Mössbauer spectroscopic study of a low temperature magnetic transition in ordered Fe-doped NiAl

Mössbauer spectroscopic (MS) measurements at ambient and cryogenic temperatures on powdered Fe-doped NiAl materials (Ni-40Al-9Fe and Ni-50Al-9Fe) exhibited paramagnetic behavior down to 17 K, with one Fe-site in the hosts. At 4.2 K, Ni-40Al-9Fe (Al deficient) remained paramagnetic, while Ni-50Al-9Fe (Ni deficient) displayed a magnetic transition, resolved in terms of one Fe environment. The internal magnetic field of the magnetically split site of Ni-50Al-9Fe was 185?±?8 kOe determined from a field distribution model. This shows that electronic and magnetic interactions in ordered Fe-doped NiAl depend on Fe site preference tendencies. The single Fe site observed at 4.2 K for the Ni-deficient alloy shows that its Fe distribution or site occupancy is not random but ordered. The interactions leading to the development of internal magnetic field in the Ni-deficient ordered alloy is temperature dependent being absent above 17 K based on MS measurements from ambient to 4.2 K.     

Oxygen-bridged hybrid metallocene-nonmetallocene polymetallic catalysts of group 4 metals for bimodal activity in olefin polymerization: synthesis, characterization, and theoretical investigation

This article describes the syntheses of two covalently linked oxygen-bridged hybrid metallocene-nonmetallocene polymetallic catalysts bearing two different catalytically active group 4 metals. The reactions of Cp*2(Me)Zr(OH) (2) with Ti(NMe2)4 and Hf(NMe2)4 led to the formation of a heterobimetallic compound Cp*2(Me)Zr(micro-O)Ti(NMe2)3 (7) and a trimetallic derivative Cp*2(Me)Zr(micro-O)Hf(NMe2)2(micro-O)Zr(Me)Cp*2 (9), respectively, under the elimination of Me2NH. The crystal data confirm the molecular structures of 7 and 9, which crystallize in the space groups P and P21/n, respectively. 9 is the first example of a crystallographically characterized heterotrimetallic complex having a Zr-O-Hf-O-Zr core. 7 bearing two active catalytic centers, namely, zirconium and titanium, exhibits bimodal activity in olefin polymerization when activated with methylalumoxane (MAO). It produces polyethylene largely controlled by the zirconium center, and polystyrene seems to be formed predominantly by the titanium center. DFT calculations were performed on the supposed cationic intermediates, revealing that a cation generated on the titanium center is sterically more accessible for monomer binding, though it is energetically less-favorable than that generated on the zirconium center.     

High effectiveness of oligothienylenevinylene as molecular wires in Zn-porphyrin and C60 connected systems

Photoinduced energy transfer and electron transfer processes have been found between the excited singlet state of Zn-porphyrin and C(60) via an oligothienylenevinylene bridge depending on the length of the oligothiophene and solvent polarity.     

Systematic coarse‐graining of semicrystalline polyethylene

In an effort to accelerate simulations exploring deformation mechanisms in semicrystalline polymers, we have created structure‐based coarse‐grained (CG) models of polyethylene and evaluated the extent to which they can simultaneously represent its amorphous and crystalline phases. Two CG models were calibrated from target data sampled from atomistic simulations of supercooled oligomer melts that differ in how accurately they represent the distribution of bond lengths between CG sites. Both models yield semicrystalline morphology when simulations are performed at ambient conditions, and both accurately predict the glass transition and melt temperatures. A thorough evaluation of the models was then conducted to assess how well they represent various properties of the amorphous and crystalline phases. We found that the model that more faithfully reproduces the target bond length distribution poorly represents the crystalline phase, which results from its inability to reproduce correlations in the structural distributions. The second model, which utilizes a harmonic bond potential and thus reproduces the target bond length distribution less accurately, represents the structure and chain mobility within the crystalline phase more realistically. Furthermore, the latter model more faithfully reproduces the vastly different relaxation timescales of the phases, a critical feature for modeling deformation mechanisms in semicrystalline polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 331–342     

Combined dealkoxycarbonylation and lactonisation of unsaturated malonates in ionic liquids

Heating unsaturated malonates with LiCl and water in [bmim][Br] or [bmim][BF₄]/[bmim][Br] produces unsaturated esters or lactones, respectively.     

Ethyl methyl 1,4‐dihydro‐4‐(3‐nitrophenyl)‐2,6‐bis(1‐piperidylmethyl)­pyridine‐3,5‐dicarboxylate

In the title compound, C₂₈H₃₈N₄O₆, the 4‐aryl substituent occupies a pseudo‐axial position approximately orthogonal to the plane of the di­hydro­pyridine ring [88.1 (3)°]. The di­hydro­pyridine ring adopts a flattened boat conformation. The H atom on the pyridine N atom is involved in a bifurcated intramolecular hydrogen bond, the acceptors being the N atoms of the two piperidyl­methyl groups [N?N 2.629 (4) and 2.695 (4) Å].