Question

5. (a) When [Mo(?5 -C5H5)(CO)3]2 is heated, it loses two CO ligands to become [Mo(?5 -C5H5)(CO)2]2, and the energies of the CO stretches change from 1960 cm?1 and 1915 cm?1 to 1859 cm?1 and 1819 cm?1 . The Mo-Mo bond length also shortens by 80 pm. Suggest plausible chemical structures for each of the compounds, and explain the change in energy of the CO stretches.

(b) Explain the following trend in the energy of the CO stretch. Predict the trend in the M-C and C-O bond lengths.

M(CO)6	?(CO), cm?1
[W(CO)6]	1977
[Re(CO)6] +	2085
[Os(CO)6] 2+	2190
[Ir(CO)6] 3+	2254

Answer 1

2 CO TVE (6+5+6)X2 =34 = 30 36 30 36-34 3 1 Co Co oc -MoMo Co CS o C Co CO (No back boy dig) (duu to back bondivg) を-o 0 08 (Co)6 C-O hI (co e (co) s(co),