Adsorption of CO on a reduced Cu/SiO2 catalyst (1 wt% Cu) results in formation of Cu-o-CO species characterized by an IR band at 2128 cm(-1). During the contact of the sample with CO two new species characterized by bands at 2045 and 2018 cm(-1) appear. Experiments on (CO)-C-12-(13) Co co-adsorption prove that they are carbonyls. The 2045 cm(-1) species are assigned to Cu-0(CO)(2) geminal complexes formed on copper atoms with a low coordination number. During evacuation the geminal species lose one CO ligand, thus being converted into linear carbonyls (band at 2018 cm(-1)). Both species are not affected by hydrogen, but easily disappear in the presence of small amounts of oxygen.