Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

The UV (3.8 eV) photolysis of atomically-dispersed Rh I (CO) 2 species supported on an Al 2 O 3 surface in the presence of N 2 at 175 K caused the replacement of CO by N 2 ligands. Therefore dinitrogen chemisorption effectively probes the coordinatively unsaturated Rh(CO) species generated during photodecomposition of Rh I (CO) 2 /Al 2 O 3 . Two infrared bands, observed at 2234 and 2048 cm -1, are attributed respectively to ν N 2 and ν CO in Rh(N 2 )(CO), and a band at 2188 cm -1 is assigned to Rh(N 2 ) 2 surface species. The assignments are based on frequencies and the relative rates of spectral development for the two N 2 -containing species. The Rh(N 2 ) 2 species on Al 2 O 3 exhibits identical N−N stretching modes to a similar species produced by matrix isolation methods. It is shown that both the Rh−CO bond and the Rh−N 2 bond may be broken by photolysis.