This work presents a simple synthesis of tetraaza macrocyclic Schiff base ligand (C40H28N4), its complex [(C40H28N4)@Fe(II)], and a novel complex of magnetite Fe3O4NPs incorporated inside tetraaza macrocyclic cavity [(C40H28N4)@Fe3O4NPs] in order to obtain well-dispersed nanoparticles. The characterization and structural identification were carried out by 1H NMR, 13C and DEPT 135 NMR spectroscopy as well by X-ray spectroscopy, FT-IR, and finally by ATG using both experimental and theoretical methods. XRD measurements indicate that the presence of Schiff's bases does not modify the crystal structure of the nanoparticles (approximately 11 nm). FT-IR was used to illuminate the presence of Fe3O4NPs in tetrahedral and octahedral sites as well as their coordination with imine (C=N) of tetraaza macrocyclic. The UV–Vis spectra and frontier molecular orbitals (FMOs) of the title compounds were calculated at TD-DFT/CAM-B3LYP-D3/6-311 G (d, p) level of theory. The corresponding calculated results yield shows a good agreement with the experimental data. The morphological characterization of the nanoparticles was carried out by SEM which revealed that the shape of the NPs was generally spherical. The SEM images also show that the nanoparticles prepared by in-situ with co-precipitation method were able to form stable complexes. Thermal characterization by ATG shows that there is 64% of the magnetite nanoparticles formed in-situ which corresponds to a grafting density of 25 mmol.g−1.