Synthetic accessibility and stability rules of NASICONs

In this paper we develop the stability rules for NASICON-structured materials, as an example of compounds with complex bond topology and composition. By first-principles high-throughput computation of 3881 potential NASICON phases, we have developed guiding stability rules of NASICON and validated the ab initio predictive capability through the synthesis of six attempted materials, five of which were successful. A simple two-dimensional descriptor for predicting NASICON stability was extracted with sure independence screening and machine learned ranking, which classifies NASICON phases in terms of their synthetic accessibility. This machine-learned tolerance factor is based on the Na content, elemental radii and electronegativities, and the Madelung energy and can offer reasonable accuracy for separating stable and unstable NASICONs. This work will not only provide tools to understand the synthetic accessibility of NASICON-type materials, but also demonstrates an efficient paradigm for discovering new materials with complicated composition and atomic structure.

K1+2xNi1−xFe2(AsO4)3(x= 0,125): un nouvel arséniate à structure de type α-CrPO4

A new arsenate K1+2xNi1−xFe2(AsO4)3(x= 1/8) {potassium nickel diiron(III) tris[arsenate(V)]} was synthesized using a flux method and its crystal structure was determined from single-crystal X-ray diffraction data. This material was also characterized by qualitative energy dispersive X-ray spectroscopy (EDS) analysis. The crystal structure belongs to the α-CrPO4-structure type, space groupImma. It consists of a three-dimensional-framework built up from FeO6and Ni0.875□1.25O6-octahedra and AsO4-tetrahedra that are sharing corners and/or edges, generating tunnels running along the [010] and [001] directions in which the potassium cations are located. The proposed structural model was validated by bond-valence-sum calculations, charge-distribution (CHARDI) and Madelung energy analyses.

Chirale Erkennung bei Tris(diimin)-Metallkomplexen, 10. Vergleich der intermolekularen Wechselwirkungs- und Packungsmuster in der Reihe [Cr(bpy)3]n+(PF6)n (n = 0 – 3) / Chiral Recognition among Tris(diimine)-metal Complexes, 10. Comparison of Intermolecular Interactions and Packing Patterns in the Series [Cr(bpy)3]n+(PF6)n (n = 0–3)

Due to their conformational rigidity, the corrugated, chiral molecular structure, and the variability in the central metal and its oxidation state, [M(bpy)3]n+ complexes are particularly well suited to study chiral recognition and to identify intermolecular interaction patterns in the crystalline state. For [Cr(bpy)3]n+(PF6)n (n=0 - 3) four oxidation states are readily accessible which allows to investigate the influence of the cation/anion ratio on the observed packing patterns.The crystal structures of all four oxidation states are governed by so-called ‘π-π-interactions’. Apparently, in molecular salts the Madelung energy is less important as compared to classical inorganic salts.Interestingly, [Cr(bpy)3](PF6) and [Cr(bpy)3](PF6)2 comprise the same homochiral layers. However, while the former crystallises as true racemate, the latter spontaneously resolves into a conglomerate. This two-dimensional building block of homochiral layers is the most popular structural motif in this class of compounds which has been observed in a great variety of racemic and homochiral stackings.