Copper(II) coordination polymers, [Cu(μ2-HL)]n⋅n(CH3)2C=O (1), [Cu(μ1-HL)(CH3OH)]n (2) and [Cu(μ1-HL)(H2O)]n (3) were isolated by recrystallization (in acetone, methanol and dimethylformamide, respectively) of an intermediate produced by a solid state ball milling reaction of CuCl2⋅2H2O with 2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)benzoic acid (H3L). Reaction under conventional fully solution-based conditions of CuCl2⋅2H2O with H3L in acetone and dimethylformamide leads to 3, and in methanol to the known monomeric compound [Cu(HL1)(H2O)(CH3OH)] (4). All the coordination polymers 1−3 act as homogenous catalysts for the peroxidative (H2O2) oxidation of acetone to acetic acid with yields up to 50% and at room temperature. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim