FTIR spectroscopic and ab initio evidence for an amphipathic character of CO bonding with silanol groups

FTIR spectroscopy provides evidence that carbon monoxide interacts with surface silanol groups of silica and silicalite to form both SiOH⋯CO and SiOH⋯OC hydrogen-bonded complexes. The C-bonded adduct shows a characteristic IR absorption band which is blue-shifted as compared to free CO (2143 cm−1), while the O-bonded adduct is characterized by a red-shifted band. Variable temperature IR spectroscopy has shown that these two hydrogen-bonded adducts are in a temperature-dependent equilibrium which involves an enthalpy change of about 2–3 kJ mol−1. Spectroscopic data are supported by ab initio cluster model calculations of different complexity levels.