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.