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 D2h (2B2g) 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.