Conclusive identification of photochemically generated volatile species of ruthenium, osmium, and rhenium using selected ion flow tube mass spectrometry

Background: Identifying volatile transition-metal species formed during photochemical vapor generation (PVG) has remained challenging, particularly for less stable volatile carbonyls and carbonyl hydrides that are difficult to identify by gas chromatography mass spectrometry (GC-MS) and ambient mass spectrometry. Here we demonstrate that selected ion flow tube mass spectrometry (SIFT-MS) provides conclusive identification of these species based on complementary low-pressure ion-molecule chemistry. Results: We first verified the approach using photochemically generated Mo(CO)6 and W(CO)6. Next, we applied paired H3O+ and NO+ reagent ions to analyze the effluent gas phase resulting during PVG of Ru, Os, and Re. Various reductive conditions described in the literature were examined using liquid media containing dilute or concentrated formic acid and transition metals as mediators. We directly identified Ru(CO)5 as the volatile species generated from all HCOOH-based media and deduced that PVG of Os yields a mixture of Os(CO)5 and Os(CO)4H2. We also established Re(CO)5H as the dominant rhenium product for the first time. Additional PVG experiments also provided data on the SIFT ionization of volatile OsO4, generated under oxidative PVG conditions, as well as carbonyls of Co and Fe arising from their use as mediators for PVG of Ru, Os, and Re. Significance: The results demonstrate that SIFT-MS analysis provides a general, mechanistically informative approach to the unambiguous assignment of reactive PVG-derived metal carbonyls, enabling the rational optimization of PVG and the broader exploration of photochemical metal volatilization pathways.