The dark blue compound [Cu2(detenoxH)(detenox)(OH)](ClO4)2 (detenoxH=4,4-dimethyl-7-(N,N-diethylamine)-5-azaheptan-2-one oxime), [Cu2(C12H27N3O)(C12H26N3O)(OH)](ClO4)2, is formed by reaction of (N,N-diethyl-ethane-1,2-diamine)copper(II) perchlorate, 4-methylpent-3-ene-2-one oxime and base. The asymmetrical dinuclear cation has ion Cu1 in asymmetrical square pyramidal coordination by the oxime nitrogen atom (Cu1–Noxime=2.041(3)Å) and the secondary amine nitrogen atom (Cu1–Nsecondary=1.995(3) Å) of a detenoxH ligand, the bridging oximato oxygen atom of the detenox− ligand bonded to Cu2 (Cu1–Ooximato=1.928(2)Å) and the bridging OH− ion (Cu1–OOH=1.928(3)Å) with rms displacements from the N2O2 plane±0.246(1) with Cu1 in the plane). The tertiary amine nitrogen atom of the detenoxH ligand is weakly coordinated axially (Cu1–Ntertiary=2.328(3)Å). Ion Cu2 is in tetrahedrally twisted square-planar coordination by a detenox− ligand, with Cu2–Noxime=1.992(3), Cu2–Nsecondary=1.979(3), Cu2–Ntertiary=2.053(3), and by the bridging hydroxide ion (Cu2–O=1.878(3)Å), with rms displacements from the N3O best plane ±0.178(2)Å, with Cu2 in the plane). The dinuclear cation has Cu1–O=N–Cu2 bridging by the oximato group of detenox− and Cu1–(OH)–Cu2 bridging by a hydroxide ion, with Cu⋯Cu=3.3136(6)Å. The components of the dinuclear cation are further linked by a hydrogen bond between the oxime OH and oximato O− groups. The effective magnetic moment of 2.21 B.M. indicates that there is no significant spin coupling.