First paramagnetic 4d transition-metal complex with a redox-active tetrathiafulvalene derivative, [Ru(salen)(PPh3)(TTF-CH=CH-Py)]BF4 [salen(2-) = N,N'-ethan-1,2-diylbis(salicylidenamine), PPh3 = triphenylphosphine, TTF-CH=CH-Py = 4-(2-tetrathiafulvalenylethenyl)pyridine

The first paramagnetic 4d transition-metal complex with a redox-active tetrathiafulvalene ligand has been synthesized. The preparation, X-ray structure, electrochemistry, and electron paramagnetic resonance measurements of [Ru(salen)(PPh3)(TTF-CH=CH-Py)](BF4) [1(BF4)] are reported. The crystal structure reveals that the paramagnetic Ru(III) (s = 1/2) center is in a tetragonally elongated octahedral geometry and the TTF-CH=CH-Py ligand is coordinated to the axial position of the Ru(III) ion through the nitrogen atom of the pyridine group. Thus, 1(BF4) is an attractive precursor to study future pi-4d interactions in dual-property conducting and magnetic materials.     

Synthesis, structure, and magnetism of heterometallic carboxylate complexes [MnIII2M(II)4O2(PhCOO)10(DMF)4], M = Mn(II), Co(II), Ni(II)

Three new homo- and heterometallic hexanuclear complexes [Mn(2)M(II)(4)O(2)(PhCOO)(10)(DMF)(4)] (with M = Mn (1), Co (2) or Ni (3) and DMF = dimethylformamide) have been synthesized by redox generation of benzoate ligands from benzaldehyde in a one-pot reaction. All of the compounds are isostructural and crystallize in the I-42d space group of the tetragonal system, data for 1: a = 27.2249(8) Angstroms, c = 25.5182(5) Angstroms, R1 = 0.0681. The crystal structure contains isolated molecules. Each molecule consists of 2 x Mn(III) surrounded by four M(II) ions to form two edge-sharing OMn(2)M(2) tetrahedra giving rise to the [Mn(2)M(4)O(2)] core. The coordination sphere of each metal is completed by the bridging benzoate ligands and DMF molecules. The magnetic susceptibilities of 1-3 have been measured in the 1.8 K < T < 300 K temperature range. The magnetic susceptibilities for 1 and 2 pass through a broad maximum at low temperature which is characteristic of the diamagnetic ground state, while for 3 no maximum is detected down to 1.8 K. The magnetic data have been interpreted quantitatively for 1 and 3 on the basis of spin exchange interactions between the metallic centers (spin Hamiltonian for a pair being H(AB) = -J(AB) S(A).S(B)). Single-crystal measurements on [Mn(6)O(2)(PhCOO)(10)(CH(3)CN)(4)] (4) show that significant magnetic anisotropy develops at low temperature.     

Synthesis, structure and magnetic properties of porous magnetic composite, based on MCM-41 molecular sieve with Fe3O4 nanoparticles

Porous magnetic composites were prepared by the synthesis of molecular sieve MCM-41 in the presence of Fe₃O₄ nanoparticles with average diameter of 15 nm. Nanoparticles were captured by porous silica matrix MCM-41, which resulted in their incorporation, as it was confirmed by TEM, SEM and X-ray diffraction. The materials possessed high surface area (392-666 m² g⁻¹), high pore volume (0.39-0.73 cm³ g⁻¹) along with high magnetic response (M_S up to 28.4 emu g⁻¹ at 300 K). Calcination of samples resulted in partial oxidation of Fe₃O₄ to α-Fe₂O₃. The influence of nanoparticles content on sorption and magnetic properties of the composites was shown. No hysteresis was found for the samples at 300 K; at 5 K, H_C was in the range 370-385 G for non-calcinated samples and 350-356 G for calcinated ones.     

Exploring physical features of anisotropic quark stars in Brans-Dicke theory with a massive scalar field via embedding approach

The main aim of this study is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity. The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks. We use a well-behaved function along with the Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors. The radii of strange compact stars viz., PSR J1416-2230, PSR J1903+327, 4U 1820-30, CenX-3, and EXO1785-248, are predicted via their observed mass for different values of the massive Brans-Dicke parameters. We explore the influences of the mass of scalar field \begin{document}$m_{\phi}$\end{document}, coupling parameter \begin{document}$\omega_{\rm BD}$\end{document}, and bag constant \begin{document}${\cal{B}}$\end{document} on state determinants and perform several tests on the viability and stability of the constructed stellar model. Conclusively, we find that our stellar system is physically viable and stable as it satisfies all the energy conditions and necessary stability criteria under the influence of a gravitational scalar field.     

Uniqueness results for fractional functional differential equations with infinite delay in Fréchet spaces

In this article, a recent nonlinear alternative for contraction maps in Fréchet spaces due to Frigon and Granas [1998, Résultats de type Leray-Schauder pour des contractions sur des espaces de Fréchet, Ann. Sci. Math. Québec 22, 161–168] is used to investigate the existence and uniqueness of solutions for fractional order functional differential equations with infinite delay.     

Effect of the intercalated cation on the properties of poly(o-methylaniline)/maghnite clay nanocomposites

A detailed study about the synthesis, characterization and properties of poly(o-methylaniline)(PoMea)/maghnite nanocomposites has been performed. Changes in the characteristics of the nanocomposites, depending on the intercalated cation between the clay layers before the synthesis, have been observed. Intercalated morphology has been detected by TEM in nanocomposites containing copper-treated maghnite (Magh-Cu), while when maghnite treated with strong acids was used (Magh-H); an exfoliated material has been obtained. Also, remarkable differences in the properties of the polymers have been observed by TG-MS and FTIR, suggesting that the polymer produced with Magh-H has a higher degree of branching. The electrochemical behavior of the polymers extracted from the nanocomposites has been studied by cyclic voltammetry. Good electrochemical response has been observed for PoMea grown into Magh-Cu but not for the one polymerized into Magh-H.     

Some Uniqueness Results for Functional Damped Semilinear Differential Equations in Frechet Spaces

A recent nonlinear alternative for contraction maps in Frechet spaces due to Frigon and Granas （Resultats de type Leray-Schauder pour des contractions sur des espaces de Frechet, Ann. Sci. Math. Quebec 22, （2）, 161-168 （1998））, combined with semigroup theory, is used to investigate the existence and uniqueness of mild solutions for first- and second-order functional semi linear and neutral damped differential equations in Frechet space.     

Tentative links between thermal diffusivity and fire-retardant properties in poly(methyl methacrylate)-metal oxide nanocomposites

Possible relationships between fire-retardant properties and thermal diffusivity for poly(methyl methacrylate) (PMMA) filled by melt blending with titanium dioxide (TiO₂), alumina (Al₂O₃) and boehmite (AlOOH) were investigated for a better understanding of the mode of action of metal oxides as fire-retardants (FR) in PMMA. Fire-retardancy was measured with a cone calorimeter and thermal diffusivity (α) by Laser Flash Analysis (LFA). LFA measurements have shown that heat dispersion is higher with titanium dioxide and boehmite than with alumina despite a larger surface area. For thermal diffusivity, discrepancies between the different nanofillers were only visible from 10 wt% onwards. Thermal degradation of PMMA-oxide nanocomposites and their thermal diffusivity could be linked. Moreover, a bi-linear relationship between the peak of heat release rate (pHRR) and the average of heat release rate (AHRR) showed the occurrence of a barrier effect.