FTIR spectra of CO adsorbed at low temperatures on CsX and KX zeolites, unlike those for CsZSM5 or NaX, reveal bands at wavenumbers below the position of the free molecule. In accordance with the electrostatic model, the bands are attributed to molecules which form side-on complexes with basic framework oxygen ions. Low values of entropy changes on adsorption, obtained for these bands from the analysis of the temperature dependence of the intensity at different pressures, testify to the rotational mobility of molecules adsorbed on anions.