Highly condensed nitridosilicates doped with Eu or Ce play an important role in saving energy by converting the blue light of (In,Ga)N-LEDs. Although nitridosilicates are known for great structural variety based on covalent anionic Si-N networks, elemental variety is restricted. Presenting a significant extension of the latter, this work describes a general access to open-shell transition-metal nitridosilicates. As a proof-of-principle, the first iron nitridosilicate, namely Fe Si N , was prepared by exchanging Ca in α-Ca Si N applying a FeCl melt (salt metathesis). The title compound was analyzed by powder X-ray diffraction, EDX, ICP-OES, combustion analysis, TG/DSC, Mössbauer spectroscopy and magnetic susceptibility measurements. Furthermore, the structure of α-Ca Si N was determined at 1073 and 1173 K confirming the anionic network of α-Ca Si N providing possible migration pathways for the ion-exchange reaction.
Nitridosilicates represent an intriguing class of materials and are typically made up of highly condensed tetrahedral network structures. Alkaline-earth nitridosilicates emerged as unique host materials for Eu doped luminophores which found broad application in phosphor-converted (pc)-LEDs. In contrast to common strategies of preparing nitridosilicates by bottom-up syntheses, we have now succeeded to post-synthetically design nitridosilicates by ion exchange in metal halide melts. We describe the syntheses of hitherto unknown but predicted alkaline-earth nitridosilicates, Mg Si N and β-Ca Si N . Both compounds were obtained by ion exchange starting from pre-synthesized nitridosilicates. In situ investigations of the ion-exchange process show that the Si-N network topology remains preserved. Therefore the reaction offers a significant increase of synthetic control with respect to classical bottom-up syntheses.
Due to the weak oxidative force of N2, nitrides are only typically formed with the less electronegative metals. Meeting this challenge, we here present Pb2Si5N8, the first nitridosilicate containing highly electron‐affine cations of a metal from the right side of the Zintl border. By using advanced synchrotron X‐ray diffraction, the crystal structure was determined from a tiny single crystal of 1×3×3 μm3 in size, revealing a significantly different bonding situation compared to all other nitridosilicates known so far. Indeed, DFT calculations confirm distinct amounts of covalency not only between Pb and N but also between formal Pb2+ cations. Thus, unprecedented cationic Pb2 dumbbells with a stretching vibration at 117 cm−1 were found in Pb2Si5N8, the first representative of a crystallographically elucidated lead nitride, stabilized by high amounts of covalency.
Based on the known linking options of their fundamental building unit, that is the SiN4 tetrahedron, nitridosilicates belong to the inorganic compound classes with the greatest structural variability. Although facilitating the discovery of novel Si–N networks, this variability represents a challenge when targeting non‐stoichometric compounds. Meeting this challenge, a strategy for targeted creation of vacancies in highly condensed nitridosilicates by exchanging divalent M2+ for trivalent M3+ using the ion exchange approach is reported. As proof of concept, the first Sc and U nitridosilicates were prepared from α‐Ca2Si5N8 and Sr2Si5N8. Powder X‐ray diffraction (XRD) and synchrotron single‐crystal XRD showed random vacancy distribution in Sc0.2Ca1.7Si5N8, and partial vacancy ordering in U0.5xSr2−0.75xSi5N8 with x≈1.05. The high chemical stability of U nitridosilicates makes them interesting candidates for immobilization of actinides.
The crystal structure of the title compound, hexaaquadichloridoeuropium(III) chloride, was redetermined with modern crystallographic methods. In comparison with the previous study [Lepertet al.(1983).Aust. J. Chem.36, 477–482], it could be shown that the atomic coordinates of some O atoms had been confused and now were corrected. Moreover, it was possible to freely refine the positions of the H atoms and thus to improve the accurracy of the crystal structure. [EuCl2(H2O)6]Cl crystallizes with the GdCl3·6H2O structure-type, exhibiting discrete [EuCl2(H2O)6]+cations as the main building blocks. The main blocks are linked with isolated chloride anionsviaO—H...Cl hydrogen bonds into a three-dimensional framework. The Eu3+cation is located on a twofold rotation axis and is coordinated in the form of a Cl2O6square antiprism. One chloride anion coordinates directly to Eu3+, whereas the other chloride anion, situated on a twofold rotation axis, is hydrogen bonded to six octahedrally arranged water molecules.
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