Propagation of an electromagnetic wave in an absorbing anisotropic medium and infrared transmission spectroscopy of liquid crystals

The theory of absorbance is developed for the entire electromagnetic spectrum of radiation in a semi-infinite anisotropic medium with a second rank dielectric tensor, the elements of which are complex and frequency dependent. The theory of the absorbance A(omega,theta) of an optically anisotropic liquid in an infrared (IR) test cell is then outlined and applied to IR transmission experiments. A formula for the dependence of A(omega,theta), on theta (theta being the angle between the electric vector and the principal optical axis) is derived from first principles. The formula, for radiation of angular frequency omega, viz, A(omega,theta)=-log(10)[10(-A(omega,0))cos(2)theta+10(-A(omega,pi2))sin(2)theta] is in agreement with that proposed by Jang, Park, Maclennan, Kim, and Clark [Ferroelectrics 180, 213 (1996) ] and confirms some of the work of Kocot, Wrzalik, and Vij [Liq. Cryst. 21, 147 (1996)]. The comments on this formula by Jang, Park, Kim, Glaser, and Clark [Phys. Rev. E 62, 5027 (2000)], and by Kocot et al. are discussed. The absorbance A(omega,0) and A(omega,pi2) have been expressed in terms of the optical properties of the material and the dimensions of the cell.     

Dielectric and optical rotatory power investigations of an antiferroelectric liquid crystal 12OF1M7 in a homeotropic cell: implications for models of the structure of ferrielectric phases

The antiferroelectric liquid crystal (AFLC) under investigation possesses different helical smectic phases. Measurements of the optical rotatory power (ORP) of these phases have elucidated the quality of this method for finding the phase transitions between several phases and for investigating their helical structure. The optical rotatory power as a function of temperature for seven wavelengths of light in the range 441 to 665 nm was measured for different phases of the AFLC material investigated, (R)-1-methylheptyl 4-(4'-n-dodecyloxybiphenyl-4-yl-carbonyloxy)-3-fluorobenzoate, with acronym 12OF1M7. The values of the pitch and the optical anisotropy in the plane of the smectic layers for the FiLC (SmC*_FI3) phase and SmC*_Aphase have been calculated from the ORP data. The results of the ORP rule out the simple clock model for describing the structure of the SmC* (SmC*_I1) and AF (SmC*_FI2) phases. The results for these phases can be explained either in terms of the modified Ising model or the highly distorted clock model. The ORP measurements establish the existence of SmC*_FI3 found already from dielectric, polarization and polarized IR spectroscopy.     

fac-Re(bpy)(CO)3(COOMe): A model metallocarboxylate complex of rhenium with a bipyridyl ligand

The title compound, fac-(2,2-bipyridyl)(carbomethoxy)rhenium tricarbonyl, crystallizes in the monoclinic system, space group P2₁/c with the following crystal data: a = 8.37551(1), b = 6.6934(1), c = 26.2098(1) Å, V(ų) = 1535.93(3), Z = 4, and = 90.0971(2). The metal environment is slightly distorted octahedral with a chelating bipyridyl ligand and a facial arrangement of the carbon monoxide ligands.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Studies on the Preparation and Properties of Some Phenolic Derivatives of Biscyclopentadienyl Molybdenum (VI) and Bisindenyl Molybdenum (VI) Oxide Dichloride

Reactions of biscyclopentadenyl molybdenum (VI) oxide dichloride (I) and bisindenyl molybdenum (VI) oxide dichloride (II) with mono-, di- and trihydroxy phenols have been studied and the phenoxide derivatives so formed have been isolated. Infrared spectra and some phenolic derivatives of these compounds have been studied.     

A novel synthesis of hexakis(trifluoromethyl)cyclotriphosphazene. Single-crystal X-ray structures of N3P3(CF3)6 and N3P3F6

Reaction of hexafluorocyclotriphosphazene (N3P3F6) with trimethyl(trifluoromethyl)silane in the presence of a catalytic amount of cesium fluoride in THF produced hexakis(trifluoromethyl)cyclotriphosphazene [N3P3(CF3)6] in 90% isolated yield. N3P3(CF3)6 is fully characterized by melting point, IR, NMR (19F, 13C, 31p), MS, and elemental analysis data. Single-crystal X-ray structures of N3P3(CF3)6 and N3P3F6 are reported.     

Crystal structures of bis(4-dimethylaminopyridinium) tetrachlorocobaltate(II) and bis-[1,3-di (ammoniummethyl)benzene]tetrachlorocobaltate(II)

The crystal structures consist of organoammonium cations hydrogen bonded to tetrahedral CoCl₄ ^2– anions. In the 4-dimethylaminopyridinium salt, [(CH₃)₂NC₅H₅NH]₂CoCl₄, pairs of cations hydrogen bond in an asymmetric fashion to two of the chlorines in each anion. The planar cations form two sets of – stacks, first parallel to the a axis and the second parallel to the b axis. The anions lie between these two nonintersecting sets of stacks. In contrast, for the second compound, [C₆H₄(CH₂NH₃)₂]CoCl₄, the tetrahedral CoCl₄ ^2– anions form layers lying parallel to the bc plane. The 1,3-di(ammoniummethyl)benzene cations crosslink adjacent anionic layers, forming a lamellar structure of alternating organic and inorganic layers.     

Dielectric and pyroelectric studies of an antiferroelectric liquid crystal

Polymorphism and polar properties of an antiferroelectric (R)-2-methylheptyloxycarbonylphenyl-4-[(4-decyloxy-3-fluoro)benzoyloxy]benzoate liquid crystal are studied. The phases are identified, and the phase transition points are determined. Dielectric constant, dielectric losses, and pyroelectric properties are studied for the orthogonal smectic SmA and tilted smectic, SmC _α ^* , SmC ^*, SmC _γ ^* , and SmC _A ^* phases. The temperature dependence of spontaneous polarization is measured by the repolarization current technique and integration of the pyroelectric constant.     

Synthesis of 4-fluororesorcinol and 4-trifluoromethylresorcinol

Less expensive, safer, and easily scaled-up methods for the synthesis of 4-fluororesorcinol and 4-trifluoromethylresorcinol have been established, including two methods to give the former compound. One involves the reaction of Selectfluor™ reagent with 1,3-dimethoxybenzene to give 2,4-dimethoxy-1-fluorobenzene followed by hydrolysis to give 4-fluororesorcinol. The overall yield of this two-step reaction is 54%. In the second case, when Selectfluor reagent is reacted directly with resorcinol, under the best reaction conditions, 4-fluororesorcinol is obtained in 66% yield. It is, however, very difficult to separate the starting material from the mono- and difluororesorcinol products. Consequently, the two-step method is the method of choice to prepare 4-fluororesorcinol. The trifluoromethyl group was incorporated into 2,4-dimethoxy-1-iodobenzene to form 1,3-dimethoxy-4-trifluoromethylbenzene followed by mild hydrolysis to give 4-trifluoromethylresorcinol. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:229–239, 1998