You have just synthesized three new compounds of the type M(CO)5(L). You acquire
ID: 809832 • Letter: Y
Question
You have just synthesized three new compounds of the type M(CO)5(L). You acquired the IR spectra of each complex and find that for compound A the shift of the co stretching frequency has red shifted 40 cm^-1 from free CO. What does this mean? Compound B shows a blue shift of 40 cm^-1 when compared to free CO. What does this mean? Finally compound C shows no shift at all when compared to free CO. What does this mean? 13e sure to clearly state what red shifted and blue shifted mean in IR spectroscopy. You answers should be grounded in MO theory.Explanation / Answer
Red shift means the location of absorption peak moves towards higher wavelength. In IR since it is plotted as the inverse of wave length, the location of the peak decreases by 40 units (cm^-1). Since the absorption takes place at a lower energy, the difference between the energy levels of MOs of the compound is decreased.
in contrast to red shift, blue shift results when the MOs are separated further away, making the transition between orbitals require more energy. The location of the peak in the IR spectra moves to higher or left hand side of the original peak. This also is an indication of extent of binding and bond length of the M-CO bonds.
In red shifted the bond length is longer than the blue shifted case.
if no shift is found, it suggests that the MOs of CO is not affected by the presence of M ion/ atom in the compound.
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