The ability to control the microstructure of magnesium dichloride (MgCl2) crystallites by electron donors was demonstrated by quantum chemical calculations, using methanol as a model donor. Investigation of sets of differently shaped MgCl2 crystallites showed the dominance of the five-fold coordinated (1 0 0) crystal surface over the four-fold coordinated (1 1 0) surface to emerge as a factor increasing crystallite stability. To study the role of electron donors in controlling MgCl2 crystallite shape, crystallites were saturated with methanol. The stability order of the crystallites was significantly affected by donor adsorption. Reverse to the case of pure MgCl2, crystallites with the highest (1 1 0) to (1 0 0) surface site ratio became the most stable after donor adsorption. This indicates control of the shape of MgCl2 crystallites to be attainable by appropriate choice of electron donor, a result utilizable in heterogeneous Ziegler-Natta olefin polymerization catalysis. (C) 2010 Elsevier B.V. All rights reserved.