Electrical conductivity and dielectric constant measurements of liquid crystal-gold nanoparticle composites

The behaviour of the anisotropic electrical conductivity of liquid crystal-gold nanoparticle (LC-GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol-capped GNPs has been investigated. The nematic-isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ_∥) and orthogonal (σ_⊥) to the director shows a much smaller but definite decrease as X increases.     

Excess differential thermodynamic properties

A strategy is described for the systematic generation of a complete set of partial derivatives of the four energy functions from a basis set of five measured properties: V_m, S_m, C_p,m (δV_m/δT)_p and either (δV_m/δp)_T or (δV_m/δp)_s. The same set of equations applies to both pure substances and either real or ideal mixtures.

Examples are given of some excess differential properties of binary mixtures which exhibit unusual sensitivity to changes in composition.     

Non-monotonic temperature dependence of the alignment of a nematic mixture on a ferroelectric substrate

Polarization optic techniques have been applied to study specific features of the anisotropic interaction between a dye-doped eutectic mixture of nematic liquid crystals p-methoxybenzylidene-p-n-butylaniline and p-ethoxybenzylidene-p-n-butylaniline and a polar surface of a ferroelectric triglycine sulphate crystal over the temperature range including the substrate Curie point T _c. It has been found that the temperature-induced structural changes in the nematic layer in the vicinity of T _c are related to the changes in the orientational part of the tensor order parameter Q_ik . The temperature dependence of the director angle θ¯, averaged over the nematic layer, has been obtained from the effective dichroism values of solute absorption. The experimental data were interpreted using the model, in which the anisotropic part of the surface energy has two terms with orthogonal easy axes.     

Broadband dielectric studies of weakly polar and non-polar liquid crystals

Complex dielectric permittivities, for two orientations of the director n, parallel (E || n) and perpendicular (E ⊥ n) to the probing electric field E, of the weakly polar liquid crystals (LCs) 4,4'-dihexylazoxybenzene (D6AOB) and 4,4'-diheptylazoxybenzene (D7AOB) as well as the non-polar LC diheptylazobenzene (D7AB) have been measured in the frequency range 75 kHz to 1 GHz. The measurements were performed in the nematic, smectic and isotropic phases of the LCs. The dielectric anisotropies Δε (=ε_||-ε_⊥) obtained from the values of dielectric permittivities at 100 kHz in the nematic phase were found to increase with decreasing temperature. However, for the DnAOBs, the Δε values are somewhat smaller than that for D7AB which does not have a permanent dipole moment. In the nematic phase two molecular relaxation processes were observed for both DnAOBs in each of the orientations—parallel and perpendicular. The four processes merge into two separate processes in the isotropic phase. For D7AB no orientational relaxations were observed in the experimental frequency range.     

Dielectric studies of the hexatic B-smectic A and crystal B-smectic A transitions

Static dielectric constants, ε_∥ and ε_⊥ as well as the low frequency dielectric dispersion of ε_∥ have been studied in the vicinity of the hexatic B-smectic A transition in n-hexyl-4'-pentyloxybiphenyl-4-carboxylate (65OBC) and n-butyl-4'-hexyloxybiphenyl-4-carboxylate (46OBC) and also near the crystal B-smectic A transition in n-(4-n-butyloxybenzylidene)-4-n-octylaniline (4O. 8). While the behaviour of the dielectric anisotropy is essentially similar for both transitions, the dispersion results show significant differences.     

Hydrogenmaleato bridged supramolecular double chains via π–π stacking interactions: syntheses, crystal structures and magnetic properties of ∞[Cu(phen)X(HL)2/2] with X=Cl (1), NO3 (2) and H2L=maleic acid

Two novel hydrogen maleato (HL) bridged Cu(II) complexes _∞¹[Cu(phen)Cl(HL)_2/2] 1 and _∞¹[Cu(phen)(NO₃)(HL)_2/2] 2 were obtained from reactions of 1,10-phenanthroline, maleic acid with CuCl₂·2H₂O and Cu(NO₃)₂·3H₂O, respectively, in CH₃OH/H₂O (1:1 v/v) at pH=2.0 and the crystal structures were determined by single crystal X-ray diffraction methods. Both complexes crystallize isostructurally in the monoclinic space group P2₁/n with cell dimensions: 1 a=8.639(2) Å, b=15.614(3) Å, c=11.326(2) Å, β=94.67(3)°, Z=4, D_calc=1.720 g/cm³ and 2 a=8.544(1) Å, b=15.517(2) Å, c=12.160(1) Å, β=90.84(8)°, Z=4, D_calc=1.734 g/cm³. In both complexes, the square pyramidally coordinated Cu atoms are bridged by hydrogen maleato ligands into 1D chains with the coordinating phen ligands parallel on one side. Interdigitation of the chelating phen ligands of two neighbouring chains via π–π stacking interactions forms supramolecular double chains, which are then arranged in the crystal structures according to pseudo 1D close packing patterns. Both complexes exhibit similar paramagnetic behavior obeying Curie–Weiss laws χ_m(T−θ)=0.414 cm³ mol⁻¹ K with the Weiss constants θ=−1.45, −1.0 K for 1 and 2, respectively.     

Dielectric studies of liquid crystals under high pressure II. Low frequency relaxation process in 4-n-pentyl-4'-cyanobiphenyl in relation to theories of the nematic state

The results of high pressure dielectric studies of 4-n-pentyl-4'-cyanobiphenyl (5CB) are analysed in terms of theories of the nematic state. The retardation factor g∥ = τ∥/τ₀ and the effective, single-particle potential of mean torque were calculated at the nematic-isotropic transition temperature T_NI and along the isothermal, isobaric and isochoric paths within the nematic phase of 5CB. The potential of mean torque is compared with the order parameter known for the same conditions. The values of parameter γ relating the potential to the volume is discussed.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

A comparison of mesogenic properties of p-carborane-1,12-dicarbaldehyde schiff's bases with their terephthaldehyde analogues

A homologous series of carborane-containing Schiff's bases 1A[n] (n = 1-10) was prepared and compared with the analogous series 1B[n] derived from terephthaldehyde. An exponential fit of the T _NI values for both series yielded a quantitative assessment of the effect of ring structure on mesophase stability. This includes the T _NI value for n→∞ (86°C for 1A[n] and 209°C for 1B[n]) and steepness of descent (0.135 for 1A[n] and 0.095 for 1B[n]). The difference in behaviour of the two series was attributed, largely, to conformational properties of the central rings A and B. Electronic interactions between the central rings and the π-substituents were investigated by UV spectroscopy and by quantum-mechanical calculations. The effect of replacement of O with CH₂ in the terminal chain of 1[n] on the namatic phase stability was assessed for n = 5-7.     

X-ray studies of the layer thickness in smectic phases

X-ray investigations of nine smectogenic substances exhibiting the smectic A_d, A₁ and crystalline E phases were performed at various temperatures. X-ray patterns yielded the layer thickness d (A_d, A₁ phases) and orthorhombic unit cell parameters (E phase). The layer thickness of the A_d phase in 4'-n-alkyl-4-cyanobiphenyls (nCBs) has different temperature coefficients for shorter (n = 8-10) and longer (n = 12-14) members, which is explained as resulting from two competing effects: a weakening with temperature of the intermolecular association energy that favours an increase in d, and the increasing number of conformers which reduces the molecular length. A small anisotropy of the thermal expansivity in the smectic phases was found by comparing the linear quantity d(T) with the linearized bulk characteristic of the system, V^-3(T), where V = 1/ρ is the specific volume, ρ is the density. Differences between the slopes of the two quantities are less in the case of the A₁ phase of two nDBTs (5-n-alkyl-2-(4'-isothiocyanatophenyl)-1,3-dioxanes). The present X-ray data and recent results of studies of the low frequency relaxation process in these compounds (under atmospheric as well as elevated pressures) give a consistent picture of molecular reorientations around the short axes in the smectic phases.     

Refined heat capacity of LaPO4 in the temperature range 0–1600 K

In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p° (T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO₆ is refined by the Rietveld method: space group F d3m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å³. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion.     

Synthesis, structure and oxygen nonstoichiometry of La0.4Sr0.6Co1−yFeyO3−δ

The samples of La_0.4Sr_0.6Co_1−yFe_yO_3−δ (y = 0.2 and 0.4) were prepared using both conventional ceramic technique and nitrate–citrate precursors technique. The phase identification was made by X-ray diffraction method. The refinement of structural parameters from the XRD and neutron diffraction measurements was performed by full profile Rietveld analysis. Neutron diffraction showed that both samples possess distorted perovskite-type structure. Oxygen nonstoichiometry was measured by chemical analysis and thermogravimetry (TG) analysis in the range 20 ≤ T/°C ≤ 900 and 2E-5 ≤ pO₂/atm ≤ 4E-1. TG-experiments indicate a relatively fast and reversible oxygen exchange at pO₂ > 1E-2 atm. Mass saturation occurs at T < 300 °C upon cooling. The absolute value of oxygen nonstoichiometry was determined by iodometric titration measurements. It was found that both samples have practically stoichiometric composition at 300 °C in air and δ increases with increasing temperature and decreasing oxygen partial pressure.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Syntheses and crystal structures of 1,2:5,6:9,10:13,14:17,18:21,22-hexabenzo-3,7,11,15,19,23-hexadehydro[24]annulene (HBC), 1,2:5,6:9,10:13,14-tetrabenzo-3,7,11,15-tetradehydro[16]annulene (QBC) and a tetracobalt complex of QBC. The first example of a transition metal complex of QBC

1,2:5,6:9,10:13,14-Tetrabenzo-3,7,11,15-tetradehydro[16]annulene, or tetrabenzocyclyne (QBC) and 1,2:5,6:9,10:13,14:17,18:21,22-hexabenzo-3,7,11,15,19,23-hexadehydro[24]annulene (HBC) have been structurally characterized by X-ray. crystallography. QBC crystallizes in two different space groups; P2₁/c with a = 10.652(3) Å, b = 10.624(2) Å, c = 19.549(4) Å, β = 93.83(2)°, V = 2207.4(8) ų, and Z = 4 and P4₁2₁2 with a = 9.330(1) Å, c = 25.497(8) Å, V = 2219.6(12) Å, and Z = 4. HBC crystallizes in monoclinic P2₁/n with a = 14.763(3) Å, b = 10.296(2) Å, c = 22.057(4) Å, β = 108.61(3), V = 3177.4(11) ų, T = 133 K, and Z = 4. Reaction of QBC with dicobaltoctacarbonyl has produced a tetracobalt complex which has been characterized by X-ray crystallography. This complex crystallizes in monoclinic P2₁/c with a = 14.699(3) Å, b = 17.188(3) Å, c = 17.254(3) Å, β = 112.63(3)°, V = 4023.5(13) ų, and Z = 4. Only two of the four C---C triple bonds of QBC bind to dicobalthexacarbonyl moieties even when excess dicobaltoctacarbonyl is used.     

Dielectric studies of liquid crystals under high pressure III. Low frequency relaxation process in 4-(trans-4'-n-hexylcyclohexyl)isothiocyanato benzene

Dielectric studies of 4-(trans-4'-n-hexylcyclohexyl) isothiocyanatobenzene (6CHBT) were performed in the pressure range 0·1-150 MPa, the frequency range 1 kHz-13 MHz and the temperature range 295-325 K. The temperature and pressure dependencies of the static permittivity ε_0∥ and of the relaxation time τ_∥ are analysed and compared with the analogous data obtained recently for 4-n-pentyl-4'-cyanobiphenyl (5CB) (Parts I and II of this series). Marked differences in the dielectric properties of the nematic phases of the two substances are observed. They are interpreted as a result of varying degrees of molecular association in particular compounds. It is concluded that in the nematic phase of 6CHBT dipole-dipole correlations do not exist or are very weak, whereas for 5CB they are easily broken by a relatively low pressure.     

Structural studies on polynuclear osmium carbonyl hydrides XXXIV. Elucidation of the molecular structure from a crystal structure of disordered (μ-H)5Os3Re(CO)12

The complex (μ-H)₅Os₃Re(CO)₁₂ crystallizes in the centrosymmetric hexagonal space group P6₃/m (C²_6h; No. 176) with a 19.087(5), c 10.963(1) Å, V 3459(3) ų, and Z = 6. Diffraction data were collected on a Syntex P2₁ automated four-circle diffractometer (Mo-K radiation, 2θ = 4.5–45.0°) and the structure was refined to R_F = 7.9% for all 1480 unique reflections (R_F = 5.4% for those 1007 data with ¦F_o¦ > 6σ(¦F_o¦)). The molecule contains a tetrahedral core of metal atoms each associated with three terminal carbonyl ligands. It is bisected by a crystallographic mirror plane. Although the hydride ligands were not located, a consideration of metal-metal distances allows the distinction between osmium and rhenium atoms and suggests that the structure is subject to a subtle form of two-fold disorder.     

Preparation and crystal structure of a 1:1 inclusion compound of 1,4,11,14-tetramethoxy-dibenzo[b,n]tetraphenylene with pyridine

The new host 1,4,11,14-tetramethoxy-dibenzo[b,n]tetraphenylene forms a 1:1 inclusion compound with pyridine, in which a pair of centrosymmetrically-related guest species are enclosed in the cage surrounded by six host molecules. C₃₆H₂₈O₄·C₅H₅N, F_W=603.68, triclinic, space group P-1, a=11.796(2), b=16.075(3), c=9.004(2) Å; =98.39(3)°, β=90.01(3)°, γ=108.19(3)°, V=1602.8(5) Å³, Z=2, F(000)=636, D_c=1.251 g/cm³, μ=0.080 mm⁻¹. The final R indices [I>2σ(I)] R₁=0.0759, wR₂=0.1970 for 5623 MoK observed data.     

Synthesis, characterization and the unpleasantly disordered crystal structure of Ir(Ome)(CO)(PPh3)2(SO4)

The adducts of O₂ and SO₂ with trans-MeOIr(CO)(PPh₃)₂ are formed in equilibria and have been characterized. Reaction of the SO₂ adduct, Ir(OMe)(SO₂)(CO)(PPh₃)₂ with dioxygen leads to the sulfato complex, Ir(Ome)(CO)(PPh₃)₂(SO₄), the structure of which has been determined. Ir(Ome)(CO)(PPh₃)₂(SO₄) crystallizes in the monoclinic system with a 11.958(2), b 14.163(3), c 12.231(2) Å, β 118.365(12)°, V 1822.7(6) ų and Z = 2. Diffraction data for 2θ = 4.5–45.0° (Mo-K) were collected with a Syntex P2₁ diffractometer and the structure was solved (assuming space group P2₁/m and an unpleasant 2-fold disordered model) and refined to R = 4.8% for all 2512 independent data (R = 3.5% for those 2042 data with ¦F_O¦ > 6σ(¦F¦)). The iridium(III) atom has a distorted octahedral coordination sphere with trans PPh₃ ligands and a cis-chelating bidentate O,O′-SO₄ group; the structure is completed by mutually cis OMe and CO ligands.     

Rotational viscosity γ1 of nematic liquid crystals as a function of temperature, pressure and density

Measurements of the rotational viscosity γ₁ and the density are presented for a mixture of 4'-methoxybenzylidenebutylaniline (MBBA) and its ethoxy homologue EBBA and a mixture of cyclohexylphenylnitriles (ZLI 2413 from Merck AG) as a function of temperature and pressure. A new set-up for the measurement of densities under pressures of up to 3kbar is described. It is shown that the pressure dependence of the kinematic rotational viscosity γ₁/ρ and the temperature dependence of γ₁ under isobaric and isochoric conditions have common features with that of the shear viscosity of isotropic liquids. Furthermore, it is found that the curves γ₁ = f(1/T) for constant p and γ₁ = g(ρ) for constant T can be shifted one onto another by an appropriate shift of the scale of the independent variable.     

The molecular structure and the puckering potential function of silacyclobutane as determined by gas electron diffraction and relaxation constraints from ab initio calculations

Gas electron diffraction is applied to determine the geometric parameters of the silacyclobutane molecule using a dynamic model where the ring puckering was treated as a large amplitude motion. The structural parameters and the parameters of the potential function were refined taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the MP2/6-311+G(d, p) level of theory. The potential function has been described as V() = V₀[(/_e)² − 1]² with the following parameters V₀ = 0.82 ± 0.60 kcal/mol and _e = 33.5 ± 2.7°, where is a puckering angle of the ring.

The geometric parameters at the minimum V() (r_a in Å, in degrees and uncertainties given as three times the standard deviations including a scale error) are: r(Si–H_ax) = 1.467(96), r(Si–H_eq) = 1.468(96), r(Si–C) = 1.885(2), r(C–C) = 1.571(3), r(C–H) = 1.100(3), CSiC = 77.2(9), HSiH = 108.3, SiCH_eq = 123.5(16), SiCH_ax = 111.9(16), CC₅H_eq = 118.4(24), CC₅H_ax = 112.3(24), HC₃H = 107.7, δ(HSiH) = 6.6, δ(HC₃H) = 7.0, where the tilts δ, HSiH, and HC₃H are estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds.