Pentacyanido(L)ferrate(III) complexes: Crystal structures, electrochemical and DFT studies (L = pyrazine, 4,4′-bipyridine, azide)

The crystal structures of two pentacyanido(L) ferrate(III) complexes, [P(C₆H₅)₄]₂[Fe(CN)₅(prz)]·4H₂O 1, [P(C₆H₅)₄]₂[Fe(CN)₅(4,4′-bipy)]·3H₂O 2, have been solved. Within the two complex anions the iron atoms are hexacoordinated by five cyanido ligands, the sixth position being occupied by the nitrogen atom arising from pyrazine and, respectively, 4,4′-bipyridine. The electrochemical properties of compounds 1, 2 and of the azido derivative, (Ph₄As)₂[Na(H₂O)₄][Fe(CN)₅(N₃)] 3, have been investigated by cyclic voltammetry. A relatively complicated redox behavior of these complexes was found, due especially to the electron transfer involving the central metallic ion that changes reversibly its oxidation state (Fe^III/Fe^II redox site) and also to the coligand (4,4′-bipyridine, pyrazine or azide) which intervenes in a distinct electron transfer. The experimental data have been rationalized through DFT calculations.     

New iron-cobalt clusters with silicon-containing dicarboxylic acids

For the first time, silicon-containing dicarboxylic acids were used to prepare two new heterotrinuclear carboxylates of the composition [Fe₂ ^IIICo^IIO(Bcpdps)₃(H₂O)₃], I, where H₂Bcpdps ≡ HOOC-C₆H₄-Si(C₆H₅)₂-C₆H₄COOH, and [Fe₂ ^IIICo^IIO(Ipds)₃(H₂O)₃], II, where H₂Ipds ≡ [HOOC-C₆H₃(CO)₂N-(CH₂)₃-(CH₃)₂Si]₂O. The precursor for these two complexes was trinuclear μ³-oxo-hexaacetate triaqua diiron(III)cobalt(II) cluster, {Fe ₂ CoO}, in which the acetate anions were subsequently substituted by silicon-containing dianions. The resulting products were characterized by elemental analysis, thermogravimetry, Fourier Transform Infrared (FTIR), Energy-Dispersive X-ray Fluorescence (EDXRF), and Mossbauer spectroscopies (MS). The investigation by MS revealed the presence of the iron(3+) ions in high spin state and having the close environment. Thermogravimetric analysis results indicated an improving in the thermal stability by replacing acetate anions with silicon-containing carboxyl ligands. This widens the temperature range in which such compounds can be used in practical applications.      

Magnetic properties of the seven-coordinated nanoporous framework material Co(bpy)(1.5)(NO(3))(2) (bpy = 4,4'-bipyridine)

The magnetic properties of the porous metal-organic complex Co(bpy)(1.5)(NO(3))(2) (bpy = 4,4'-bipyridine), investigated by SQUID magnetometry, EPR and heat capacity measurements, are reported. The tongue-and-groove structure of this complex is formed by the assembly of T-shaped building blocks, where each Co is bound to three bpy ligands. Co(ii) is hepta-coordinated by three N atoms from the bpy units, and four O atoms from two nitrate groups. Experimental results showed a large crystal field effect induced anisotropy with a zero field splitting of Δ = 198 K between the ground and excited Kramers doublets, a factor of two larger than previously reported values in Co(ii) hepta-coordinated complexes. EPR revealed orthorhombic crystal field anisotropy, with gyromagnetic principal values of g(1)(*) = 6.1, g(2)(*) = 4.2 and g(3)(*) = 2.2, in an S(*) = 1/2 effective spin on the ground state Kramers doublet. Ab initio simulations allowed us to assign the anisotropy easy axis of magnetization to the binary symmetry axis of the molecule, aligned with the Co-N apical direction of the T-block.     

Thermooxidative stabilization of a MDI

Samples of flexible PU foam were prepared from a polyol (Elastoflex W 5516/115) and an isocyanate prepolymer (Iso 145/8), both commercial Elastogram products. For the thermooxidative stabilization, two phenolic compounds were used, separately or in mixture. These compounds were: 2,6-di-t-butyl-4-methyl-phenol (non-reactive) (AO-1), 3,5-di-t-butyl-4-hydroxy-benzyl alcohol (reactive, AO-2), used in total mass% of 0.3/1.5. The TG/DTG/DTA curves were drawn up in dynamic air, with a heating rate of 10 °C min⁻¹, until 500 °C. For the unstabilized sample a single thermodegradative TG step, with a maximum rate at 268–270 °C was observed, whereas for the stabilized samples, supplementary steps at higher temperature were observed. The changes in the TG/DTG/DTA parameters are not in a single relationship with the mass% of the stabilizator, due to the following: AO-1 is easily migrated out from PV, especially, at higher concentrations. AO-2 had positive effect at all studied concentrations. But the most remarkable effect is the synergetic effect of a 1:1 mixture of AO-1 and AO-2.     

Ferroelectricity in mixtures of mesogenic and nonmesogenic compounds

It is shown that by adding potassium nitrate (1 % by weight) to compensated cholesteric mixtures (cholesteryl chloride-cholesteryl myristate 63.63:36.37% by weight and cholesteryl laurate-cholesteryl chloride 35.65% by weight) or to smectic sitosteryl undecilenate, the mixtures exhibit ferroelectric behaviour. Values of P_s = 10-⁹ - 10-⁸ C/cm² were obtained in the high-temperature range. In compensated cholesteric mixtures, the spontaneous polarisation reached a minimum at a temperature corresponding to the cholesteric-nematic transition. The results are explained by assuming coupling between the dipoles of the antiferroelectric KNO₃ and the dipoles of the mesogenic compound.     

Structure and interaction potentials in solid-supported lipid membranes studied by X-ray reflectivity at varied osmotic pressure

Highly oriented solid-supported lipid membranes in stacks of controlled number N ≃ 16 (oligo-membranes) have been prepared by spin-coating using the uncharged lipid model system 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The samples have been immersed in aqueous polymer solutions for control of osmotic pressure and have been studied by X-ray reflectivity. The bilayer structure and fluctuations have been determined by modelling the data over the full q-range. Thermal fluctuations are described using the continuous smectic Hamiltonian with the appropriate boundary conditions at the substrate and at the free surface of the stack. The resulting fluctuation amplitudes and the pressure-distance relation are discussed in view of the inter-bilayer potential.     

Geometrical Dissipation for Dynamical Systems

On a Riemannian manifold (M, g) we consider the k?+?1 functions F ₁, . . . , F _k , G and construct the vector fields that conserve F ₁, . . . , F _k and dissipate G with a prescribed rate. We study the geometry of these vector fields and prove that they are of gradient type on regular leaves corresponding to F ₁, . . . , F _k . By using these constructions we show that the cubic Morrison dissipation and the Landau-Lifschitz equation can be formulated in a unitary form.     

Parameter motivated mutual correlation analysis: Application to the study of currency exchange rates based on intermittency parameter and Hurst exponent

We present a novel method for the parameter oriented analysis of mutual correlation between independent time series or between equivalent structures such as ordered data sets. The proposed method is based on the sliding window technique, defines a new type of correlation measure and can be applied to time series from all domains of science and technology, experimental or simulated. A specific parameter that can characterize the time series is computed for each window and a cross correlation analysis is carried out on the set of values obtained for the time series under investigation. We apply this method to the study of some currency daily exchange rates from the point of view of the Hurst exponent and the intermittency parameter. Interesting correlation relationships are revealed and a tentative crisis prediction is presented.