The electronic properties and structure of a complex incorporating a self-interstitial (I) and two oxygen atoms are presented by a combination of deep level transient spectroscopy (DLTS), infrared absorption spectroscopy and ab-initio modeling studies. It is argued that the IO 2 complex in Si can exist in four charge states (IO 2 - , IO 2 0 , IO 2 + , and IO 2 ++ ). The first and the second donor levels of the IO 2 complex show an inverted location order in the gap, leading to a E(0/ ++) occupancy level at E v + 0.255 eV. Activation energies for hole emission, transformation barriers between different structures, and positions of LVM lines for different configurations and charge states have been determined. These observables were calculated by density-functional calculations, which show that they are accounted for if we consider at least two charge-dependent defect structures.