The lighter rare gas complexes with Mg+ are known from both computational and spectroscopic determinations to have weakly bound (2)Sigma(+) ground states with much more strongly bound low-lying (2)Pi(1/2,3/2) excited states. In extensive configuration interaction calculations including large relativistic effects, we show that for Rn the picture is dramatically different with strongly avoided crossings in the (2)Pi curves due to charge-transfer states. The avoided crossings leave the (2)Pi states much more weakly bound. It was found that the lowering of the Rn ionization potential relative to Xe, producing the low-lying states, can be attributed almost entirely to the large spin-orbit splitting of the Rn+ P-2 states. Variations in crossing interactions are readily explained in terms of two-component spinors.