Structural study of p-nitrophenylhydrazonomalononitrile and its conjugate base. Evidence for extensive charge delocalization in the hydrazono anion

Abstract

The molecular structures of p-nitrophenylhydrazonomalononitrile and the tetraethylammonium salt of its conjugate base, hydrazono anion, have been determined from X-ray diffraction data. Bond and dihedral angles confirm the planar framework of both the hydrazone and the hydrazon anion. Evidence for extensive charge delocalization in the hydrazono moiety is provided by a comparison of bond lengths between the neutral and anionic species. A quinonoid-type interaction is stronger in the hydrazone than in the hydrazono anion, contrary to the results of AM1 calculations. The observed structural feature is closely related to the function of some arylhydrazonomalononitriles as efficient uncouplers of oxidative phosphorylation in mitochondrial systems.