I want to calculate optical basicity of some oxides like Silica powder, Manganese oxides, Iron oxides etc. But I came across many formulas for the same in the literature. Which one to choose and why?
See
https://hal-univ-artois.archives-ouvertes.fr/hal-00103593/document
The optical basicity is built on Lewis acidity concept and is particularly adapted to the study of non aqueous non protonated systems. This parameter first obtained from UV spectroscopic measurements is a ‘measure’ of the donating electron power of O2- to the Mn+ cation in MOy oxideIndeed the polarizing power of Mn+ influences the capacity of O2- ions to give a part of their electronic charge to other cations in the solid phase, and as such it depends on M coordination. Therefore Λ characterizes the electron acceptor power of the Mn+ cation as well as the electron donor power of O2-, and the result is that it characterizes the acidity of the whole solid vs. the same O2- base. For example, Λ MgO = 0.78 (Λ VIMg2+ = 0.78, in which valence and coordination of VIMg2+ are VI and +2). The reference chosen by Duffy et al. is CaO for which Λ = 1.0. Duffy’s scale is satisfactory for most s-p oxides but not for transition metal oxides. Examples are WO3, MoO3 and V2O5, the optical basicity Λ of which was found greater than 1.0 which is the value of basic CaO.
For CaO, SiO2 select Duffy’s scale
The main reason is that the optical basicity of transition metal oxides cannot be directly measured because the own d orbitals of cations are involved and because their metal-oxygen bonds have an ioniccovalent character. This problem was side-stepped by Portier et al.9,10 who succeeded in building a similar scale, but based that time on a new parameter, the Iono-Covalent Parameter ICP. ICP, which is an adimensional number, accounts for the influence of the covalence of metal-oxygen bond on the acid strength of the metallic cation, and is calculated by equation [3]: ICP = log P - 1.38χ + 2.07 [3] where P is the polarizing power of the cation (P = z/r2 , z = formal charge, r = Shannon ionic radius.
For TiO2 select Iono-Covalent Parameter ICP
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