Atomically Precise Lanthanide-Iron-Oxo Clusters Featuring the ϵ-Keggin Ion

Atomically precise molecular metal-oxo clusters provide ideal models to understand metal oxide surfaces, self-assembly, and form-function relationships. Devising strategies for synthesis and isolation of these molecular forms remains a challenge. Here, the synthesis of four Ln-Fe oxo clusters that feature the ϵ-{Fe₁₃} Keggin cluster in their core is reported. The {Fe₁₃} metal-oxo cluster motif is the building block of two important iron oxyhydroxyide phases in nature and technology, ferrihydrite (as the δ-isomer) and magnetite (the ϵ-isomer). The reported ϵ-{Fe₁₃} Keggin isomer as an isolated molecule provides the opportunity to study the formation of ferrihydrite and magnetite from this building unit. The four currently reported isostructural lanthanide-iron-oxo clusters are fully formulated [Y₁₂Fe₃₃(TEOA)₁₂(Hyp)₆(μ₃-OH)₂₀(μ₄-O)₂₈(H₂O)₁₂](ClO₄)₂₃ ⋅ 50 H₂O ( 1 , Y₁₂Fe₃₃ ), [Gd₁₂Fe₃₃(TEOA)₁₂(Hyp)₆(μ₃-OH)₂₀(μ₄-O)₃₂(H₂O)₁₂](ClO₄)₁₅ ⋅ 50 H₂O ( 2 , Gd₁₂Fe₃₃ ) and [Ln₁₆Fe₂₉(TEOA)₁₂(Hyp)₆(μ₃-OH)₂₄(μ₄-O)₂₈(H₂O)₁₆](ClO₄)₁₆(NO₃)₃ ⋅ n H₂O (Ln=Y for 3 , Y₁₆Fe₂₉ , n=37 and Ln=Gd for 4 , Gd₁₆Fe₂₉ n=25; Hyp=trans-4-Hydroxyl-l -proline and TEOA=triethanolamine). The next metal layer surrounding the ϵ-{Fe₁₃} core within these clusters exhibits a similar arrangement as the magnetite lattice, and Fe and Ln can occupy the same positions. This provides the opportunity to construct a family of compounds and optimize magnetic exchange in these molecules through composition tuning. Small-angle X-ray scattering (SAXS) and high-resolution electrospray ionization mass spectrometry (HRESI-MS) show that these clusters are stable upon dissolution in both water and organic solvents, as a first step to performing further chemistry towards building magnetic arrays or investigating ferrihydrite and magnetite assembly from pre-nucleation clusters.     

Distance dependence of the reaction rate for the reduction of metal cations by solvated electrons: a picosecond pulse radiolysis study

The decay of the solvated electron generated by picosecond electron pulse radiolysis is studied by broad-band transient absorption measurements in ethylene glycol solutions containing decimolar concentrations of Cu(2+), Ni(2+), and Pb(2+) metal cations. Analysis of the nonexponential kinetics of the decays reveals molecular parameters of the electron transfer reaction. It is found that the reaction occurs at long distance for Cu(2+) solutions and is only limited to contact distance in the case of Ni(2+) solutions. The distribution of reaction distance strongly depends on the free enthalpy change of the reactions.     

Picosecond pulse radiolysis study of highly concentrated nitric acid solutions: formation mechanism of NO3• radical

The formation of nitrate radical, NO(3)(?), is observed for the first time directly by picosecond pulse radiolysis of highly concentrated nitric acid solutions. The experimental yield of NO(3)(-) ionization is deduced from the pulse-probe transient absorption measurements in the visible region where this radical absorbs. On the basis of the value of the extinction coefficient of nitrate radical at 640 nm equal to 1300 M cm(-1), the experimental yield of NO(3)(?) at 20 ps is found to be around 0.36 × 10(-7), 1.33 × 10(-7), and 2.85 × 10(-7) mol J(-1) for 1, 3.5, and 7 M nitric acid solutions, respectively. Relative to the dose absorbed by nitric acid by the direct effect, we find an unexpected high formation yield of the nitrate radical within the electron pulse. Therefore, we suggest that the trapping of the positive hole, H(2)O(?+), by NO(3)(-) also contributes to the formation of NO(3)(?) within the electron pulse. Moreover, after the pulse and within 4 ns, the beginning of the reaction of OH(?) radical with undissociated nitric acid is observed for the most concentrated nitric acid solution.     

Visibility graph similarity: A new measure of generalized synchronization in coupled dynamic systems

Synchronization is defined as interdependencies among coupled dynamic systems. In most coupled systems the intrinsic and internal variants, and the interdependencies among their subsystems are not accessible. Therefore, in order to quantify the interdependencies among the coupled systems, attempts have been made through measuring the synchronization between their outputs represented mostly as time series. In this paper a new method, called Visibility Graph Similarity (VGS), is presented as a method of measuring Generalized Synchronization. First, each time series is reconstructed as a trajectory in a state space. Next, a Distance Time Series (DTS) is created from a sequence of relative distances of the states to a reference state. Subsequently, a visibility graph (VG) is constructed using DTS. Then, a sequence of degrees of the VG, called Degree Sequence (DS), is obtained. Correlation of the DSs of two coupled systems is called VGS and is presented as a measurement of similarity of dynamics of the coupled systems. The synchronization measurement performance of the VGS is compared with synchronization likelihood (SL) and the classical cross correlation method using two identical and non-identical models of two coupled Henon map over the entire time domain. Also, it is compared with SL for tracing temporal synchronization using both models. It is shown that VGS provides a more accurate measure of the overall synchronization compared with SL. It is more reliable for measuring weak couplings compared with the cross correlation method. Moreover, VGS uses fewer parameters and detects the temporal synchronization sooner than the SL.     

Surface tension and energy in multivariant martensitic transformations: phase-field theory, simulations, and model of coherent interface

The Ginzburg-Landau theory for multivariant martensitic phase transformations is advanced in three directions: the potential is developed that introduces the surface tension at interfaces; a mixed term in gradient energy is introduced to control the martensite-martensite interface energy independent of that for austenite-martensite; and a noncontradictory expression for variable surface energy is suggested. The problems of surface-induced pretransformation, barrierless multivariant nucleation, and the growth of an embryo in a nanosize sample are solved to elucidate the effect of the above contributions. The obtained results represent an advanced model for coherent interface.     

Acid?Base Properties of Adenosine 5′‐Monophosphate,Guanosine 5′‐Monophosphate,and Inosine 5′‐Monophosphate in Aqueous Solutions of Methanol

The protonation constants of adenosine 5′‐monophosphate, guanosine 5′‐monophosphate, and inosine 5′‐monophosphate were determined in binary mixtures of H₂O containing 0, 10, 15, 20, 25, 30, 35, 40, 45, and 50% MeOH, using a combination of potentiometric and spectrophotometric methods at a constant temperature (25°) and constant ionic strength (0.1 mol?dm^?3 NaClO₄). The protonation constants were analyzed using the normalized polarity parameter (E ), and Kamlet, Abboud, and Taft (KAT) parameters. A linear correlation of log K vs. the normalized polarity parameter was obtained. Dual‐parameter correlation of log K vs. π* (dipolarity/polarizability) and α (H‐bond‐donor acidity), as well as π* and β (H‐bond‐acceptor basicity) also gives good results in various aqueous organic solvent mixtures. Finally, the results are discussed in terms of the effect of solvent on the protonation equilibria.     

Synthesis and photovoltaic properties of a furan-diketopyrrolopyrrole-fluorene terpolymer

We report the synthesis of two solution-processable reduced band gap donor–acceptor conjugated polymers p(C8-DPP-F) and p(C12-DPP-F), composed from 9,9-dioctylfluorene as the donor moiety, diketopyrrolopyrrole (DPP) moiety as the acceptor moiety and furan bridges. Two different alkyl chains, n-dodecyl and n-octyl were used on the DPP moiety and the impact of this structural modification evaluated in detail. Both polymers exhibited similar optical and electrochemical properties with optical band gap of around 1.75 eV as result of LUMO levels near −3.4 eV and high-lying HOMO levels of ∼5.2 eV. Bulk heterojunction photovoltaic devices using these polymers electron donors along with PC₇₀BM as the electron acceptor, gave power conversion efficiency of 1.60% and 0.75% for p(C12-DPP-F) and p(C8-DPP-F) respectively.     

Characterization and Studies on Grafting of Methyl Methacrylate onto PAN Fibers

The graft copolymerization of methyl methacrylate (MMA) onto commercial acrylic fibers (PAN) has been studied using Azobis(isobutyro)nitrile (AIBN) as an initiator. MMA grafting initiated by radicals formed from thermal decomposition of AIBN. In this study, the effects of monomer and initiator concentration, time and temperature reaction on the grafting yield have been investigated.

The optimum conditions for this grafting reaction were obtained with an MMA concentration of 0.7 M, an AIBN concentration of 0.0073 M, a reaction temperature of T=85°C and with a 60 min reaction time.

The fiber structure has been investigated by different experimental techniques of characterization such as Fourier transform infrared spectroscopy (FT‐IR), calorimetric analysis (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water absorption and the physical and mechanical properties has also been investigated in this study. The thermal analysis data showed that by increasing grafting yield, little changes have occurred in fibers samples up to 13.5% of grafting yield and the thermal transitions of grafted fibers have approximately the same behavior compared with the raw fibers sample. Grafting also slightly affected the fiber morphology. The experimental data of mechanical properties clearly show that by increasing grafting yield, max extension will decrease but this change up to 13.5% grafting yield is barely noticeable. Grafting of poly MMA improved water absorption.     

Picosecond pulse radiolysis of direct and indirect radiolytic effects in highly concentrated halide aqueous solutions

Recently we measured the amount of the single product, Br(3)(-), of steady-state radiolysis of highly concentrated Br(-) aqueous solutions, and we showed the effect of the direct ionization of Br(-) on the yield of Br(3)(-). Here, we report the first picosecond pulse-probe radiolysis measurements of ionization of highly concentrated Br(-) and Cl(-) aqueous solutions to describe the oxidation mechanism of the halide anions. The transient absorption spectra are reported from 350 to 750 nm on the picosecond range for halide solutions at different concentrations. In the highly concentrated halide solutions, we observed that, due to the presence of Na(+), the absorption band of the solvated electron is shifted to shorter wavelengths, but its decay, taking place during the spur reactions, is not affected within the first 4 ns. The kinetic measurements in the UV reveal the direct ionization of halide ions. The analysis of pulse-probe measurements show that after the electron pulse, the main reactions in solutions containing 1 M of Cl(-) and 2 M of Br(-) are the formation of ClOH(-?) and BrOH(-?), respectively. In contrast, in highly concentrated halide solutions, containing 5 M of Cl(-) and 6 M of Br(-), mainly Cl(2)(-?) and Br(2)(-?) are formed within the electron pulse without formation of ClOH(-?) and BrOH(-?). The results suggest that, not only Br(-) and Cl(-) are directly ionized into Br(?) and Cl(?) by the electron pulse, the halide atoms can also be rapidly generated through the reactions initiated by excitation and ionization of water, such as the prompt oxidation by the hole, H(2)O(+?), generated in the coordination sphere of the anion.