Spectroscopic evidence has been obtained for the existence of [Ir(C₅H₅)(H₃)(PR₃)]⁺, a complex in which one ligand is formally H₃⁺. Devise a plausible molecular orbital scheme for the bonding in the complex, assuming that an angular H₃ unit occupies one coordination site and interacts with the eg and t_2g orbitals of the metal. An alternative formulation of the structure of the complex, however, is as a trihydro species with very large coupling constants (see J. Am. Chem. Soc., 1991, 113, 6074 and the references therein, and especially J. Am. Chem. Soc., 1990, 112, 909 and 920). Review the evidence for this alternative formulation.