Bulking up CpBIG: A Penta-Terphenyl Cyclopentadienyl Ligand

The modification of cyclopentadienyl ligands with carefully selected substituents is a widely used strategy to tune their steric and electronic properties. We describe the synthesis of an extremely bulky penta-terphenyl cyclopentadienyl ligand (CpT5) by arylation of cyclopentadiene. Deprotonation reactions with various group 1 metals and bases afforded a complete series of alkali metal salts MCpT5 with M = Li to Cs. The compounds were isolated as solvate-free salts, which were characterized by multinuclear NMR spectroscopy, UV-vis spectroscopy and elemental analysis. Single-crystal X-ray diffraction studies on LiCpT5, NaCpT5 (crystallized as a solvate with one THF molecule per formula unit) and KCpT5 revealed the formation of metallocene-like sandwich structures in the solid state.

Crystal structure of diethanolbis(thiocyanato)bis(urotropine)cobalt(II) and tetraethanolbis(thiocyanato)cobalt(II)–urotropine (1/2)

The reaction of one equivalent Co(NCS)2 with four equivalents of urotropine (hexamethylenetetramine) in ethanol leads to the formation of two compounds, namely, bis(ethanol-κO)bis(thiocyanato-κN)bis(urotropine-κN)cobalt(II), [Co(NCS)2(C6H12N4)2(C2H6O)2] (1), and tetrakis(ethanol-κO)bis(thiocyanato-κN)cobalt(II)–urotropine (1/2), [Co(NCS)2(C2H6O)4]·2C6H12N4 (2). In 1, the Co cations are located on centers of inversion and are sixfold coordinated by two terminal N-bonded thiocyanate anions, two ethanol and two urotropine ligands whereas in 2 the cobalt cations occupy position Wyckoff position c and are sixfold coordinated by two anionic ligands and four ethanol ligands. Compound 2 contains two additional urotropine solvate molecules per formula unit, which are hydrogen bonded to the complexes. In both compounds, the building blocks are connected via intermolecular O—H...N (1 and 2) and C—H...S (1) hydrogen bonding to form three-dimensional networks.

Domain matching epitaxy stabilized metastable, tetragonal BiFeO3 on symmetry-mismatched c-plane ZnO

We report the stabilization of metastable tetragonal BiFeO3 epilayer on ZnO(0001) surface. X-ray reciprocal space map characterizations show that the BiFeO3 film is of true tetragonal symmetry, but not the commonly observed monoclinic structure. The critical thickness of the tetragonal BiFeO3 is higher than 140 nm, much larger than that reported previously. Despite the considerable lattice mismatch and symmetry mismatch, tetragonal BiFeO3 can be formed on ZnO(0001) though domain matching epitaxy which is featured by anisotropic growth. We show that by taking into account the elastic energy during the initial semi-coherent growth, the tetragonal phase is lower than the thermally stable rhombohedral phase in total energy by 70 meV per formula unit. Moreover, local piezoelectric characterizations reveal a coercive field of 360 kV/cm and a piezoelectric constant of 48 pm/V. The integration of tetragonal BiFeO3 with robust ferroelectricity on the platform of ZnO has potentials for all-oxide electronics applications.

Direction Curves Associated with Darboux Vectors Fields and Their Characterizations

In this paper, we consider the Darboux frame of a curve α lying on an arbitrary regular surface and we use its unit osculator Darboux vector D ¯ o , unit rectifying Darboux vector D ¯ r , and unit normal Darboux vector D ¯ n to define some direction curves such as D ¯ o -direction curve, D ¯ r -direction curve, and D ¯ n -direction curve, respectively. We prove some relationships between α and these associated curves. Especially, the necessary and sufficient conditions for each direction curve to be a general helix, a spherical curve, and a curve with constant torsion are found. In addition to this, we have seen the cases where the Darboux invariants δ o , δ r , and δ n are, respectively, zero. Finally, we enrich our study by giving some examples.

Assessing the importance of cation size in the tetragonal-cubic phase transition in lithium garnet electrolytes.

Lithium garnets are promising solid-state electrolytes for next generation lithium-ion batteries. These materials have high ionic conductivity, a wide electrochemical window and stability with Li metal. However, lithium garnets have a maximum limit of 7 lithium atoms per formula unit (e.g. La3Zr2Li7O12), before the system transitions from a cubic to a tetragonal phase with poor ionic mobility. This arises from full occupation of the Li sites. Hence, the most conductive lithium garnets have Li between 6-6.55 Li per formula unit, which maintains the cubic symmetry and the disordered Li sub-lattice. The tetragonal phase, however, forms the highly conducting cubic phase at higher temperatures, thought to arise from increased cell volume and entropic stabilisation permitting Li disorder. However, little work has been undertaken in understanding the controlling factors of this phase transition, which could enable enhanced dopant strategies to maintain room temperature cubic garnet at higher Li contents. Here, a series of nine tetragonal garnets were synthesised and analysed via variable temperature XRD to understand the dependence of site substitution on the phase transition temperature. Interestingly the octahedral site cation radius was identified as the key parameter for the transition temperature with larger or smaller dopants altering the transition temperature noticeably. A site substitution was, however, found to make little difference irrespective of significant changes to cell volume.

On the mixing time of coordinate Hit-and-Run

We obtain a polynomial upper bound on the mixing time $T_{CHR}(\epsilon)$ of the coordinate Hit-and-Run (CHR) random walk on an $n-$ dimensional convex body, where $T_{CHR}(\epsilon)$ is the number of steps needed to reach within $\epsilon$ of the uniform distribution with respect to the total variation distance, starting from a warm start (i.e., a distribution which has a density with respect to the uniform distribution on the convex body that is bounded above by a constant). Our upper bound is polynomial in n, R and $\frac{1}{\epsilon}$ , where we assume that the convex body contains the unit $\Vert\cdot\Vert_\infty$ -unit ball $B_\infty$ and is contained in its R-dilation $R\cdot B_\infty$ . Whether CHR has a polynomial mixing time has been an open question.

Jadeite and its relatives: fake news or a real tool to constrain shock conditions?

Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Sometimes, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)M2(Al)M1(Si2)TO6 – (Ca)M2(Al)M1(AlSi)TO6 – (□)M2(Si)M1(Si2)TO6 with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields and synthesis pathways, considered together with textural constraints, have specific implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences puts in a new light many previous conclusions about the shock histories preserved in particular meteorites.

Crystal structure and Hirshfeld surface analysis of bis(6,7,8,9-tetrahydro-11H-pyrido[2,1-b]quinazolin-5-ium) tetrachloridozincate

The title compound, (C12H15N2)2[ZnCl4], is a salt with two symmetrically independent, essentially planar heterocyclic cations and a slightly distorted tetrahedral chlorozincate dianion. N—H...Cl hydrogen bonds link these ionic constituents into a discrete aggregate, which comprises one formula unit. The effect of hydrogen bonding is reflected in the minor distortions of the [ZnCl4]2− moiety: distances between the cation and chlorido ligands engaged in classical hydrogen bonds are significantly longer than the others. Secondary interactions comprise C—H...π hydrogen bonding and weak π–π stacking. A Hirshfeld surface analysis indicates that the most abundant contacts in packing stem from H...H (47.8%) and Cl...H/H...Cl (29.3%) interactions.

Simultaneous tuning of the magnetic anisotropy and thermal stability of $$\alpha ^{''}$$-phase Fe$$_{16}$$N$$_{2}$$

Simultaneously enhancing the uniaxial magnetic anisotropy ($$K_u$$ K u ) and thermal stability of $$\alpha ^{''}$$ α ′ ′ -phase Fe$$_{16}$$ 16 N$$_{2}$$ 2 without inclusion of heavy-metal or rare-earth (RE) elements has been a challenge over the years. Herein, through first-principles calculations and rigid-band analysis, significant enhancement of $$K_u$$ K u is proposed to be achievable through excess valence electrons in the Fe$$_{16}$$ 16 N$$_{2}$$ 2 unit cell. We demonstrate a persistent increase in $$K_u$$ K u up to 1.8 MJ m$$^{\text {-}3}$$ - 3 , a value three times that of 0.6 MJ m$$^{\text {-}3}$$ - 3 in $$\alpha ^{''}$$ α ′ ′ -Fe$$_{16}$$ 16 N$$_{2}$$ 2 , by simply replacing Fe with metal elements with more valence electrons (Co to Ga in the periodic table). A similar rigid-band argument is further adopted to reveal an extremely large $$K_u$$ K u up to 2.4 MJ m$$^{\text {-}3}$$ - 3 in (Fe$$_{0.5}$$ 0.5 Co$$_{0.5}$$ 0.5 )$$_{16}$$ 16 N$$_{2}$$ 2 obtained by replacing Co with Ni to Ga. Such a strong $$K_u$$ K u can also be achieved with the replacement by Al, which is isoelectronic to Ga, with simultaneous improvement of the phase stability. These results provide an instructive guideline for simultaneous manipulation of $$K_u$$ K u and the thermal stability in 3d-only metals for RE-free permanent magnet applications.

Experimental recalibration of the Cr-in-clinopyroxene geobarometer: improved precision and reliability above 4.5 GPa

The pressure dependence of the exchange of Cr between clinopyroxene and garnet in peridotite is applicable as a geobarometer for mantle-derived Cr-diopside xenocrysts and xenoliths. The most widely used calibration (Nimis and Taylor Contrib Miner Petrol 139: 541–554, 2000; herein NT00) performs well at pressures below 4.5 GPa, but has been shown to consistently underestimate pressures above 4.5 GPa. We have experimentally re-examined this exchange reaction over an extended pressure, temperature, and compositional range using multi-anvil, belt, and piston cylinder apparatuses. Twenty-nine experiments were completed between 3–7 GPa, and 1100–1400 °C in a variety of compositionally complex lherzolitic systems. These experiments are used in conjunction with several published experimental datasets to present a modified calibration of the widely-used NT00 Cr-in-clinopyroxene (Cr-in-cpx) single crystal geobarometer. Our updated calibration calculates P (GPa) as a function of T (K), CaCr Tschermak activity in clinopyroxene $$\left( {a_{{{\text{CaCrTs}}}}^{{{\text{cpx}}}} } \right)$$ a CaCrTs cpx , and Cr/(Cr + Al) (Cr#) in clinopyroxene. Rearranging experimental results into a 2n polynomial using multiple linear regression found the following expression for pressure:$$P\left( {{\text{GPa}}} \right) = 11.03 + \left( { - T{ }\left( {\text{K}} \right){\text{ ln}}(a_{{{\text{CaCrTs}}}}^{{{\text{cpx}}}} ) \times 0.001088{ }} \right) + \left( {1.526 \times {\text{ln}}\left( {\frac{{{\text{Cr}}\#^{{{\text{cpx}}}} }}{{T{ }\left( {\text{K}} \right)}}} \right)} \right){ }$$ P GPa = 11.03 + - T K ln ( a CaCrTs cpx ) × 0.001088 + 1.526 × ln Cr # cpx T K where $${\text{Cr}}\#^{{{\text{cpx}}}} = \left( {\frac{{{\text{Cr}}}}{{{\text{Cr}} + {\text{Al}}}}} \right)$$ Cr # cpx = Cr Cr + Al , $$a_{{{\text{CaCrTs}}}}^{{{\text{cpx}}}} = {\text{Cr}} - 0.81 \cdot {\text{Cr}}\#^{{{\text{cpx}}}} \cdot \left( {{\text{Na}} + {\text{K}}} \right),$$ a CaCrTs cpx = Cr - 0.81 · Cr # cpx · Na + K , with all mineral components calculated assuming six oxygen anions per formula unit in clinopyroxene.Temperature (K) may be calculated through a variety of geothermometers, however, we recommend the NT00 single crystal, enstatite-in-clinopyroxene (en-in-cpx) geothermometer. The pressure uncertainty of our updated calibration has been propagated by incorporating all analytical and experimental uncertainties. We have found that pressure estimates below 4 GPa, between 4–6 GPa and above 6 GPa have associated uncertainties of 0.31, 0.35, and 0.41 GPa, respectively. Pressures calculated using our calibration of the Cr-in-cpx geobarometer are in good agreement between 2–7 GPa, and 900–1400 °C with those estimated from widely-used two-phase geobarometers based on the solubility of alumina in orthopyroxene coexisting with garnet. Application of our updated calibration to suites of well-equilibrated garnet lherzolite and garnet pyroxenite xenoliths and xenocrysts from the Diavik-Ekati kimberlite and the Argyle lamproite pipes confirm the accuracy and precision of our modified geobarometer, and show that PT estimates using our revised geobarometer result in systematically steeper paleogeotherms and higher estimates of the lithosphere‒asthenosphere boundary compared with the original NT00 calibration.