Iron Pentazolate Complex: Isoelectronic Species of Ferrocene but with a Planer Structure

Energetic pentazolate compound generally releases extremely large energy in the explosion and generates environment-friendly nitrogen as the main product. Cyclo-N₅⁻ as the mono-dentate ligand always forms planer structure by σ-type bonds between center metal cation and ligands in most of the metal pentazolate complexes based on the corresponding XRD results, which is completely different from the well-known perpendicular structure of ferrocene with the η⁵-π-bonds, although it is known for us that cyclo-N₅⁻ is isoelectronic species of the pentadienide anion C₅H₅⁻. In order to understand the differences between the planer Fe(N₅)₂ and ‘sandwich-like’ Fe(η⁵-C₅H₅)₂, here we design Fe(η⁵-N₅)₂ with η⁵-π-bonds as the possible isomer of the planer Fe(N₅)₂. Besides the mono-dentate planer Fe(N₅)₂, Cyclo-N₅⁻ is possibly as a bidentate ligand to coordinate with Fe²⁺ to form η²-σ-bond. Therefore, the three isomers of Fe(N₅)₂ and its isoelectronic Fe(η⁵-C₅H₅)₂ are compared including their structures of ligands, bonding structures, coordinative pathways and reactivity in the decompositions by applying the DFT and CPMD calculation. The results indicate the formation of σ-type Fe−N bonds between Fe²⁺ and mono-dentate cyclo-N₅⁻ is the most favored.