Effect of Pressure on Crystal-Field Energy and Covalency in Octahedral Complexes of Ni2+, Co2+, and Mn2+

Abstract

The effect of pressure has been measured on the absorption spectra of NiCl₂, NiBr₂, Ni(NH₃)₆Cl₂, CoCl₂, CoBr₂, MnCl₂, and MnBr₂. The pressure shifts in every case correspond to increase in crystal field strength. To account for the shifts in a quantitative manner it is necessary to presume that the Racah parameter B decreases with increasing pressure. This can be interpreted as an increase in covalency at high pressure. From the data on MnCl₂ and MnBr₂ it is possible to establish limitations on the possible range of values of the parameter ε introduced by Koide and Pryce to describe covalency in transition metal complexes.