(A,B,C) Triplet of Infrared OH Bands of Zeolitic H-Complexes

The phenomenon of the (A,B,C) triplet of infrared OH bands at-2800,-2400 and-1700 cm-', well-known for strong X-OH-Y molecular H-complexes in solutions, liquids, and solids, is studied for the first time for surface H-complexes using CD3CN and CCl3CN adsorption on deuterated H-ZSM5 and H-FeSil zeolites. A direct experimental proof is given that the minimum between the A and B bands of D-complexes occurs at nearly exactly the 26(OD) in-plane bending overtone frequency of the perturbed OD group. This verifies the resonance theory of the (A,B) doublet by Claydon and Sheppard. In reference to zeolites this means that the-2800 and-2400 cm- ' OH bands recently found in adsorption of many basic molecules on zeolitic OH groups are actually pseudobands, caused by the subdivision of the very broad v(0H) f kv-(OH-Y) superposition band of the perturbed OH groups by Evans transmission window at the 26(OH)-2600 cm- ' frequency.