Gas-phase properties and fragmentation behavior of cationic, dinuclear iron chloride clusters Fe2Cln+ (n=1-6)

Sector-field mass spectrometry is used to probe the fragmentation patterns of cationic dinuclear iron chloride clusters Fe2Cln+ (n = 1-6). For the chl orine-rich, high-valent Fe2Cln+ ions (n = 4-6), losses of atomic and molecu lar chlorine prevail in the unimolecular and collision-induced dissociation patterns. Instead, the chlorine deficient, formally low-valent Fe2Cln+ clu sters (n = 1-3) preferentially undergo unimolecular degradation to mononucl ear FeClm+ ions. In addition, photoionization is used to determine IE(Fe2Cl 6) = 10.85 +/- 0.05 eV along with appearance energy measurements for the pr oduction of Fe2Cl5+ and Fe2Cl4+ cations from iron(III) chloride vapor. The combination of the experimental results allows an evaluation of some of the thermochemical properties of the dinuclear Fe2Cln+ cations: e.g., Delta H- f(Fe2Cl+) = 232 +/- 15 kcal/mol, Delta H-f(Fe2Cl2+) 167 +/- 4 kcal/mol, Del ta H-f(Fe2Cl3+) = 139 +/- 4 kcal/mol, Delta H-f(Fe2C4+) 113 +/- 4 kcal/mol, Delta H-f(Fe2Cl5+) = 79 +/- 5 kcal/mol, and Delta H-f(Fe2Cl6+) = 93 +/- 2 kcal/mol. The analysis of the data suggests that structural effects are mor e important than the formal valency of iron as far as the Fe-CI bond streng ths in the Fe2Cln+ ions are concerned.