Stabilization of magnesium dichloride surface defects by mono- and bidentate donors

We evaluate the stabilization of magnesium dichloride surfaces by mono- and bidentate electron donors typically used in heterogeneous Ziegler-Natta olefin polymerization catalysis: tetrahydrofuran, ethyl benzoate, 2,2-dimethyl 1,3-dimethoxy propane, 2S,2R-di(2-tetrahydrofuryl) propane, dimethyl phthalate, and dimethyl succinate. Structural defects are generated into the ideal (104) and (110) MgCl₂ surfaces, and both ideal and defective surfaces are saturated by the donors. The quantum chemical calculations (PBE0 density functional theory method), performed with periodic boundary conditions, show that all donors stabilize all surfaces. Stabilization energy of the surfaces by the ethers is linearly dependent on surface site coordination, the four-coordinate (110) surface being stabilized the most, the five-coordinate (104) surface the least, and all the defective structure fitting in between the two limiting cases of the ideal surfaces. However, the esters can additionally stabilize the defective surfaces depending on the steric effects at the point of coordination. The results suggest that defects need to be taken into account to properly address the surface-donor complexation.