High Surface Area and Z′ in a Thermally Stable 8-fold Polycatenated Hydrogen-bonded Framework

1,3,5-Tris(4-carboxyphenyl)benzene assembles into an intricate 8-fold polycatenated assembly of (6,3) hexagonal nets formed through hydrogen bonds and π-stacking. One polymorph features 56 independent molecules in the asymmetric unit, the largest Z′ reported to date. The framework is permanently porous, with a BET surface area of 1095 m2 g−1 and readily adsorbs N2, H2 and CO2

The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Synthesis, Crystal Structure, and Magnetic Properties of R₂Mg₃SiPn₆ (R = La, Ce; Pn = P, As)

Four new quaternary pnictides, R₂Mg₃SiPn₆ (R = La, Ce; Pn = P, As), were synthesized via high-temperature solid-state reactions and gas-phase transport reactions with iodine. Their crystal structures were determined by single crystal X-ray diffraction. All four compounds are isostructural and crystallize in a new structure type in the orthorhombic space group <i>Pnma</i> (No. 62, <i>Z</i> = 4), Pearson symbol <i>oP</i>48. The crystal structures of R₂Mg₃SiPn₆ are composed of two-dimensional puckered MgP₃ layers, which are connected in a three-dimensional framework by P–P dimers and MgSiP₄ double-tetrahedral chains. Rare-earth cations are encapsulated inside the channels of the framework running along [010]. Quantum-chemical calculations predict that La₂Mg₃SiP₆ is an indirect narrow bandgap semiconductor. The Mg–P bonding in MgP₄ tetrahedra and MgP₆ octahedra was analyzed by means of crystal orbital Hamilton population (COHP) analysis. Magnetic characterization of Ce-containing compounds confirmed the trivalent nature of cerium atoms and revealed complex ferrimagnetic ordering at low temperatures

A Solution for Solution-Produced β‑FeSe: Elucidating and Overcoming Factors that Prevent Superconductivity

A new low-temperature solvothermal synthesis of superconducting β-FeSe has been developed using elemental iron and selenium as starting materials. We have shown that syntheses performed in aerobic conditions resulted in the formation of nonsuperconducting antiferromagnetic β-FeSe, whereas syntheses performed in ultra-dry and oxygen-free conditions produced superconducting β-FeSe. Detailed characterization of both types of samples with magnetometry, resistivity, Mössbauer spectroscopy, synchrotron X-ray and neutron powder diffraction, and pair-distribution function analysis uncovered factors that trigger the loss of superconductivity in β-FeSe. Vacancies in the iron sublattice and the incorporation of disordered oxygen-containing species are typical for nonsuperconducting antiferromagnetic samples, whereas a pristine structure is required to preserve superconductivity. Exposure to ambient atmosphere resulted in the conversion of superconducting samples to antiferromagnetic ones. This synthetic method creates new possibilities for soft chemistry approaches to the synthesis and modification of iron-based superconductors

NH₄FeCl₂(HCOO): Synthesis, Structure, and Magnetism of a Novel Low-Dimensional Magnetic Material

Solvothermal synthesis was used to create a low-dimensional iron­(II) chloride formate compound, NH₄FeCl₂­(HCOO), that exhibits interesting magnetic properties. NH₄FeCl₂­(HCOO) crystallizes in the monoclinic space group <i>C</i>2/<i>c</i> (No. 15) with <i>a</i> = 7.888(1) Å, <i>b</i> = 11.156(2) Å, <i>c</i> = 6.920(2) Å, and β = 108.066(2)°. The crystal structure consists of infinite zigzag chains of distorted Fe²⁺-centered octahedra linked by μ₂-Cl and syn-syn formate bridges, with interchain hydrogen bonding through NH₄⁺ cations holding the chains together. The unique Fe²⁺ site is coordinated by four equatorial chlorides at a distance of 2.50 Å and two axial oxygens at a distance of 2.08 Å. Magnetic measurements performed on powder and oriented single-crystal samples show complex anisotropic magnetic behavior dominated by antiferromagnetic interactions (<i>T</i>_N = 6 K) with a small ferromagnetic component in the direction of chain propagation. An anisotropic metamagnetic transition was observed in the ordered state at 2 K in an applied magnetic field of 0.85–3 T. ⁵⁷Fe Mössbauer spectroscopy reveals mixed hyperfine interactions below the ordering temperature, with strong electric field gradients and complex noncollinear arrangement of the magnetic moments

Chemical Excision of Tetrahedral FeSe₂ Chains from the Superconductor FeSe: Synthesis, Crystal Structure, and Magnetism of Fe₃Se₄(en)₂

Fragments of the superconducting FeSe layer, FeSe₂ tetrahedral chains, were stabilized in the crystal structure of a new mixed-valent compound Fe₃Se₄(en)₂ (en = ethylenediamine) synthesized from elemental Fe and Se. The FeSe₂ chains are separated from each other by means of Fe­(en)₂ linkers. Mössbauer spectroscopy and magnetometry reveal strong magnetic interactions within the FeSe₂ chains which result in antiferromagnetic ordering below 170 K. According to DFT calculations, anisotropic transport and magnetic properties are expected for Fe₃Se₄(en)₂. This compound offers a unique way to manipulate the properties of the Fe–Se infinite fragments by varying the topology and charge of the Fe-amino linkers