Iron Bispentazole Fe(η5-N5)2, a Theoretically Predicted High-Energy Compound: Structure, Bonding Analysis, Metal-Ligand Bond Strength and a Comparison with the Isoelectronic Ferrocene

Abstract

Quantum-chemical calculations with gradient-corrected (B3LYP) density functional theory have been carried out for iron bispentazole and ferrocene. The calculations predict that Fe(eta5-N5)2 is a strongly bonded complex which has D5d symmetry. The theoretically predicted total bond energy that yields Fe in the 5D ground state and two pentazole ligands is Do = 109.0 kcal mol(-1), which is only 29 kcal mol(-1) less than the calculated bond energy of ferrocene (Do = 138.0 kcal mol(-1); experimental: 158 +/- 2 kcal mol(-1)). The compound Fe(eta5-N5)2 is 260.5 kcal mol(-1) higher in energy than the experimentally known isomer Fe(N2)5, but the bond energy of the latter (Do = 33.7 kcal mol(-1)) is much less. The energy decomposition analyses of Fe(eta5-N5)2 and ferrocene show that the two compounds have similar bonding situations. The metal-ligand bonds are roughly half ionic and half covalent. The covalent bonding comes mainly from (e1g) eta5-N5- --> Fe2+ pi-donation. The previously suggested MO correlation diagram for ferrocene is nicely recovered by the Kohn-Sham orbitals. The calculated vibrational frequencies and IR intensities are reported.

Kinetic Stability and Propellant Performance of Green Energetic Materials

“…Furthermore, the pentazole anion (3) is expected to form strong ferrocene-like sandwich complexes in the presence of metal cations (e.g., Fe 2 + ), [38] which should favor its formation in solution. Since it is not inconceivable that the same might apply for oxopentazolate (4), experimentalists attempting synthesis should consider including metal ions also in this case.…”

Experimental Detection of the Pentazole Anion, N5(-)

“…Theoretical calculations from our and other (1,5,8,(13)(14)(15)(16)(17)(18)(19) research groups predict that the unknown pentazole anion (see Figure 1) has a first ionization potential and activation energy barrier toward decomposition that might be high enough to provide a stabile salt. As a result, a worldwide effort is underway to synthesize this anion.…”

Cesium and barium as honorary d elements: CsN 7 Ba as an example

“…A Fe(N 5 ) 2 ferrocene analogue has been suggested independently by Lein et al [8]. Pentazole metal compounds, like NaN 5 ,K N 5 ,M g(N 5 ) 2 , Ca(N 5 ) 2 , and Zn(N 5 ) 2 , have also been predicted recently by Burke et al [9].…”