COMPUTATIONAL, SPECTROSCOPIC, AND CRYSTALLOGRAPHIC DETERMINATION OF THE MOLECULAR-STRUCTURES OF CO ADDUCTS OF VASKA-TYPE COMPLEXES TRANS-IRL2(CO)(2)X

The products of CO addition to Vaska-type complexes, trans-Ir(PH3)(2)(CO)(2)X (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-zeta plus polarization function quality. The calculated trigonal-bipyramidal structure of Ir(PH3)(2)(CO)(2)Cl differs significantly from the results of a previous crystallographic structure determination of Ir(PPh(3))(2)(CO)(2)Cl for which significant disorder and crystal decomposition. during data collection were reported. In particular, the calculated OC-Ir-CO angle (133-138 degrees) is significantly greater than the reported crystallographic value (121 degrees). Results of a crystallographic (X = I, 131 degrees) and IR spectroscopic (X = CI, 132 degrees; I, 133 degrees) reinvestigation are in good agreement with the calculations. The origin of the distortion from idealized trigonal-bipyramidal geometry is briefly discussed.