Four novel Cu^II complexes {Na[Cu₄(hmp)₄(CHOO)₃](ClO₄)₂·H₂O}_n (1), [Cu₈(hmp)₈(CH₃COO)₆](ClO₄)₂ (2), [Cu₄(hmp)₄(CH₃CN)₂(ClO₄)₂(H₂O)₂](ClO₄)₂ (3), and [Cu₄(hmp)₄(CH₃COO)₂(H₂O)₄](ClO₄)₂·2H₂O (4) with Hhmp = 2-(hydroxymethyl)pyridine were prepared by structural modulation at room temperature. Taking advantage of the steric hindrance of the ancillary ligands, the 1D copper chain (1) is successfully cut down into the octa-nuclear copper cluster (2) with the unchanged antiferromagnetic [Cu₄O₄] open-cubane that is further separated into weak antiferromagnetic [Cu₄O₄] (3) and then modulated to be the ferromagnetic tetra-nuclear [Cu₄O₄] cluster (4). The obtained four complexes allow us to systematically investigate their magnetic properties and find the rules for further magnetic investigations. The results showed that there exist antiferromagnetic interactions between Cu(II) ions in 1–3, while 4 displays ferromagnetic behaviour. The best fitting results to the experimental magnetic susceptibilities gave J₁ = J₂ = J₃ = −2.26 cm⁻¹, g = 2.11 for 3 and J₁ = 37.05 cm⁻¹, J₂ = −0.62 cm⁻¹, J₃ = −0.62 cm⁻¹, g = 2.13 for 4.