Ligand field spectra of hydrazine complexes of NiII, and the spectrochemical position of hydrazine

Abstract

Solid nickel(II)-hydrazine complexes, Ni(N2H4)2X2 and Ni(N2Ht)3X2, have ligand-field spectra corresponding to those expected for [trans-NiN4X2] and [NiN6] chromophores respectively. This contrasts with solution spectra of hydrazine complexes, where hydrazine is often unidentate and is often only partially substituted in the coordination sphere. The present study thus affords a unique occasion to establish the spectrochemical properties of the hydrazine ligand. The spectrochemical position of hydrazine is practically coincident with that of other diamines, and higher than that of, say, ammonia. The axial field strength is unusually low, and the nephelauxetic ratio unusually high in the trans-disubstituted octahedral chromophores [NiN4X2]. These date imply that (in these complexes) hydrazine can acquire a conformation which is particularly favorable for the formation of stable σ bonds, and that the axial field is particularly weak, thus implying weak σ-covalent character of the axial bonds and hence poor σ-delocalization and low nephelauxetic effect.