IR spectra and structures of saturated ruthenium cluster carbonyl cations Ru n (CO) m + ( n = 1-6).

A series of saturated ruthenium cluster carbonyls (Ru(CO) 5 + , Ru 2 (CO) 9 + , Ru 3 (CO) 12 + , Ru 4 (CO) 14 + , Ru 5 (CO) 16 + and Ru 6 (CO) 18 + ) have been synthesized in the gas phase and subsequently characterized by infrared spectroscopy. Their size-specific IR spectra in the region of the carbonyl stretch vibration (1900-2150 cm -1 ) and in the region of the Ru-C-O bending modes (420-620 cm -1 ) are obtained by infrared multiple photon dissociation spectroscopy. The structures of these cluster carbonyls are assigned by comparison with results from density functional calculations. A multitude of differently activated CO ligands are identified in these cationic cluster carbonyls, reaching from terminal, over non-symmetrically bridging (semi-bridging) ligands with varying degrees of interaction to additional Ru atoms towards symmetrically bridging CO ligands.