High‐Pressure Synthesis of a Nitrogen‐Rich Inclusion Compound ReN₈⋅x N₂ with Conjugated Polymeric Nitrogen Chains

Abstract

A nitrogen-rich compound, ReN ⋅x N , was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, ReN ⋅x N is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [-N=N-] that constitute the framework have not been previously observed in any compound. Ab initio calculations on ReN ⋅x N provide strong support for the experimental results and conclusions.

Synthesis of FeN4at 180 GPa and its crystal structure from a submicron-sized grain

“…Recently, Bykov and co-workers synthesized two compounds containing polymeric nitrogen chains, viz. an inclusion compound ReN 8 ÁN 2 (Bykov et al, 2018b) and iron tetranitride, FeN 4 (Bykov et al 2018a) via the reaction between Fe or Re and nitrogen in a laser-heated diamond anvil cell (DAC). The crystal structures of these compounds were studied at pressures up to 135 GPa by means of single-crystal X-ray diffraction (SCXRD).…”

Novel Rhenium Carbides at 200 GPa

“…They are built up of CRe 6 or NRe 6 trigonal prisms, and even Re–C and Re–N interatomic distances at the same pressures are very similar , . Contrary, the structures of ReC 2 and ReN 2 have nothing in common and there are no signs of formation of rhenium polycarbides with more than two carbon atoms per a formula unit at least up to 180(7) GPa and 3000 ± 300 K, unlike to the rhenium‐nitrogen system . Such differences can be linked a tendency of nitrogen to form di‐nitrogen and poly‐nitrogen anions (based on N4 units, ) at high‐pressures and high‐temperatures (HPHT), whereas rhenium carbides do not reveal formation of polycarbon anions at such conditions.…”

High‐Pressure Synthesis of Metal–Inorganic Frameworks Hf4N20⋅N2, WN8⋅N2, and Os5N28⋅3 N2 with Polymeric Nitrogen Linkers

“…The structure of WN 8 ⋅N 2 has the orthorhombic space group Immm with one W and two N atomic positions. WN 8 ⋅N 2 is isostructural to previously reported inclusion compound ReN 8 ⋅N 2 . W atoms are eightfold coordinated by four planar polydiazenediyl nitrogen chains with conjugated π‐systems (Figure g, Scheme ).…”

“…The frameworks of all of the compounds 1 – 3 and ReN 8 ⋅N 2 are built of a set of standard units: N−N dumbbells, discrete N 3− anions and polydiazenediyl chains. An important factor for the stability of the polydiazenediyl chains is a resonance, which imparts partial double‐bond character for nitrogen–nitrogen bonds.…”

“…This imposes additional restrictions on the geometry of the system, namely, because of the sp 2 hybridization of nitrogen atoms, a metal must be in the same plane as the coordinating nitrogen chain. It is indeed the case for the compounds 1 – 3 studied in the current work and ReN 8 ⋅N 2 , which enables us to suggest that the covalent character of the transition metal–nitrogen bonds is one of the important factors for the framework architecture: the imposed geometry constraints lead to the formation of framework structures, rather than to the densest packing of atoms even at ultrahigh pressures. Another factor stabilizing the compounds 1 – 3 is the inclusion of nitrogen molecules into the pores.…”