Experimental evidence of two-band behavior of MgB2

The break-junction tunneling has been systematically investigated in MgB2. Two types of the break-junction contacts have been exploited on the same samples, which demonstrated tunnel contact like (SIS) and point contact like (SnS) behavior. Both of them have shown the existence of the two distinct energy gaps. We have observed also the peculiarities on the I(V)- characteristics related to Leggett's collective mode assisted tunneling. --> Corresponding author address: [email protected]: 14 pages, 6 figures, 1 table; corrected typos and fig

Vanadium (V) and titanium (IV) compounds with 2-[hydroxy(diaryl)methyl]-8-hydroxyquinolines: Synthesis, structure and catalytic behaviors to olefin polymerization

A series of oxovanadium (V) and titanium (IV) complexes stabilized by [ONO]2− type ligands-2-[hydroxy(diaryl)methyl]-8-hydroxyquinolines (2–3) were synthesized in high yields and characterized by elemental analysis, NMR-, IR spectroscopy and mass spectrometry. The molecular structures of the representative complexes 4 and 7 were confirmed by single-crystal X-ray diffraction, and revealed distorted octahedral geometry at Ti and tetragonal pyramid in V complex. Titanium-based catalytic systems were found to be active in the ethylene and 1-hexene polymerization and copolymerization, but only in the presence of a binary co-catalyst Et2AlCl/Bu2Mg. Vanadium-based systems were active in the same reactions in the presence of Et3Al2Cl3 or Et2AlCl mixed with CCl3CO2Et reactivator. The amount of co-monomer incorporated by these systems have reached 23 mol%. When applied in the presence of aliphatic solvents vanadium complexes catalyze 1-hexene oligomerization yielding dimers and trimers. When the same process is carried out in toluene, the solvent got alkylated by monomers and light oligomers (Friedel–Crafts reaction). © 2016 Elsevier Lt

Synthesis and reactivity in ethylene oligomerization by heteroscorpionate dibromonickel(II) complexes

Novel heteroscorpionate ligands were synthesized by a Peterson rearrangement during the reaction of 2-pyridinecarboxaldehyde (or 2-quinolinecarboxaldehyde) and 1,1-carbonyl-bis(pyrazoles). Nickel(II) dibromide reacts with these ligands in THF to give the heteroscorpionate dibromo complexes of general formula LNiBr2. Crystal structures of two full-sandwich heteroscorpionate Ni(II) complexes were determined. Preliminary studies of catalytic activity in ethylene oligomerization using different organoaluminum cocatalysts were performed. The addition of one equivalent of triphenylphosphine resulted in increased catalytic activity for most examples. The catalyst system of (2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel(II) dibromide/Et2AlCl/PPh3 dimerized ethylene with an activity of 650 g oligomer mol−1 Ni h−1 while the share of 1-butene in the mixture has reached 75%. Tris(3,5-dimethylpyrazol-1-yl)methyl nickel(II) dibromide, activated by Et2AlCl/PPh3 produced isobutylene (75% of the butene fraction). © 201

Synthesis and reactivity in ethylene oligomerization by heteroscorpionate dibromonickel(II) complexes

Novel heteroscorpionate ligands were synthesized by a Peterson rearrangement during the reaction of 2-pyridinecarboxaldehyde (or 2-quinolinecarboxaldehyde) and 1,1-carbonyl-bis(pyrazoles). Nickel(II) dibromide reacts with these ligands in THF to give the heteroscorpionate dibromo complexes of general formula LNiBr2. Crystal structures of two full-sandwich heteroscorpionate Ni(II) complexes were determined. Preliminary studies of catalytic activity in ethylene oligomerization using different organoaluminum cocatalysts were performed. The addition of one equivalent of triphenylphosphine resulted in increased catalytic activity for most examples. The catalyst system of (2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel(II) dibromide/Et2AlCl/PPh3 dimerized ethylene with an activity of 650 g oligomer mol−1 Ni h−1 while the share of 1-butene in the mixture has reached 75%. Tris(3,5-dimethylpyrazol-1-yl)methyl nickel(II) dibromide, activated by Et2AlCl/PPh3 produced isobutylene (75% of the butene fraction). © 201

Vanadium (V) and titanium (IV) compounds with 2-[hydroxy(diaryl)methyl]-8-hydroxyquinolines: Synthesis, structure and catalytic behaviors to olefin polymerization

A series of oxovanadium (V) and titanium (IV) complexes stabilized by [ONO]2− type ligands-2-[hydroxy(diaryl)methyl]-8-hydroxyquinolines (2–3) were synthesized in high yields and characterized by elemental analysis, NMR-, IR spectroscopy and mass spectrometry. The molecular structures of the representative complexes 4 and 7 were confirmed by single-crystal X-ray diffraction, and revealed distorted octahedral geometry at Ti and tetragonal pyramid in V complex. Titanium-based catalytic systems were found to be active in the ethylene and 1-hexene polymerization and copolymerization, but only in the presence of a binary co-catalyst Et2AlCl/Bu2Mg. Vanadium-based systems were active in the same reactions in the presence of Et3Al2Cl3 or Et2AlCl mixed with CCl3CO2Et reactivator. The amount of co-monomer incorporated by these systems have reached 23 mol%. When applied in the presence of aliphatic solvents vanadium complexes catalyze 1-hexene oligomerization yielding dimers and trimers. When the same process is carried out in toluene, the solvent got alkylated by monomers and light oligomers (Friedel–Crafts reaction). © 2016 Elsevier Lt

Heterometallic fullerides of Fe and Cu groups with the composition K2MC60 M Fe 2, Fe 3, Co 2, Ni 2, Cu 1, Cu 2, Ag 1

Heterometallic fullerides with composition K2MC60, synthesized by exchange chemical reaction of K5C60 or K4C60 with chlorides of metals Fe and Cu groups have been investigated by X ray diffraction, magnetic resonance, Raman and Mössbauer spectroscopy. Magnetization and susceptibility measurements have also been carried out. Metal chlorides from Fe and Cu groups enable to cover the whole range of electronic configuration of metal from d5 to d10. Heterometallic fullerides with M Cu 2, Fe 2, Fe 3 and Ni 2 appeared to be superconductors with Tc 13.9 16.5 K. Ferromagnetism and superconductivity coexist in investigated fulleride K2Fe 3C6

Novel titanium(IV) complexes stabilized by 2-hydroxybenzyl alcohol derivatives as catalysts for UHMWPE production

A series of titanium (IV) complexes (2, 5-7) stabilized by a substituted 2-hydroxybenzyl alcohols (1, 4) – were synthesized. Structures of complexes 6-7 were determined by X-ray diffraction. Titanium atom in the tetrameric complex 6 has an octahedral environment created by chlorine atom and five oxygen atoms. The main structural feature of 7 is a centrosymmetric Ti4O6 cage which is built of two seco-norcubanes Ti4O3 sharing a common Ti2O2-face. A coordination polyhedron around the titanium atoms is the distorted octahedron, with the long Ti─μ-O and short Ti─O bonds. All resulting complexes are moderately or highly active in ethylene polymerization in the presence of {3Et2AlCl + Bu2Mg} binary co-catalyst. Resulting polymers are linear ultrahigh molecular weight polyethylenes (up to 7.9 106 g/mole). Polymers are suitable for the modern processing methods – the solvent-free solid state formation of super high-strength (tensile strength over 2.0–2.4 GPa) and high-modulus (elastic modulus up to 130 GPa) oriented film tapes. © 2018 Elsevier B.V

NNNO-Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins

The unprecedented observation of odd carbon number olefins is reported during nickel- catalyzed ethylene oligomerization. Two complexes based on Co (II) and Ni (II) with novel tetradentate heteroscorpionate ligand have been synthesized and fully characterized. These complexes showed the ability to oligomerize ethylene upon activation with various organoaluminum compounds (Et2AlCl, Et3Al2Cl3, EtAlCl2, MMAO). Ni (II) based catalytic systems were sufficiently more active (up to 1900 kg·mol (Ni)−1·h−1·atm−1) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh3 as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg·mol (Ni)−1·h−1·atm−1 and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl2 produce up to 5 mol. % of odd carbon number olefins; two probable mechanisms for their formation are suggested – metathesis and β-alkyl elimination. © 2020 John Wiley & Sons, Ltd