A quantum mechanical study on the reactivity and acidity of the LiAlO2-benzoic acid soft chemical reaction
Abstract Solid α-LiAlO 2 exchanges Li + for H + when in contact with molten benzoic acid yet γ-LiAlO 2 does not. Electronic structure calculations on both solid phases show that the reason for Li being substitutable solely in α-LiAlO 2 arises mostly from the difference in Li electrophilicities. Thus, the less acidic Li atom in the α-phase is exchanged against a proton whereas the Li atom in γ-LiAlO 2 is too strong a Lewis acid for the proton to “drive out”. Furthermore, while Li atoms are more weakly bonded within the structural matrix than Al atoms, there is a significantly smaller Li-O binding energy in the α-compared to the γ-phase and the less acidic Li atom (α) is thermodynamically more labile. Finally, one finds a large difference in the energetic behavior upon dislocation of a Li atom from its equilibrium position in the α- and γ-phases. Despite having a high activation barrier, there is a finite kinetic chance for a Li atom to escape from its equilibrium position only in α-LiAlO 2 .