Mesogenic behaviour of two series of orthopalladated polar inline derivatives and their organic ligands (II)

One series of 4-n-octyl-N-(4-X-benzylidene)anilines and two series of polar orthopalladated complexes derived from these of type Pd₂(μ-Y)₂ p-X-C₆H₃-CH = N-C₆H₄-C₈H₁₇₂; X: -H, -F, -Cl, -Br, -NO₂, -CN, -CH₃, -OCH₃, -CF₃, -COOCH₃, -OCOCH₃ and -OCOQH₅; Y: -OAc and -Cl; have been synthesized and their mesogenic properties studied. In the polar Schiff bases used as organic ligands, the polar end group determines both the presence of the mesophase and the type of mesophase exhibited. In the complexes, however, it is the central structure of the molecule that practically always determines mesogenic behaviour. No acetato-bridged complex is mesogenic. All the chloro-bridged complexes, however, show mesogenic behaviour. All these compounds show smectic A mesophases with the exception of the CN compound, which only exhibits a nematic mesophase.     

Mesogenic behaviour in some pyrazole and isoxazole derivatives

Several aromatic β-diketones with a different number of alkyloxy groups in the aromatic rings and their derived pyrazoles, isoxazoles and thallium (I) complexes have been synthesized. The potential mesomorphic properties of these compounds have been investigated by optical microscopy, DSC and X-ray diffraction. The pyrazoles and isoxazoles with one chain in each aromatic ring are mesogenic, showing smectic A and smectic C mesophases, whereas the pyrazoles and isoxazoles with two chains per ring and the β-diketones and thallium complexes are not. The mesogenic potentiality is shown to be related to the molecular linearity and to the number of alkyloxy groups. To the best of our knowledge, this is the first time liquid crystal properties have been described for pyrazole and isoxazole derivatives.     

Mesogenic behaviour in some pyrazole and isoxazole derivatives

Abstract

Several aromatic β-diketones with a different number of alkyloxy groups in the aromatic rings and their derived pyrazoles, isoxazoles and thallium (I) complexes have been synthesized. The potential mesomorphic properties of these compounds have been investigated by optical microscopy, DSC and X-ray diffraction. The pyrazoles and isoxazoles with one chain in each aromatic ring are mesogenic, showing smectic A and smectic C mesophases, whereas the pyrazoles and isoxazoles with two chains per ring and the β-diketones and thallium complexes are not. The mesogenic potentiality is shown to be related to the molecular linearity and to the number of alkyloxy groups. To the best of our knowledge, this is the first time liquid crystal properties have been described for pyrazole and isoxazole derivatives.     

A new series of dinucleating macrocyclic ligands and their complexes of zinc(II)

A new category of dinucleating macrocyclic Schiff base ligands with ring sizes from 34- to 52-membered have been synthesised employing metal template procedures involving the reaction of o-phenylenediamine with a series of α,ω-bis(3′-hydroxy-4′-formylphenyloxy)alkanes in the presence of calcium(II), barium(II) or manganese(II). The latter cations act as ‘transient’ templates for formation of the corresponding metal-free Schiff base macrocyclic ligands, H₄Lⁿ (where n signifies the number of carbons in each linking bis-alkoxy chain); the macrocycles corresponding to n = 4, 6 and 8 were isolated and characterised while, for n = 1, in which single methylene groups acts as the bridges between salicyl moieties, the cyclic product was used directly for preparation of its dinuclear complex, [Zn₂L¹], without prior isolation. Evidence for the templating role of barium in the preparation of H₄L⁶ and H₄L⁸ was obtained by isolation of the corresponding species of type H₄Lⁿ·2Ba(ClO₄)₂ (n = 6 or 8) as ‘intermediates’ before generation of the respective metal-free macrocycles. Reaction of zinc(II) acetate with the free macrocycles in methanol yielded complexes of type [Zn₂Lⁿ] in all cases. A related non-cyclic ligand, H₂L⁰ and its corresponding mononuclear complex, [ZnL⁰]·H₂O, were also synthesised and its spectral properties compared with those of the macrocyclic derivatives. The elemental analyses, ¹H NMR, IR, UV–Vis and MS spectra of the respective zinc complexes in each case were in accord with the formation of the expected 2:2 condensation product. The results of DFT calculations to probe aspects of the electronic and structural natures of both H₂L¹ and H₄L⁴ are briefly presented.     

Cobalt(II), copper(II), nickel(II) and zinc(II) complexes of two novel Schiff base ligands and their antimicrobial activity

Two new, Schiff base ligands containing cyclobutane and thiazole rings, 4-(1-methyl-1-mesitylcyclobutane-3-yl)-2-(2,4-dihydroxybenzylidenehydrazino)thiazole (L¹H) and 4-(1-methyl-1-mesitycyclobutane-3-yl)-2-(2-hydroxy-3-methoxybenzylidenehydrazino)thiazole (L²H) and their mononuclear complexes with a 1:2 metal-ligand ratio have been prepared with acetate salts of Co^II, Cu^II, Ni^II and Zn^II in EtOH. The structures of the ligands and their complexes have been established by microanalyses, i.r., u.v.–vis., ¹³C- and ¹H-n.m.r. spectra, and by magnetic susceptibility measurements. The complexes are mononuclear. Thermal properties of the ligands and complexes have been studied by t.g.a. and d.s.c. techniques. Antimicrobial activities of the ligands and their complexes have been tested against eight different microorganisms. Some of the complexes and L¹H were found to be active against some of the microorganisms studied.     

Synthesis of two naphthyl-containing homologous series of mesogenic ligands and the related metallomesogens containing Cu(II)

Two new naphthyl-containing homologous series of mesogenic ligands, the 4-n-alkoxy-2-hydroxybenzylidene-2'-naphthylamines (series I) and 4(4'-n-alkoxybenzoyloxy)-2-hydroxybenzylidene-2'-naphthylamines (series II), as well as the related metallomesogens of higher homologues containing a Cu(II) atom, have been synthesized. All the ligands and complexes were characterized by a combination of elemental analysis and standard spectroscopic methods. In series I, n-heptyloxy and n-octyloxy derivatives are non-mesogenic whereas the remaining higher members synthesized exhibit a monotropic nematic mesophase. In series II, all the members synthesized exhibit an enantiotropic nematic mesophase. All the metallomesogens of series I synthesized exhibit a monotropic smectic A mesophase, except for the n-octyloxy derivative, which is non-mesogenic, whereas metallomesogens of series II exhibit enantiotropic nematic mesophases up to the n-tetradecyloxy derivatives; the n-tetradecyloxy and n-hexadecyloxy derivatives also exhibit smectic C mesophases. All the members of series II and their metallomesogens exhibit mesophases with wide temperature ranges and greater thermal stability as compared to series I and their metallomesogens, respectively. The mesomorphic properties of both the present series and their metallomesogens are compared with each other and with other structurally related series to evaluate the effect of the naphthalene moiety on mesomorphism.     

Mesogenic ketohexose and aldopentose derivatives: anomalous behaviour of the alkyl D-fructopyranosides

The thermotropic and lyotropic behaviour of a number of alkyl ketopyranosides, alkyl ketofuranosides, an alkyl pentopyranoside and an alkyl pentofuranoside were studied. With the exception of the alkyl beta-D-fructopyranosides, all the compounds display the expected smectic A* phases. The three alkyl fructopyranoside homologues studied (octyl, decyl and dodecyl) display a novel, rather viscous mesophase (monotropic), the nature of which is as yet unclear. The unknown phase is not a smectic A phase, because a phase transition from smectic A* to phase X is observed for both the decyl and the dodecyl derivative. The lyotropic behaviour of all the compounds in this study is quite similar to that reported earlier for other monoalkylated monosaccharide derivatives, except that the unknown phase X is again observed for the fructopyranoside derivatives.     

Mesogenic ketohexose and aldopentose derivatives: anomalous behaviour of the alkyl D-fructopyranosides

The thermotropic and lyotropic behaviour of a number of alkyl ketopyranosides, alkyl ketofuranosides, an alkyl pentopyranoside and an alkyl pentofuranoside were studied. With the exception of the alkyl beta-D-fructopyranosides, all the compounds display the expected smectic A* phases. The three alkyl fructopyranoside homologues studied (octyl, decyl and dodecyl) display a novel, rather viscous mesophase (monotropic), the nature of which is as yet unclear. The unknown phase is not a smectic A phase, because a phase transition from smectic A* to phase X is observed for both the decyl and the dodecyl derivative. The lyotropic behaviour of all the compounds in this study is quite similar to that reported earlier for other monoalkylated monosaccharide derivatives, except that the unknown phase X is again observed for the fructopyranoside derivatives.     

Phenyl-cyclohexyl enaminoketone ligands and their Cu(II) complexes

The liquid crystalline properties of 1-(alkylamino)-3-[(4'-hexyl-trans-cyclohexyl-4'-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the S_A phase in both ligands and complexes, whereas long chains promote S_C and crystal H phases for the ligands or S_A and S_C phases for the complexes. A partly bilayer smectic A_d phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data.     

Phenyl-cyclohexyl enaminoketone ligands and their Cu(II) complexes

Abstract

The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the S_A phase in both ligands and complexes, whereas long chains promote S_C and crystal H phases for the ligands or S_A and S_C phases for the complexes. A partly bilayer smectic A_d phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data.     

The coordination behaviour of ferrocene-based pyridylphosphine ligands towards Zn(II), Cd(II) and Hg(II)

The reaction of Group 12 metal dihalides MX(2) with the P,N-ligands [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-2-py)] (1) (2-py = pyrid-2-yl), [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-CH(2)-2-py)] (2) and [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-3-py)] (3) (3-py = pyrid-3-yl) was investigated. For a 1 : 1 molar ratio of MX(2) and the respective ligand, three structure types were found in the solid state, viz. chelate, cyclic dimer and chain-like coordination polymer. The M(II) coordination environment is distorted pseudo-tetrahedral in each case. The P-M-N angle is much larger in the chelates (≥119°) than in the ligand-bridged structures (≤109°). 1 prefers the formation of chelates [MX(2)(1-κ(2)N,P)]. 3 forms coordination polymers [MX(2)(μ-3)](n). With the more flexible 2 all three structure types can occur. Dynamic coordination equilibria were observed in solution for the molecular complexes obtained with 1 and 2. NMR data indicate that the N- and P-donor sites interact most strongly with Zn(II) and Hg(II), respectively. While the formation of bis(phosphine)mercury complexes (soft-soft) was easily achieved, no bis(pyridine)zinc complex (borderline-borderline) could be obtained, which is surprising in view of the HSAB principle.     

Cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens

The synthesis and evaluation of the liquid crystalline properties of non-conventional liquid crystals, consisting of two non-identical mesogenic segments interconnected via a paraffinic chain spacer, are of considerable current interest. In particular, chiral dimesogens possessing a cholesteryl ester unit as the chiral entity joined to other aromatic mesogens through a polymethylene spacer have shown unique and interesting thermal behaviour. In continuation of our investigations on this topic, here we present the synthesis and characterization of the first examples of cholesterol-based unsymmetrical dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal-organic systems (metallomesogens). Our studies reveal that the dimesogenic bidentate ligands exhibit multiple mesophases, whereas their metal complexes stabilize only the mesophase.     

Two-photon luminescence from polar bis-terpyridyl-stilbene derivatives of Ir(III) and Ru(II)

Four structurally related iridium(III) and ruthenium(II) complexes bearing two polar terpyridyl-stilbene derived chromophores 4-(4-{2-[4-(methoxy)phenyl]ethenyl}phenyl)-2,2'-6',2'-terpyridine (ttpyeneanisole) and 4-(4-{2-[phenyl]ethenyl}phenyl)-2,2'-6',2'-terpyridine (tpystilbene) have been synthesised and characterised in the solid state and in solution. In the solid state, the dihedral angle subtending the pyridyl and tolyl groups of 27.1° in the Ir(III) complex [Ir(ttpyeneanisole)(2)]·3PF(6) is more acute than in the Ru(II) derivative [Ru(tpystilbene)(2)]·2PF(6) (35.5°), indicating the presence of a greater degree of π-delocalisation across the terpyridine unit in the former compound. Their luminescence properties in fluid solution have been investigated following both resonant and non-resonant excitation. We have shown that each of the complexes undergoes two-photon excitation when excited in the near infrared (740 to 820 nm), with two-photon absorption cross sections in the range 11-67 × 10(-50) cm(4) s photon(-1). The larger cross sections for the Ir(III) complexes reflect the differences observed in the solid state. This work therefore demonstrates that such complexes are promising as luminescent markers for 3D imaging and illustrates that simple functionalisation of the chromophores and the choice of metal can lead to marked enhancements in the two-photon cross sections (σ(2)) compared to those of simpler heteroleptic polypyridyl based derivatives.     

Azetidines as ligands in the Pd(II) complexes series

The preparation of palladium (II) complexes having sterically congested azetidines as ligands is described. Diastereomerically pure α-alkylamino and α-alkylimino azetidines react with Na₂PdCl₄ to afford the corresponding bidendate Pd(II) complexes, whereas 2-cyano azetidines can be used to access bidendate Pd(II) complexes containing an amino-imidate moiety. Preliminary study of the catalytic activity of these new complexes in the Suzuki cross-coupling reaction is presented.     

Cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens

The synthesis and evaluation of the liquid crystalline properties of non-conventional liquid crystals, consisting of two non-identical mesogenic segments interconnected via a paraffinic chain spacer, are of considerable current interest. In particular, chiral dimesogens possessing a cholesteryl ester unit as the chiral entity joined to other aromatic mesogens through a polymethylene spacer have shown unique and interesting thermal behaviour. In continuation of our investigations on this topic, here we present the synthesis and characterization of the first examples of cholesterol-based unsymmetrical dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal-organic systems (metallomesogens). Our studies reveal that the dimesogenic bidentate ligands exhibit multiple mesophases, whereas their metal complexes stabilize only the mesophase.     

Synthesis and characterization of TCNQ derivatives of Ni(II) and Cu(II) with pyrazole-based ligands

Reactions between nickel(II) and copper(II) salts [M(L) _n ](ClO₄)₂ [L: 2-(pyrazole-1-ylmethyl)pyridine; n = 3 for Ni(II) and n = 2 for Ni(II) and Cu(II)] and LiTCNQ or mixture of LiTCNQ/TCNQ and Et₃NH(TCNQ)₂ yielded [Ni(L)₃](TCNQ)₂ · H₂O, [Ni(L)₂(TCNQ)₂], [Ni(L)₃](TCNQ)₃, [Ni(L)₂(TCNQ)₃], and [Cu(L)₂(TCNQ)₃] · 3H₂O. These complexes were characterized by infrared, electronic absorption, variable temperature magnetic moments and electron paramagnetic studies. Magnetic moments increase with increase in temperature attributed to contribution from TCNQ, which has also been examined by electron paramagnetic resonance.     

Achiral banana-shaped mesogenic bidentate ligands and their Cu(II) and Pd(II) complexes

The first achiral bent-core banana-shaped bidentate ligands and their Cu(II) and Pd(II) metal complexes have been synthesized and investigated for mesomorphic behaviour. The bidentate ligands exhibit only one enantiotropic mesophase. The ligand having C 6 -alkoxy chains shows a mesophase that has been assigned as a two-dimensional B 1 phase while the C 8 and C 10 homologues stabilize the fluid B 2 mesophase showing antiferroelectric switching characteristics. In constrast, their corresponding Cu(II) and Pd(II) metal complexes are non-mesomorphic.     

Achiral banana-shaped mesogenic bidentate ligands and their Cu(II) and Pd(II) complexes

The first achiral bent-core banana-shaped bidentate ligands and their Cu(II) and Pd(II) metal complexes have been synthesized and investigated for mesomorphic behaviour. The bidentate ligands exhibit only one enantiotropic mesophase. The ligand having C6 -alkoxy chains shows a mesophase that has been assigned as a two-dimensional B1 phase while the C8 and C10 homologues stabilize the fluid B2 mesophase showing antiferroelectric switching characteristics. In constrast, their corresponding Cu(II) and Pd(II) metal complexes are non-mesomorphic.     

Laws of complex formation in a series of azo-substituted pyrocatechol derivatives and their tin(II) complexes

Physicochemical properties of new reagents, azo-substituted pyrocatechol derivatives and their tin(II) complexes, are studied. The acid-base properties of the hydroxy groups (pK′_i, pK″_i), parameters of complex formation reactions (pH, temperature, time), and instability constants of the complexes formed (pK _i) are determined. Quantitative correlations between the dissociation constants (pK′_a) of the functional analytical group, and the electronic Hammett constant σ for a substituent (pK′_a-pH₅₀ of the complex formation reaction), as well as between pK′_a and instability constants of the complexes (pK _a), are established. The quantitative correlations established allow the prediction of the physicochemical properties of the reagents and tin(II) complexes with new reagents of this class with the same functional analytical group (FAG) but other substituents.