W. Haase

A new asymmetric N5O2-donor binucleating ligand and its first FeIIFeIII complex as a model for the redox properties of uteroferrin

A new N,O-donor binucleating ligand, 2-bis[{(2-pyridylmethyl)-aminomethyl}-{(2-hydroxybenzyl)(2-pyridylmethyl)}-aminomethyl]-4-meth (H2BPBPMP), and its first binuclear FeIIFeIII complex have been prepared in order to provide synthetic analogues for the coordination environment on the active site of purple acid phosphatases. The complex [FeIIFeIII(BPBPMP)(OAc)2]ClO4·CH3OH was obtained from a self-assembled type reaction between Fe(ClO4)2· 6H2B, H2BPBPMP and sodium acetate trihydrate in methanol. The complex has been characterized by IR, CHN, molar conductivity, magnetic susceptibility, Mossbauer, electronic absorption spectroscopies and electrochemical methods of analyses, and turns out to be the first synthetic analogue for the redox properties (E°′=0.38 V versus NHE) of uteroferrin.

Direct theoretical abinitio calculations in exchange coupled copper (II) dimers: Influence of structural and chemical parameters in modeled copper dimers

The influence of structural and chemical parameters on the singlet–triplet splitting (2J=ΔEST ) in modeled exchange coupled oxygen‐bridged dimeric copper (II) complexes is studied, using an ab initio method followed by a perturbation development of the configuration interaction. The effect of varying the Cu–O–Cu′ angle and the Cu–O distance in the Cu2O2 core of modeled dimers is calculated. The results are comparable to the experimental ones. Changes in the geometric coordination around the copper (II) atom and around the oxygen atom of the core are studied. The results show that the magnitude of the exchange coupling strongly depends on both of these factors. Electronegativity effects are studied by varying the counterion in the model and by changing from alkoxo‐bridged to hydroxo‐bridged copper (II) dimers.

Domain mode—A novel relaxation process in ferroelectric liquid crystals

Abstract New relaxation processes are observed in ferroelectric liquid crystals with considerable high spontaneous polarization. These processes are attributed to the formation of ferroelectric domains in FLC cells. The domains have different characteristic periodicities and relaxation times in the bulk of FLC cell and near the surfaces of the electrodes. Characteristic relaxation processes are found in the dielectric response at frequencies VDB and VDS corresponding to both cases. The behaviour of dielectric strengths δϵv;DB and δϵDS versus d.c. field, spontaneous polarization and pitch of the helix is investigated.

Antiferroelectric behaviour of achiral mesogenic polymer mixtures

Abstract X-ray structure determination and pyroelectric and piezoelectric measurements have been carried out on mesogenic mixtures composed of achiral side chain polymers and their monomers. Certain mixtures show antiferroelectric polarization hysteresis loops in the mesophase which was shown to be a bilayered smectic C, while the two components of the mixtures taken alone show no antiferroelectricity. The results obtained on the polymer-monomer mixtures are interpreted in terms of the smectic C structure with alternating tilt which, from a symmetry viewpoint, is allowed to be antiferroelectric. The antiferroelectric mixtures, on being cooled to the glassy state under a d.c. electric field applied, reveal high pyroelectric coefficients with prospects for application as IR detectors.

Electrically tunable waveguide laser based on ferroelectric liquid crystal

Laser action in a waveguide configuration has been demonstrated in a planar alignment cell of dye-doped chiral smectic liquid-crystal mixtures with a short pitch helical structure. In this configuration, doped dye can effectively be excited by a pump beam illuminating perpendicularly the helical axis and the laser light emitted along the helical axis propagates in the waveguide. Lasing wavelength can be tuned by adjusting the periodicity of the helical pitch upon applying the electric field.

Synthesis, structure and magnetism of a tetranuclear Fe(III) complex containing an [Fe4(μ3-O)2]8+ core

Abstract The tetranuclear Fe(III) complex [L2Fe2(μ3-O)2(μ2-CH3COO)3(Sao)2Fe2]X (X=ClO4, (1), PF6 (2)), where L is the cyclic amine 1,4,7-trimethyl-1,4,7-triazacyclononane and Sao is the dianion of salicylaldoxime (H2Sao), has been synthesized and characterized on the basis of elemental analysis, IR, electronic, Mossbauer spectroscopy and variable-temperature (4–285 K) magnetic susceptibility measurements. The molecular structure has been established by X-ray diffraction of 2. The structure consists of an [Fe2wing(μ3-O)2Fe2body]8+-butterfly core. Each Fe(III) ion is in a distorted octahedral environment. The two Fe(Sao)+ units function as bridges between two terminal ‘wing’ iron ions through their deprotonated oximate oxygen and represent the ‘body’ iron ions in the tetranuclear core. Three acetate groups are singly bridging between the iron ions. Mossbauer spectra display two quadrupole doublets, consistent with two different high-spin ferric sites. Magnetic susceptibility measurements reveal a diamagnetic ground state with antiferromagnetic exchange interactions among the four high-spin ferric centers. The exchange coupling constant J12 (‘body-body’ interaction) could not be determined due to prevailing spin frustration, but the ‘wing-body’ antiferromagnetic interaction, J, was evaluated to be −46 cm−1 [H=−2J(S1·S3+S2·S3+S1·S4+S2·S4)−2J12S1·S2].

Order parameter and packing studies in nematic and smectic A phases by x‐ray diffraction

X‐ray diffraction measurements have been made on the nematic phase of T15 (4‐cyano‐4’‐n‐pentyl‐p‐terphenyl), as well as on the nematic and smectic A phases of RNO2 [4’‐nitrophenyl‐4‐(4’‐n‐hexyloxy‐benzoyloxy)‐cinnamate]. The x‐ray equipment used allows comparably high resolution measurements of liquid crystals. The inner reflexes show that both compounds possess a bilayer structure supposed as overlapping of polar cyano or nitro group of one molecule and the phenyl ring of the neighboring molecule. The molecular orientational distribution function f (β) has been calculated on the basis of intensity simulations of the outer reflexes. The orientational order parameter P2(cos β), P4(cos β), 〈P2〉 and 〈P4〉 have been determined from f (β). A strong decrease of 〈P2〉 and 〈P4〉 is observed at the smectic A–nematic phase transition temperature of RNO2.

Columnar phases of achiral vanadyl liquid crystalline complexes

Two liquid crystalline vanadyl complexes have been studied by frequency domain dielectric spectroscopy over the range 10 mHz to 13 MHz. The materials exhibit two or three columnar phases denoted Colro, Colrd, and Colhd that were identified by X-ray diffraction. In the higher temperature Colrd phase, a relaxation process in the kHz range is observed that is attributed to the reorientation about the molecular short axis. A pronounced dielectric relaxation process shows up in the low temperature Colro phase at hertz and sub-hertz frequencies. This slow relaxation is assigned to reorientation of the molecular dipoles within the polar linear chains, which are aligned along the columns axis. Triangular wave switching studies at low frequency reveal processes inside the Colro phase which are most probably due to ionic/charges relaxations but a ferroelectric switching for an achiral discotic system cannot be ruled out completely. Below the Colro phase there is an orientationally disordered crystalline Crx phase with disordered side chain dipoles. A dielectric relaxation process connected with the intramolecular relaxation of the alkoxy side chains, similar to the beta-process of polymers, has been found in the lower temperature Crx phase.

The domain mode in ferroelectric liquid crystals; electrooptical and dielectric investigations

Abstract The formation of ferroelectric domains in the smectic C* (SmC*) phase of ferroelectric liquid crystals with considerable high spontaneous polarization is observed using electrooptical methods. The temperature dependence of the corresponding domain modes DB (bulk) and DS (surface) is studied by dielectric spectroscopy. The behaviour of the dielectric strengths and the relaxation frequencies of these processes is investigated. The activation energies of the DB and the DS modes are given assuming the validity of the Arrhenius law.

On the Molecular Polarizability of Nematic Liquid Crystals

Abstract The refractive indices and the densities of CB-7, PCH-7 and CCH-7 are measured. An equation that relates the optical frequency permittivity tensor to the molecular polarizability tensor for nematic liquid crystals is obtained. The derived equation gives consistent results not only for the nematic phase, but also for both the solid and isotropic liquid states.