The titile compound, C(18)H(20)Cl(2)N(2)O(2), crystallizes as a monoclinic form in the space group P2(1)/n, with Z' = 1/2. It is polymorphic with the previously reported orthorhombic form [Kubono, Tsuno, Tani & Yokoi (2008). Acta Cryst. E64, o2309]. In the present polymorph, the mol-ecule lies on a crystallographic inversion centre at the piperazine ring centroid. An intra-molecular O-H⋯N hydrogen bond forms an S(6) ring motif. Inter-molecular C-H⋯O hydrogen bonding generates a C(5) chain motif propagating along the b axis, forming sheets parallel to (02) with a first-level graph set S(6)C(5)R(6) (6)(34).
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