Synthesis and Molecular Structure of Bis(ethylenediamine)acetatonickel(II)hexafluoridophosphate Complex [Ni(en)2(CH3CO2)]PF6. An Unexpected Acetylacetonato Cleavage Reaction

The title complex was synthesized by an unusual reaction between [Ni(acac)₂(H₂O)₂] and ethylenediamine in water solution. The crystal structure of 1 shows the nickel(II) core in a tetragonally distorted octahedral environment coordinated to two ethylenediamine molecules and one acetate ligand. This is the first example of a mononuclear bis(ethylenediamine)nickel(II) complex, where the oxygen atoms of the auxiliary ligand are in cis configuration. The compound exhibits an extensive association between the complex cation and the respective anion through classical N–H ··· O and N–H ··· F intermolecular hydrogen bonds, which generate a supramolecular 3D arrangement in the solid state.     

Electronic states of F2CO as studied by electron energy-loss spectroscopy and ab initio calculations

This paper reports on the first measurements of the electron impact electronic excitation cross-sections for carbonyl fluoride, F(2)CO, measured at 30 eV, 10° and 100 eV, 5° scattering angle, while sweeping the energy loss over the range 5.0-18.0 eV. The electronic-state spectroscopy has been investigated and the assignments are supported by quantum chemical calculations. The energy bands above 9.0 eV and the vibrational progressions superimposed upon it have been observed for the first time. Vibronic coupling has been shown to play an important role dictating the nature of the observed excited states, especially for the low-lying energy region (6.0-8.0 eV). New experimental evidence for the 6(1)B(2) state proposed to have its maximum at 12.75 eV according to the vibrational excitation reported in this energy region (11.6-14.0 eV). The n = 3 members of the Rydberg series have been assigned converging to the lowest ionization energy limits, 13.02 eV ((2)B(2)), 14.09 eV ((2)B(1)), 16.10 ((2)B(2)), and 19.15 eV ((2)A(1)) reported for the first time and classified according to the magnitude of the quantum defects (δ).     

Supramolecular assembly of new heteropolymetalic molecules based on tetraiminodiphenolate macrocycle and hexacyanometallate anions: Magnetostructural and spectroscopic properties

Herein we report on the synthesis, single crystal X-ray structure, spectroscopic and magnetic properties of [{Cu₂(tidf)(H₂O)}₂(μ-CN)₂Fe(CN)₄]·6H₂O (1), [Cu₂(tidf)(H₂O)₂][Ni(CN)₄] (2) and [Cu₂(tidf)(H₂O)₂][Fe(CN)₅NO]·H₂O (3) (tidf = a Robson type macrocyclic ligand obtained on condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane). Complex (1) is pentanuclear; two paramagnetic dicopper(II) units are linked by a hexacyanoferrate(II) ion through two cyano-bridges. All compounds exhibit extensive, three-dimensional, supramolecular structures supported by classic hydrogen bonding between the coordinated aqua ligands, water molecules and cyano groups. Magnetism as a function of the temperature of complexes 1-3 is consistent with a strong antiferromagnetism with exchange parameters 2J estimated −783(29), −913(2), −905(1), respectively.     

Porous Membranes of Montmorillonite/Poly(vinylidene fluoride‐trifluorethylene) for Li‐Ion Battery Separators

Porous membranes of poly(vinylidene fluoride‐trifluoroethylene) with different contents of montmorillonite (MMT) particles were prepared. The filler content does not affect the porous morphology but leads to an increase in the average pore size, porosity and electrolyte uptake up to 16 μm, 85 % and 325 %, respectively, for a membrane with 16 wt% of MMT particles. The mechanical properties, ionic conductivity and its temperature stability are improved by the presence of clays. The electrochemical stability reveals a stable operation window up to 5 V. The overall characteristics of the membranes for battery separators are optimized for the 4 wt% MMT filler content.     

Electronic State Spectroscopy of 1,4-Pentadiene As Studied by VUV Photoabsorption Spectroscopy and ab Initio Calculations

We present high resolution VUV photoabsorption spectra of 1,4-pentadiene, C(5)H(8), over the wavelength range 115-247 nm (10.8-5.0 eV). These spectra reveal several new features not previously reported in the literature. These measurements are complemented by the first ab initio calculations for the three most abundant conformational isomers of 1,4-pentadiene, C(5)H(8), which we then use in the assignment of valence and Rydberg transitions. Calculations of the two lowest energy ionic states of 1,4-pentadiene are also presented and compared with the experimental data available in the literature. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of 1,4-pentadiene in the upper stratosphere (20-50 km).     

Chiral spiro-β-lactams from 6-diazopenicillanates

Chiral spiro-β-lactam derivatives have been prepared via stereoselective 1,3-dipolar cycloaddition of 6-diazopenicillanates. Using dipolarophiles such as acrylonitrile, acrylates or methyl vinyl ketone spiro-2-pyrazoline-β-lactams were obtained, whereas the cycloaddition with N-substituted-maleimides afforded spiro-1-pyrazoline-β-lactams. 6-Diazopenicillanates also reacted with electron-deficient alkynes to give the corresponding spiro-3H-pyrazole-β-lactam as single product. The observed stereoselectivity can be explained considering that the major product results from the addition to the less sterically hindered α-side of the β-lactam. Microwave-induced denitrogenation of spiro-1-pyrazoline-β-lactams allowed the stereoselective synthesis of novel spirocyclopropyl-β-lactams. The rationalization of the observed selectivity was supported by electronic structure calculations.     

Determination of copper,iron, nickel and zinc in ethanol fuel by energy dispersive X-ray fluorescence after pre-concentration on chromatography paper

This paper presents an alternative analytical method employing energy dispersive X-ray fluorescence (EDXRF) to determine copper, iron, nickel and zinc ions in ethanol fuel samples after a pre-concentration procedure. Our pre-concentration strategy utilizes analyte retention on cation exchange chromatography paper, a convenient substrate for direct EDXRF measurements. The repeatability, expressed in terms of RSD of standard solutions containing 0.25 μg mL⁻¹ of Cu, Fe, Ni and Zn, and calculated from fifteen consecutive measurements, was 2.5, 2.8, 3.0, and 2.7%, respectively. The limits of detection (LOD), defined as the analyte concentration that gives a response equivalent to three times the standard deviation of the blank (n = 10), were found to be 13, 15, 15 and 12 μg L⁻¹ for Cu, Fe, Ni and Zn, respectively. The proposed method was applied to Cu, Fe, Ni and Zn determination in hydrated ethanol fuel samples collected from different gas stations.     

Rigidity of Area-Minimizing Hyperbolic Surfaces in Three-Manifolds

We prove that if M is a three-manifold with scalar curvature greater than or equal to ?2 and Σ?M is a two-sided compact embedded Riemann surface of genus greater than 1 which is locally area-minimizing, then the area of Σ is greater than or equal to 4π(g(Σ)?1), where g(Σ) denotes the genus of Σ. In the equality case, we prove that the induced metric on Σ has constant Gauss curvature equal to ?1 and locally M splits along Σ. We also obtain a rigidity result for cylinders (I×Σ,dt ²+g _Σ), where I=[a,b]?? and g _Σ is a Riemannian metric on Σ with constant Gauss curvature equal to ?1.     

Optical characterization of 316L stainless steel coated with sol–gel titania

In this work 316L stainless steel substrates were coated with sol–gel derived films by means of the dip-coating technique. Titanium isopropoxide and ethanol were used as chemical precursor and solvent, respectively. The dip-coating step was performed using withdrawal speeds of 6 mm/min, 30 mm/min, and 60 mm/min. Next, the samples were heat treated in air for 30 min at 100 °C, 300 °C, and 400 °C. The processed composites were examined by FTIR and UV–vis spectroscopies. We observed that the materials prepared in this work can exhibit a variety of colors depending on the heat treatment temperature, withdrawal speed, and precursor:solvent molar ratio used in their processing. It is an important finding since this behavior could lead to architectural application of these materials. We believe that the changes observed in the UV–vis spectra and the colors of these samples could be related to the variation of the coating thickness as the processing conditions were modified. FTIR tests revealed that the ratio between the intensities of features ascribed to hydroxyl groups and TiO bonds decreased as the heat treatment temperature was increased. On the other hand, the ratio between bands related to TiOTi and TiO bonds decreased when the heating temperature was raised from 100 °C to 300 °C.     

The optimal decay rate for a weak dissipative Bresse system

In this work we consider the Bresse system with frictional damping operating only on the angle displacement and we show that under a certain assertion the solution decays polynomially and the decay rate is optimal.