A density functional study of the adsorption of pyridine, 2-vinylpyridine, and 4-vinylpyridine onto a silica surface

The interaction of pyridine, 2-vinylpyridine, and 4-vinylpyridine with silica surfaces represented by model clusters is studied within the framework of the density functional theory to shed light on the different trend towards polymerization showed by the vinyl derivatives of pyridine. It is found that pyridine interacts more strongly with silica clusters than its derivatives, whereas 2-vinylpyridine, in its turn, exhibits a larger interaction energy than 4-vinylpyridine. It is also found that the interaction pattern is dominated in all cases by the formation of a hydrogen bond between the nitrogen atom and a hydroxyl group of the silica cluster, a second, very weak hydrogen bond is formed in some of the systems, though. A natural bond orbital analysis and the calculation of harmonic vibrational frequencies allow to confirm those findings. Finally, it is proposed that the trend of not forming nanocomposites when using 2-vinylpyridine is mainly due to the involvement of its vinyl group in a weak hydrogen bond to an oxygen atom of the silica surface avoiding to polymerize and not due to a weak acid-base interaction nor steric effects as it was previously supposed. (C) 2003 Elsevier B.V. All rights reserved.