Cationic Pb2 Dumbbells Stabilized in the Highly Covalent Lead Nitridosilicate Pb2Si5N8

Cationic Pb₂ dumbbells were found in the first representative of a nitridosilicate containing a metal from the right side of the Zintl border. Intercationic Pb−Pb distances are in the range known from Zintl anions, which exhibit attractive interactions between Pb atoms. Indeed, DFT calculations combined with Raman spectroscopy show evidence for an attractive covalent interaction between neighboring Pb cations in Pb₂Si₅N₈.

Abstract

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.

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