Pathways to a variety of homoleptic transition-metal carbonyl cations have now been deve...

Pathways to a variety of homoleptic transition-metal carbonyl cations have now been developed.

a. Three such cations are [Hg(CO)₂]²⁺, [Pt(CO)₄]²⁺ and [Os(CO)₆]²⁺. Predict which of these has the lowest energy carbon oxygen stretching vibration in the infrared. (See H. Willner, F. Aubke, Angew. Chem. , Int. Ed. , 1997 , 36 , 2402.)

b. The cation [{Pt(CO)₃}₂]²⁺ is believed to have the structure shown, with D_2d symmetry. Predict the number of carbon–oxygen stretching bands observable in the infrared for this ion, and predict the approximate region in the spectrum where these bands might be observed.