High-Pressure Synthesis of Pd(N5)2·N2: One-Dimensional Pentazolate Coordination Polymer with Guest Nitrogen Molecules

Abstract

Pentazolates, an emerging family of nitrogen-rich materials featuring the aromatic cyclo-N5– anion, typically crystallize as nonpolymeric or three-dimensional (3D) coordination networks, whereas low-dimensional (1D and 2D) forms remain exceptionally rare. Here, we exploit the square-planar coordination preference of d8 Pd2+ to achieve dimensional control and synthesize Pd(N5)2·N2, the first high-pressure 1D pentazolate coordination polymer. The compound forms in a laser-heated diamond anvil cell at 118 GPa and 2900 K, while lower-pressure experiments yield only PdN2 dinitride. The crystal structure of Pd(N5)2·N2 was determined by synchrotron single-crystal X-ray diffraction from a multigrain sample and corroborated by density functional theory calculations. This discovery establishes a strategy for engineering low-dimensional pentazolate-based materials and potentially enabling dimensional control in other polynitrides. We also provide an overview of experimentally synthesized high-pressure pentazolates and discuss how cation properties influence their synthesis pressures, thereby improving understanding of pentazolate formation pressures.