The preparation of Cu(en)2 was performed accoerding to the method reported
in the literature [26] as follows: a solution of copper (II) acetate monohydrate (0.624
g, 3.12 mmol) was stirred in acetone (25 mL) at room temperature. A solution of
ethylenediamine (0.42 ml, 6.28 mmol) in acetone (10 ml) was added dropwise to
copper acetate solution over a period of 10 minutes and stirred at room temperature
for 1 hour