A new polymorph of [Cu2Cl2(CH2=CH–CH2)2O] has been obtained by an alternating‐current electrochemical synthesis starting from CuCl2 and triallylphosphite. Diallylether was obtained in statu nascendi via transetherification of triallylphosphite. The structure is monoclinic, space group P21/n, a = 7.6738(7), b = 6.5128(4), c = 18.2689(18) Å, β = 91.644(11)°, V = 912.67(13) Å3 (at 150 K), Z = 4; R1 = 0.0339, wR2 = 0.0822. Flexibility of the organic ligand and weak interactions copper···halogen have been identified as the main reasons enabling polymorphism in molecular π‐complexes of copper(I).

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