Computational, Spectroscopic, and Crystallographic Determination of the Molecular Structures of CO Adducts of Vaska-Type Complexes trans-IrL₂(CO)₂X

The products of CO addition to Vaska-type complexes, trans-Ir(PH₃)₂(CO)₂X (X = Cl, I), have been calculated by use of ab initio electronic structure methods with effective core potentials on all non-hydrogen atoms and basis sets of double-ζ plus polarization function quality. The calculated trigonal-bipyramidal structure of lr(PH₃)₂(CO)₂Cl differs significantly from the results of a previous crystallographic structure determination of lr(PPh₃)₂(CO)₂Cl for which significant disorder and crystal decomposition during data collection were reported. In particular, the calculated OC–Ir–CO angle (133–138°) is significantly greater than the reported crystallographic value (121°). Results of a crystallographic (X = I, 131°) and IR spectroscopic (X = Cl, 132°; I,133°) reinvestigation are in good agreement with the calculations. The origin of the distortion from idealized trigonal-bipyramidal geometry is briefly discussed.