The Oxidation State of Ni in the Nickel Oxide Electrode and Related Nickel Oxide Compounds: II. Geometric Evidence.

The electronic structures of the nickel oxide electrode NOE, NiOxOH2-x for x0-1.6 and the related nickel oxide materials including the NiO- LiNiO2 - NiO2 series and the Ni4 compounds, KNiO2IO4 and BaNiO3, have been investigated utilizing geometric data such as the Ni-OH and Ni-O bond lengths published in the literature. The electronic structures deduced from these bond lengths agree with those found using spectroscopic data, which were presented in the preceding paper. In addition, the observed shortening of the Ni-O bond length in the NiO - LiNiO2 - NiO2 series is shown to arise from covalent shortening. The implications of this newly proposed electronic structures are as follows i the charging reaction for the NOE can be viewed as OH- Ni2 -- O- Ni2 H e-, where Ni2 reminds us that the OH- and O- anions are attached to the Ni2 ion, which remain unchanged ii the electron conduction in the charged NOE is in the oxygen layer and iii the coloration of the NOE upon charging is due to the 3d Ni2 -- 2p O-, metal-to-oxygen, charge transfer in the charged NOE.