Pentazolate Anion: A Rare and Preferred Five-Membered Ligand for Constructing Pentasil-Zeolite Topology Architectures

As the fourth full-nitrogen structure, the pentazolate anion (cyclo-N₅ ^- ) was highly coveted for decades. In 2017, the first air-stable non-metal pentazolate salt, (N₅ )₆ (H₃ O)₃ (NH₄ )₄ Cl, was obtained, representing a milestone in this field. As the latest member of the azole family, cyclo-N₅ ^- is comprised of five nitrogen atoms. Although significant attention has been paid to the potential of cyclo-N₅ ^- as an energetic material, its poor thermostability hinders any practical application. However, the unique ring structure and multiple coordination capability of cyclo-N₅ ^- provide a platform for the fabrication of various structures, among which pentasil-zeolite topologies are the most intriguing. In addition, the introduction of structure-directing auxiliaries enables the self-assembly of diverse topological architectures, potentially imparting cyclo-N₅ ^- with the potential to impact wide-ranging areas of coordination chemistry and topology. In this minireview, different pentasil-zeolite topologies based on metal-pentazolate frameworks are evaluated. To date, three zeolitic and zeolite-like topologies have been reported, namely the melanophlogite (MEP), chibaite (MTN), and unj topologies. The MEP topology consists of two nanocages, Na₂₀ N₆₀ and Na₂₄ N₆₀ , whereas the MTN topology contains Na₂₀ N₆₀ and Na₂₈ N₈₀ nanocages. Furthermore, the unj topology features multiple homochiral channels consisting of two helical chains. Various possible strategies for obtaining additional pentasil-zeolite topologies are also discussed.