The dianions PtCl62- and PtBr62- belong to the small class of doubly charged species whose gas phase photoelectron spectra have been measured and show clearly discernible structures. Here we study the electronic structure of the PtX62-(X=F,Cl,Br) dianions and the associated electron detachment energies theoretically. Relativistic effects including spin-orbit splittings are investigated at the self consistent field level by comparing nonrelativistic all-electron computations with results obtained using the Douglas-Kroll and the Dirac-Fock Hamiltonians as well as relativistic effective core potentials. Electron correlation effects, which are known to substantially influence detachment energies of mono- and dianionic species, are addressed at the configuration interaction and two propagator based levels of theory employing the relativistic effective core potentials. Moreover, we study the repulsive Coulomb barriers of the PtX62- systems within the dianion frozen orbital static approximation. Our findings strongly disagree with the standard textbook molecular orbital diagram of coordination compounds as well as with the tentative assignment of the spectroscopists. In particular, the five highest orbitals of PtCl62- and PtBr62- exhibit almost exclusively ligand character. The theoretical results are explained in terms of the charge distribution within the gas phase dianions, and the impact on assigning the photoelectron spectrum is discussed. (C) 2003 American Institute of Physics.