Crystals of Co3O4 have been prepared from thermal decomposition of molecular precursors derived from salicylic acid and cobalt (II) acetate or chloride at 500 degrees C. A cubic phase Co3O4 micro- and nanocrystals have been obtained. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The images of electron microscopes showed octahedral crystals of Co3O4. The volume and polarizability of the optimized structures of molecular precursors have been calculated and related to the particle size. The optical band gap of the obtained crystals has been measured. The results indicated two optical band gaps with values 2.65 and 2.95 eV for (E-g1) (E-g2), respectively. (C) 2013 Elsevier B.V. All rights reserved.