INFRARED-SPECTRA OF (ETA(6)-C6H2ME4)CR(CO)(3) ADSORBED ON SILICA AND SILICA-ALUMINA

Durene Cr(CO)(3) adsorbed on silica which had been preheated at 973 K either by H-bonding between surface silanol groups and the pi-electron s of durene rings or by O-ligation of carbonyl ligands to electron-def icient Lewis acidic Si atoms in the silica surface. Lewis acidic sites were generated during high temperature pretreatment by condensation o f surface silanol groups forming exposed strained siloxane bridges. He at treatment of silica in water vapour at 973 K removed strained surfa ce sites and subsequent adsorption of durene Cr(CO)(3) at 298 K primar ily involved only H-bonding interactions. In contrast, the adsorption of durene Cr(CO)(3) on silica-alumina which had been preheated at 773 K was dominated by O-ligation to Lewis acidic sites with little eviden ce for H-bonding. Ligand loss from molecules adsorbed at Lewis acidic sites led to sub-carbonyl surface species and bicarbonate anions.