Predicted Polymeric and Layered Covalent Networks in Transition Metal Pentazolate M(cyclo-N5)x Phases at Ambient and High Pressure: Up to 20 Nitrogen Atoms per Metal

In this work, we report an ab initio prediction of 12 different solid-state phases based on the combination of pentazolate anions (cyclo-N5–) and transition metals (Hf4+, Rh3+, Ir3+, Fe2+, Ni2+, Pd2+, and Ag+). To our delight, multiple coordination networks are discovered at ambient and high pressure, ranging from one-dimensional to three-dimensional metal–inorganic frameworks. The viability of each predicted M­(cyclo-N5)x, with x = 1–4, is investigated by verifying their thermodynamic, dynamic, and thermal stabilities. Metal-pentazolate interactions are indeed expected to stabilize this cyclic nitrogen ring, enabling the synthesis of these compounds. For M = Fe, Ni, and Pd, two-dimensional lamellar compounds are obtained, showing moderate exfoliation energies, suggesting their possible experimental synthesis. Finally, most of the predicted phases display excellent detonation properties and combustion enthalpy. As expected by their high nitrogen content (up to 20 nitrogen atoms per metal in Hf­(N5)4), these metal-pentazolate complexes might serve as new high-energy density materials.