Homodinuclear cobalt(II) complexes of the tetraiminediphenol macrocycle were synthesized by employing the process of Schiff base condensation reaction of 2,6-diformyl-4-methylphenol and 4-substituted-o-phenylenediaminesin the presence of cobalt(II) template. The spectroscopic techniques and mass spectrometry were utilized so as to carry out the characterization for the obtained complexes. On implementing thermal analysis, the complexes were found to exhibit high thermal stability such that they form Co$_3$O$_4$ nanoparticles on thermal decomposition. The diffraction peaks appearing in the X-ray diffraction (XRD) spectra indicated that the nanoparticles were crystalline in nature. Scanning electron microscopy (SEM) was used to identify the surface morphology of Co$_3$O$_4$ nanoparticles. Energy dispersive X-ray spectroscopy (EDS) was undertaken so as to check the chemical purity and stoichiometry of Co$_3$O$_4$ nanoparticles. Thesize of Co$_3$O$_4$ nanoparticles of all the four complexes was found to be 20–40 nm resulting out of transmission electron microscopy (TEM) which also showed that the nanoparticles were spherical in shape. It has been authenticated withexperimental evidence that the substituent present on the macrocycles has made substantial impact on the surface morphology, particle size and band gap of Co$_3$O$_4$. UV–Vis spectroscopic technique clearly reveals the quantum confinementeffects of the title material.