Three novel Cobalt salicylaldimine–urea complexes {[CoxLy(H2O)n]Clz; where, L = 1,3-bis(salicylaldehydimine) urea Schiff base; x, y = 1 or 2; n = 2 or 8; z = 0 or 2} were synthesized by one-pot solvothermal treatment of methanolic solutions of urea, salicylaldehyde, and cobalt chloride at 120 C for 3 h. Subsequently, normal spinel-type Co3O4 nanoparticles, with an average crystallite size in the range 22–38 nm, were easily produced via thermal decomposition of the synthesized complexes at 400 C for 2 h. The synthesized compounds were characterized by elemental analysis, thermal analysis (TG-DTA/DTG), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–Vis spectroscopy, transmission electron microscopy (TEM) and EI mass spectroscopy. Investigation of the optical properties of the produced cobalt oxide, using UV–Vis spectroscopy, confirmed its semiconducting properties by revealing two optical band gabs in the range of 1.42–1.50 and 1.83–1.95 eV.