Infrared (IR) spectrometry was used to characterize the surface adduct formed upon interaction of Ru 3 (CO) 1 2 with dehydroxylated MgAl 2 O 4 (spinel) prepared in a high-surface-area form. IR spectra of the adsorbed metal carbonyl showed strong evidence for a terminal-to-bridge shift of CO ligands and attendant coordination, via a μ-CO group, to coordinatively unsaturated Al 3 + ions (Lewis acid centres) at the spinel surface. An IR absorption band was observed at 1604 cm - 1 , and assigned to the surface bound μ-CO ligand. The remaining terminal CO groups gave a complex IR absorption in the 1970-2100 cm - 1 range.