The adsorption of acetonitrile on H-[Fe]ZSM-5 and H-[Al]ZSM-5 was studied using microcalorimetry, temperature-programmed desorption (TPD), and FTIR in order to characterize the differences between the Bronsted acid sites in these two materials. Each technique showed that acetonitrile forms 1:1, stoichiometric adsorption complexes with Bronsted sites associated with framework Fe (FeOHSi) and framework Al (AlOHSi). The heats of formation of the complexes differ slightly, 95 +/- 5kJ/mol on H-[Fe]ZSM-5 compared to 110 +/- 5 kJ/mol on H-[Al]ZSM-5, suggesting that the hydrogen bonds at FeOHSi sites may be slightly weaker. The FTIR also shows that the vibrational modes associated with the hydroxyls in the complexes are different in the two materials and again indicates that there may be slightly weaker hydrogen bonds at FeOHSi sites. However, the differences between the two types of complexes are relatively small, and the nu(CN) stretching frequency for both types of site are the same, 2298 cm(-1). The implications of this for the characterization of solid acids is discussed.