Chemical bond and hybridization in nickel compounds

Abstract

By means of ultraviolet reflectance and valence band photoemission one can get a scale of ionicity for nickel halides. The fraction of ionic character of the chemical bond, from 0.72 in ${\mathrm{NiI}}_{2}$ to 0.80 in ${\mathrm{NiCl}}_{2},$ evaluated with the Phillips theory has been related to the ground state d electron counts $〈{n}_{\mathrm{dn}}〉$ calculated from $\mathrm{Ni}2p$ core photoemission. While the chemical trends of cluster model parameters are in general well reproduced, a systematic discrepancy in band gap values (2--3 eV) has been found by comparing core-level results with optical and photoconductivity data.