Cyano-bridged structures based on [MnIIN3O2-macrocycle)]2+: a synthetic, structural, and magnetic study

Reactions between the complex [MnII(L)]2+, where L is a N3O2 macrocyclic ligand, and different cyanometalate precursors such as [M(CN)n]m- (M(III) = Cr, Fe; M(II) = Fe, Ni, Pd, Pt) lead to cyano-bridged molecular assemblies exhibiting a variety of structural topologies. The reaction between [MnII(L)]2+ and [FeII(CN)6]4- forms a trinuclear complex with formula [(MnII(L)(H2O))2(FeII(micro-CN)2(CN)4)] x 2MeOH x 10H2O (1) which crystallizes in the triclinic space group P1. The reaction between [MnII(L)]2+ and [M(II)(CN)4]2-, where M(II) = Ni (2), Pd (3), Pt (4), gives rise to three isostructural linear chain compounds with stoichiometry [(MnII(L))(M(II)(micro-CN)2(CN)2)]n and which crystallize in the monoclinic space group C2/c. The self-assembly between [MnII(L)]2+ with [M(III)(CN)6]3-, where M(III) = Cr (5), Fe (6, 7, 8), forms three types of compounds. Compounds 5 and 6 are isostructural (monoclinic, space group P2(1)/n), and the structures comprise anionic linear chains [(MnII(L))(M(III)(micro-CN)2(CN)4)]n(n-) with cationic trinuclear complexes [(MnII(L)(H2O))2(M(III)(micro-CN)2(CN)4)]+ as counterions. Using an excess of K3[FeIII(CN)6], an analogous compound to 6 but with K+ as counterion is obtained (7), which crystallizes in the triclinic space group P1. Compound 8 consists of 2-D layers with formula [(MnII(L))3(FeIII(micro-CN)4(CN)2)(FeIII(micro-CN)2(CN)4)]n x 2nMeOH; it crystallizes in the monoclinic space group P2(1)/n. The magnetic properties were investigated for all samples. In particular, compound 5, which shows antiferromagnetic exchange interactions between Mn(II) and Cr(III) ions through cyanide bridging ligands, has been studied in detail; the magnetic exchange parameter amounts to J = -7.5(7) cm(-1). Compound 8 shows a magnetically ordered phase below 6.4 K which is confirmed by M?ssbauer spectroscopy; two hyperfine split spectra were observed below Tc from which IJI values of 2.1 and 1.6 cm(-1) could be deduced.     

Generalized Lyapunov–Schmidt Reduction Method and Normal Forms for the Study of Bifurcations of Periodic Points in Families of Reversible Diffeomorphisms

We introduce a general reduction method for the study of periodic points near a fixed point in a family of reversible diffeomorphisms. We impose no restrictions on the linearization at the fixed point except invertibility, allowing higher multiplicities. It is shown that the problem reduces to a similar problem for a reduced family of diffeomorphisms, which is itself reversible, but also has an additional ? ^q -symmetry. The reversibility in combination with the ? ^q -symmetry translates to a 𝕋 ^q -symmetry for the problem, which allows to write down the bifurcation equations. Moreover, the reduced family can be calculated up to any order by a normal form reduction on the original system. The method of proof combines normal forms with the Lyapunov–Schmidt method, and makes repetitive use of the Implicit Function Theorem. As an application we analyze the branching of periodic points near a fixed point in a family of reversible mappings, when for a critical value of the parameters the linearization at the fixed point has either a pair of simple purely imaginary eigenvalues that are roots of unity or a pair of non-semisimple purely imaginary eigenvalues that are roots of unity with algebraic multiplicity 2 and geometric multiplicity 1.     

Subharmonic branching at a reversible 1:1 resonance

We investigate the bifurcation of q-periodic points from a fixed point of a 2-parameter family of n-dimensional reversible diffeomorphisms (n ≥ 4). The focus is on the codimension 2 non-semisimple 1:1 resonance case, that is, when the linearization at the fixed point has a pair of double eigenvalues on the unit circle, exp ( ± 2iπp/q) (with gcd(p, q) = 1), with geometric multiplicity 1. Through a modified version of Lyapunov Schmidt reduction, the reduced bifurcation equations are obtained. These are then analysed using reversible normal form theory and (reversible) singularity theory. We obtain the existence of two branches of symmetric q-periodic orbits bifurcating from the fixed point. We also describe the corresponding bifurcation scenario for a family of reversible systems in the case of a two-fold resonance, cfr. [12 Knobloch, J. and Vanderbauwhede, A., Hopf bifurcation at k-fold resonances in reversible systems, Preprint Technische Universiteit at Ilmenau, No. M 16/95. [Google Scholar] 5 Buzzi, C.A. and Lamb, J.S.W., Reversible equivariant Hopf bifurcation. Archive for Rational Mechanics and Analysis. In press. [Google Scholar]].     

Characterization by fourier transform infrared spectroscopy (FT-IR) and 2D IR correlation spectroscopy of PAMAM dendrimer

FT-IR and 2D correlation spectroscopy were employed to study the microstructural changes occurring during phase transitions of a liquid crystal poly(amidoamine) codendrimer (PAMAM (L1)16(L2)16) generation 3, functionalized on the terminal groups by one-chain promesogenic calamitic units (4-(4'-decyloxybenzoyloxy)salicylaldehyde (L1)) and two-chain promesogenic calamitic units (4-(3',4'-didecyloxybenzoyloxy)salicylaldehyde (L2)). Spectral modifications associated with molecular conformation rearrangements allowing for molecular shape change on going from a liquid-crystalline organization to another were found. The transition temperatures were calculated, and they are in good agreement with the DSC data. Spectral analysis gives evidence of the LC phase transitions and to an additional transition associated with the existence of conformers. Various types of hydrogen bonding have been established.     

Thermal stability of second generation carbosilane dendrimers with peripheral ammonia groups

Spinel nickel zinc ferrite nanowires were successfully prepared in mesoporous silica SBA-15 as a host matrix. The powder was annealed at a range of temperatures (500–900 °C) with heating rate 0.5 °C/min. The required NiZnFe₂O₄ phase was obtained at 700 °C. The specific surface area S_BET data revealed that the surface area of the mesoporous silica after annealing was decreased from 821 to 90 m²/g which indicated that the spinal ferrite fills the channels of mesoporous materials. The one-dimensional spinel nanostructures were characterized by X-ray diffraction, infrared spectroscopy, vibrating sample magnetometer, and transmission electron microscopy before and after a selective removal of the silica template in aqueous solution of NaOH or HF. The presence of SBA-15 lowers the formation temperature of nickel zinc ferrite nanowires compared to the corresponding bulk material. The magnetic properties revealed a high saturation magnetization level (~43 emu/g) for the Ni–Zn nanowires at 900 °C.     

Temporal trends of carbon monoxide (CO) and radon (222Rn) tracers of urban air pollution

Journal of Radioanalytical and Nuclear Chemistry - The use of carbon monoxide (CO) and radon (222Rn) during 1 year continuous monitoring in Bucharest, Romania in relation with other air...     

Gelatin Reinforced with CNCs as Nanocomposite Matrix for Trichoderma harzianum KUEN 1585 Spores in Seed Coatings

Increasing interest on sustainable agriculture has led to the development of new materials which can be used as seed coating agents. In this study, a new material was developed based on gelatin film reinforced with cellulose nanocrystals (CNC) which was further used as nanocomposite matrix for Trichoderma harzianum KUEN 1585 spores. The nanocomposite films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), showing the formation of new hydrogen bonds between the components with a good compatibility between them. Measurements of water contact angles and tests of water vapor sorption and swelling degree revealed an improvement in the water vapor absorption properties of the films as a result of their reinforcement with CNC. Furthermore, by adding the Trichoderma harzianum KUEN 1585 spp. in the seed coating material, the germination percentage, speed of germination and roots length of the corn seeds improved. The polymeric coating did not inhibit the growth of T. harzianum KUEN 1585, with this material being a good candidate in modern agriculture.     

Characterization of fungal degraded lime wood by FT-IR and 2D IR correlation spectroscopy

The action of soft-rot fungus Chaetomium globosum has been studied. The decayed lime wood samples were observed for different periods of exposure. The degree of decay was determined by weight loss which was of 50.4% after 133 days. The samples were analyzed by FT-IR and 2D IR correlation spectroscopy.The intensity bands assigned to different vibrations from cellulose and hemicelluloses show a decrease, while the intensities of the bands assigned to C–O vibrations due to the formation of oxidized structures increase. At the same time, the intensity of the band assigned to C–O in metoxyl groups from lignin shows a decrease with increasing exposure time. The differences between reference and decayed wood spectra were examined in detail using 2D correlation spectroscopy and the second derivative analysis for two exposure time periods — of 0–70 days and 70–133 days. The formation of reactive species due to oxidation reactions induced by enzymes and the demethoxylation of the lignin structure was evidenced.