Structure of N2H4•+ formed in X-irradiated Li(N2H5)SO4 single crystals

Abstract

X-irradiated Li(N₂H₅)SO₄ single crystals were investigated using ESR and ENDOR spectroscopy at several temperatures. The hydrazine radical cation N₂H₄^•+ was selectively produced by irradiation at room temperature. From the analysis of the orientation dependent ENDOR spectra, the ¹H-hfc tensors of the cation radical were precisely obtained and the radical structure was supported by theoretical calculations. It is suggested that the cation radical has a planar π* structure D_2h (²B_2g) in the crystal down to 230 K. By using the evaluated ¹H-hf tensor the powder ESR line shape was successfully simulated. Concomitant with the radical formation, the N–N bond of N₂H₄^•+ is suggested to reorient so as to optimize hydrogen bond interactions. ¹H-ENDOR line splitting for the N₂H₄^•+ radical was observed at temperatures below 230 K. Apparently this splitting is due to a reversible structural change where one of the NH₂ moieties in N₂H₄^•+ becomes slightly bent out of the molecular plane, whereas the other one remains planar. This deformation evidently arises from interactions between the cation radical, adjacent H₂N–NH₃⁺ molecules and the SO₄–LiO₄ framework. Interacting N₂H₅⁺···N₂H₄^•+···N₂H₅⁺ molecules along the c-axis are proposed to explain the deformation mechanism.