Data on ethylene polymerization over supported LFeCl2/MgCl2 catalysts {L = 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridyl} containing AIR(3) (R = Me, Et, i-Bu, or n-Oct) as an activator are presented. These catalysts are highly active (100-300 kg of polyethylene/g of Fe b bar of C2H4) and stable in ethylene polymerization at 70-80 degrees C. Data on the effects of the iron content, AIR(3) type, Al(i-Bu)(3) concentration, and hydrogen presence on the catalyst activity are presented. The molecular structure of polyethylene produced with these catalysts (including the molecular masses, molecular mass distribution, branching, and number of C C bonds) has been studied; data on the effects of AIR, and hydrogen on the molecular structure are presented. (c) 2005 Wiley Periodicals, Inc.