Thermotropic ionic liquid crystals of pyridinium octylphosphate A N.M.R. and X-ray study

Abstract

A thermotropic ionic lamellar phase from non-stoichiometric pyridinium octyl-phosphates has been investigated by multinuclear N.M.R. and X-ray diffraction. At room temperature and above, this phase is formed for pyridine to octylphosphoric acid molar ratios from 0.2 to 0.8.²H and ¹³C relaxation experiments show that the pyridinium ion undergoes a very anisotropic motion with D_zz > D_xx ? D_yy, z and x being the perpendicular direction to the ring and the c ₂ symmetry axis, respectively. The order parameters given by the ²H quadrupolar splittings and the ¹³C chemical shift anisotropy (CSA) are S_zz = 0.13, S_yy = -0.08 and S_xx = -0.05, showing that the pyridinium ring is preferentially oriented parallel to the lamellar plane. The ³¹P CSA and the C1-P dipolar splitting yield S_zz = 0.33 and S_xx ? S_yy for the octylphosphate anion. The order parameters of alkyl C-H bonds have been obtained from the J resolved two-dimensional ¹³C N.M.R. spectra of oriented samples. Two limiting conformational models have been considered to calculate the S _CH. One of them is reasonably consistent with the structure derived from X-ray experiments and has been used to calculate the dipolar ³¹P relaxation. Taking into account the CSA contribution, the relaxation measurements performed at 36, 121 and 202 MHz show that the octylphosphate anion undergoes a quasi-axial reorientation about the long molecular axis x with D∥/D⊥ = 4 and D⊥ ? 10⁷ rad/s at 300 K.     

Calculation of the rotational magnetic moments of the ammonia and water molecules

We calculate the rotational magnetic moments and the corresponding g-factors for water and ammonia. Our results are g_xx = 0.397, g_yy = 0.769 and _zz = 0.345 for water and g_xx = g_yy = 0.69 and g_zz = 0.51 for ammonia. The experimental values are g_xx = 0.585, g_yy = 0.742 and g_zz = 0.666 for water and g_xx = g_yy = 0.56 and g_zz = 0.484 for ammonia.     

Polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S2P(O-iso-C3H7)2}]n: Synthesis, structure, and 13C and 31P CP/MAS NMR spectra

The crystalline polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S₂P(O-iso-C₃H₇)₂}] _n (I) was obtained and examined by solid-state ¹³C and ³¹P CP/MAS NMR spectroscopy. Diagrams of the χ² statistic were constructed from the complete ³¹P MAS NMR spectra and used to calculate the ³¹P chemical shift anisotropy (δ_aniso = (δ _zz − δ_iso)) and the asymmetry parameter (η = (δ _yy − δ _xx )/(δ _zz − δ_iso)). The ³¹P chemical shift tensor has a nearly axial symmetry (η = 0.22, δ _zz < δ _yy ≈ δ _xx ). The MAS NMR spectral patterns correspond to the negative sign of δ_aniso (δ _zz < δ _yy < δ _xx ), which indicates bridging or chelating-bridging coordination of the dithiophosphate ligands (Dtph). X-ray diffraction analysis revealed a polymeric structure of compound I. The polymer chain consists of alternating mononuclear [Tl{S₂P(O-iso-C₃H₇)₂}] molecules with opposite spatial orientations. The Dtph ligands are coordinated in a mixed, chelating-μ₃-bridging fashion. The shape of the ³¹P NMR signal was interpreted in terms of the ³¹P-^203,205Tl coupling pattern proposed from crystallographic data.     

Anisotropy analysis of the surface stress in Ag stepped surfaces with the modified embedded atom method

The surface stresses in Ag stepped surfaces (910), (710), (510), (410), (310), (210), (320), (430) and (540) have been calculated by using the modified embedded atom method (MEAM). The surface stresses in the surface plane τ_xx (along the step edge) and τ_yy (normal to the step edge) have similar orders of magnitude as the surface energy. For surfaces having the (100) and (110) terraces, the change of τ_xx and τ_yy is very small and the variation of the surface energy is smooth. The stress τ_zz (normal to the surface plane) is always tensile in the unrelaxed state. The linear variation of the change in surface energy per unit change in elastic strain , and (i.e. τ_xx ? γ, τ_yy ? γ and τ_zz) with the angle α between the (hk0) and (100) planes has a turning point corresponding to the (210) surface. The anisotropic ratio in the stepped surface having the (110) terrace is larger than that having the (100) terrace, and the wider the (110) terrace or the narrower the (100) terrace, the larger the ratio τ_yy/τ_xx. Copyright © 2006 John Wiley & Sons, Ltd.     

Solute alignment in liquid crystal solvents The Saupe ordering matrix for anthracene dissolved in uniaxial liquid crystals

We have described a theory for U, the potential of mean torque of rigid solutes at infinite dilution in a uniaxial liquid crystal phase; this may be used to calculate (S_xx - S_yy) and S_zz, the principal elements of the Saupe ordering matrix. In its simplest form U(ω) contains only second-rank terms and the dependence of the biaxiality (S_xx - S_yy) is determined by ω, a parameter which describes the departure of the potential of mean torque from cylindrical symmetry, and is predicted to be temperature independent. If dispersion forces are responsible for the magnitude of the orientational order parameter then ω should be independent of the solvent and depend only on the anisotropy in the electric polarizability of the solute. Indeed, this independence should result for any pair potential which can be factorized into a product of solute and solvent properties. These predictions are tested here by determining values of S_zz and (S_xx - S_yy) for anthracene-d₁₀ as a solute in several liquid crystal solvents, from the quadrupolar splittings obtained from the deuteron N.M.R. spectra. It is found that ω has a strong dependence on the nature of the solvent, which demonstrates that the solute ordering cannot be determined primarily by dispersion forces, or by a factorizable potential. There is also a weaker temperature dependence of λ observed for each binary mixture, and we show how this might be caused by a dependence of ω on solvent ordering, or by the inclusion of a fourth-rank term in U(ω).     

Synthesis, structure, and 13C and 31P CP/MAS NMR of crystalline modifications of the polynuclear thallium(I) O,O′-dicyclohexyl phosphorodithioate complex [Tl{S2P(O-cyclo-C6H11)2}]n

Two crystalline modifications (Ia and Ib) of the polynuclear thallium (I) O,O′-dicyclohexyl phosphorodithioate complex [Tl{S₂P(O-cyclo-C₆H₁₁)₂}] _n have been synthesized and characterized by CP/MAS NMR (¹³C, ³¹P). From full ³¹P CP/MAS NMR spectra, the χ² plots were constructed to calculate the ³¹P chemical shift anisotropy ³¹P − δ_aniso = (δ_zz − δ_iso) and asymmetry parameters η = (δ _yy − δ _xx )/(δ _zz − δ_iso). The data obtained for the O,O′-dicyclohexyl phosphorodithioate (Dtph) groups (in both modifications) are evidence that the ³¹P chemical shift tensors are intermediate between rhombic and axially symmetric. However, whereas the rhombic component dominates for Ia, the tensor for Ib is close to axially symmetric (for δ _zz < δ _yy ≈ δ _xx ). The same pattern of the MAS spectra corresponding to negative δ_aniso (δ _zz < δ _yy < δ _xx ) points to a bridging or terminal/bridging coordination mode of the Dtph groups. X-ray crystallography shows that complex Ib has a polynuclear structure (of the chain polymer type). The chains are composed of alternating structurally nonequivalent noncentrosymmetric binuclear molecules [Tl₂{S₂P(O-cyclo-C₆H₁₁)₂}₂]. All Dtph ligands have the terminal/μ₃-bridging coordination mode.     

Transitions between the B2 phase and more usual smectic phases in binary systems of banana-shaped with calamitic mesogens

Deuterium NMR spectroscopy is used to study a ring-deuteriated chiral liquid crystal 4-(2-methylbutyl)oxycarbonylphenyl 4-(10-undecenyloxy)benzoate. The quadrupolar and proton-deuteron dipolar splittings, and deuteron quadrupolar and Zeeman spin-lattice relaxation times were measured as a function of temperature in the smectic A phase at two different Larmor frequencies. The derived spectral densities of motion at different temperatures were analysed simultaneously using a rotational diffusion model which also includes internal ring rotations. Motional parameters (D _⊥, D _∥, D _R) and order parameter tensors (S_zz , S_xx -S_yy ) were obtained. Although the present data seem insufficient to draw a definitive conclusion, we believe that it is possible for this particular chiral molecule to have D_⊥ >D_∥ , which is different from non-chiral rod-like liquid crystals.     

The two-photon excitation spectrum of a carbazole single crystal at 4.2 K

The low-energy system in the polarized two-photon excitation spectrum of carbazole at 4.2 K has been measured by detecting fluorescence pulses from deliberately added anthracene. Herzberg—Teller activity was detected for Some A₁ vibrations. The two-photon operators contribute to the two-photon cross section in the order yy ≈ zz ? xx.     

Paramagnetic absorption of pentavalent molybdenum in polycrystalline tin dioxide

Part of molybdenum introduced in SnO₂ by various methods is found to be stabilized in the pentavalent state at substitutional positions. The ESR spectra of Mo⁵⁺ ions are characterized by the following parameters: g_xx = 1.891; g_yy = 1.835 and g_zz = 1.923, A_xx = 24 G, A_yy = 30 G and A_zz = 70 G. There are, in addition, two sets of superhyperfine structures due to the two tins located along the crystallographic c axis (290 G) and to the four tins lying in a diagonal plane of the unit cell containing four oxygens (51 G), consistent with a 3d_x²-y² + λ 3d_z2 ground state. The variations of the Mo⁵⁺ ESR spectrum upon heating the samples in various atmospheres (O₂, H₂) suggest that molybdenum enters the SnO₂ lattice also as Mo⁴⁺.     

H 2 O-D2O Solvent Isotope Effect on Excess Molar Volumes of 3-Methylpyridine Solutions

Densities of 3-methylpyridine (3-MP) + water and 3-methylpyridine + heavy water were measured in the 3-MP mole fraction range 0.002–0.04 from 298 to 318 K. The excess molar volumes of 3-MP + D₂O mixtures were found to be more negative than those of 3-MP + H₂O mixtures. The partial molar volume of 3-MP at infinite dilution is smaller in D₂O than in H₂O which suggests that 3-MP causes a structure-breaking effect in water which is more pronounced in D₂O. It was found that the volume change with concentration in dilute solutions of 3-MP in water and heavy water can be adequately described by the pair-wise interaction of the solute molecules. The molal volume second-virial coefficient, V _xx , is positive indicating that the water molecules are less structured in the cospheres of the solute pairs than in the bulk solvent. The temperature dependence of V _xx displays a maximum at around 308 K in the case of D₂O solutions, whereas V _xx increases almost linearly with temperature in H₂O solutions.     

Mössbauer effect of FeOCl-pyridine complex

A Mössbauer effect study has been conducted on FeOCl-pyridine complex in the temperature range between 4.2° and 298°K. The isomer shift relative to Fe metal and the quadrupole splitting at 298°K are 0.36 ± 0.01 and 0.92 ± 0.01 mm/sec, respectively. An antiferromagnetic ordering occurs at 65 ± 3°K. The internal magnetic field is 435 ± 10 kOe at 4.2°K. The z axis of the electric field gradient tensor (|V_zz|> |V_xx| ? |V_yy|, η being small) is shown to be parallel to the direction of the internal magnetic field and perpendicular to the crystalline b axis.     

The diethyl dithiophosphate complex of tetraphenylantimony(V) and its solvated form, [Sb(C6H5)4{S2P(OC2H5)2}] · 1/2 C6H6: Synthesis, crystal structure, and 13C, 31P CP/MAS NMR study. an example of monodentate coordination of dithio ligands

The O,O′-diethyl dithiophosphate complex of tetraphenylantimony(V) [Sb(C₆H₅)₄{S₂P(OC₂H₅)₂}] (I) and its benzene-solvated form I · 1/2C₆H₆ (II) were synthesized and studied by high-resolution solid-state ¹³C and ³¹P NMR (MAS NMR). The diethyl dithiophosphate (Dtph) groups in I and II were quantitatively characterized by the ³¹P chemical shift anisotropy (δ_aniso), the asymmetry parameter (η), and the principal values of chemical shift tensors (δ _xx , δ _yy , δ _zz ). The calculation of the anisotropy parameters included construction of χ² statistic diagrams from full ³¹P MAS NMR spectra. In both complexes, the Dtph groups were found to have mainly axially symmetric ³¹P chemical shift tensors (for δ _zz < δ _xx ≈ δ _yy ) with similar anisotropy parameters (δ_aniso and η), which is due to their identical S-monodentate function. According to X-ray diffraction data, II has a trigonal bipyramidal (TBP) molecular structure with Smonodentate coordination of Dtph in the TBP axial position and outer-sphere position of the benzene molecule. The desorption of the outer-sphere benzene solvent molecules from structure II, which was noted in MAS NMR experiment, passes through the formation of three intermediate solvated forms with benzene content n < 1/2.     

Electron paramagnetic resonance and optical studies of Cu2+ doped bis(thiourea)cadmium chloride single crystal

Electron paramagnetic resonance (EPR) and optical studies have been carried out on Cu²⁺ doped bis(thiourea)cadmium chloride single crystal, which belongs to a potential semi-organic non-linear material, at room temperature. The spin Hamiltonian parameters were determined as g_xx = 2.04331, g_yy = 2.04373, g_zz = 2.05750 and A_xx = 91G, A_yy = 115G, A_zz = 136G. These parameters suggest that the spectroscopic splitting parameter g and hyperfine splitting parameter A exhibit rhombic symmetry. The optical study reveals that the non-linear optical property of the host lattice has been enhanced due to Cu²⁺ doping.     

Synthesis, structure, and 13C and 31P CP/MAS NMR of the tetraphenylantimony(V) di-iso-propyl phosphorodithioate complex [Sb(C6H5)4{S2P(O-iso-C3H7)2}] and its solvated form [Sb(C6H5)4{S2P(O-iso-C3H7)2}] · 1/2C6H6: An example of the monodentate coordination of dithio ligands

The crystalline tetraphenylantimony(V) O,O′-di-iso-propyl phosphorodithioate complex [Sb(C₆H₅)₄{S₂P(O-i-C₃H₇)₂}](I) and its solvated form [Sb(C₆H₅)₄{S₂P(O-i-C₃H₇)₂}] · 1/2C₆H₆(II) were synthesized. Solid compounds I and II were studied by MAS NMR (¹³C, ³¹P). The ³¹P NMR chemical shift anisotropy ³¹P δ_aniso = (δ _zz ? δ_iso) and asymmetry parameter η = (δ _yy ? δ _xx )/(δ _zz ? δ_iso) were calculated using χ ² plots constructed on the basis of the ³¹P MAS NMR data. The O,O′-di-iso-propyl phosphorodithioate ligands in both complexes are characterized by predominantly the axially symmetric ³¹P chemical shift tensor (for the case δ _zz < δ _xx ≈ δ _yy ) with close values of anisotropy parameters (δ_aniso and η), which reflects their identical S-monodentate structural function. X-ray crystallography showed that II has a trigonal-bipyramidal molecular structure with the uncommon monodentate coordination of the Dtph ligands through an S atom in an axial position of the trigonal bipyramid and the benzene molecule in the outer sphere.     

Structural elucidation of transition metal complex by single crystal EPR study

Single crystal EPR studies of Mn(II) doped hexaaquazincdiaquabis(malonato) zincate [Zn(H₂O)₆][Zn(mal)₂(H₂O)₂] have been carried out at room temperature using X-band spectrometer to identify the location of the dopant. Single crystal rotations along the three orthogonal axes show more than 30 line pattern EPR spectra indicating the presence of two types of dopant ions in the host lattice, with intensity ratio of 6:1. However, the latter could not be followed due to its low intensity during crystal rotations. The spin-Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations are: g_xx = 1.972, g_yy = 2.000, g_zz = 2.023, A_xx = 8.95, A_yy = 9.48, A_zz = 9.93 mT, D_xx = −34.49, D_yy = −3.26, D_zz = 37.74 mT and E = 15.6 mT. The direction cosines of one of the principal values of g match with that of Zn-O bond in the host lattice, suggesting that the Mn(II) ion entered the lattice substitutionally. The large value of E is indicative of low symmetry of the substitutional site, in accordance with the crystal structure of the isomorphous [Zn(H₂O)₆][Cu(mal)₂(H₂O)₂]. Covalency of Mn-O bond, estimated from Matamura’s plot, is 9%. Various admixture coefficients, bonding and optical parameters have also been calculated.     

C Anisotropic chemical shift in a single crystal of benzophenone

The ¹³C resonance of the carbonyl carbon in a single crystal of benzophenone was studied by Fourier transform NMR at room temperature. Rotation patterns about the three cyrstallographic axes yielded the orientations of the major axis systems of the chemical shift tensor σ relative to the crystallographic axes for the four molecules in the unit cell. The principal elements of σ were found to be: σ_xx = −79 ± 4, σ_yy = −36 ± 4, and σ_zz = +94 ± 4 ppm , relative to CS₂. The Z axis of the nearly axially symmetric σ tensor was found to be perpendicular to the plane spanned by the carbonyl carbon and the carbon and oxygen atoms directly bound to it.     

Détermination des Axes Propres et des Valeurs Principales du Tenseur ḡ dans deux Radicaux Libres Nitroxydes par Étude de Monocristaux

The low temperature phase structure of the nitroxide radical 2,2,6,6-tetramethyl piperidin-1-oxyl (Tanane) is isomorphic of 2,2,6,6-tetramethyl-4-piperidinol-1-oxyl (Tanol). An ESR study of single crystals yielded the principal values and position of principal axes of the ? tensor in these two radicals. The major significant differences observed in Tanol are a moderate decrease in the g_xx, g_yy and g_zz values, and a deviation of the principal axes situated in the molecular mirror plane from the N? O bond and π-orbital, respectively (8° ± 2°). The intermolecular hydrogen bond is probably responsible for this fact.     

Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.