High-nitrogen-content energetic BNn+ (n = 4–16) clusters

Abstract

Nitrogen-rich materials have attracted considerable attention in recent years as potential high-energy-density materials (HEDMs). However, their metastability poses substantial challenges for synthesis under ambient conditions. Here, we employ a novel strategy to explore energetic and structural features of the nitrogen-rich BN_n⁺ (n = 4–16) clusters by doping with the light non-metal boron. A series of boron-doped nitrogen clusters, with nitrogen content ranging from 83% to 96%, were obtained by laser ablation and analyzed via time-of-flight mass spectrometry. The results indicate that the BN₆⁺ cluster is dominant in the mass spectrum, while the BN₁₂⁺ cluster exhibits the highest abundance after cooling the cluster source with liquid nitrogen. To further confirm the experimental results, extensive structure searches for BN_n⁺ (n = 4–16) clusters are conducted using the CALYPSO method and density functional theory (DFT) calculations. The calculations show that BN₆⁺ (singlet) exhibits a planar [B(NN)₃]⁺ three-branched geometry with D_3h symmetry, while BN₁₂⁺ (singlet) adopts a [(linear-N₆)B(N₃)₂]⁺ branched geometry with C₁ symmetry. Stability analyses reveal the relatively high structural stabilities of BN₆⁺ and BN₁₂⁺ clusters and agree well with the experimental findings. Notably, the gas-phase enthalpy of formation of the BN₁₂⁺ cluster is remarkably high, −1385.10 kJ mol⁻¹, suggesting its potential as a high-energy building block for HEDM construction. The present findings enhance the structural diversities of non-metal-doped nitrogen clusters, and offer new perspectives for the rational design and synthesis of nitrogen-rich energetic materials.