In the solid-state structure of the Schiff base salen [salen = N,N’-ethylenebis(salicylideneiminato)] zirconium dichloride complex Zr(salen)Cl-2(THF), C20H22Cl2N2O3Zr, a quadridentate ligand, occupies four sites in the pseudopentagonal bipyramidal coordination. The coordination sphere is completed by one THF molecule, and two chloride ions are forced into the trans-position. Removal of THF, while Zr(salen)Cl-2(THF) is heated in toluene, leads to a six-coordinated complex with the two chloride ligands assuming the cis-position. This property was successfully utilized in the preparation of a homogeneous Zr(salen)Cl-2 catalyst precursor. Heating of Zr(salen)Cl-2(THF) in toluene in the presence of SiO2 causes deposition of Zr(salen)Cla on to the silica support, producing a heterogeneous catalyst, which shows an acceptable activity in ethylene polymerization at 80 degrees C and at low ethylene pressures in the presence of the cocatalyst methylaluminoxane.