Rules of hierarchical melt and coordinate bond to design crystallization in doped phase change materials

While alloy design has practically shown an efficient strategy to mediate two seemingly conflicted performances of writing speed and data retention in phase-change memory, the detailed kinetic pathway of alloy-tuned crystallization is still unclear. Here, we propose hierarchical melt and coordinate bond strategies to solve them, where the former stabilizes a medium-range crystal-like region and the latter provides a rule to stabilize amorphous. The Er0.52Sb2Te3 compound we designed achieves writing speed of 3.2 ns and ten-year data retention of 161 °C. We provide a direct atomic-level evidence that two neighbor Er atoms stabilize a medium-range crystal-like region, acting as a precursor to accelerate crystallization; meanwhile, the stabilized amorphous originates from the formation of coordinate bonds by sharing lone-pair electrons of chalcogenide atoms with the empty 5d orbitals of Er atoms. The two rules pave the way for the development of storage-class memory with comprehensive performance to achieve next technological node.

Covalent Immobilization of Polyaniline Doped with Ag+ or Cu2+ on Carbon Nanotubes for Ethylene Chemical Sensing

Multi-walled carbon nanotubes (MWCNTs) are promising materials for chemical gas sensing because of their high electrical and mechanical properties and significant sensitivity to changes in the local environment. However, high-content MWCNT films suffer from the low tunability of the electrical resistance, which is crucial for high chemoresistive sensing performance. This study reports the conjugation of MWCNTs and oligomers of polyaniline (PANI) doped with Ag+ or Cu2+ incorporated into a PVC/polyacrylate. MWCNTs were sonicated in n-methyl pyrrolidine (NMP), and PANI was conjugated via a 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and an N-hydroxysuccinimide (EDC/NHS) process. MWCNT/PANI Ag+ or Cu2+ conjugates were doped to form a coordinate bond. The doped conjugates were successfully incorporated into the PVC/polyacrylate. These MWCNT/PANI conjugates doped were exposed to different concentrations of ethylene gas to examine their feasibility for ethylene detection.

Antimony lone electronic pair as a stereoelectronic barrier to stibatrane

To examine the effect of 5s2 lone electron pair of antimony atom on the reaction of antimony trifluoride and triethanolamine in the presence of sodium methylate, the crystal structure of the reaction product -2-fluoro-6-(2-hydroxyethyl)-1,3-dioxa-6-aza-2-stibacy-cylooctane (1-fluoro-2-hydrostibatrane) FSb (OCH2CH2)2NCH2CH2OH) was confirmed. In the compound structure, the hydrogen atom of the 2-hydtoxyethyl group of each molecule forms an intermolecular hydrogen bond with the oxygen atom of one of the five-membered SbOCH2CH2N half-cycles in a neighbouring molecule. A geometry of both five-member N-C-C-O-Sb heterocycles, end-capped by transannular N→Sb bond in the 1-fluoro-2-hydrostibatrane molecule, is almost identical. C-O, C-C, N-C interatomic distances and valence angles in two endocyclic units (NCCOSb) are comparable to those observed in RSi(OCH2CH2)3N silatranes. A coordination polyhedron of the Sb atom can be represented as a transition from a bisphenoid to Sb(O3)N trigonal pyramid, with a nitrogen atom at the apex and three oxygen atoms in the base. The N→Sb transannular coordinate bond length is 2.402(4) Å, which is 0.40 Å greater than the Sb-N covalent bond standard length. The Sb-F bond (1.997(4) Å) is 0.12 Å longer than that in the SbF3 molecule, and insignificantly shorter than that of the Sb-Fax (2.028(3) Å) in the SbF3Gly crystalline complex. The fluorine atom substantially strays from the N→Sb axis to the direction of O(1) and O(2) atoms. The oxygen atom of the 2-hydroxyethyl group lies at a distance of 2.899(3) A from that of Sb, intermediate between the valence bond length and the sum of the Van der Waals radii of these atoms. Combined with the F atom position, one can assume the 1-fluoro-2-hydrostibatrane crystal structure as a “frozen” state of the SNi(Sb) type nucleophilic attack of the oxygen atom, uncompleted because of its repulsion by the 5s2 lone electronic pair of antimony atom.

Interfacial Adhesion and Microstructure of Epoxy/Aluminium Particulate Nanocomposites

Fibres anisotropy and their poor adhesion to the epoxy matrix are challenges in developing polymeric epoxy composite for structural applications. Filling of epoxy with reinforcing particles has potential for producing isotropic composites. In this study, epoxy-aluminium particulate composites were developed through combined-stir-techniques. Their interfacial adhesion and microstructural properties were examined. Results obtained indicated bonding of aluminium particles to epoxy through bidentate coordinate bond. Variations observed in the Fourier Transform Infrared spectrographs (FTIR) of both composites’ grades confirm discrepancies in interactions of aluminium micro and nanoparticles with epoxy. A good interfacial adhesion of aluminium nanoparticle with epoxy established by both optical and scanning electron microscopes is an indication of good mechanical performance of the epoxy composites.

Co-ordination ability of Vinyl Imidazole(VIm), Imidazole(Im), Indazole(In), Ammonia(NH3) and Dimethyl sulphoxide (DMSO) Ligands in Ruthenium Complexes

Few essential electronic properties of potential anti-cancer complexes are examined using quantum mechanical calculations. The co-ordination ability of these ligands with the central Ru metal has been assessed. The ionization energies and HOMO-LUMO gaps are used to explain the coordinate bond formation between ligand and Ru. The variation of charges from natural population analysis(NPA) of the donor sites of ligands is fairly similar to the trends in the coordinate bond distances despite the presence of other ligands in these Ru complexes. Slight variation of coordinate bonds (Ru-donor site) has been found. In addition, Cl dissociation energies from these complexes do not vary much and the trend of the energy values are similar to oxidation energies of these complexes. The NPA charges and HOMO-LUMO electron density mapping indicate that the electron density around Ru metal is increasing, which suggests that the migration of electron density is towards Ru.

Designing Crystallization to Tune the Performance of Phase-Change Memory: Rules of Hierarchical Melt and Coordinate Bond

While alloy design has practically shown an efficient strategy to mediate two seemingly conflicted performances of writing speed and data retention in phase-change memory, the detailed kinetic pathway of alloy-tuned crystallization is still unclear. Here, we propose hierarchical melt and coordinate bond strategies to solve them, where the former stabilizes a medium-range crystal-like region and the latter provides a rule to stabilize amorphous. The Er0.52Sb2Te3 compound we designed achieves writing speed of 3.2ns and ten-year data retention of 161°C. We provide a direct atomic-level evidence that two neighbor Er atoms stabilize a medium-range crystal-like region, acting as a precursor to accelerate crystallization; meanwhile, the essential reason of stabilization originates from the formation of coordinate bonds by sharing lone-pair electrons of chalcogenide atoms with the empty d orbitals of Er atoms. The two rules pave the way for the development of storage-class memory with excellent comprehensive performance to achieve next revolutionary technology node.

Application of New Efficient Hoveyda–Grubbs Catalysts Comprising an N→Ru Coordinate Bond in a Six-Membered Ring for the Synthesis of Natural Product-Like Cyclopenta[b]furo[2,3-c]pyrroles

The ring rearrangement metathesis (RRM) of a trans-cis diastereomer mixture of methyl 3-allyl-3a,6-epoxyisoindole-7-carboxylates derived from cheap, accessible and renewable furan-based precursors in the presence of a new class of Hoveyda–Grubbs-type catalysts, comprising an N→Ru coordinate bond in a six-membered ring, results in the difficult-to-obtain natural product-like cyclopenta[b]furo[2,3-c]pyrroles. In this process, only one diastereomer with a trans-arrangement of the 3-allyl fragment relative to the 3a,6-epoxy bridge enters into the rearrangement, while the cis-isomers polymerize almost completely under the same conditions. The tested catalysts are active in the temperature range from 60 to 120 °C at a concentration of 0.5 mol % and provide better yields of the target tricycles compared to the most popular commercially available second-generation Hoveyda–Grubbs catalyst. The diastereoselectivity of the intramolecular Diels–Alder reaction furan (IMDAF) reaction between starting 1-(furan-2-yl)but-3-en-1-amines and maleic anhydride, leading to 3a,6-epoxyisoindole-7-carboxylates, was studied as well.

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL STUDIES OF NI (II) COMPLEXES WITH SCHIFF BASE CO-LIGAND DERIVED FROM 5,6-DIAMINO-1,10-PHENANTHROLINE AND BENZENE-1,4-DICARBALDEHYDE

The Schiff base (PDB) was synthesized by refluxing ethanolic solution of 5,6-diamino-1,10-phenanthroline with Benzene-1,4-dicarbaldehyde for 3 hours. Similarly the complexes were synthesized by refluxing equimolar solution of PDB with [Ni(phen)2Cl2] and [Ni(bpy)2Cl2] for 5 hours each and characterized by FTIR, UV-visible, Mass and Elemental Analysis. The absorption band in IR spectrum of PDB at 1593 cm-1 was assigned to C=N stretching frequency which was shifted to 1550 cm-1 and 1549 cm-1 in the spectra of [Ni(phen)2PDB](PF6)2 and [Ni(bpy)2PDB](PF6)2 respectively. The new absorption bands at 721 cm-1 and 754 cm-1 in the spectra of both complexes were due to M-N coordinate bond. The UV- visible absorption band at 390 nm was due to p®p* transitions for azomethine. The low energy band at 450 nm for both complexes is due to MLCT Ni(dp) ®PDB(p*) transition. The molecular ion peak (M)+ in the mass spectra for PDB and the complexes were observed at 443 m/z, 984.75 m/z and 940.95 m/z respectively. The compounds were evaluated for antimicrobial activities, by well diffusion method against bacteria using agar nutrient as the medium and fungi using potato dextrose agar as medium. The free Schiff base has low activity compared to the complexes with inhibition zone between 4.0 mm to 6.6 mm whereas the complexes ranges from 7.5 mm to 11.2 mm.