Supramolecular assembly [Cu^II₂(μ-bpypz)₂Br_1.25(H₂O)_0.75]Br_0.75·2.25H₂O (1) was prepared by using 3,5-di(2-pyridyl)pyrazole (Hbpypz). Assembly 1 consists of supramolecular dimers of dinuclear species based on doubly bpypz⁻ bridged dinuclear building blocks. The supramolecular dimer is flexible as a result of π⋯π interactions. Compound 1 undergoes reversible structural transformation in the solid state involving reversible apical-ligand substitution at the copper centers upon hydration–dehydration.