The IR spectra of the title compounds are recorded and an assignment of the normal modes in terms of local symmetry is suggested by comparison with those observed in analogous molecules. A set of force constants calculated for simplified models confirms most of the experimental assignments and reflects the symmetry of the complexes under study. ThefCOof the two different CO groups in the cationic complexes indicated that CO groups cis to the halide ligand should be more selective towards nucleophiles.