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 Ir(PH₃)₂(CO)₂Cl differs significantly from the results of a previous crystallographic structure determination of Ir(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.