Infrared spectra of isotopically substituted XCo(CO)₄ (X=H, EtC(O), EtOC(O) and EtOC(O)CH₂) molecules

In this paper we present a series of observations on the infrared spectra of DCo(CO)₄ (in comparison with HCo(CO)₄) as well as of the ^l3CO-exchanged derivatives of HCo(CO)₄, EtOC(O)CH ₂Co(CO)₄, EtOC(O)Co(CO)₄ and EtC(O)Co(CO) ₄. Calculated frequencies and intensities for HCo( ¹²CO)_n(¹³CO)_4-n based on the C-O factored force field approximation predict data in excellent agreement with that observed experimentally. Splitting of the E band in the complexes R-Co(CO)₄ is shown to depend on reduction of local site symmetry and appears to be greatest for R groups containing a local dipole capable 'of through-space' interaction with the three equatorial carbonyls. The analysis of the infrared absorption bands for the ^l3CO-substituted compounds sheds light on the nature of bonding and symmetry of these molecules, and the extent of interaction between the organic substituent and the four CO groups in the cobalt tetracarbonyl compound.