Effects of surface basic sites on the photolysis of iron carbonyls adsorbed on silica

Abstract

Photolysis of iron carbonyls adsorbed on various types of silica was investigated by IR spectroscopy. While the photolysis of Fe(CO) 5 led to the selective formation of Fe 3(CO) 12 on any silica samples, the hydride species [HFe 3(CO) 10 − was formed to some extent on one of the samples (denoted sample A) in the presence of gas phase water. The hydride species was also obtained by the photolysis of Fe 3(CO) 12 adsorbed on sample A in the presence of gaseous water, although the photodecomposition of Fe 3(CO) 12 to Fe(CO) 5 occurred on the other samples under the same condition. The hydride formation was suppressed or enhanced by surface modification with a small amount of formic acid or pyridine respectively. This result indicates that the hydride formation is due to base catalysis in a photochemical secondary process as has been observed on alumina, and sample A contains a trace of weak basic sites induced by impurities. The photochemical behaviour of iron carbonyls adsorbed on solid surfaces is discussed in terms of the nature of surfaces and stability of the reaction products on surfaces.