IR Spectroscopic study of hydrogen bonding using a metal carbonyl probe

Abstract

The interaction of different hydrogen bond donors with [M(CO)₅L] [L = (E)-1,2-di-4-pyridylethene, M = Cr or W] was studied by means of IR spectroscopy. A clear shift to higher wavenumbers of the E and A₁ carbonyl vibration modes upon addition of the hydrogen bond donors is observed. The binding isotherms allowed calculation of both the equilibrium constants and free energies of formation of the adducts. These parameters depend on the nature of the carbonyl compound used, the pK_a of the hydrogen bond donor and the steric hindrance of its A–H bond.