The invention relates to a complex comprising a magnesium dihalide and an
electron donor. It is a complex of the magnesium dihalide and the electron
donor and has the formula (I):
MgX.sub.2.multidot.[R(OR').sub.n ].sub.m (I)
wherein MgX.sub.2 is the magnesium dihalide and R(OR').sub.n is the
electron donor, X is a halogen, R is an n-valent C.sub.1 -C.sub.20
aliphatic group, an n-valent C.sub.7 -C.sub.27 araliphatic group or an
n-valent C.sub.2 -C.sub.22 acylic group, R' is a C.sub.1 -C.sub.20 alkyl
group or a C.sub.7 -C.sub.27 aralkyl group, n is a number from 1 to 6 and
m is defined as a number 0.5.ltoreq.m.ltoreq.2.0. The invention also
relates to the preparation process of such a complex, as well as the use
thereof for the preparation of olefin polymerization catalyst components.
