Linkage isomerism in coordination polymers

The use of the recently prepared polynitrile ligand tcnopr3OH(-) ([(NC)(2)CC(OCH(2)CH(2)CH(2)OH)C(CN)(2)](-)) with different salts of Fe(II), Co(II), and Ni(II) has led to a very rare example of linkage isomerism in a coordination chain. These pairs of linkage isomers can be formulated as [M(tcnopr3OH-κN,κO)(2)(H(2)O)(2)]; M = Fe (1), Co (3), and Ni(5) and [M(tcnopr3OH-κN,κN')(2)(H(2)O)(2)]; M = Fe (2), Co (4), and Ni (6). Compounds 1-2, 3-4, and 5-6 are three pairs of linkage isomers since they present the same formula and chain structure and they only differ in the connectivity of the polynitrile ligand bridging the metal ions in the chain: through a N and an O atom (1κN:2κO-isomer) or through two N atoms (1κN:2κN'-isomer). The magnetic properties show, as expected, very similar behaviors for both isomers.     

Mixed metallic Ba(Co,Fe)X(0.2)O(3-δ) (X = F, Cl) hexagonal perovskites: drastic effect of Fe-incorporation on structural and electronic features

Starting from the parent 10H-Ba(5)Co(5)X(1-x)O(13-δ) (trimeric strings of face-sharing CoO(6) octahedra with terminal CoO(4) tetrahedra, stacking sequence (chhch')(2)) and 6H-Ba(6)Co(6)X(1-x)O(16-δ) (similar with tetrameric strings, stacking sequence chhhch') hexagonal perovskites forms (X = F, Cl; c, h = [BaO(3)] layers ; h' = [BaOX(1-y)] layers), we show here that the Fe incorporation leads to large domains of solid solutions for both X = F and Cl but exclusively stabilizes the 10H-form independently of the synthesis method. In this form, the lowest concentration of h-layers is stabilized by a sensitive metal reduction with increasing the Fe ratio. In a more general context of competition between several hexagonal perovskite polymorphs available for most of the transition metals, this redox change is most probably the key factor driving 1D (face-sharing chains) to 3D (corner-sharing) connectivities. Strikingly, ND data evidence the location of oxygen deficiencies in the tetrahedral (Co/Fe) coordination. This effect is exaggerated at high temperature, while (Co/Fe)O(4-δ) coordinations are completed by the displacement of X(-) anions toward the (Co/Fe) sphere of coordination following a "push-and-pull" mechanism within h'-[BaOX(1-y)] layers. The Fe-incorporation is also accompanied by increasing conduction gaps with predominant 1D variable range hopping. The full series show antiferromagnetic behavior with increasing T(N) as [Fe] increases. For Fe-rich compounds T(N) is estimated about 600 K, as rarely observed for hexagonal perovskite compounds. Finally, magnetic structures of all iron-doped compounds show a site-to-site AFM ordering, different of the magnetic structure of Co-only parent compounds. Here, DFT calculations predict low-spin octahedral Co configurations, but high-spin Fe species in the same sites.     

Circularly polarized few-optical-cycle solitons in Kerr media: A complex modified Korteweg-de Vries model

We consider the propagation of few-cycle pulses (FCPs) in cubic nonlinear media exhibiting a “crystal-like” structure, beyond the slowly varying envelope approximation, taking into account the wave polarization. By using the reductive perturbation method we derive from the Maxwell–Bloch–Heisenberg equations, in the long-wave-approximation regime, a non-integrable complex modified Korteweg-de Vries equation describing the propagation of circularly polarized (CP) FCPs. By direct numerical simulations of the governing nonlinear partial differential equation we get robust CP FCPs and we show that the unstable ones decays into linearly polarized half-cycle pulses, whose polarization direction slowly rotates around the propagation axis.     

Dark-managed solitons in inhomogeneous cubic–quintic–septimal nonlinear media

Nonlinear Dynamics - We investigate the inhomogeneous higher-order nonlinear Schrödinger (INHLS) equation including cubic–quintic–septic (CQS) nonlinear terms and gain or loss with...     

Solitary wave solutions for high dispersive cubic-quintic nonlinear Schrödinger equation

We consider the higher-order dispersive nonlinear Schrödinger equation including fourth-order dispersion effects and a quintic nonlinearity. This equation describes the propagation of femtosecond light pulses in a medium that exhibits a parabolic nonlinearity law. By adopting the ansatz solution of Li et al. [Zhonghao Li, Lu Li, Huiping Tian, Guosheng Zhou. New types of solitary wave solutions for the higher-order nonlinear Schrödinger equation. Phys Rev Lett 2000;84:4096], we find two different solitary wave solutions under certain parametric conditions. These solutions are in the form of bright and dark soliton solutions.     

Syntheses of donor acceptor biobased photocurable water‐soluble resins based on poly‐l‐lysine

We report a new kind of coating using UV waterborne technique with a biobased poly(amino acid) resin. Firstly we performed the thermal polycondensation of l ‐lysine during 15 h at 150 °C to synthesize water‐soluble oligomers of poly‐l ‐lysine (PLL) with 5–6 monomer units. These oligomers were then transformed in mild conditions to give photocurable water‐soluble resins. We grafted on the poly‐l ‐lysine backbone, allyl and maleamic acid functional groups, with a grafting rate close to 65% thanks to allyl glycidyl ether and maleic anhydride respectively. The influence of the reaction time and the reagents ratio on the grafting rate was investigated. Hence, the donor/acceptor photopolymerization of the mixture of allyl ether‐poly‐l ‐lysine (PLL‐g‐AE) with maleamic acid‐poly‐l ‐lysine (PLL‐g‐MA) in aqueous solution gave yellow transparent films. The degree of conversion and other kinetic parameters have been studied and detailed. This work contributes to the development of materials based on renewable resources and cleaner processes. It opens a new pathway to both fundamental and applied‐driven research. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 955–963     

Preparation and characterization of CeO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> aerogels supported ruthenium for catalytic wet air oxidation of p-hydroxybenzoic acid

Catalytic wet air oxidation of an aqueous solution of p-hydroxybenzoic acid was conducted over ruthenium catalysts (1 wt%) supported on CeO₂–Al₂O₃ aerogels mixed oxides at 140 °C and 50 bars of air. We study the effect of the amount of CeO₂ in the catalyst. We found that the optimal cerium content in the Al₂O₃ support was 20 wt%. The activity of the Ru/Al₂O₃ and Ru/CeO₂ was also tested for comparison. It was found that the addition of CeO₂ on the alumina support improves the activity of Ru catalysts. The activity of the samples decreases in the following order: Ru/Ce–Al (20) > Ru/Ce–Al (10) > Ru/Ce–Al (5) ≈ Ru/Al₂O₃ > Ru/CeO₂. Samples characterization was performed by means of N₂ adsorption–desorption, XRD, UV–Vis, TPR, SEM and TEM.     

1-Soliton solution of the Klein-Gordon-Schrodinger’s equation with power law nonlinearity

This paper obtains the 1-soliton solution of the Klein-Gordon-Schrödinger’s equation with power law nonlinearity. The solitary wave ansatz is used to carry out the integration. Both 1 + 1, 1 + 2 and 1 + N dimensional cases are considered.     

Splitting of resonant and scattering frequencies under shape deformation

It is well known that the main difficulty in solving eigenvalue problems under shape deformation relates to the continuation of multiple eigenvalues of the unperturbed configuration. These eigenvalues may evolve, under shape deformation, as separated, distinct eigenvalues, and the splitting may only become apparent at high orders in their Taylor expansion. In this paper, we address the splitting problem in the evaluation of resonant and scattering frequencies of the two-dimensional Laplacian operator under boundary variations of the domain. By using surface potentials we show that the eigenvalues are the characteristic values of meromorphic operator-valued functions that are of Fredholm type with index 0. We then proceed from the generalized Rouché's theorem to investigate the splitting problem.     

Two‐Orbital Three‐Electron Stabilizing Interaction for Direct Co2+As3+ Bonds involving Square‐Planar CoO4 in BaCoAs2O5

The quest for new oxides with cations containing active lone‐pair electrons (E) covers a broad field of targeted specificities owing to asymmetric electronic distribution and their particular band structure. Herein, we show that the novel compound BaCoAs₂O₅, with lone‐pair As³⁺ ions, is built from rare square‐planar Co²⁺O₄ involved in direct bonding between As³⁺E and Co²⁺ d_z2 orbitals (Co? As=2.51 Å). By means of DFT and Hückel calculations, we show that this σ‐type overlapping is stabilized by a two‐orbital three‐electron interaction allowed by the high‐spin character of the Co²⁺ ions. The negligible experimental spin‐orbit coupling is expected from the resulting molecular orbital scheme in O₃AsE–CoO₄ clusters.