ICP-SIFT/MS study of gas-phase reactions of atomic metal cations with pyridine at room temperature: Kinetics and periodicities in reactivity

Abstract

Chemical reactions of 18 singly-charged atomic metal ions with pyridine were studied in the gas phase at room temperature (295±2K) in helium at a total pressure of 0.35±0.02Torr using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Observations are reported for 4 group I and II main group cations and 14 group III–VII transition metal cations. Addition of up to 5 pyridine molecules is observed with the number added generally decreasing from left to right on the periodic table, from 5 to 3, with the exception of group I cations which add only 2. The number of added pyridine molecules shows a good correlation with the ligand field stabilization energy (LFSE); atomic metal cations with a higher stabilization energy add more pyridine molecules. Some atomic metal cations exhibit pyridine ring cleavage, predominantly by elimination of acetylene, C2H2, with one example of HCN elimination usually observed in pyridine ring cleavage. The reaction efficiency was measured to be high, mostly ≥50%, for both addition and ring cleavage. The exceptions are the group I metal cations for which addition is 10 times slower.