Crystal structure of a zwitterionic azaallyl zirconiumamide complex bearing a Zr+-μ-CH3—B− moiety and one equivalent of n-hexane as a solvent

The zirconiumamide complex [(cyclohex-1-enyl)cyclohexylamido]bis(dicyclohexylamido)[methyltris(pentafluorophenyl)borato]zirconium(IV) hexane monosolvate, [Zr{N(C6H11)2}2{N(C6H11)(C6H9)}{BCH3(C6F5)3}]·C6H14, is zwitterionic and bears a Zr+—μ-CH3—B− moiety. The reaction of tris(dicyclohexylamido)methylzirconium with the strong Lewis acid tris(pentafluorophenyl)borane results in the formation of an azaallyl zirconium motif by the loss of H2 in one dicyclohexylamido ligand, as shown by single-crystal X-ray diffraction. The ZrIV cation is coordinated to the N atoms of two dicyclohexylamido ligands, the π-system of one azaallyl ligand, and to the μ-CH3—B unit, resulting in a distorted tetrahedral coordination environment. The Zr—N distance to the azaallyl ligand is elongated, whereas the Zr—C distance to this moiety is found to be shortened in comparison with those to the two Cy2N groups (Cy is C6H11)

Zwitterionic d⁰ Metal Complexes [(Cy₂N)₃M]⁺[(μ-Me)B(C₆F₅)₃]⁻ (M = Ti, Zr, Hf) Derived from Tris(dicyclohexylamido)methyl Metal Precursors

The synthesis and characterization of tris­(dicyclohexyl)­amido hafnium complexes ClHf­(NCy₂)₃ (<b>1-Hf</b>) and MeHf­(NCy₂)₃ (<b>2-Hf</b>) are presented. The reactions of the group 4 derivatives of this compound class (MeM­(NCy₂)₃; M = Ti (<b>2-Ti</b>), Zr (<b>2-Zr</b>), Hf (<b>2-Hf</b>)) with B­(C₆F₅)₃ are investigated. Their reactions with strong Lewis acids lead to the first examples of zwitterionic group 4 complexes employing three amido ligands at the electrophilic metal center ([(Cy₂N)₃M]⁺[(μ-Me)­B­(C₆F₅)₃]⁻). The solid-state structures of all of the betaines (<b>3-Ti</b>, <b>3-Zr</b>, <b>3-Hf</b>) are presented and compared. In all homologues the methyl group is abstracted by the Lewis acid but remains in interaction with the electron-deficient metal center, resulting in a linearly bridging methyl group. The M···C distances of <b>3-M</b> are elongated by 0.25 Å (av) in comparison to <b>2-M</b>

Zwitterionic d⁰ Metal Complexes [(Cy₂N)₃M]⁺[(μ-Me)B(C₆F₅)₃]⁻ (M = Ti, Zr, Hf) Derived from Tris(dicyclohexylamido)methyl Metal Precursors

The synthesis and characterization of tris­(dicyclohexyl)­amido hafnium complexes ClHf­(NCy₂)₃ (<b>1-Hf</b>) and MeHf­(NCy₂)₃ (<b>2-Hf</b>) are presented. The reactions of the group 4 derivatives of this compound class (MeM­(NCy₂)₃; M = Ti (<b>2-Ti</b>), Zr (<b>2-Zr</b>), Hf (<b>2-Hf</b>)) with B­(C₆F₅)₃ are investigated. Their reactions with strong Lewis acids lead to the first examples of zwitterionic group 4 complexes employing three amido ligands at the electrophilic metal center ([(Cy₂N)₃M]⁺[(μ-Me)­B­(C₆F₅)₃]⁻). The solid-state structures of all of the betaines (<b>3-Ti</b>, <b>3-Zr</b>, <b>3-Hf</b>) are presented and compared. In all homologues the methyl group is abstracted by the Lewis acid but remains in interaction with the electron-deficient metal center, resulting in a linearly bridging methyl group. The M···C distances of <b>3-M</b> are elongated by 0.25 Å (av) in comparison to <b>2-M</b>

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology of nested magnetic surfaces needed for good confinement is realized, and that the measured deviations are smaller than one part in 100,000. This is a significant step forward in stellarator research, since it shows that the complicated and delicate magnetic topology can be created and verified with the required accuracy

Major results from the first plasma campaign of the Wendelstein 7-X stellarator

After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3 1019 m-3, central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre.Peer reviewe

Major results from the first plasma campaign of the Wendelstein 7-X stellarator

\u3cp\u3eAfter completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3 10\u3csup\u3e19\u3c/sup\u3e m\u3csup\u3e-3\u3c/sup\u3e, central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre.\u3c/p\u3