexes have been prepared by the interactions of 1-(5-substituted-1,3,4-oxadiazol-2-yl)3-phenylthioureas and copper(II) sulphate and their structures have been confirmed by elemental analyses and magnetic measurements as well as by spectroscopy. The complexes have been tested for pesticidal activity.     

Supramolecular helical stacking of metallomesogens derived from enantiopure and racemic polycatenar oxazolines

The present report undertakes a challenge of general interest in supramolecular chemistry: the achievement of helical organizations with controlled structure. To achieve this target we considered the possibility of inducing supramolecular chirality using molecules that were designed to organize into columnar mesophases. The use of oxazoline-derived ligands and metal coordination served as tools to prepare molecules with a phasmidic-like structure, which show columnar organization in the liquid crystalline state. To ensure the formation of chiral mesophases, these complexes bear stereogenic centers in the rigid coordination environment of the metal. X-ray and circular dichroism experiments have revealed that chirality transfer does indeed take place from the chiral molecule to the columnar liquid crystal organization. This chiral columnar organization appears as a helix consisting of stacks of molecules that rotate with respect to one another along the column while maintaining their mean planes parallel to each other. In fact, it has been concluded that packing of these polycatenar molecules must be more efficient upon rotation of a molecule with respect to the adjacent one along the column. Furthermore, the same type of helical supraorganization has been found to be present in the mesophase of the racemic mixture and the mixture of diastereomers prepared from the racemic ligand. In this case, segregation of the optical isomers is proposed to occur to give rise to both types of helix (right-handed and left-handed).     

Novel heterocyclic selenazadiphospholaminediselenides, zwitterionic carbamidoyl(phenyl)-phosphinodiselenoic acids and selenoureas derived from cyanamides

2,4-Bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide (Woollins’ reagent, WR) reacts with cyanamides (1a-h) in refluxing toluene to afford a series of novel selenazadiphospholaminediselenides (RR′NCN(PhP(Se)SeP(Se)Ph, R=C₆H₅(CH₂)_1-3, 4-n-C₁₀H₂₁C₆H₄ and 4-BrC₆H₄CH₂; R′=H, CH₃, C₂H₅ and C(O)OC₂H₅2a-g). Post-treatment of the reaction mixture with water led to the formation of carbamidoyl(phenyl)phosphinodiselenoic acids (RR′NC(NH₂)P(SeH)₂Ph, R=C₆H₅(CH₂)_2-3, 4-n-C₁₀H₂₁C₆H₄ and 4-BrC₆H₄CH₂; R′=H and CH₃, 3b, 3c, 3e and 3f) and selenoureas (RR′NC(Se)NH₂, R=C₆H₅(CH)_1-2; R′=CH₃ and OC(O)C₂H₅, 4f and 4h) in moderate to excellent yields. All new compounds are characterised spectroscopically and five X-ray crystal structures are reported.     

Novel heterocyclic organoboranes

Novel heterocyclic organoboranes are obtained from the interaction of an organic isocyanate and heterocyclic aminoboranes     

Voltammetric behaviour of heterocyclic systems. Pyridyl-substituted benzimidazoles,benzoxazoles and benzothiazoles

The voltammetric properties, measured at a dropping mercury electrode, have been studied for a series of 18 pyridyl-substituted heterocyclic bases [benzimidazoles, benzoxazoles and benzothiazoles]. The corresponding quarternary salts, obtained by reaction with methyl iodide, were also studied. The reduction potential was found to be dependent on the nature of the benzimidazole, benzoxazole or benzothiazole moiety and on its position on the pyridine ring as well as on the presence of a positive charge. The reversibility of the voltammetric waves was found to be function of the system structure. The effects of proton donors on the voltammetric behaviour of the bases was also investigated.     

Polymethine dyes derived from heterocyclic bases containing condensed thiophene rings

The synthesis of polymethine dyes of the cyanine and merocyanine series derived from 3-methylthionaphtheno[2,3-b]pyridine, 3-methylthionaphtheno[3,2-b]-pyridine, 6-methylthieno[2,3-b]thieno[2,3-b]-pyridine, and 6-methylthieno[3,2-b]thieno[2,3-b]pyridine is described. The color of the dyes obtained is discussed. It has been shown that the replacement of vinylene groups by sulfur atoms in one of the two benzene rings of the hetero residue in 2-substituted 5,6-benzoquinolines in cyanine dyes leads to a bathochromic shift of the absorption maxima.For part VI, see [8].     

Polymethylene dyes derived from heterocyclic bases containing condensed thiophene rings

Some new polymethine dyes of the cyanine and merocyanine series which are derivatives of 5- and 6- thienopyridines are synthesized. Replacement of a vinyl group at a sulfur atom in the condensed benzene ring of quinoline in dyes which are derivatives of this base, always leads to a bathochromic shift of the absorption maximum of the corresponding dyes.     

Synthesis of some novel heterocyclic dyes derived from pyrazole derivatives

Diazotized aryl amines were coupled with 3-substituted 5-amino pyrazoles to produce a series of novel 3-substituted 5-amino-4-arylazopyrazoles. Also, 3-substituted 5-amino-pyrazoles were diazotized and coupled with different phenols to give the corresponding novel 3-substituted 5-aryl azo pyrazoles. These dyes were characterized by elemental analysis and spectral data, applied to different types of fibres (wool, polyester and a blend of wool/polyester as disperse dyes) and their fastness properties were evaluated.     

Novel diphenysulphapyrimidine acetates derived from chalcones

Cyclocondensation of sulphaguanidine acetate with chalcones in dimethylsulphoxide at 110° gave 4,6-diphenylsulphapyrimidine acetates.     

Synthesis of some heterocyclic compounds derived from indole as antimicrobial agents

Recently, indoles are considered interesting heterocyclic compounds due to their wide range of biological activities such as antimicrobial activity. Herein, some new indole derivatives containing heterocyclic moieties were synthesized using 3-chloro-1H-Indole-2-carbaldehyde (1) as a starting material, then allowed to react with compounds containing active methylene under Knoevenagel condensation and afforded the corresponding compounds (2, 3, 9). Also, the compound (1) when allowed to react with hydrazine derivatives gave the corresponding thiosemiccarbazone, semicarbazone, and hydrazone derivatives (4, 5, 6). Reaction of thiosemicarbazone derivatives with α-halognated carbonyl compounds gave the thiazolyl indole derivatives (10, 12a–b). Cyclic chalcones (11a–c) were obtained when compound (10) reacted with different aromatic aldehydes. The structures of all new synthesized compounds were confirmed on the basis of spectral analysis, IR, 1H NMR, 13C NMR, and MS spectroscopy. All synthesized compounds were evaluated for their antimicrobial activity. Compounds (2, 5, 7, 8, 11a, 12a) showed high antibacterial activity and compounds (3, 6, 9, 10, 11a, 12a) showed high antifungal activity.     

Novel heterocyclic derivatives of quinuclidine

Treatment of ethyl 3-quinuclidinone-2-carboxyIate (III) with appropriate reagents gave 2,3-fused heterocycles including pyrazolol, aminopyrimidinone, and aminopyridazinone types. The thiourea derivative of III could not be cyclized. Triazoline, pyrazoline, and isoxazoline derivatives were prepared by 1,3-dipolar cycloadditions to the 2- and 3-positions of methyl 2,3-dehydroquinuclidine-3-carboxylate (XIIIa). Such facile formation of cycloaddition products was not possible with 2,3-dehydroquinuclidine, which reacted only with phenylazide (in poor yield). Structural assignments for the products of cycloaddition were made by analogy, but alternative structures could not be ruled out by the nmr or mass spectra.     

Mixed copper-lanthanide metallomesogens

This paper describes the first examples of heteropolynuclear metallomesogens that contain both a transition metal ion and a trivalent lanthanide ion. Adducts were formed between a mesomorphic [Cu(salen)] complex (salen=2,2'-N,N'-bis(salicylidene)ethylenediamine) with six terminal tetradecyloxy chains and a lanthanide nitrate (Ln=La, Gd). Different stoichiometries were found, depending on the lanthanide ion: a trinuclear copper-lanthanum-copper complex [La(NO(3))(3)(Cu(salen))(2)] and a binuclear copper-gadolinium complex [Gd(NO(3))(3)Cu(salen)]. The compounds exhibit a hexagonal columnar mesophase (Col(H)) over a wide temperature-range with rather low melting temperatures. Although the clearing point could be observed for the parent [Cu(salen)] complex, the mixed f-d complexes decomposed in the high-temperature part of the mesomorphic domain before clearing. On the basis of X-ray diffraction measurements and molecular modelling, a structural model for the mesophase of the metal complexes is proposed.