The use of the monoanionic Schiff base ligand (E)-4-(2-hydroxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one in transition (Co, Ni and Cu) coordination chemistry yields mono-, tetra- and pentanuclear coordination clusters (CCs) with different structural motifs. An organic transformation occurs in the ligand in the Cu compound for which theoretical studies are presented. Solution studies, topological issues and magnetic studies are discussed. The present results demonstrate the richness of the coordination chemistry of this monoprotic organic ligand, which promotes the formation of high-nuclearity CCs.