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The Local Hard−Soft Acid−Base Principle: A Critical Study
(ACS, 1997) Roy, Ram Kinkar
The recently proposed local hard−soft acid−base principle characterizes the reactive centers of two systems on the basis of equal Fukui functions or/and equal local softnesses. We make a quantum chemical study of this principle using ab initio and density functional calculations in cases where the global softnesses of the reacting systems are different. We consider reactions of a dimer cluster model of faujasite X-type zeolite with the probe molecules CO, NH3, and H2O.
Local reactivity descriptors to predict the strength of Lewis acid sites in alkali cation-exchanged zeolites
(Elsiever, 2004-05) Roy, Ram Kinkar
Lewis acidity of alkali cation-exchanged zeolite is studied using local reactivity descriptors based on hard-soft acid–base (HSAB) concept. The local softness for nucleophilic attack (sx+), local softness for electrophilic attack (sx−) and their ratio, which is called `relative electrophilicity' (sx+/sx−), are calculated for the exchanged cations and Lewis acidity of the cations is found to decrease in the order: Li+ > Na+ > K+ > Rb+ > Cs+. Calculated blue shift of CO vibrational frequency (Δν) and interaction energy of CO molecule with alkali cation-exchanged zeolite clusters vary linearly with sx+/sx− values.