Induced crystal G phase through intermolecular hydrogen bonding II. Influence of alkyl chain length of n-alkyl p-hydroxybenzoates on thermal and phase behaviour

A new series of intermolecular hydrogen-bonded complexes have been synthesized using p-n-alkoxybenzoic acid (alkyl chain length varies from propyl- to decyl- and dodecyl-) and methyl p-hydroxybenzoate moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Further, the stabilization of intermolecular hydrogen bonding in solution was studied by IR spectroscopy. A detailed IR spectral investigation in the solid and dissolved states suggests that the acid and phenol groups act as proton donor and proton acceptor, respectively. The thermal studies also reveal the inducement of a crystal G phase in the complexes.     

Induced crystal G phase through intermolecular hydrogen bonding II. Influence of alkyl chain length of n-alkyl p-hydroxybenzoates on thermal and phase behaviour

A new series of intermolecular hydrogen-bonded complexes have been synthesized using p-n-alkoxybenzoic acid (alkyl chain length varies from propyl- to decyl- and dodecyl-) and methyl p-hydroxybenzoate moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Further, the stabilization of intermolecular hydrogen bonding in solution was studied by IR spectroscopy. A detailed IR spectral investigation in the solid and dissolved states suggests that the acid and phenol groups act as proton donor and proton acceptor, respectively. The thermal studies also reveal the inducement of a crystal G phase in the complexes.     

Induced crystal G phase through intermolecular hydrogen bonding VII. Influence of non-covalent interactions on mesomorphism and crystallization kinetics

A series of intermolecular hydrogen bonding complexes, 2,2'-bipyridine: p- n-alkoxybenzoic acids (BP : nABA) was isolated from liquid crystalline p-n-alkoxybenzoic acids (nABA) (where n represents alkoxy carbon numbers, 3 to 10 and 12) and a non-mesogen, 2,2'-bipyridine (BP). The thermal and phase behaviour of these complexes was studied by thermal microscopy and differential scanning calorimetry (DSC). These studies revealed the induction of tilted smectic F and crystal G phases. The structural elucidation pertaining to the formation of intermolecular hydrogen bonding was carried out by a detailed IR spectral investigation. Comparative crystallization kinectic studies using DSC, performed on two representative compounds, showed different forms of the crystallization process. The magnitudes of the Avrami exponent n suggests two different mechanisms operate for individual members leading to sporadic three-dimensional growth. Nevertheless, an overall unique mechanism is predicted to operate at each crystallization temperature investigated, while the Avrami constant b shows a temperature dependence suggesting a strong influence of alkoxy terminal groups on the rates of nucleation.     

Wide nematic phases induced by hydrogen-bonding

New series of hydrogen-bonded supramolecular complexes, In/IIm, were prepared and investigated for their mesophase behaviour. The complexes were prepared through hydrogen-bonding between equimolar amounts of 4-alkoxyphenylazo-benzoic acids as the proton donors and non-mesomorphic 4-alkoxyphenylazo pyridines as the proton acceptors. The length of the terminal alkoxy chains was varied systematically on both terminals of the supramolecular complexes. The formation of 1:1 hydrogen-bonded complexes was confirmed by differential scanning calorimetry (DSC) and FTIR spectroscopy. All of new complexes were characterised by DSC and polarised light microscopy (PLM). It was found that the prepared complexes are dimorphic, possessing smectic C (SmC) and nematic (N) phases with relatively wide ranges. A comparison was made between the present series of complexes and the previously investigated isomers of the simple 4-alkoxybenzoic acids with the 4-(4?-pyridylazophenyl)-4??-alkoxybenzoates, revealed the stability of the nematic phase is dependent on the length of the acid component.     

Induced crystal G phase through intermolecular hydrogen bonding VII. Influence of non-covalent interactions on mesomorphism and crystallization kinetics

A series of intermolecular hydrogen bonding complexes, 2,2'-bipyridine: p- n-alkoxybenzoic acids (BP : nABA) was isolated from liquid crystalline p-n-alkoxybenzoic acids (nABA) (where n represents alkoxy carbon numbers, 3 to 10 and 12) and a non-mesogen, 2,2'-bipyridine (BP). The thermal and phase behaviour of these complexes was studied by thermal microscopy and differential scanning calorimetry (DSC). These studies revealed the induction of tilted smectic F and crystal G phases. The structural elucidation pertaining to the formation of intermolecular hydrogen bonding was carried out by a detailed IR spectral investigation. Comparative crystallization kinectic studies using DSC, performed on two representative compounds, showed different forms of the crystallization process. The magnitudes of the Avrami exponent n suggests two different mechanisms operate for individual members leading to sporadic three-dimensional growth. Nevertheless, an overall unique mechanism is predicted to operate at each crystallization temperature investigated, while the Avrami constant b shows a temperature dependence suggesting a strong influence of alkoxy terminal groups on the rates of nucleation.     

meso-四(对烷氧基苯基)卟啉镁配合物的合成、表征和性能研究

合成了一系列meso-四(对烷氧基苯基)卟啉镁配合物,用UV-Vis,1H NMR,IR,MS,元素分析等确证了配合物的结构,总结了镁与卟啉类配体配合的UV-Vis,1H NMR,IR数据.采用差示扫描量热法(DSC)和偏光显微镜(PM)研究了该系列配合物的液晶性能,发现6个配合物具有液晶性;考察了烷氧基链长、配位金属离子和分子空间结构对液晶性能的影响.     

Emissive ‘zinc(II)-salphen’ core: building block for columnar liquid crystals

A series of half-discoid [N₂O₂]-donor tetradentate alkoxy substituted salicylaldimine ligands, [N,N′-di- (4-n-alkoxysalicylidene)-4-Cl-l,2-diamino-benzene] (L; n?=?12, 14, 16 and 18) have been prepared. The reaction of the ‘salphen’-type Schiff base ligand with Zn(OAc)₂.4H₂O afforded a series of mononuclear zinc(II) complexes. The ligands and the corresponding zinc(II) complexes were characterised by elemental analysis, Fourier transform infrared, proton nuclear magnetic resonance and ultraviolet-visible spectroscopy. Although the ligands are non-mesogenic, columnar mesomorphism is induced upon complexation with the metal. The p2gg symmetry of the rectangular columnar phase is confirmed by variable temperature powder X-ray diffraction study. Two ‘half-disc’-shaped molecules with four alkoxy legs are presumed to self-assemble via a dimeric interaction filling the space. In contrast to the ligands, the zinc(II) complexes all exhibited moderately intense green emission at room temperature both in solution and in the solid state. Density functional theory calculation, carried out using a DMol3 program, revealed a distorted square planar geometry for the complexes. The mesomorphic and photoluminescence property of the zinc complexes are collated as a function of spacer substituent, as well as alkoxy carbon chain length.     

偶氮型液晶冠醚的合成与表征

以4'-正烷氧基联苯-4-甲酸和顺(反)-4,4'-双(4-羟基苯基偶氮)二苯并-14-冠-4为中间体, 通过溶液缩合反应, 合成了一系列偶氮型液晶冠醚. 并用元素分析、核磁共振、紫外可见分光光度计、红外光谱、基质辅助激光解析电离飞行时间质谱、示差扫描量热法和偏光显微镜对其进行了表征. 随分子末端烷氧基碳原子数增加, 化合物4I和4II的熔点(T_m)和液晶态的清亮点(T_i)逐渐降低, 液晶态温度范围较宽.     

Supramolecular liquid crystals formed by hydrogen bonding between a benzocrown-bearing stilbazole and carboxylic acids

The mesomorphism of hydrogen bonded complexes formed between 4'-carboxybenzo-15-crown-5 stilbazolyl ester (CBCSE) as proton acceptor and carboxylic acids as proton donors is discussed. CBCSE is a monotropic mesogen, forming a nematic phase upon quench cooling. A total of 32 hydrogen bonded complexes has been studied. Hydrogen bonding with carboxylic acids stabilizes the nematic phase, and/or induces a smectic A (SmA) phase. CBCSE forms 1:1 complexes (molar ratio) with alkanoic acids (fatty acids) and 2:1 complexes with alkanedioic acids. None of these proton donors is a mesogen itself, but the hydrogen bonded complexes are. The influence of the chain or spacer length on the transition temperatures is discussed. Besides the homologous series of the alkanoic and alkanedioic acids, the following carboxylic acids were used in this study: diglycolic acid, pyridine-2,6-dicarboxylic acid, 4-dodecyloxybenzoic acid, 3,4-bis(dodecyloxy)benzoic acid, 2,3,4-tris(dodecyloxy)benzoic acid and 3,4,5-tris(dodecyloxy)benzoic acid, phthalic acid, isophthalic acid and terephthalic acid.     

Mesomorphic behaviour and TSDC measurements of ortho-metallated palladium(II) and platinum(II) complexes with S,O-donor co-ligands

A series of ortho-metallated Pd and Pt complexes containing an imine ligand carrying three alkoxy chains and N-benzoylthiourea derivatives as co-ligands were prepared and their liquid crystalline properties investigated. Their structures were assigned based on elemental analysis, IR and ¹H NMR spectroscopy, whereas thermal properties were investigated by differential scanning calotimetry and polarising optical microscopy. All the compounds exhibit monotropic transitions involving nematic and smectic A phases, with the mesomorphic behaviour strongly related to the type of N-benzoylthiourea as well as the metal centre used. The thermally stimulated depolarisation current technique was employed to determine the conduction mechanism, phase transition temperature and the activation energies for one of the ortho-metallated Pd complexes.     

Supramolecular liquid crystals formed by hydrogen bonding between a benzocrown-bearing stilbazole and carboxylic acids

The mesomorphism of hydrogen bonded complexes formed between 4'-carboxybenzo-15-crown-5 stilbazolyl ester (CBCSE) as proton acceptor and carboxylic acids as proton donors is discussed. CBCSE is a monotropic mesogen, forming a nematic phase upon quench cooling. A total of 32 hydrogen bonded complexes has been studied. Hydrogen bonding with carboxylic acids stabilizes the nematic phase, and/or induces a smectic A (SmA) phase. CBCSE forms 1:1 complexes (molar ratio) with alkanoic acids (fatty acids) and 2:1 complexes with alkanedioic acids. None of these proton donors is a mesogen itself, but the hydrogen bonded complexes are. The influence of the chain or spacer length on the transition temperatures is discussed. Besides the homologous series of the alkanoic and alkanedioic acids, the following carboxylic acids were used in this study: diglycolic acid, pyridine-2,6-dicarboxylic acid, 4-dodecyloxybenzoic acid, 3,4-bis(dodecyloxy)benzoic acid, 2,3,4-tris(dodecyloxy)benzoic acid and 3,4,5-tris(dodecyloxy)benzoic acid, phthalic acid, isophthalic acid and terephthalic acid.     

meso-四(对烷氧苯基)卟啉金属配合物的合成和性能研究(II)

合成了Zn、Pb两个系列卟啉金属配合物12个,其中6个为未见文献报道的新化合物,用元素分析、IR、UV、^1HNMR、MS确证了其结构。总结了Zn、Pb与卟啉类配体配合的IR、UV、^1HNMR判据。研究了这两个系列化合物的液晶性能,发现9个化合物具有液晶性。     

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.     

Liquid crystalline thiadiazole derivatives: new ferroelectric thiadiazole derivatives

A series of optically active thiadiazole Schiff's bases were prepared and their liquid crystalline properties were studied. Chirality was achieved by introducing an asymmetric carbon atom into the alkoxy group. Thus, 2-( p -active-alkoxyphenyl-imine)-5-( p - n -alkoxy)phenyl-1,3,4-thiadiazoles were synthesized. Their structures were characterized using elemental analysis, and IR, 1 H NMR and mass spectroscopies; their thermal properties were determined using DSC and polarized light microscopy. All the compounds are enantiotropic liquid crystals, and most of them exhibited both chiral smectic C* and cholesteric mesophases. Only one of them did not show a smectic C* phase.     

Trimetallic Nickel–Lanthanum and Nickel–Gadolinium Metallomesogens

Adducts were formed between a mesomorphic Ni(salen) complex [salen=2,2′-N,N′-bis(salicylidene)ethylenediamine] with six terminal alkoxy chains and a lanthanide nitrate (Ln=La, Gd). Different alkoxy chain lengths were used: OC¹²H²⁵, OC¹⁴H²⁹, OC¹⁶H³³ and OC¹⁸H³⁷. Trinuclear nickel–lanthanum and nickel–gadolinium complexes [Ln(NO³)³{Ni(salen)}²] were obtained. The compounds exhibit a wide-temperature-range hexagonal columnar mesophase (Col^H) with rather low melting points. The mesophase stability ranges of both the parent nickel complexes and the nickel–lanthanide complexes decrease with increasing chain length. A decrease in the mesophase stability range over the lanthanide series was also observed. The results are compared with those of similar copper–lanthanide complexes. A marked difference is the higher thermal stability of the nickel–lanthanide complexes in comparison with the copper–lanthanide complexes.     

Synthesis,characterization and biological activities of mononuclear and binuclear Fe(III) complexes with some symmetric and unsymmetric Schiff-base ligands

A series of mononuclear and binuclear Fe(III) complexes of some new symmetrical and unsymmetrical Schiff bases containing quinoline derivatives were synthesized and characterized by elemental and thermal analysis, conductance measurements and IR spectra. In mononuclear complexes, the unsymmetric Schiff bases are monobasic tetradentate towards the Fe(III) ion. However, in binuclear complexes, the symmetric Schiff-base ligands behave as monobasic bidentate towards each Fe(III) ion. The structure of the solid complexes are discussed and based on magnetic susceptibility measurements, electronic and ESR spectral studies. The biological activities of the ligands and their complexes are reported.     

Neutral and zwitterionic glycine.H(2)O complexes: A theoretical and matrix-isolation Fourier transform infrared study

The H-bond interaction between glycine and H2O has been studied by a combined theoretical (DFT(B3LYP)/6-31++G(**)) and experimental (matrix-isolation FT-IR) methodology. The 1:1 and 1:2 complexes of the most stable conformation (I) of glycine appear to be neutral complexes which have been vibrationally characterized in detail. The higher stoichiometry complexes (glycine).(H2O)n with n larger than 3 are demonstrated to be zwitterionic H-bonded complexes. A set of characteristic IR absorption bands for this zwitterionic structure has been observed in low-temperature Ar matrices. This would be the first experimental IR evidence for proton transfer occurring between the NH2 and COOH groups of amino acids by a H-bonded water molecular channel in isolated conditions.     

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.     

Nematic and smectic mesophases in a new series of Cu(II) organometallic complexes

The synthesis and the phase behaviour of a homologous series of copper, bis[N-[[4-[4-(alkoxy)benzoyloxy],2-hydroxyphenyl]methylene]-methanamino] complexes is reported. They all exhibit thermotropic mesomorphism. The thermal stability range of the mesophase decreases slightly with increasing length of the alkoxy terminals. With the onset of smectic mesomorphism, for alkoxy groups containing ten carbon atoms, the stability interval of the nematic phase decreases progressively so that the compound containing 14 carbon atoms in the alkoxy terminal chains exhibits only smectic mesomorphism. Optical texture analysis suggests the smectic C nature of the phase in all cases. The enthalpies for the liquid crystal-isotropic transition have been measured and they are comparatively low. Remarkably low values have also been measured for the melting enthalpies of the smectogenic members of the series. These are associated with solid phase polymorphism which is discussed briefly.     

Structure and intermolecular interactions in complexes with hydrogen bond of a series of bifunctional nitrogen-containing compounds

By means of IR absorption spectra, low temperature ¹H and ¹⁵N NMR spectra, and quantum chemical calculations we study the structure of complexes with hydrogen bond of molecular and ionic character formed by nitrogen-containing compounds able to be both proton donors and acceptors simultaneously and the interaction specificity in them. Spectroscopic, steric, and thermodynamic characteristics of diphenyltriazene, 3,5-dimethylpyrazole, and diphenylformamidine homoassociates and heterocomplexes of these compounds with carboxylic acids and various proton donating molecules are obtained. Quantum chemical calculations of the structure of complexes and vibrational frequencies in IR spectra are made in the harmonic approximation and with regard to anharmonicity corrections. Calculations taking into account anharmonicity of vibrations are shown to produce the results closest to the experimental data.