INFRARED SPECTROSCOPIC STUDIES OF THE REACTIONS BETWEEN CO2(CO)8, H-2 AND D2

The reaction of Co2(CO)8 with D2 does not have as product the expected DCo(CO)4 only but gives rise to a mixture of DCo(CO)4 and HCo(CO)4. This phenomenon, observed also with other metal carbonyl hydrides, was explained by the fact that the reaction-vessel walls were covered by a polymeric layer of water which caused a very fast exchange with the deuterium in DCo(CO)4, and hence this was the source of hydrogen in the formation of HCo(CO)4. In this present work, we attempt to obtain alkane solutions of DCo(CO)4 with very high deuteride content in order to study the spectral and chemical properties of this elusive compound. In concentrated solutions of DCo(CO)4, having only traces of Co2(CO)8, an absorption band at 2048 cm-1 was observed, and attributed to a C-O stretching fundamental mode of DCo(CO)4. This band corresponds to the 2052 cm-1 band found in HCo(CO)4. In both cases it can be assigned to the a1 mode in which the axial and equatorial CO groups stretch out of phase. Another band, the total symmetric nu(C-O) mode at 2116.3 cm-1, is only 0.4 cm-1 lower in energy than the corresponding band of HCo(CO)4. The extinction coefficients for several significant absorption bands of DCo(CO)4 were calculated. The high pressure IR spectroscopic analysis, previously applied to calculate cobalt carbonyl concentrations in a three-component system, has proven itself to be quite accurate in the present case as well. Using the quantitative data obtained, the equilibrium constants for the reaction between Co2(CO)8 and D2 were obtained. Finally, the effect of the presence of H2O or D2O on H/DCo(CO)4 mixtures was studied and compared to the exchange with H-2 and D2 in the gas phase.