Matrix and Polymer Soft-Landing Isolation of Selected Acids with Pyridine and Poly(4-vinylpyridine): A Comparative Infrared Spectroscopic Study of Hydrogen Bonding

Hydrogen bonding plays a key role in the formation of nanostructures, as it is the “glue” between layers that are built by the layer-by-layer technique. Poly(4-vinylpyridine) (PVP) is one of the most commonly used polymers in these sandwich-structured films, often in conjunction with poly(carboxylic acid)s such as poly(acrylic acid) in the PVP/PAA interpolymer complex. In addition, PVP is commonly used as a polymer matrix for embedding semiconductor nanoparticles. In this study, hydrogen-bonded complexes of water, formic acid, and pentachlorocyclopropane, with pyridine in a traditional matrix isolation experiment and PVP in a novel “polymer soft-landing” isolation experiment, have been characterized for the first time at 16 K. Changes in vibrational modes of the proton donor species and in some cases pyridine modes provided ample evidence for complex formation. In the case of water and pentachlorocyclopropane, the matrix and polymer soft-landing results were quite similar, whereas formic acid formed a significantly different complex with pyridine in the argon matrix than with the pyridine ring on the PVP polymer. This work demonstrates clearly the benefit of using both the conventional matrix isolation technique and our polymer soft-landing variation in tandem to probe the structure of these complexes and thus elucidate the nature of the C–H···N, C–H···OC, and O–H···N linkages.