Li18P6N16—A Lithium Nitridophosphate with Unprecedented Tricyclic [P6N16]18− Ions

• Published in: Chemistry : a European journal 2017-02, Vol.23 (9), p.2185-2191
• Main Authors: Bertschler, Eva‐Maria, Dietrich, Christian, Janek, Jürgen, Schnick, Wolfgang
• Format: Article
• Language: English
• Subjects: Chemistry; conductivity; Crystals; Diffraction; high-pressure chemistry; nitrides; phosphates; solid-state structure; Spectrum analysis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201605316

Li18P6N16 was synthesized by reaction of LiPN2 and Li7PN4 at 5.5 GPa and 1273 K employing the multi‐anvil technique. It is the first lithium nitridophosphate obtained by high‐pressure synthesis. Moreover, it is the first example received by reaction of two ternary lithium nitrides. The combination of high‐pressure conditions with a Li3N flux enabled a complete structure determination using single‐crystal X‐ray diffraction. The hitherto unknown tricyclic [P6N16]18− anion is composed of six vertex‐sharing PN4 tetrahedra forming one vierer‐ and two additional dreier‐rings. To confirm the structure, Rietveld refinement, 7Li and 31P solid‐state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To validate the ionic properties, the migration pathways of the Li+ ions were evaluated, and the conductivity and its temperature dependence were determined by impedance spectroscopy measurements. In order to obtain a clearer picture of the formation mechanism of this compound class, different synthetic approaches were compared, enabling targeted syntheses of unprecedented P/N‐anion topologies with intriguing properties. Novel anion topology: Li18P6N16 is the first lithium nitridophosphate prepared by high‐pressure synthesis according to two different approaches. The structure contains unprecedented tricyclic anions surrounded by Li+ ions. The migration pathways of the latter were calculated by TOPOS and indicate ion conductivity, which was confirmed by impedance measurements.