The intermetallic phase FeGa3 belongs to the rare examples of substances with transition metals where semi-conducting behavior is found. The necessary electron count of 17 ve/fu can be formally derived from eight Fe-Ga and one Fe-Fe two-center two-electron bond. The situation is reminiscent of the well-known Fe-2(CO)(9) scenario, where a direct Fe-Fe two-center two-electron bond was shown to not be present. Fe-Fe interaction in FeGa3 and its substitution variants reprecents the crucial point for explanation of electronic, thermal bonding analysis in position space of FeGa3 and Fe-2(CO)(9) on transport, and optical properties of this material. Chemical the basis of the topology of the electron localizability indicator distribution, QTAIM atoms, two- and three-center delocalization indices, domain natural orbitals, IQA analysis, and an evaluation of the Fe-Fe dissociation energy yields a complete picture of the partially compensated Fe-Fe bond, which is nevertheless strong enough to be of decisive importance. Structural reinvestigation of differently synthesized single crystals leads to the composition Fe1+xGa3 (0 <= x <= 0.018), where the additional Fe atoms are predicted from DFT/PBE calculations to yield a magnetic moment of about 2 mu(B)/Fe-2 atom and metallic in-gap states. Accompanying magnetization and ESR measurements are consistent with this picture.