Intramolecular disorder and its relation to mesophase structure in lyotropic liquid crystals

NMR SPDE measurements are reported for the lamellar (dispersions and multibilayer stacks) and hexagonal phases of sodium octanoate/octanol/D₂O mixtures. In the lamellar L_β and L_γ (gel) phases the octyl chains are rigid and perfectly ordered, while in the lamellar L_α and hexagonal phases they are flexible and disordered. In particular, the measurements show that in the fluid lamellar L_α phase, there is a marked discontinuity in the octyl chain flexibility at the C₅-C₆ segment; this behaviour is identical to that previously reported for the alkyl end-chains in smectic 4,4′-di-n-octyloxyazoxybenzene. In contrast, in the hexagonal phase, there is an effectively continuous flexibility gradient along the whole length of the octyl chain as in nematic 4,4′-di-n-octyloxyazoxybenzene. The behaviour in the lamellar phase is attributed to interference between cooperative conformational modes and localized random thermal fluctuations.     

Ternary liquid—liquid equilibria and their representation by modified NRTL equations

Experimental liquid—liquid equilibrium data are reported for the systems acetonitrile—acetone—cyclohexane at 318.15 K and acetonitrile—methyl acetate—cyclohexane at 313.15 K. Two modified forms of the NRTL equation proposed by Renon are presented by substituting local surface fractions for local mole fractions and further by including Guggenheim's combinatorial entropy for athermal mixtures whose molecules differ in size and shape. The resultant equations involve three adjustable parameters and are extended to multicomponent systems without adding ternary (or higher) parameters. Calculated results of vapor—liquid and liquid—liquid equilibria for typical binary and ternary mixtures are presented.     

The nonmetal-metal transition and phase separation in the europium-ammonia system

The coexistence curve of EuNH₃ solutions has been determined by visual observation and electron paramagnetic resonance (EPR). A nonmetal-metal transition is evident in EuNH₃ solutions, and the miscibility gap is the most pronounced among the metal-ammonia (MNH₃) systems that have been studied. The critical concentration and temperature are 1.30 mole% metal and 321 K, respectively. The coexistence curve has a parabolic shape within close vicinity of the critical point, which strongly suggests the existence of long-range interactions and cluster formation. EPR spectra indicate that the cation-electron interactions in these solutions are weak, so that the valence-electron concentration in MNH₃ solutions is probably the primary factor in determining the nature of the nonmetal-metal transition. The coexistence curve and associated critical parameters for EuNH₃ solutions are compared to those obtained for other MNH₃ solutions.     

EPR study of Gd3+ ions in β-alumina single crystals

Single crystals of β-alumina doped with Gd³⁺ have been obtained by high-frequency induction melting of a NaAlO₂Al₂O₃ mixture and slow cooling, followed by a Gd³⁺Na⁺ exchange in molten GdCl₃. In these crystals, Gd³⁺ occupies only one out of the several possible sites, in the spinel block and not in the conduction plane (which could be anticipated from the ionic radius of the ion). The EPR data can be described by a spin Hamiltonian which includes trigonal terms. The b₂⁰ value is close to 0.08 cm^?1. These results suggest a localization of the ion either in the 4f-layer tetrahedra, or in an interstitial site. The second possibility, which is consistent with charge compensation (due to nonstoichiometry in β-alumina) by interstitial oxygen ions seems more likely.     

Formation and phase transition of cobalt molybdate in cobalt oxide-molybdenum trioxide-alumina system

In the cobalt oxide-molybdenum trioxide-alumina system with a molar ratio of 1:1:1, the amounts of the high-temperature modification (a) of CoMoO₄ formed during heating from 500 to 800°C and the low-temperature modification (b) formed by phase transition during the subsequent cooling to room temperature are influenced by the kinds of alumina used, such as α-, γ- and calcined γ-aluminas. Powder X-ray diffraction analysis revealed that in an α-alumina system formation of a-CoMoO₄ is most favorable at a calcination temperature of 500°C and phase transition from a- to b-CoMoO₄ during cooling is enhanced by higher calcination temperatures. In the γ-alumina system, formation of a-CoMoO₄ is slight at 500°C but increases with increase in the calcination temperature, as does slightly the degree of phase transition from a- to b-CoMoO₄ upon cooling. In a system containing calcined γ-alumina, formation of a-CoMoO₄ similar to α- and γ-alumina systems was observed to occur at 500°C and 800°C, respectively, together with phase transition to b-CoMoO₄ during cooling. The degree of dispersion in the CoOMoO₃ coexistent system is affected by the particle size of aluminas, such as coarse α-, fine amorphous γ- and calcined γ-alumina consisting of both sizes, as observed with electron microscopy. Presence of finer γ-alumina is considered to suppress or retard the solid state reaction and phase transition.     

Boron hydride reduction of transition metal—acetyl complexes

Acetyl complexes of iron(II) and ruthenium(II) of the type (π-C₅H₅)(CO)LM(COCH₃), where L = PPh₃, P(OPh)₃, P(cyclohexyl)₃, PMe₂Ph or CO for M = Fe, and PPh₃ for M = Ru, are rapidly reduced to the corresponding ethyl complexes by BH₃ · THF or B₂H₆/C₆H₆. In some cases hydrido complexes of the type (π-C₅H₅)(CO)LMH are also formed. The reaction has been studied by use of ¹H NMR and the spectrum of (π-C₅H₅)(CO)(PPh₃)FeC₂H₅, which shows several unusual features, is discussed in detail. It is suggested that the rate of reduction increases with increasing electron density at the metal centre.Acetyl complexes of other transition metals, i.e. Ir, Pt, Pd, Co and Mo, are also reduced to the corresponding ethyl compounds by B₂H₆/C₆H₆.     

Phase transition in V5O9

Electrical resistivity, magnetic susceptibility, and heat capacity of V₅O₉ have been measured through its phase transition temperature (T_t) around 129 K. The associated changes in enthalpy and entropy were found to be 2095 J/mole and 19.24 J/mole · deg., respectively. A qualitative thermodynamic analysis has been attempted to correlate the crystal symmetry, electrical, magnetic, and heat capacity behavior at T_t. The metal-semiconductor transition appears as a consequence of the crystallographic order-disorder process, since the electrical and magnetic contributions to configurational entropy change are relatively small.     

Thermal properties of hydrazinium fluorometallates of the first row transition elements

Thermal analyses of hydrazinium fluorometallates of the first row transition elements and zinc are described. The intermediate compounds of the thermal decompositions are either ammonium fluorometallates or adducts of metal fluorides with hydrazine. The end products of the thermal analyses are in all cases metal fluorides, except in the case of the copper compound where elemental copper is obtained.     

Thermodynamics of complex formation in ternary liquid mixtures containing acetonitrile

Vapor—liquid and liquid—liquid equilibria and excess enthalpies for ternary mixtures formed from acetonitrile, benzene, n-heptane, toluene, and carbon tetrachloride are successfully correlated with a modified version of the associated solution theory proposed by Lorimer and Jones in 1977, which assumes two types of self-association for acetonitrile and binary complexes between acetonitrile and unsaturated hydrocarbons and does not include any ternary parameters.     

Preparation and properties of PdPSe single crystals

Single crystals of PdPSe were shown to be n-type semiconductors. Weak Pauli paramagnetic behavior was observed, which is consistent with the presence of delocalized electrons. Electrical measurements showed a room-temperature resistivity ? = 70 ohm-cm, activation energy of resistivity E_a = 0.32 eV, and Hall mobility μ = 34 cm² V^?1 sec^?1. Photoelectronic measurements in aqueous solutions of $\text{I}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}{}_3$ indicate that PdPSe has high quantum efficiencies below 800 nm. The indirect optical band gap is 1.28(2) eV.     

Preparation of chlorodivinylborane transition metal complexes and their nucleophilic substitution at boron

Chlorodivinylborane (I) prepared in situ from boron trichloride and dimethydivinyltin, reactions under photochemical conditions with ironpentacarbonyl and cyclopentadienyldicarbonylcobalt to give (η⁵-chlorodivinylborane)tricarbonyliron (II) and (η⁵-chlorodivinylborane)cyclopentadienylcobalt (III), respectively, in high yield. Complexes II and III readily undergo base-assisted nucleophilic substitution at boron.     

Thermal studies on 2,6-xylyliminodiacetato compounds of some transition metal ions

Some new 2,6-xylyliminodiacetato compounds of Mn(II), Fe(III), Ni(III), Zn(II) and Cd(II) have been prepared in aqueous media. The thermal behaviour of these compounds has been studied by TG, DTG, and DSC techniques. Heats of dehydration have been calculated from the DSC curves.     

Mass spectrometry of π-complexes of transition metals XI. Manganese and rhenium vinylidene complexes

The mass spectra of (π-C₅H₅)_nM_n(CO)(L)₁(L′) (M = Mn, Re; L = CO, P(C₆H₅)₃, P(OC₆H₅)₃; L′ is a vinylidene ligand) are reported and characterised by strong dehydrogenation of the rhenium complexes. In bimetallic analogues, the ReRe bond is stronger than the MnMn.     

Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids

A water-in-oil-in-water emulsion liquid membrane system is used to transport alkali metal and alkaline earth cations from an external alkaline aqueous source phase through an organic membrane containing a crown ether carboxylic acid and into the internal acidic aqueous phase of the emulsion droplet. The influence of varying the crown ether carboxylic acid structure upon the selectivity and efficiency of competitive metal ion transport is examined.     

Gunshot residue determination by high-performance liquid chromatography with electrochemical detection

A procedure for the detection of gunshot residue via the organic constituent diphenylamine is described. The method incorporates high-performance liquid chromatography with electrochemical detection.     

Reaction of acetylenes with transition metals: VIII. π-allylpalladium complexes from acetylenes and alkenes

Coupling of diarylacetylenes with alkenes in the presence of dichlorobis(benzonitrile)palladium gives chloro(syn-1-chloro-anti-1-aryl-syn-3-alkyl)-π-allylpalladium complexes.     

Laser induced predissociation of SF6 clusters

Dimer predissociation is sensitively detected as attenuation of the SF⁺₅ ion signal from a SF₆ molecular beam crossed by a line tunable cw CO₂ laser. The dimer spectra show a double peak structure which is assigned to the symmetric and anti-symmetric combination of the v₃ vibration. The minimum observed linewidth is 3 cm^?1 fwhm.