In the current study, four new phenolic oxime ligands (HL1ox-HL4ox) containing diazo groups (-N$=$N-) were synthesized and used for liquid-liquid extraction of heavy metal ions [Cu(II), Ni(II), and Zn(II)]. The new compounds were characterized by analytical and spectroscopic methods. Solid-state structures of HL1ox-HL3ox were determined by single-crystal X-ray diffraction studies. Hirshfeld surface analysis of the compounds was performed to determine the contribution of different intermolecular contacts to the stability of the structures. The HL1ox-HL4ox ligands showed higher extraction performance for Cu(II) ion than Ni(II) and Zn(II) ions. The effect of pH on extraction capacity was investigated and the oxime compounds showed high extraction capacity at low pH values. The effects of the substitute groups (at the meta position of the phenol ring) on the extraction were investigated. Within the oxime ligands, the HL3ox compound exhibited higher extraction capacity for Cu(II) ions. The better extraction value of HL3ox is attributed to the weak hydrogen bond type interactions, which result in more stable complexes.