Question

In the solid state, the structure of Co₂(CO)n contains two bridging carbonyls.

a) Draw the structure of Co₂(CO)n.

b) Explain why the CO stretching frequency of bridging carbonyls occurs in 1800 to 1900 cm-1 region, whereas the CO stretching frequency of the terminal CO's, i.e., CO's bound to an individual Co atom appear 2000 to 2100 cm-1 range

Answer 1

Answer – a) We are given, Co₂(CO)n contains two bridging carbonyls and we need to the draw the structure of Co₂(CO)n and in this one we assume n = 8, since n is not specify it is as follow –

b) The CO stretching frequency of the terminal CO's, i.e., CO's bound to an individual Co atom appear 2000 to 2100 cm^-1 range, but when it is gets flanked between two Co then there is electron donating group gets increase and there is more electron density on the carbonyl and that affected on the C-O bond and it gets stretched already due to the electron repelling between O and on C atom, so there is need low stretching frequency to stretch the C-O bond. So it is showing the CO stretching frequency of bridging carbonyls occurs in 1800 to 1900 cm^-1 region, instate 2000 to 2100 cm^-1 range.