Density functional theory unrestricted calculations at the BPW91/6-311+G* level of theory have been used to explore the potential energy surface of MO. complexes (M = Sc-Zn, n=1-2). Nine physico-chemical properties were selected to characterize each of the MOn complexes to conduct a chemotopological study. Our results show that the similarity relations between the group-VIIIB elements (Fe, Co and Ni) are transferred to their corresponding MO, complexes. A classification of M-O interactions in the MO, complexes based on the QTAIM methodology is introduced. (C) 2016 Elsevier B.V. All rights reserved.